ELECTRONICS WORLD + WIRELESS WORLD JULY 1994 £1.95 FREE with this issue Hall effect device pack* *First 500 replies, UK & Eke only AUDIO New look to amplifier design. COMPUTING Sorting signals from noise APPLICATIONS Using Hall to good effect DESIGN Oscillators in perspective RF ENGINEERING Millimetre wave devices 9 770959 11 833004 Denmark DKr. 70.00 Germany DM 15.00 Greece Dra.760 Holland Dfl. 14 Italy L 7300 IR £3.30 Spain Pts. 780 Singapore SS 12.60 USA $6.70 A REED BUSINESS PUBLICATION 0 7>
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ELECTRONICSWORLD+ WIRELESS WORLDJULY 1994 £1.95
FREE with this issueHall effect device pack**First 500 replies, UK & Eke only
THE WORLDS No.1 BEST SELLINGUNIVERSAL PROGRAMMING AND TESTING SYSTEM.
The PC82 Universal Programmer and Tester is aPC -based development tool designed toprogram and test more than 1500 ICs. The latestversion of the PC82 is based on the experiencegained after a 7 year production run of over100,000 units.
The PC82 is the US version of the SunshineExpro 60, and therefore can be offered at a verycompetitive price for a product of such highquality. The PC82 has undergone extensivetesting and inspection by various major ICmanufacturers and has won their professionalapproval and support. Many do in fact use thePC82 for their own use!
The PC82 can program E/EPROM, Serial PROM,BPROM, MPU, DSP, PLD, EPLD, PEEL, GAL, FPL,MACH, MAX, and many more. It comes with a 40pin DIP socket capable of programming deviceswith 8 to 40 pins. Adding special adaptors, thePC82 can program devices up to 84 pins in DIP,PLCC, LCC, QFP, SOP and PGA packages.
The unit can also test digital ICs such as the TTL74/54 series, CMOS 40/45 series, DRAM (evenSIMM/SIP modules) and SRAM. The PC82 caneven check and identify unmarked devices.
Customers can write their own test vectors toprogram non standard devices. Furthermore itcan perform functional vector testing of PLDsusing the JEDEC standard test vectors createdby PLD compilers such as PALASM, OPALjr,ABLE, CUPL etc. or by the user.
The PC82's hardware circuits are composed of 40set pin -driver circuits each with TTL I/O control,D/A voltage output control, ground control,noise filter circuit control, and OSC crystalfrequency control. The PC82 shares all the PC'sresources such as CPU, memory, I/O hard disk,keyboard, display and power supply.
A dedicated plug in card with rugged connectingcable ensures fast transfer of data to theprogrammer without tying up a standard parallelor serial port. Will work in all PC compatiblesfrom PC XT to 486.
The pull -down menus of the software makes thePC82 one of the easiest and most user-friendlyprogrammers available. A full library of fileconversion utilities is supplied as standard.
The frequent software updates provided bySunshine enables the customer to immediatelyprogram newly released ICs. It even supportsEPROMs to 16Mbit.
Over 20 engineers are employed by Sunshine todevelop new software and hardware for thePC82. Not many competitors can boast of similarsupport!
Citadel, a 32 year old company are the UK agentsand service centre for the Sunshine range ofprogrammers, testers and in circuit emulatorsand have a team of engineers trained to givelocal support in Europe.
* More sold worldwide than any other ofits type.
* UK users include BT, IBM, MOD, THORNEMI, MOTOROLA, SANYO, RACAL
* High quality Textool or Yamaichi zeroinsertion force sockets.Rugged screened cabling.
* High speed PC interface card designedfor use with all PC models from XT to486.
* Over 1500 different devices (includingmore than 100 MPU's) supported.
* Tests and or identifies a wide range oflogic devices.
NOW SUPPLIED WITH SPECIAL VALUEADDED SOFTWARE (worth over f300 ifbought seperately):
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Our stocked range of own manufactured andimported Sunshine products include:
* Super fast EPROM Erasers.* 1, 4 & 8 gang EPROM 8Mbit production
programmers.* Battery operated portable EPROM
programmers.* "In circuit" Emulators.* Handy pocket IC testers.
ORDERING INFORMATION
PC82 complete with interface card,cable, software and manual only L3U3
Please add f7 carriage (by overnight courier) forUK orders, £20 for export orders, and VAT whereapplicable.
ACCESS, MASTERCARD, VISA or CWO.Official orders are welcome from Governmentbodies & local authorities.
Free demo disk with device list available.
* Software supplied to write own testvectors for custom ICs and ASICs etc.
* Protection circuitry to protect againstwrong insertion of devices.
Ground control circuitry using relayswitching.
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CONTENTS
FEATURES
CMR UNDER TEST 540Designers often need to treasuresmall signals superimposed onlarge voltages but information oncommon -mode rejection from ICmanufacturer data is rarely morethan superficial. In a worli-exclusive review, consultant BenDuncan compares this vitalparameter in eleven of the topinstrumentation amplifiers.
COMMON -EMITTER POWER AMPLIFIERS 548Taken by the idea of linearisation using square law fets,Doug Self investigates the driving of power amplifier loadsvia collectors rather than emitters. Findings suggest thatdesigners are looking from the wrong perspective.
ACQUIRING DATA FROM NOISE 554In travelling to its destination, a signal from a sensor caneasily become corrupted by EMI, losses and noise sources.Dave Robinson looks various ways of removing theimpurities.
GRAPH PLOTTING IN WINDOWS 559Reviewer Allen Brown enthuses about a new softwarepackage designed specifically for plotting complexengineering data under Windows - MicroCal's Origin.
COHERER-BASED RADIO 563A century ago, radio -signal detectors comprising metalparticles in a glass tube were at the forefront of wirelesstechnology. George Pickworth has been reproducing earlyequipment based on the 'coherer' and shares the results ofhis test transmissions.
NEW WAVE MICROWAVES 570Mike Hosking looks at the variety of active millimetre -wave devices now available for specific communicationsapplications including receiving, generating and mixing.
APPLYING HALL TO GOOD EFFECT 576Integrated Hall -effectswitches and linear -output devices havehundreds of uses, rangingfrom motor speed controlto current monitoring.Martin Eccles looks at ahandful of them.
FREE: Hall -effectsensors,
USING RF TRANSISTORS 606Design criteria for transformers used in rf systems are verydifferent from those of their if counterparts. In an extractfrom their book RF Transistors: principles and practicalapplications, Norm Dye and Helge Granberg discuss thedifferences and provide an insight into the noveltransformer solutions available to the rf designer.
REGULARS
COMMENTEuropean R&D or Euro-waste?
531 NEW PRODUCTS 591Scores of the industry's new products presented in a formatdesigned to save you time.
NEWS 532Video games set to become the driving force behindmicroprocessor design; 200MHz serial speed-up forVME; Intel to drop X86 architecture rumour.
RESEARCH NOTES 536Gunn diode breaksfrequency and powerboundaries, The wobblethat gave birth to a planet,Laser that could reshapeconventional technology,Physicists find theirmissing link, Solar powerreaps energy benefits.
APPLICATIONS 583Battery -powered micro -ohm meter, power -fail and resetfor PCs, Easy to use programmable oscillator.
DESIGN BRIEF 586Exploring the LC oscillator in detail reveals that it israther more sophisticated than it first appears. IanHickman explains.
CIRCUIT IDEAS 600Digital sinewave generator, Spare inverter converts 5V to±15V, Square waves from a 555, Inrush current limiter,High -torque position servo, Monitor shows three-phasesequence, Electronic fuse, Two -wire switch statusdetection, Isolated I2C bus interface.
In next month's issue:. Build a teletext card using LaurenceCook's proven design presented complete with PCB.
THE AUGUST ISSUE IS ON SALE FROM JUNE 30
July 1994 ELECTRONICS WORLD + WIRELESS WORLD
SMALL SELECTION ONLY LISTED - EXPORT TRADE AND QUANTITY DISCOUNTS - RING US FOR YOUR REQUIREMENTS WHICH MAY BE IN STOCK
NEW LOW PRICE - NEW COLOUR
HP141TSPECTRUM ANALYSERS
TESTEDHP141T + 8552A or B IF- 8553B RF- 1kHz - 110Mc/s-
A IF £600 or B IF - £700.HP141T + 8552A or B IF - 8554B RF - 100kHz -
1250Mc/s -A IF £800 or B IF - £900.HP141T + 8552A or B IF - 8555A RF - 10Mc/s - 18GHz-A IF £1400 or B IF - £1600. The mixer in this unitcosts £1000, we test every one for correct gainbefore despatch.
HP141T + 8552A or B IF - 8556A RF - 20Hz - 300kHz -A IF £600 or B IF- £700.
HP ANZ UNITSAVAILABLE SEPARATELYNEW COLOUR - TESTED
Mainframe Plus 8552A IF Plug -In Plus 8556A RF Plug-In 20Hz - 300kHz Plus 8553B RF Plug -In 1kHz -110Mc/s. Tested with instructions -000.
Marconi TF2008 - AM -FM signal generator - also sweeper - 10Kcis - 510McIs - from E250 - testedto £400 as new with manual - probe kit in wooden carrying box.
HP Frequency comb generator type 8406 -£400.HP Vector Voltmeter type 8405A - E400 to £600 - old or new colour.HP Sweep Oscillators type 8690 A & B + plug -ins from 10Mds to 18GHz also 18-40GHz. P.O.R..HP Network Analyzer type 8407A + 8412A + 8501A - l0OKc/s -110Mc/s -0500 - E1000.HP Amplifier type 8447A - 1-400Mc/s f200 - HP8447F. 1-1300Mc/s £400.HP Frequency Counter type 5340A - 18GHz 11000- rear output £800.HP 8410 -A -B -C Network Analyzer 110Mc/s to 12GHz or 18GHz - plus most other units and
displays used in this set-up -8411a 8412 8413 8414 8418 8740 8741 8742 87438746- 8650. From E1000.
Racal/Dana 9301A - 9302 RF Millivoltmeter - 1.5-2GHz - E250 -E400.Racal/Dana Counters 9915M -9916 - 9917 - 9921 -£150 to £450. Fitted FX standards.Racal/Dana Modulation Meter type 9009 - 8Mc/s - 1.5GHz - E250.Marconi RCL Bridge type TF2700 -£150.Marconi/Saunders Signal Sources type - 60588 - 6070A - 6055A - 6059A - 6057A - 6056 -
£250-1350. 400Mds to 18GHz.Marconi TF1245 Circuit Magnification meter + 1246 & 1247 Oscillators - 1100-1300.Marconi microwave 6600A sweep osc., mainframe with 6650 PI - 18-26.5GHz or 6651 PI - 26.5-
40GHz £1000 or PI only £600. MF only £250.Marconi distortion meter type TF2331 - E150. TF2331A - 200.Tektronix PlugIns 7A13 - 7A14 - 7A18 - 7A24 - 7A26 -7A11 -7M11 -7S11 - 7D10 - 7S12 - S1
7904 - 7834 - 7104 - 7623 - 7633.Alltech 757 Spectrum Analyser - 001 22GHz - Digital storage + readout - £2000.Marconi 6155A Signal Source - 1 to 2GHz - LED readout - £400.Barr & Stroud Variable filter EF3 0.1Hz - 100kds + high pass + low pass - f150.Marconi TF2163S attenuator - 1GHz. £200.Famell power unit H60/50 -E400 tested. H60/25 - £250.Racal/Dana 9300 RMS voltmeter - £250.HP 8750A storage normalizer -£400 with lead + S.A or N,A Interface.Marconi TF2330 - or TF2330A wave analysers - £100-150.Racal/Dana signal generator 9082 - 1.5-520Mc/s - E500.Racal/Dana signal generator 9082H - 1.5-520Mc/s - £600.Tektronix -7514 -7711 -7S11 -7S12 - S1 - S2 - S39 -S47 - S51 - S52 - S53 -7M11.Marconi mod meters type TF2304 - £250.HP 5065A rubidrum vapour FX standard - £2.5k.Systron Donner counter type 60548 - 20Mc/s - 24GHz - LED readout - El k.Racal/Dana 9083 signal source - two tone- £250.Systron Donner - signal generator 1702 - synthesized to 1GHz - AM/FM - £600.Tektronix TM515 mainframe + TM5006 mainframe - E450 - £850.Rhodes & Schwartz power signal generator SLRD-280 - 2750Mc/s - £250-1600.Ball Efratom rubidrum standard PT256B-FRKL -£1000.Farnall electronic load type RB1030-35 - E350.Racal/Dana counters - 9904 - 9905 - 9906 -9915 - 9916 - 9917 - 9921 - 50Mc/s - 3GHz - £100-
E450 - all fitted with FX standards.HP4815A RF vector impedance meter c/w probe - £500-1600.Marconi TF2092 noise receiver. A, B or C plus filters -£100-1350.
Marconi TF2091 noise generator. A, B or C plus filters - £100-1350.HP180TR, HP182T mainframes 1300-1500.Fluke 8506A thermal RMS digital multimeter. £400.Philips panoramic receiver type PM7900- 1 to 20GHz - £400.Marconi 6700A sweep oscillator + 6730A -1 to 2GHz - £500.HP8505A network ANZ + 8503A S parameter test set + 8501A normalizer - 14k.Racal/Dana VLF frequency standard equipment. Tracer receiver type 900A + difference meter
type 527E + rubidium standard type 9475 - £2750.HP signal generators type 626 - 628 - frequency 10GHz - 21GHz.HP 432A - 435A or B - 436A - power meters + powerheads - Mc/s - 40GHz - E200-11000.Bradley oscilloscope calibrator type 192 - E600.Barr & Stroud variable filter EF3 0.1Hz - 100Kds + high pass + low pass -£150.Marconi TF2370 spectrum ANZ -110Mds - £900.Marconi TF2370 spectrum ANZ + TK2375 FX extender 1250Mc/s + 1st gen -11.5k.HP8614A signal generator 800Mc/s - 2.4GHz, new colour £400.HP8616A signal gen 1.8GHz - 4.5GHz, new colour £400.HP 3325A syn function gen 20Mc/s -11500.HP 3336A or B syn level generator - 1500-1600.HP 3586B or C selective level meter - 1750-11000.HP 3575A gain phase meter 1Hz - 13Mds - £400.HP 8671A syn microwave 2 - 6.2GHz - 12k.HP 8683D S/G microwave 2.3 - 13GHz - opt 001 - 003 - 14.5k.HP 8660 A -B -C syn S/G. AM + FM + 10Kds to 110Mds PI - 1Mds to 1300Mds - 1Mc/s to
2500Mc/s - 1750-12800.HP 8640B S/G AM -FM 512Mc/s or 1024Mds. Opt 001 or 002 or 003 -0300-E1250.HP 8656A S/G AM -FM 0.1 - 990Mds - E1500.HP 86228 Sweep PI - 01 -2.4GHz + ATT -11750.HP 8629A Sweep PI -2 - 18GHz - £1000.HP 862908 Sweep PI -2 -18GHz - £1250.HP 86 Series Prs in stock - splitband from 10Mds -18.6GHz -E250-Elk.HP 8620C Mainframe - 1250. IEEE - £500.HP 8615A Programmable signal source- 1MHz- 50Mc/s - opt 002 -El k.HP 8601A Sweep generator .1 -110Mds - £300.HP 4261A LCR meter + 16038A test leads -1400.HP 4271B LCR meter 1MHz digital meter + 16063A test adaptor - E850.HP 4342A 0 meter 22kHz - 70Mc/s 16462A + qty of 10 inductors - £850.HP 3488A HP -18 switch control unit - £500 + control modules various -1175 each.HP 3561A Dynamic signal ANZ - £3k.HP 8160A 50Mds programmable pulse generator - £1400.HP 853A MF ANZ + 85588 - 0.1 -1500Mc/s -12500.HP 8349A Microwave Amp 2 - 20G Hz Solid state - E1500HP 3585A Analyser 20Hz - 40Mc/s - £4k.HP 85698 Analyser .01 - 22GHz - E5k.HP 3580A Analyser 5Hz - 50kHz -Elk.HP 1980B Oscilloscope measurement system - £600.HP 3455A Digital voltmeter - £500.HP 3437A System voltmeter -1300.HP 3581C Selective voltmeter -E500.HP 5370A Universal time interval counter - E450.HP 5335A Universal counter - 200Mc/s - 1500.HP 5328A Universal counter - 500Mc/s - E250.HP 6034A System power supply -0- 60V -0- 10 amps - 1500.HP 3960A 3964A Instrumentation tape recorders - 1300-1500.HP 5150A Thermal printer - E250.HP 1645A Data error analyser - £150.HP 4437A Attenuator -1150.HP 3717A 7OMc/s modulator - E400.HP 3710A - 3715A - 3716A - 3702B - 3703B - 3705A - 3711A - 3791B - 3712A - 3793B
microwave link analyser - P.O.R.HP 3730A+ 8 RF down converter - P.O.R.HP 3552A Transmission test set -1400.HP 3763A Error detector - £500.HP 3764A Digital transmission analyser -1600.HP 3770A Amp delay distortion analyser - E400.HP 3780A Pattern generator detector -E400.HP 3781A Pattern generator - E400.HP 3781B Pattern generator Weill- 1300.HP 3782A Error detector - £400.HP 37828 Error detector (bell) - E300.HP 3785A Jitter generator + receiver - £750 -Elk.HP 8006A Word generator - £100-E150.HP 8016A Word generator - £250.HP 8170A Logic pattern generator -E500.HP 59401A Bus system analyser -1350.HP 59500A Multiprogrammer HP- IB - £300.Philips PM5390 RF syn - 0.1 - 1GHz - AM + FM -E1250.Philips PM5519 Colour T.V. pattern generator- £250.S.A. Spectral Dynamics S0345 spectrascope 111 - LF ANZ- £2500.Tektronix R7912 Transient waveform digitizer - programmable -1400.Tektronix 496 Analyzer lkHz - 1.8GHz - 13.5k.Tektronix TR503 + TM503 tracking generator 0.1 - 1.8GHz - El k - or TR502.Tektronix 576 Curve tracer + adaptors - 1900.Tektronix 577 Curve tracer + adaptors -ENO.Tektronix 1502/1503 TDR cable test set -11000.Tektronix 7L5 LF analyser -0 - 5Mc/s -1800. OPT 25 - 11000.Tektronix AM503 Current probe + TM501 m/frame -£1000.Tektronix SC501 - SC502 - SC503 - SC504 oscilloscopes - 175-1350.Tektronix 465 -4658 - 475 2213A 2215 2225 2235 2245 2246 1250-11000.Kikusui 100Mc/s Oscilloscope COS6100M -1350.Farnell PSG520 Signal generator -1400.Nicolet 3091 LF oscilloscope -El 000.Racal 1991 -1992 -1988 - 1300Mc/s counters - 1500-1900.Tek 2445 150Mc/s oscilloscope - 11400.Fluke 80K-40 High voltage probe in case - BN -£100.Racal Recorders - Store 4 - 4D -7 - 14 channels in stock -1250 -1500.Racal Store Horse Recorder & control - 1400-1750 Tested.EIP 545 microwavel8GHz counter -E1200.Fluke 510A AC ref standard - 400Hz - £200.Fluke 355A DC voltage standard - E300.Schlumberger 5229 Oscilloscope - 500Mc/s - £500.Solartron 1170 FX response ANZ - LED dislay - E280.Wiltron 610D Sweep Generator + 6124C PI - 4- 8GHz - £400.Wiltron 610D Sweep Generator + 61084D PI - 1Mc/s - 1500Mc/s -1500.Time Electronics 9814 Voltage calibrator -1750.Time Electronics 9811 Programmable resistance - 1600.Time Electronics 2004 D.C. voltage standard - £1000.HP 8699B Sweep PI YIG oscillator .01 - 4GHz - E300. 86908 MF - £250. Both 1500.Schlumberger 1250 Frequency response ANZ - 12500.Dummy Loads & power att up to 2.5 kilowatts FX up to 18GHz - microwave parts new and ex
B&K Items in stock - ask for list.W&G Items in stock - ask for list.Power Supplies Heavy duty + bench in stock- Farnell -HP- Weir- Thurlby - Racal etc. Ask for list.
ITEMS BOUGHT FROM HM GOVERNMENT BEING SURPLUS. PRICE IS EX WORKS. SAE FOR ENQUIRIES. PHONE FOR APPOINTMENT OR FOR DEMONSTRATIONOF ANY ITEMS, AVAILABILITY OR PRICE CHANGE. VAT AND CARRIAGE EXTRA
ITEMS MARKED TESTED HAVE 30 DAY WARRANTY. WANTED: TEST EQUIPMENT -VALVES -PLUGS AND SOCKETS-SYNCROS-TRANSMITTING AND RECEIVING EQUIPMENT ETC.
European R&D or Euro-waste?It looks as if the Clinton administrationis prepared to go further than everbefore in directly intervening to
encourage manufacturing activity.The EU, which has always been
prepared to subsidise research, but hasbeen reluctant to finance manufacturingdirectly, must now start to take notice: incertain critical markets, it looks as if theEU could fall hopelessly behind the restof the world.
One of these is flat -panel displays forwhich the US Government has justannounced a $1bn support programmeaimed directly at manufacturers.
Japan has a 95 per cent share of theworld flat panel market - nowapproaching $5bn and set to grow to$20bn within the decade. Just as withsemiconductors in the 80s, such animbalance threatens trade wars, shortagesand over -pricing in the 90s as Japan,quite naturally. exploits its monopoly.
Europe, for many years, backed R&Dinto flat panel technology. Although thisresulted in a successful series ofprogrammes, no European companyexcept Philips, is going to massmanufacture the panels.
Without mass manufacture, Europe willglean little benefit from the money spenton R&D. European electronics equipmentmanufacturers will have to pay highJapan -dictated prices.
President Clinton has been smarter thanthe EU. He has insisted, as a pre-condition of getting Federal R&D funds,
that the recipients put up a similaramount to build factories.
That is reminiscent of the famous chipR&D programmes which the JapaneseMinistry of International Trade andIndustry initiated in the 70s and 80s togive Japan a world -class semiconductorindustry - manufacturing was aprecondition for the R&D money.
The lesson for Europe is clear: givingmoney to scientific programmes is allvery well but that doesn't produce futurerevenues from which profits can be takento fund the next generation of R&D.
Yet though everyone in Europe is keento spend government money on R&D,there is practically no one ready to takethe commercial risk of putting high-techcomponents into volume manufacturing.
It is absolutely clear to everyone,except Europe's leaders, that the peoplewho can afford to take the risk - the bigcompanies - won't take it but those whoare prepared to take the risk - smallentrepreneurs - can't afford it.
The EU must therefore seek to create anenvironment for the entrepreneur toundertake high-tech manufacturing -fiscally, technically and socially.
For if manufacturing does not happenas the result of R&D then R&D isessentially no more than intellectualonanism - failing to produce the seed fornext -generation products.
David Manners - Electronics Weekly
Electronics World + Wireless World is published monthly. Bypost, current issue £2.25, back issues (if available) £2.50.Orders, payments and general correspondence to L333,Electronics World + Wireless World, Quadrant House, TheQuadrant, Sutton, Surrey SM2 5AS. TIx:892984 REED BP G.Cheques should be made payable to Reed BusinessPublishing Group.Newstrade: IPC Marketforce, 071 261-5108.Subscriptions: Quadrant Subscription Services, OakfieldHouse, Perrymount Road, Haywards Heath, Sussex RH163DH. Telephone 0444 445566. Please notify change ofaddress. Subscription rates 1 year (normal rate) £30 UK and£43 outside UK.USA: $52.00 airmail. Reed Business Publishing (USA),Subscriptions office, 205 E. 42nd Street, NY 10117.
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Microprocessor game is the real businessMicroprocessor evolution will in futurebe driven by the demands of games,
not PCs, says Len Perham, president andchief executive officer of Integrated DeviceTechnology.
"The games people are looking fortremendously high performance processors -one of the top five has asked me for a 64 -bitprocessor with a 800Mbit data rate,"
Perham added: "We're developing it, andwe can see it costing only $20." IDT is alicensee of the Mips micro architecture.
Perham also sees the manufacturers ofgames machines moving inexorably into thecomputer market. "By the year 2000,Nintendo will be a computer company," hepredicted.
The advantage which the games machinemakers have over the computer companies isthat they have to manufacture to very lowcosts. "Nintendo and Sega say you can't sellin volume for more than £250," said Perham.
NEC, Toshiba and Sony hold rights to theMips processor.
It will not only be dedicated gamesmachines that will require this power. Theset -top controller driving remote terminals,the home entertainment system and homesecurity will demand 64 -bit performancebecause the graphics take so muchprocessing power.
High flyers: the performance demands of videogames coupled with enormous potential salesvolumes are now more important tomicroprocessor development than businessapplications.
Faster technology for speeding motoristshe automatic intelligent recognition
I system, named Talon, designed torecognise the most obscured, tilted ordamaged vehicle number plates is latestpiece of technology to persecute motorists.
The system uses neural networks fornumber plate pattern recognition. In itssimplest form it consists of a camera,illuminator and a plate recognition unit(PRU) which contains the programmableDSP hardware. The PRU consists of animage grabber board, a general purpose PC
board and a DSP board on which the neuralnetwork is implemented.
The system triggers automatically whenencountering the right colour (yellow orgrey) or image of a number plate.
The plate is then segmented intoindividual characters before being fed intothe recognition process that uses proprietaryneural network techniques implemented onfive Texas Instruments TM320050 DSPchips.
All imperfections associated with number
James Thomas, Director of Risc microdevelopment at IBM, concurs: "Set -tops andPDAs are going to be the explosive areas ofthe second half of the 90s," he toldDataquest's recent European semiconductorIndustry Conference in London. "Kids,"concludes IDT's Perham, "can absorb asmuch computer power as you can give them."
Ordinary PCs can operate as effectivevideo game players by placing video gamemachines onto PC cards. This approach isbeing taken by game player designer 3D0which is working on custom chips that willallow it to sell its system as a PC plug-inboard. Atari, with its 64 -bit Jaguar gamesystem recently signed a deal with SigmaDesigns to produce a board combiningJaguar with Sigma's full motion videotechnology.
The US based Software Publisher'sAssociation (SPA) estimates that about 27percent of US households own a personalcomputer. About a third of those PCs werepurchased within the last year. As pricescontinue to fall for PC hardware andsoftware, the SPA predicts that demand forpowerful home based PCs will continue togrow. David Manners, Electronics Weekly.
plates are included in the training data whichmakes the recognition process resilient tonoise such as dirt, poorly defined ordistorted characters. In this way the networkis also trained to de -skew and de -rotate inorder to recognise the plate.
Talon recognises number plates inapproximately 0.25s. The success rate ishigher than 90 per cent.
Talon works in many weather conditionsand for night vision any off -the -shelfinfrared camera and illuminator can be used.Plate shadowing can be eliminated withinfrared filters on the camera.
The system was originally developed by
Camcorder controlledby the eyeCanon of Japan claims to have developedthe first camcorder which is controlledby eye movements. To focus, thecamcorder uses infrared light todetermine where the user's eye is lookingin the field of view. It then focuses onthis point automatically. Other camerafunctions are operated by the userlooking at icons displayed alongside theimage in the viewfinder.
111111MIXIMMUIMMIEMIAnritsu ML93B/ML92B Optical power meter with sensor £2000Anritau ME538C Microwave system analyser (Rx + Tx) £3500BAK 2511 +1621 Vibration test set £2000BAK 2511 Vibration meter C1500BAK 2515 Vibration analyser £4500Daymarc 1735 Transistor tester/sorter (with all cgs) C5000Dranetx 305 Phase meter £250Dymar 1585 AF Power meter £175
Dymer 2085 AF Power meter £200Farnell RB 1030-35 Electronic load 1Kw £450Farnell AMM/B Automatic modulation meter £150Farnell 2081 R/F Power meter POAFeedback TWG300 Test waveform generator £200Fischer Betascope 2040/2060 Coating thickness computer 8 nondestructive coating measurement instrument 8 many jigs and extras ...
all for C2000Fluke 8840A Multimeter (IEEE) C300Fluke 515A Portable calibrator C500Fluke 5200A Programmable AC calibrator POAFluke 8010A Digital multimeter £125Fluke 8922A True RMS voltmeter POAFluke 95020 Current shunt POAGay Milano FTMIC/FTM3C -FTM- Fast transient monitor £250General Rad 1858 LCR Digibridge £250General Red 1621 Precision capacitance measurement system POAHewlett Packard 80TR Display unit with 8755B swept. amp. an 8350Hewlett Packard 32006 VHF oscillator, 10-500MHz £175Hewlett Packard 3400A RMS voltmeter 0150Hewlett Packard 3406A Broadband samping voltmeter C175Hewlett Packard 3437A System voltmeter C350Hewlett Packard 3476A Digital multimeter C100Hewlett Packard 3479A Digital voltmeter, 4 wire system. IEEE C650Hewlett Packard 3490 Digital multimeter POAHewlett Packard 3702B/3705A/3710A/3716A Microwave linkanalyser £1500Hewlett Packard 3730A Down converter (with 3738A or 3737A) C200Hewlett Packard 3760/3761 Data gen error detector ... each C300Hewlett Packard 3762/3763 Data gen - error detector each £350Hewlett Packard 3777A Channel selector £250Hewlett Packard 3779A Primary multiplex analyser C800
Hewlett Packard 400E/F AC voltmeterHewlett Packard 4193A Vector impedance meterHewlett Packard 4204A Oscillator 10Hz - 1MHzHewlett Packard 435A Power meter (less sensor)Hewlett Packard 456A AC current probeHewlett Packard 4156 SWR meterHewlett Packard 5335A Universal counter with t EEEHewlett Packard 5342A Microwave freq. count. 18GHzHewlett Packard 7402 Recorder with 17401A x 2 plug -ins .Hewlett Packard 80058 Pulse generatorHewlett Packard 8011A Pulse gen. 0.1Hz - 20MHzHewlett Packard 80128 Pulse generatorHewlett Packard 8013B Pulse gen. 1Hz - 50MHzHewlett Packard 8406A Frequency comb. generatorHewlett Packard 8443A Tracking gen/counter with IEEEHewlett Packard 84458 Automatic presetterHewlett Packard 8601A 110MHz Gen/sweeper 110MHzHewlett Packard 86200 Sweep oscillator mainframeHewlett Packard 8750A Storage normaliserHewlett Packard 938A Freq. doublerHewlett Packard 86408 with opt 001Keithley 197 20MHz with IEEELyons PG73N/PG75/PG2B/PG Pulse generatorMarconi 2019A 80KHz - 1040MHz sig. gen.Marconi 2306 Programmable interfaceMarconi 2337 Automatic dist. meterMarconi 2356 20MHz level oscillatorMarconi 2432A 500MHz digital freq. meterMarconi 2610 True RMS voltmeterMarconi 2830 Multiplex testerMarconi 2831 Channel access switchMarconi 5390 1GHz signal gen.Marcon I 6920 Power sensor
Marconi 2022E (10KHz.1.01GHz) sig. gen £1650Marconi 2010A (10KHz-1.04GHz) sig. gen 61650Philips PM 2525 Multimeter WF IEEE £850Philips PM 5167 10MHz lunctiongen. £400Philips PM 5190 LF synthesizer w/th GPIB £1300
Philips PM 5519 Colour TV pattern gen. £400Philips PM 5716 Pulse generator high freq. mos C600Philips PM 5770 Pulse gen. - 1MHz -100MHz £150Philips PM 6672 1GHz timer/Counter WF IEEE £850Philips PM 8272 XYT chart recorder £500Photodyne 800 Fibre optic attenuator £350ProJectina C19345 Microscope 0800Racal Dana 202 Logic analyser + 68000 disassembler £250Racal Dana 3100 40-130MHz synthesiser £750Racal Dana 5002 Wdeband level meter £650Racal Dana 5003 Digital m/meter £150Racal Dana MOO Microprocessing timer/count. 52MHz C250
Reza' Dan 909 Modulation meter 0225Awe, Dana 8081 Synth. sig. gen. 520MHz £550Racal Dana 90)84 Synth. sig. gen. 104MHz £450Racal Dana 8242D Programmable PSU 25V -2A £300Racal Dana 92465 Programmable PSU 25V -10A £400Racal Dana 8303 True RMS/RF level meter £650Racal Dana 041 LCR databrldge £250Racal Dana 9500 Universal timer/counter 100MHz £200Racal Dana 917 UHF frequency meter 560MHz £175Racal Dana 8919 UHF frequency meter 1GHz £275Rohde 8 Schwarz BN36711 Digital 0 meter £400Solartron Schlumb 1170 Freq. response analyser £500TeKtronix TM503, SG503, PG506, TG501 Scope calibrator £2200Tektronix 834 Data comms analyser £500WAG SPM12 Level meter 200Hz-6MHz £500WAG PS12 Level generator 200Hz-6MHz 0500WAG SPM60 Level meter 6KHz-18.6MHz £500WAG PS60 Level generator 6KHz-18.6MHz £500WAG PS6 Level generator 6KHz-18.6Mhz £250WAG SPM6 Level meter 6KHz-18 6MHz £250Watanabe WTR211 3 pen plotter 0250Wavetek 157Programmable waveform synthesiser . ..... 0300Wayne Kerr 6424/N LCR Component meter setWayne Kerr 8250 LCR meter (as new) 01000Wayne Kerr 642 Autobalance universal bridge £200Weller D800/0801 Desoldering station 0175
Weller 0900 Desoldering station C150Wftron 352 Low freq. differential input phase meter 0350
SPECIAL OFFERS - Phoenix 5500A Telecoms analyser. exdemo. as taw with 12 months calibration v 12 months guaranteefiled with 1..24 interface. A variety of interface options available -Ring/Fax for details. Navtel 9440 Protocol analyser, ex. demo. asnew 08000 new - cost now 03500. Navtel 9410 PCB based protocolanalyser ex demo as new £3000 new - cost now £1500.
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SEETRAX CAE - RANGER - PCB DESIGNRangerl £100
* Schematic capture linked to PCB* Parts and wiring list entry* Outline (footprint) library editor* Manual board layout* Full design rule checker* Back annotation (linked to schematic)* Power, memory and signal autorouter -1.50
All systems upward compatible. Trade-in deals available.
Call Seetrax CAE for further information \demo packs.Tel 0705 591037 Fax 0705 599036
Ranger2 £599All the features of Rangerl plus* Gate & pin swapping (linked to schematic)* Track highlighting* Auto track necking* Copper flood fill* Power planes (heat -relief & anti -pads)* Rip -up & retry autorouter
Ranger.3 £3500All the features of Ranger2 plus* UNIX or DOS versions* 1 Micron resolution and angles to 1/10th degree* Hierarchical or flat schematic* Unlimited design size* Any -shaped pad* Split power planes* Optional on-line DRC* 100% rip -up & retry, pusi' & shove autorouter
Big speed-up for VMEJuly will see the first production shipmentsof a Spanceiver chip for high speed serial
data transfers across the VMEbus.Called Autobahn, and developed jointly by
Motorola and German real-time boardmaker PEP Modular Computers, thetechnique essentially provides a serialbypass, with transfer rates of between 200and 400Mbyte/sec, to the 32 -bit or 64 -bitparallel bus transfers occurring on a standardVMEbus backplane.
Balloting to accept Autobahn as an ANSIstandard should be completed by the end ofthe year, according to PEP president JosefKreidl.
Autobahn was developed because thetraditional way of boosting data throughputis to increase the word width or increase theclock frequency or both. But this cannot goon indefinitely because of the respectivetrade-offs of more board space and greaterpower dissipation.
Using a high speed serial link to transmitlarge amounts of data avoids many of theseproblems. The crucial device needed toconvert the 32 - bit parallel data into a
200Mbyte/s serial stream is Motorola'sSpanceiver.
Kraus points out that the high speed of ECLcan be achieved without a corresponding risein power dissipation. The net result is that thepower overhead associated with using theAutobahn Spanceiver chips is about100Mbyte/s/W when performing transfers of200Mbyte/s. This compares with figures of8Mbyte/s/W for a typical VMEbus systemtransferring 32bit parallel data at a rate ofonly 40Mbyte/s.
The Spanceiver is also designed tominimise the protocol overhead, the timetaken to set up transmissions. The chipcontains a novel phase locked loop (PLL)design combined with a start stop oscillatorthat allows data to be transmitted in burstswithout preamble bits. This means that whentransmission starts, the PLL locks on thefirst sync bit so that the normal settlingperiod required for clock recovery iseliminated. The data transfer is nearlyoverhead free with only one sync bit neededfor every byte transmitted. The bit error ratewill also be reduced. David Darcy.
New conversion leads the fieldUS firm Comlinear believes it hasdeveloped an analogue -to -digital
converter (ADC) architecture capable ofproviding 12 -bit performance at conversionrates as high as 50MHz.
The subranging architecture uses noveltechniques in the second stage to minimisethe comparator count, avoiding theassociated power dissipation penalty whileboosting conversion speed.
The firm has designed a 12 -bit 25MHzADC called the CLC950, which it claimshas a better performance than any othermonolithic converter of its class on themarket. It is to be followed early next yearby the CLC951 device with a 12 -bit, 30MHzperformance and a third chip with a targetconversion rate of 50MHz.
In a classic subranging ADC architecturethe comparator ladder is split into severalsmaller blocks or ranges. This schemereduces power consumption and savessilicon area. Conversion errors caused by aninput being close to a sub -range boundary
Fine vision of the futureK I ikon, the world's top maker of stepper
NA machines for lithography on chips, hasstarted the R&D programme for the 16Gbitdram under the auspices of the Japanesegovernment backed research organisationSortec.
Nikon says it has already developedlithographic techniques for feature sizesdown to 0.05jtm using a an X-ray with a13nm wide beam, and a feature size of0.015 -micron using a 4.5nm X-ray beam.
are usually detected by having a smallnumber of extra comparators either side ofthe boundary. The errors are then correcteddigitally.
The subranging technique is closelyrelated to the two stage residue architecture.Both techniques need an overlap betweenthe first and second stages, typically of twobits to correct for overall system errors. (sixbits plus eight bits would be needed for a12 -bit converter).
The Comlinear architecture converts fivebits in the first stage using a classic flashcomparator ladder. However, according toengineer Kurt Rentel, the innovative secondstage needs no overlap nor does it employsignal averaging techniques.
The CLC950 has a signal-to-noise ratio(SNR) of 65dB for a full-scale analogueinput at 12.49MHz. However, the spuriousfree dynamic range (SFDR) is 70dB risingto 74dB for a 9.96MHz analogue input. TheSNR is then 66dB.Simon Parry, Electronics Weekly.
Nikon's schedule for the stepper is to have itavailable for chip companies by 1999 whenit is expected that the first prototypes of16Gbit DRAMs will be made.
The current leading technology dram inmass production is the 16Mbit made on0.5jim processes. It is expected to besucceeded by: 64Mbit on a 0.35µm process;256Mbit on 0.25µm; 1Gbit on 0.15µm;4Gbit on 0.065jtm, and 16Gbit on 0.035µm.
Intel to kill offageing family?
Solid rumours out of Intel claim that theUS microprocessor company's next -but-
one device will break with the existing x86architecture, relying on x86 emulation tomaintain compatibility with older systems.Sources say that the P7, that will appearclose to the end of this decade, will be apure risc design unlike the current Pentiumand its successor, the P6, which mix risc andcisc designs.
Asked if it were true that the P7 wouldhave to emulate some x86 instructions anIntel spokesman said: "We're really nottalking about the P7 yet publicly. It's soearly in the development of that product that Idoubt there is much locked in concrete yet."
The company would hope that a riscdesign for the P7 will allow it to keep upwith microprocessor rivals such as thePowerPC. The P7 will be able to separatelyprocess cisc and risc instructions with thecisc instructions being processed in ahardware emulation of an x86microprocessor.
Intel plans to introduce its successor to thePentium, code -named P6 by the end of1995. This device is expected to be sold as atwo -chip module featuring the CPU with256kbytes of high speed cache memory.
Devereux diesFrederick Leslie Devereux, who retired in 1965 as Editorof Wireless World, has died.
Born in Birmingham on May 5, 1900, "Dev"developed an interest in "wireless" very early, while atschool. In 1917, he went to the Admiralty Board ofInvention and Research at Harwich as a lab. mechanicworking on asdic and in 1918 joined the anti-submarinedivision of the Royal Navy as a midshipman. Later, hejoined his father's manufacturing jewellery business, butdecided instead to take a degree in physics fromBirmingham. Armed with that, he went into soundbroadcasting, worked on receiver development, wrote onthe subject for the Birmingham Post and naturallygravitated to WW, eventually becoming Assistant Editorunder H F Smith' and Editor in 1957.
His knowledge of the industry was prodigious,particularly of the audio side. He appeared to knoweveryone, sometimes using this knowledge to bullynervous potential authors into writing for the journal, eventhough he knew the result might be in pidgin English.
His sense of humour was usually well to the fore andfrequently in use to cut cocky journalists down to size.
My own experience of this was when I had written apiece about the 1963 deliberations on the choice of colourtelevision system in and proudly submitted it for hiscomments. "You know, they have to chop trees down toprint this stuff; it's a pity to waste them, don't you think?",he said. "Go away and rewrite it, preferably in English".
It was Dev who accepted Arthur C Clarke's 1945 pieceon the possibility of communications satellites againstthe advice of his colleagues who thought it wasnonsense. He took it home with him, did the sums and,realising it was feasible, went ahead, thereby presentingthe journal with a cachet that has lasted fifty years.Philip Darrington
534 ELECTRONICS WORLD + WIRELESS WORLD July 1994
Tektronix Das 9100 Logic analysers. Complete - £700.Nicolet 800A Logic Analysers - 48 Ch -16 Bit - £450.HP7580B-7585B Drafting Plotter -£1,000.Bradley 127 DC Voltage Calibrator - £250.Bradley 1259 AC Calibrator + Ration Transformer 1255 + PI 12548 50 C ;60-400-1 KC/s - £250.Marconi 6460/1 Power Meters + Heads RF various - £250 ea.Marconi 6460 Power Meters + Heads RF various - £150 ea.Marconi CT499 MIcll RF Watt Meter Absorption 1-3-10-30-100W -50ohm+70ohmConvertor Adaptor - £350. Includes RF Adaptors Low Loss.HP59500A Multiprogrammer Interface.HP6940B Multiprogrammer or HP6941B - £100-£200.Datalab DL1200 Waveform Recorder- £300.Solatron 1170 FX Response ANZ-Led - £300.HP59401A Bus System ANZ.STC Optical Fibre Reflectometer OFR6 - £300.HP3497A Data Acquisition Control Unit - £300.Redifon Synthesized Receiver R1001-CW-AM-USB-LSEi-PIC-STORE-LedReadout - 15KC/s-30MC/s- £600.Racal LA1117 Piccolo Modem -£150.Redifon RFS11 Pre -Selector - Post Selector -1MC/s-32MC/s - £200.Sayrosa 3-39MC/s Programmable Freq Syn-Type607+607B - £200-£300.Racal TA1816 1Kw Solid State Transmitter - MA1034+3 Pare Amps -£1.000.H.C.D. Research Ltd Precision Oscillator 1519 5000/1000KHz - £250.Nimbus 400Hz Convertor Mains - 240AC-500C/s Input -Output 115V-400Hz -500V/A Programmable 0-125V. G500 FPL- £300. G200R as above -200V/A - £200.Hedinair Monfford Environmental Ovens etc. Big +Small -£200-£1,000.ICL Clean Linez Unit - £300.HP6943A Multiprogrammer extenders - £300.HP6525A DC P.U.O.-4000V-50M/A- £350.Polaroid +, CR-9 Cameras for Oscilloscopes -£100.HP3710A IF -BB Transmitter, HP3702B IF/BB Receiver +3705A Phase Detector- £250.Moor & Reed Frequency Convertor 400C/s 3 Phase Type SFC 6K/3AXR - SolidState - 2OAmps/Mains 240V AC-50C/s Input - £600.HP7586B Plotter Large Quantity Accessories Pens etc- HP-IB-RS2320 -£1,000.Benson 16 BZ80 Asynchrome Interface + Accessories & Pens etc - £600.lmtec 6000 Microfilm Reader & Printer, A4 -A2 sizes -Plain Paper - Various Lenses - £750.Fluke Y5020 Current Shunt- £150.B&K 2107 FX Analyser -£250.B&K BFO 1022 - £200.Tektronix Spectrum ANZ-1L5-50HZ - 1MC/s - £150 -1L20-10MC/s-4200MC/s - £250.FARNELL P.U. AP60-50-60V-50Amps -£1,000.Tracor 527E Frequency Difference Meter - £350.HP8900B Peak Power Calibrator - £250.B&K 2425 Electronic Voltmeter - £200.HP4437A 600 ohms Attenuator - £150.HP6177C DC Current Source - £250.B&K Two Channel Level Recorder- £400.Tektronix 2213 60MC/s Oscilloscope - £300 -2213A - £350.Tektronix 2215 60MC/s Oscilloscope - £350.Tektronix 2445 150MC/s Oscilloscope -£1,200.Tektronix 2246 100MC/s Oscilloscope -£1,000.Tektronix 2225 150MC/s Oscilloscope - £800.Tektronix 2245 100MC/s Oscilloscope - £700.Tektronix 491 Spectrum ANZ 10MUs-40GHC -£1,000.Farnell P.U. H30/100 - £500.Schlumberger S1 4922 Radio Code ANZ - £400.Aerial Array on metal plate 9"x9" containing 4 aerials plus Narda detector. 100-11GHZ using N type and SMA Plugs & Sockets - ex equip - £100.Marconi TF2175 Power Amplifier - 1.5MC/s-520MC/s + Book - £100.Schlumberger 2741 Programmable Microwave Counter - 10HZ-7.1GHZ - £750.Schlumberger 2720 Programmable Universal Counter- 0-1250MC/s - £600.Tektronix 576 Calibration Fixture - 067-0597-99 - £250.Texscan Rotary Attenuators BNC/sMA -0-10-60-100DBS - £50-£150.HP809C Slotted Line Carriage - Various frequencies to 18GHZ- £100-£300.HP532-536-537 Frequency Meters Various Frequencies- £150-£250.S.E. Lab SM215 Mkll Transfer Standard Voltmeter - 1000 Volts.Ailtech Stoddart P7 Programmer - £200.HP6181 DC current source - £150.HP59501A HP-IB Isolated D/A Power supply programmer.HP3438A Digital Multimeter -£150.HP6177c DC Current Source - £150.HP6207B DC Power Supply - £100.HP741B AC/DC differential voltmeter standard (old colour) - £100.HP6209B DC Power Unit- £100.Fluke 431C High voltage DC supply.Tektronix M2 Gated Delay Calibration fixture -067-0712-00.Tektronix Precision DC Divider Calibration fixture - 067-0503-00.Tektronix Overdrive Recovery Calibration fixture - 067-0608-00.HP50117 Logoc Trouble Shooting Kit- £150.PPM 8000 Programmable Scanner.Fluke 730A DC Transfer Standard.B&K 4815 Calibrator Head -£150.B&K 4812 Calibrator Head - £150.HP FX Doubler 938A or 940A - £300.HP461A Amplifier 1KC-150MC/s - Old Colour -£100.Ailtech Precision Automatic noise figure indicator type 75- £250.Adret FX Synthesizer 2230A - 1MC/s - £250.Marconi TF2512 RF Power Meter -10 or 30 Watts - 50 ohms - £80.Marconi 2830 Multiplex Tester.Marconi 2828A Digital Simulator.Marconi 2831 Channel Access Switch.Marconi TF2337A Automatic Distortion Meter- £150.HP489A Micro -Wave Amp-1-2GHZ - £500.Fluke 893A Differential Meters -£100 ea.EG&G Parc Model 4001 Indicator 4203 Signal Averager Pl.
Tecktronix Plug -In AM503-PG501-PG508-PS503A-PG502.Cole Power Line Monitor T1085 - £250.Claude Lyons LCM1P Line Condition Monitor - £250.Bell & Howell TMA3000 Tape Motion Analyser- £250.HP5345A Automatic Frequency Convertor- .015-4GHZ - £350.HP320013 VHF Oscillator - 10-500MC/s- £200.Sencore SC61 Waveform ANZ-Microprocessor 60-100MC/s - £350.Schlumberger 3531D Date Acquisition System - £300.Marconi 6700A Sweep Oscillator with 1-2GHZ PI 6730A - £400.B&K 2218 Sound Level Meter- £600.EIP 331 18GHZ Counter -Microwave - Led - £700.EIP 3510 18GHZ Counter -Microwave - Led - £800.EIP 451 18GHZ Counter -Microwave - Led - £900.EIP 545 18GHZ Counter -Microwave - Led -£1,200.Systron Donner 6054D 18GHZ Counter- Led - £800.Systron Donner 6057 18GHZ Counter - Microwave - Nixey - £600.HP5340A 18GHZ Counter Microwave -Led -£1,200.HP5340A 18GHZ Counter Microwave -Nixey - £800.Systron Donner 6061 18GHZ Counter Microwave- Nixey- £500.Austron 6014 FX Multiplier- £250.Austron 2004 Receiver Loran - £250.Austron 1201A Linear Phase Recorder- £250.Austron 2010A Disciplined FX Standard- £250.Microtel MSR-903 Microwave Receive' - .03-18GHZ - AM -FM - £2,000.Microtel MSR-903 Microwave deceiver-.1-18GHZ-AM-FM-£2,000.Microtel MSR-903A 18GHZ FX Counter for Above -£1,000.Ailtech NM17/27 EMI/Field Intensity Meter- .01-32MC/s -£1,000.Ailtech NM37/57 EMI/Field Intensity Meter- 30-1000MC/s -£1,000.Ailtech NM65T EMI/Field Intensity Meter - 1-10GHZ - £1,000.Fluke 5205A Power Amp -£1,200B&K 1623 Tracking Filter.B&K 2607 Measuring Amp.B&K 2134 Sound Intensity AnalyserB&K 280 Microphone Power Supply.B&K 4408 Two Channel Microphone Selector.B&K 4910 Stroboscope.B&K 1606 Pre -Amp Vibration.B&K 4420 Distribution Analyser.B&K 1014 B.F.O. Oscillator.B&K J2707 Power Amplifier.B&K 2305 Level Recorders.B&K 2307 Level Recorders.B&K 7003 Tape Recorders.B&K 2615 Charge Amplifier.Fluke 9010A Micro -systems trouble shooter & many Pods - £350 + Pods or Probe.Racal/Dana 5002 Wide Band Level Meter.Racal/Dana 5006 Digital Multimeter.Racal/Dana 5005-S-4622 Digital Multimeter.AVO RM215 - L/2 AC/DC Breakdown _eakage & Ionisation Tester -12400-£450.Fluke 80K -40 High Voltage Probes -New in Case- £100.Watkins Johnson 340A-4 RX LF-1-800KC/s AM-FM-CW - Led Readout- £750.Watkins Johnson DMS -105A Demcdulator-AM-FM-SSB- Led Readout - £600.Watkins Johnson RS -111-1B-40 V -IF Receiver -30MC/s-1000MC/s - AM-FM-CW - Pan Display - £700.Watkins Johnson 373A-2 HF Receiver- 0.5-30MC/s -AM-FM-CW - f400-£500.Watkins Johnson Receivers from 114C/s to 10,000MC/s also Tuning Heads -Amps -Counter Readouts - Signal Displays - Distribution Amps - HF Multicouplers -IF Demodulators- Signal Monitdrs etc.Racal MA1720 TX Drive Units 1-30MC/s - £500-£750.Racal MA1723 TX Drive Units 1-30MC.:/s -£1,000-£1,500.Racal MA1724 TX Drive Units 1.6-25AC/s - £500.Racal RA1792 HF RX-100KC/s-30ME,Vs -£1,000 Back Lighting.Racal RA1772 HF RX-15KC/s-30MG/s - £600.Racal RA17L HF RX .5MC/s-3OMC/s- £100-£250.Plessy PR2250G & H-HF RX LF to 30 MC/s-Memory-Led Readout -£650-£1,000.B&K 2609 Measuring Amp - £250.B&K 1613 Filter - £100.B&K 4215 Artificial Mouth - £250.B&K 4219 Artificial Voice - £250.B&K 4220 Piston Phone - £120.Dynamic Sciences R-1250 Tempet Receiver -100HZ-1000MC/s - AM -FM - £2,000HP3406A Sampling Voltmeter (Broadband) - New Colour- £200.HP7404A Oscillograph Recorder -4 Track - £350.HP9872B Plotter- 4 pen - £300.HP117108 .01-11MC/s - Down Convector for 8640B - £350.HP11720A Pulse Modulator- 2-18GHz -£1,000.HP8403A Modulator -0.4-12.4GHz i 8731-8735B) Modulators - £100-£250.HP Pin Modulators for above - Various frequencies -0.4-12.4GHz -£150.HP8699B Sweep Plug-in - 0.1-4GHz - Using Yigs-Solid State - £300.HP8690B Mainframe - £250. All PI available - .1-40GHz Sweep.Racal -SG Brown Comprehensive Headset Tester(with artific,al head) Z1A200/1 - £350.Marconi 8938 AF Power Meter - £200.Microwave Systems MOS/3600 Microwave Frequency Stabilizer -1GHz-40GHz - £1,000.ACL SR -209-6 Field Intensity Meter deceiver - Pl's - 5MC/s-4GHz - P.O.R.Ailtech 136 Precision Test RX+13505 Head - 2-4GHZ - £350.SE Lab Eight Four FM 4 Channel Recorder- £200.Datron 1065 Auto Cal Digital Multimeter & Instruction Manual - £400.Datron 1061 Auto Cal Digital Multimeter & Instruction Manual - £400.Racal MA259 FX Standard - Output 100 KC/s - 1-5MC/sInternal Nicad Battery- £150.Edwards E2M8 Rotary Vacuum Pumps - Brand New & Boxed - £500 ea.Fluke 9100A Troubleshooter & Pods - New Boxed -£750-£1,000.HP1140 & 1743 Oscilloscopes 100MC/s - £300-£450.Tektronix PI 7A19 -7A29 -3A -4 -6 -7m11 -Tektronix 7000 Series Oscilloscopes We can supply all variations of Main Framesand Plug -ins for this range from stock up to 1GHz - £300-£3,000.
All items in this advert are in stock at time of printing, most items are held in quantity at both ourwarehouses which is probably the largest stock of electronic surplus in the UK.
Bulk and trade buyers from UK and abroad are welcome by appointment to bring own transport for quick purchasing and loading of listed and non -listed items.
Gunn diode blasts through output and frequency limitsR esearchers at Litton Solid State in Santa
Clara. California, and the US ArmyResearch Laboratory in New Jersey andMaryland have taken Gunn diode technologyto new limits of frequency and efficiency.JD Crowley and colleagues have developed awell-behaved indium -phosphide device
anode contact1\l'InP substrateN'buffer layer
60 iirn N*active layercathode contract
Exceeding the performance of any Gunn diodeavailable to date, this indium -phosphide deviceachieves 65mW at 138GHz with 2.6%conversion efficiency.
capable of generating 65mW of cw power at138GHz with an efficiency of 2.6%(Electronics Letters, Vol 30, No 6).
For reasons of its higher efficiency, indiumphosphide is generally preferred to galliumarsenide for frequencies above 35GHz.
Up until now, though, very little work hasbeen done with Gunn diodes above 100GHz.Yet, because of their reliability, low cost andease of use, these devices have enormouspotential for use in radio astronomyreceivers, short range radio links and high -resolution atmospheric radars.
By normal standards the new device isexceptionally thin, though the authors saythis style of construction is necessary toreduce the positive parasitic series resistanceof the InP substrate and also to reduce skineffect losses.
The method of fabrication involves vapour
The wobble that gives birth to a planet
discovered planets beyond our ownSolar System are familiar in scientificcircles. Now, after much scepticism, itappears that the astronomical world istaking such claims seriously followinginterpretation of 'wobbles' found in apulsar.
Pulsars are rapidly rotating condensedstars that take their name from the powerfulradio pulses they beam into space every fewmilliseconds. Three years ago British radioastronomer Andrew Lyne thought he hadfound minor perturbations in the otherwisehighly regular radio emissions from apulsar. He conjectured that minorirregularities in one pulsar's beat could onlybe due to the gravitational tug of objects inthe vicinity - in other words, planets.
Lyne's calculations were subsequentlyproved wrong. But they inspired AlexanderWolszczan of the Pennsylvania StateUniversity and Dale Frail of the NationalRadio Astronomy Observatory to undertakeobservations of another pulsar, code -namedPSR 1257+12. A year later, using newtechniques to analyse signals from the305m Arecibo radio telescope in PuertoRico, they found perturbations in thepulsar's rhythm that could not be explainedby any error in experimental procedures.The evidence this time was very muchstronger. But the astronomical communitywas still in no rush to conclude that planetswere responsible.
Now Wolszczan's latest calculations,
analysis (Science, Vol 264, p.538), haveconvinced, it seems, even the mostsceptical.
In the same issue of Science Fred Rasio ofthe Institute for Advanced Study atPrinceton says: "It would be difficult toimagine any other way the data could befooling us".
So small is the perturbation in the pulsar'stick that Wolszczan had initially expected totake five years to come up with a definitiveresult. He describes the perturbation asbeing so slight that detecting it is liketransporting a snail a distance of 1500 lightyears, making it crawl at its usual pace,attaching a transmitter to it and thenmeasuring its movement to within a fewmillimetres a second.
Two years' of data from the pulsar(located in the constellation of Virgo) revealthe existence of two orbiting bodies eachwith about three times the mass of theEarth. Fortuitously they have closely relatedorbital periods of 66.6 and 98.2 days and, atthat approximately 2:3 ratio, pass each otherfrequently and have a short overall orbitalpattern. The result has been that Wolszczanand his team have been able to digmeaningful signals out of the noise in threeyears, rather than the expected five.
What has finally convinced Wolszczan'scolleagues is the predictive aspect of hisanalysis. Back in 1992, soon after hediscovered the first convincing pulsar'wobbles', he used his data to predict
phase epitaxial deposition, after which theback side of the wafer is polished chemo-mechanically using a bromine -methanolsolution. Metallisation and the fitting of anintegral heatsink are then followed by theetching of individual mesas.
When packaged and fitted in a WR-6waveguide oscillator circuit, each diode wasfound to perform with adequate stability overa 0-50°C range.
Frequency variation with temperature was-5MHz/°C, while output power wasmaintained within a few milliwatts over theentire temperature range.
Based on these experimental findings, theresearchers confidently claim that low-cost,simple solid-state sources can now beconstructed in the 140GHz range for use aslocal oscillators, drivers for multipliers, or aslow power transmitters.
subsequent pulse patterns. The fact thatlater recordings have been exactly on targeteliminate most possibilities of flaws in thedata analysis - and also effects of theEarth's movements, which were not fullyaccounted for in Andrew Lyne's study.
The story is not yet complete by anymeans. Wolszczan says that the timing -datapoint to the existence of a third moon -sizedobject that orbits the pulsar every 25 days.There are also hints of a fourth body in amuch larger orbit. All these planets are, ofcourse, much too far away to detect ineither the visible or the infra -red parts of thespectrum. So it is extremely unlikely thatthey'll ever be 'seen' in the conventionalsense. Though Nasa is soon to inaugurateAseps (astronomical studies of extra -solarplanetary systems) using ground -basedtelescopes to search for large planets arounda hundred much -nearer stars.
As ever, the $64,000 question is: do theselatest planetary discoveries increase theodds of ever finding life elsewhere in theUniverse?
In the statistical sense the answer must beyes, though it is unlikely that such lifewould exist on planets circling a pulsar.
Wolszczan comments: "If you envisagesomeone with lead armour to protect themagainst the high energy radiation from thepulsar, maybe there are such creatures. Butthe sort of life we're accustomed to cannotpossibly exist on a planet like that".
536 ELECTRONICS WORLD + WIRELESS WORLD July 1994
RESEARCH NOTES
Laser that could reshape conventional technology
AAsemiconductor laserdesigned on a fundamentally
new principle may open up awhole range of applications: fromnovel ways to detect air pollution,to collision avoidance radars forcars. Developed by FedericoCapasso and his colleagues atAT&T Bell Laboratories inMurray Hill, New Jersey, the newquantum cascade laser producesinfra red radiation in parts of thespectrum that other lasers cannoteasily reach.
What makes the device specialis that the wavelength isdetermined, not by the chemistryof the semiconductor material,but by its physical structure.
Unlike an ordinarysemiconductor laser, whoseemission occurs when excitedelectrons cross the intrinsic band -gap of the material, the AT&Tlaser generates its radiation whenelectrons spill down an 'energystaircase' of sandwich -likequantum wells. These steps canbe made in different sizes, so thelaser can cover a wide range ofthe infra -red spectrum.
The only semiconductor laserscapable of operating in the farinfra -red have been based on
Conventional laser
Conductionband rboo
0000
Bandgap
WIV
eoee4 Valanceape band
Quantum cascade laser8 3.5 2.8 mm
CDC)(_
\AWN\0_C COO
3.5 3.0 3.0 rrm
Semiconductor quantum -cascade laser operates on an entirely new pr nciple. When current flows,
electrons pass down the structure. Each time the an electron hits an energy -level step, a photon isemitted which in turn stimulates other photons by bouncing between mirrored surfaces.
Until now, the only lasers capableof producing far -infra -red havebeen mercury -cadmium -telluridetypes, which are difficult tofabricate . This new device usesaluminium indium arsenide andindium gallium arsenide
mercury cadmium telluride -adifficult material to fabricate.
The idea of using quantumwells to make a laser goes backto the early 1970s when an IBMteam led by Leo Esakisuggested using such wells toconstrain electrons to specificenergies or wavelengths. Theteam predicted that whenelectrons tunnelled from well towell they would emit radiationof a wavelength determined bythe geometry of the structure.Through the 80s, experimentsat MIT and AT&T showed thatit was indeed possible to createsuch quantum wells by delicatemolecular beam epitaxy. Thetechniques were extremelycomplex however and, althoughsequential electron tunnellingwas achieved, no radiation wasemitted.
The latest results, achieved ina device with 25 active regions
is the end product of hundreds of attemptsusing nanometre-scale sandwiches ofaluminium indium arsenide and indiumgallium arsenide. Main snag, at the time ofwriting, is that the whole assembly needs tobe cooled to 90K and can only be operatedin pulsed mode. But this shouldn't be aserious limitation; it is only because thedevice is so inefficient. Without suchoperating constraints the necessarily largeforward current would otherwise cause it tooverheat.
On the credit side, the new 'staircase' laserhas a much narrower spectrum than normalband -gap devices -a direct product of itsoperating principle. Electron energies aredefined by the structure of the device so theycan be specified extremely closely.
As yet the laser is still at the experimentalstage and cannot be considered a practicaldevice. But for a technology that is less thansix months old, progress has been dramatic.And once the efficiency problems have beenovercome commercial applications areexpected to follow very quickly.
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 537
RESEARCH NOTES
Physicists find their missing linkPhysicists at the Fermi NationalAccelerator Laboratory near Chicago
have discovered what they believe is the lastfundamental building block of matter. Thetop quark has come to light after decades ofhigh energy experiments in which protonsand anti -protons have been smashed into eachother at speeds approaching that of light.From more than a million million suchcollisions, the team have isolated about adozen events providing strong circumstantialevidence for the top quark.
Over 20 years ago Murray Gell-Mann, aCaltech physicist developed what is nowknown as the "standard model" of everything.His model postulates that all matter consistsof various combinations of six quarks and a
Scientistsbelieve thatthe 'top' quarkis the last fun-damentalbuilding blockof matter.These are thefour familiesof three gen-erations ofelementaryparticle con-stituents.
matching set of six lighter particles,collectively called leptons (see table).
Its undoubted neatness and symmetryappeal immensely to physicists.
Up to now, most of the quarks - the nameitself comes from James Joyce's 'Finnigan'sWake' - have obligingly turned up in theresults from big atom -smashing experiments:except that is for the top quark.
The 'strange' quark was discovered in theearly 1950s, while 'charm' and 'bottom'showed up two decades later. But without`top', the standard model could hardly beregarded as complete.
In the continuing search, the main problemfacing quark hunters is that such particles,because of the tightness with which they bind
Generation
Family 1 2 3 Electriccharge
neutrinos
neutrinos Ve V V- 0
charged electron muon tauon -1leptons e- u- T-
quarks up charm CI +?
quarks down strange beauty -13
Periodic table of elementary particle constituents
Solar power reaps efficiency benefitsEnvironment-conscious engineers have
long dreamed of being able to generateelectricity - efficiently - from sunlight. Solarcells have no moving parts and little to wearout; create no pollution, consume no scarcefossil fuels and last for 20 years or more. Inmany senses they would be the perfectsource of power. But they have four maindrawbacks: they only work during the day,they are expensive, they are inefficient andthey produce unpredictable amounts of dc.
Yet as environmental considerationsbecome more important and as prices fall,solar cells are being taken increasinglyseriously, especially in situations where anintermittent supply of low -voltage electricityis acceptable.
The main factor behind the recent surge ofinterest in solar cells is their rapidlyimproving efficiency. One example ofprogress is a low-cost cell made in the USAby a research group called United SolarSystems. This joint venture of Canon andEnergy Conversion Devices has developed acell based on a thin film of amorphous siliconthat will capture sunlight with an efficiencyof 10.2%. Two years ago, the best figure forthis type of low-cost cell was about 6%.
The new cell is a triple sandwich of siliconwith silicon/germanium alloys deposited ona panel of stainless steel. The constructionnot only helps a wider spectrum of lightenergy to be absorbed, but can also bephysically bent.
Previously, most solar cells capable ofefficiencies greater than 10% were madefrom single crystals of silicon orpolycrystalline silicon. Such cells (and thosemade from III -V compounds) arenecessarily much more expensive than theiramorphous silicon counterparts.
Even so, they too have been gettingprogressively better. A recent report(Physics World, April 94) describes arecord -breaking solar cell from the Japanesecompany Mitsubishi. They claim to haveachieved an efficiency of 14.2% in whatthey believe is a commercially viable cellmade of polycrystalline silicon. Theprevious record for this type of cell was10.9%.
These efficiency figures may seem verylow compared with, say, a steam generator.But once a solar cell is installed, the runningcosts are virtually nil. And even if the cell isonly 10% efficient, a lm square of it will
together, cannot be observed directly. Freequarks do not exist in nature, and in the caseof the top quark, they rarely exist in any form.To create them requires smashing protonsand anti -protons together with enormousenergies, the particles annihilating themselvesin a blaze of energy, comparable on a smallscale with that of the Big Bang that initiatedthe Universe.
It is from this blaze of pure energy thatquarks sometimes condense.
Even then, quarks can remain irritatinglyelusive. On a BBC World Serviceprogramme, Dr Bill Carrithers, one of theFermilab team described it like this: "The topquark decays instantaneously after beingproduced. So what we look for are signaturesof its daughters or even grand -daughters asthe particles decay down to the ones we seein the detector. We then work backwards toreconstruct what the top quark must havelooked like".
What is particularly fascinating about thetop quark is its mass. Latest estimates suggestthat is about as heavy as an atom of gold -by far the most massive of all the sub -atomicparticles.
Next step for particle physicists, afterfinding events to strengthen the evidence forthe top quark, will be to track down anotherentity called the Higgs boson. This particle,also predicted by the standard model, mayexplain the mystery of why some quarks aremore massive than others.
It could even explain why they have massat all.
still generate 100W of electricity in fullsunlight.
What these recent advances are nowdemonstrating is the closing gap betweensolar -generated power and that generated bythe burning of fossil fuels.
According to some industry figures, thecost of solar power will not need to fall bymuch more than a factor of two before itbecomes cost-effective for supplementingthe ac grid. A coalition of US companies isalready pledged to install 50MW of solarpower over the next six years.
Here in the UK the climate may (literally)be less favourable: less sunlight and variableweather, especially in winter whenelectricity demand is high. Expensive land isalso frequently cited as a major obstacle.
The way forward, according to manyexperts would be to fit solar panels to thewalls and roofs of buildings and use theresulting power for supplementary purposes,using efficient dc -to -ac converters whennecessary.
Research Notes is written by JohnWilson of the BBC World Service.
538ELECTRONICS WORLD + WIRELESS WORLD July 1994
0 16
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0
How good is the common-
mode rejection capabilityof today's high performanceanalogue ICs in real worldtest circuits? How docurrent -feedback ICs fare?Design consultant BenDuncan presents here aworld exclusive -acomparitive study of cmrperformance for elevenleading linear ICs.
COMPONENTS
CMRunder test
nstrumentation amplifiers are front ends for signals arriv-ing from hostile environments. They are available inmany forms, but for the most part they have twin, dif-
ferential or balanced inputs.Unwanted common -mode signals - hum, noise, dc, etc -
and dangerous voltages are generally attenuated or can-celled out. Gain is restricted to wanted, differential signals,
which are often smaller thanthe unwanted interference.
Instrumentation amplifiers- or in -amps - can be builtfrom discrete components,but most applications nowuse integrated circuits.Integrated -circuit data sheetscontain a figure for common-
mode rejection, cmr, usuallyat a spot frequency. Most alsohave a graph showing howcmr degrades with increasingfrequency. But how far canthis information be trustedwhen the test levels, topologyand critical passive compo-nent values are rarely speci-fied? And how much doescmr change when surround-ing component tolerances areimperfect, or the circuit topol-ogy changes?
Although common -mode rejection is a key feature allow-ing signals to be distinguished from interference, manyapplications will also need instrumentation amplifiers withgood performance in other dynamic areas such as noise,slew and bandwidth.
My reason for being interested in op -amp cm rejection istaken up in the panel.
The contendersTable 1 lists devices considered. They are chosen for theircombination of the following attributes.
High gain -bandwidth product. In order to provide abandwidth of 1MHz at +40dB or more gain, minimumgain -bandwidth product was limited to 100MHz .Currentfeedback helps immensely here but is not a prerequisite.Many good in -amps and op -amps from manufacturers suchas AD, Bun -Brown and LTC are ineligiblebandwidths below 500kHz at +40dB. The LT1028 ismarginal but included for illustration.
When selecting examples of current -feedback op -amps,I noticed that Analog Devices' current feedback op -ampdata hampers the designer by omitting gain/bandwidthplots. These are needed all the more because with currentfeedback ordinary loop -gain -proportional bandwidth rela-tionships do not arise.
Low noise. To avoid adding significantly to inevitablenoise from the input attenuator-network, in most cases onlydevices with a noise figure of less than 5nV/'Hz were cho-sen, with noise from a typical input attenuator contributingabout 5nV/41-1z I .
The rather noisier AMP05, and only slightly over -noisyHA2548, have been accepted because of their wider band-width and much higher slew limit. With current feedbackop -amps in this class of circuitry, current noise dominates.This is because certain resistor values in practical circuit-ry capable of withstanding high cm voltage need to behigher than the ideal for current feedback.
Slew rate. As a minimum limit for slew rate I chose10V/µ s. For switch -mode power supplies, the AMPO5 ismarginal, while HA2548, AD829, and the AD811 and 818respectively meet and exceed the maximum requirement.
Offsets. DC gain may be over 100 so offsets need to below. Offsets that do not displace the smallest wanted sig-nals by more than 10% are not too problematical. Servocontrol of dc might be attractive, but the ideal differentialsummation almost doubles the parts count.
Common -mode voltage. Common -mode voltage capa-bility, or cmv, is greater than ±10V for the devices chosen.
540ELECTRONICS WORLD + WIRELESS WORLD July 1994
COMPONENTS
ISee text
C10 - 10p
depend on the topology used. Figure 1 showsthe simplest scheme for handling high cmv. Iarranged it to allow either IC op -amps or in -amps to be plugged into the front end network.Instrumentation amplifiers were connected viaa short, tightly twisted pair.
Compared to a previously published ver-sion2 of Fig.. 1, resistor values are lower. Also,recovery gain for the op -amp version, R6/RI, is
set for +18dB.
R6160 k
4.18 V
Output51
Fig. 1. First ofthree common -mode rejectiontest circuits. Modeswitch setting andCr depend on the
0 device under test.PRI and R3 enable
CMRHFIC Op - Amp:
-18 V
TC 12- 10pF
+18 V
Output51 0
IC In - Amp:
-18 V
CMR FinePR .2 1 k
the cmr to befinely trimmed.Likewise Cr andTC1 allow theinput capacitancesto be finelybalanced formaximum hf cmr.Potentiometer PRIis unaffected bymost op -amptypes, but requiredadjustment withthe different in -amp types.
many modem, very high speed op -amps, with±5 to ±7V maximum supplies.
Common -mode rejection. Last but not least,the highest cmrr is sought up to at least100kHz or below. Makers' specifications arequite variable here.
High cmv topologies comparedCommon -mode rejection performance will
20 k
CMRLFPR. 1 681
131 100
R220 k
R3100 R5
681
mode
Open for In - AmpsClose for Op - Amps
RI 681.0.522 k. 0.5 R2
Fig. 2. Two op -amps use shunt feedback and common -mode voltage is actively subtracted. With thiscircuit, imperfect cancellation prevented deep nulls. For cmr better than -8OdBr above 100kHz,
layout is critical.
Table 1. Dynamic specifications of shortlisted IC operational and instrumentationamphfiers, based on manufacturers' data.
Part Maker Noise BW CMR Slew +Vs
@1 kHz @40dB @100kHz limit max
nV/ Hz MHz -dB V/ps volts
Instrumentation amplifiers:AMPO5 CFB AD 16 3 57 5-7.5 18
INA103 BB 1 0.7 85 15 25
SSM2016 CFB AD 0.8 1 na 10 36
SSM2017CFB AD 0.95 1 97 10-17 22
Op -amps:AD797 AD 0.9 0.814.5* 56 12.5-20 18
AD811CFB § AD 1.9 50t 70 2500 18
AD818 AD 10 2.6t 65 400-500 18
AD829 AD 2 0.66/7.5t 83 230 18
HA5137 Harris 3.4 1 60 35 17.5
HA2548 Harris 8.3 1.5 62-74 120 20
LT1028 Lin Tech 1.1 0.5 80 11-15 22
Notes: All figures typical.Higher with decomp C.
t Estimated from ancillary data.§ Noise current 20pANHz.
CMV@±15vvolts
11.511-128.38
1213.5-14.512-14.313.5-14.5127-1011-12
CFB = current feedback. SSM2016, 2017 & AMPO5 employ some cfb.
Even if there is enough gain -bandwidthproduct to support higher gain, this is aboutthe maximum without adding complexity-[. Asshown, RI's value is as low as reasonably pos-sible. With R6 at 160ki1, parasitic capacitancestarts to affect bandwidth just above 1MHz.
Figure 2 shows another scheme describedby Jung45, using two op -amps. Monolithic in -amps are not applicable here. Shunt feedbackmeans that neither op -amp front-end seesappreciable cmv, provided the feedback isoperative.
Output of /CI is adjusted via PRI to pre-cisely cancel /C2 output originating from thelower input. Any cmv is manifest at the outputof /CI. For a given recovery gain, noise gainin /C2 is intrinsically 10dB higher comparedto Fig.1: at 50dB, it comprises 10dB from thedirect input, and 40dB to make up /CI output.Recovery gain is kept to just +10dB accord-ingly. Potentiometer PR2 provides phase trim,forming a T -network in conjunction with C1,for best cancellation at hf.
Figure 3 also uses two op-amps6. At R6,7junction, the differential -mode signal sums tozero, leaving the full cmv. A cancellation sig-nal is fed forward across the differential inputsby /CI, actively suppressing the cmv it readsat the junction. Unlike the previous circuit, ICin -amps are applicable for /C2, and preferable,as the active impedances to ground are then in
principle symmetrical.Depth of hf cmr trim with the trimmer
capacitors depends on ICI. A high slew rateand generous bandwidth is important for ICI ifcmvs above 10kHz are expected. Otherwiseprogressively disorganising cancellation at vhfshows up as a spiky, un-nullable residue.
Test environmentAll the test circuits had local wideband decou-pling typically comprising 100nF+10µF. Inaddition they were powered by a lowimpedance, low noise Thurlby ±16V lab sup-ply. Trimmer potentiometers were Boums cer-met types and trimmer capacitors were minia-
ture low -k ceramics.All tests were performed
with Holsworthy 0.5%,5Oppm/°C metal film resis-tors in all the criticalgain/cmr determining posi-tions - including the attenu-ator front end. Each test cir-cuit was driven from theAudio Precision generatorwith the hot and cold inputsjoined, i.e. in common -mode test or `cmtsr mode.
In all graphs, cmr+n isplotted in dBr below a
hypothetical output of+34dBV, i.e. 49V rms, toemphasise cm residue at the
expense of noise. The noisefloor will be much nearerwith small differential -modesignals.
For Figs 4-21, the AudioPrecision test set plots
July 1994 ELECTRONICS WORLD + WIRELESS WORLD541
COMPONENTS
cmr+n versus frequency in two bandwidths.Upper plots are from 10Hz up to 200kHz witha bandwidth from less than 10Hz to more than500kHz. The lower plot is a narrower sweepwith a -1dB bandwidth from 400Hz to 22kHz. Difference between the two can help indicatehow much cmr in the upper plot is receivernoise (+n).
Despite the high reference level and 1/3rdoctave sweep, often only noise is extant in thenarrow band plots; literal cmr can only be esti-mated. In most cases diminishing cmr above100kHz has been kept at bay by deft trim-ming.
Although the test set stops short of 1MHz,any rise can only go so far in the invisible tophalf decade from 200kHz-1MHz. In manycases, a little cmr decay above 200kHz is oflittle significance. When double checked, thecmr curves' repeatability was about ±3dB at200kHz, ±2dB at 20kHz and ±1dB at 100Hzfor wideband readings. Narrow -band plotswere about 0.5dB closer.
Results Figs 4-14 show typical cmr+n ver-sus frequency plots for the first eleven devicesin Table 1 using test circuit Fig. 1. All thedevices achieve at least -90dB across the500kHz measurement bandwidth. This isreferred to a hypothetical 49V/+34dBV levelhowever. Referred to 1V/OdBV, cmrr is amore prosaic -56dB.
In some cases, Fig. 6 for example, the 'real'cmr curve behind the noise appears to be the-6dB/octave slope that can be drawn downfrom 200kHz on the upper plot to intercept thenarrow -band plot at about 20kHz7
On this basis, you can estimate that If cmr ismore than -130dBr, or better than -96dBV.
With careful trimming, even the narrow-
band residue up to 5kHz in the lower plots ispredominantly noise. The ranking has much in
20 k. 0.5WAR1
In
R2YyMt
20 k. 0.5
iwE:1100
CMRLF
R3
--- Compact node - - -
R610 k. 0.5
R710 k. 0.5
common with the noise densities shown inTable 1. but with some surprises. This is inpart because uniform extrapolation from lkHznoise density out to 200kHz may be pre-sumptuous. As you might expect, by having20pA/IHz noise in conjunction with resistorvalues as high as 160kO, the AD811 current -feedback op -amp appears to have the poorestcm rejection, Fig. 13. Effective total -noisedensity, Vn+/, is above lOnV/'IHz, empha-sising the part.
Figures 15-17 show typical cmr+n versusfrequency with test circuit Fig. 2. High -fre-quency kinks in Fig. 15 show that cmrinvolves non-linear phenomena. The residueslooked like distortion harmonics and thenulling was only bluntly effectual. Common -
mode voltage cancellation is critical. Minutechanges in lead dress and component posi-tioning had a large bearing on performance.Figure 16, with an un-compensated AD829shows how PR1,2 can interact, depending ontrim sequence. Such interaction can possiblybe overcome, and better cmr attained by usingthe AD829's diverse compensation facility,with the compensation on /CI set at 68pF.Compensation on /C2 requires tuning below60pF for best results. With extra attention todetail, cmr+n may go lower, but the best resultattained in these tests was -88dBr or -54dBV,as shown in Fig. 15.
Figures 18-20 illustrate performance of testcircuit Fig. 3. The 2017 was chosen for /C2, tokeep the circuitry simple with little trade-off.Other in -amps and IC op -amps were tested in/C2 position. Differences broadly corre-sponded with Figs. 4-14, where stable. Butsome had vhf oscillations, or cmr+n versusfrequency anomalies. These were helped nodoubt by the abnormal source impedances pre-sented to /CZ's inverting input in the midst of
47R value = Ohms. % Tol
Fig. 3. Nearly all the common -moderejection is provided actively by ICrwith surrounding resistor bridge.Trimmer C1 is set to prevent vhfoscillation. Layout is not too critical,though brevity of the upper node whenTC2 is an op -amp will enable bestperformance at high frequencies.
(a)
CMRHF
Op - Amp Connection:
In - Amp Connection:
(b)
R8100 k
7
IC .1
51Output
WA 0R11
/CI 's feedback loop.Below 10kHz, cmr+n performance with an
AD829 or HA5 I 37 for ICI is clearly a littlebetter than the results from the other test cir-cuits. These devices were chosen for theirgood performance in test circuit Fig. 1.
Inevitably, the trade-off with active cancella-tion is poorer high frequency performancecompared with the passive method of Fig. 1.
Finally in this section, Fig. 21 shows howsome of the circuits outperform the AudioPrecision test equipment. Fortunately, cmrejection is not superimpositive.
The measurements appear to demonstratethat the 100kHz cmr of the op -amps and in -
amps is both over- and under -stated by theirmakers., However cmrr depends on referencesand conditions, which are not so clearlydefined.
What is clear is that surprisingly similar andrepeatably high cmrs can be attained by all themodem IC op -amps and in -amps tested. Thesehigh cmrrs can be maintained up to surpris-ingly high frequencies, given informed layoutand careful trimming - particularly with thetest circuit of Fig. I.
Simulating cm rejection with SpiceFew of the op -amps tested here were availableas Spice models but I evaluated those thatwere and others with MicroCAP-IV.
Harris's models do not presently cover cmr.Models for AD797 and 829 do, but since thedevices have more than the basic five pins -i.e. inputs, output and power - they need 'hardpinning' for MicroCAP to run. This meansthat a six -pin op -amp shape has to be createdor called up. Even if you do not need the com-pensation pin, MicroCAP will not accept itsimply being disposed of by connecting it toground via a resistor -a common trick withsome other Spice simulators.
Other models had peculiarities, requiringtweaking to make them run. The AD845model has a hyphen which causes difficultybecause MicroCAP version 4 is written in C+.
Of ten Spice models tested, only five ranfirst time and plotted cmr. These were AnalogDevices' AD811, 818, Burr -Brown's OPA27and 604; and Linear Technology's LT1028.Burr -Brown had the best documentation - abooklet - while Analog Devices had the mostmodels with cmr included.
Detailed examination of the different mak-ers' models revealed behaviour that couldtrick the unwary. First, cmr can be 'tuned'way beyond its specifications by use of RCbridge values minutely offset from perfectmatching. Second, tuning in this way revealsdifferent ultimate depths and hf decay slopes.Few match the classical model of cmr decaywith frequency - any more than the AudioPrecision plots of Figs 4-20 do.
Thanks to Joe Buxton and other staff atAnalogue Devices in the USA for guidance onSpice and cmr.
542 ELECTRONICS WORLD + WIRELESS WORLD July 1994
COMPONENTS
Ben Duncan Research CM-HCM1X AMPL(dBr vs FREQ(Hz) 26 FEB 9417:21:18
-50.00
-60.00
-70.00
-80.00
-90.00B --.-''
-100.0I
A-110.0
10 100 1k 10k 100k 200k
Fig. 4. Common -mode rejection for AD797 degrades above 500kHz, but thenarrow -band plot does not show a corner.
Ben Duncan Research CMHV-1D AMPL(dBr) vs FREQ(Hz) 06 MAR 94 21:47:21
-50.00
-60.00
-70.00
-80.00
-90.00 ).---------"
-100.0 .-------110.0
- -10 100 1k 10k 100k 200k
Fig. 6. Common -mode rejection of the SSM2016 audio in -amp degradesgracefully above 20kHz and is only 10dB worse at 200kHz. Its narrow -bandcmr+n is one of the best but begins rising above 1kHz. Remember this device
employs some current feedback.
Ben Duncan Research CMHV-1f AMPL(dBr) vs FREQ(Hz) 26 FEB 9419:22:54
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.-110.0
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Fig. 8. Some current feedback is used in the SSM2017 audio IC. It performssimilarly to the AD797 of Fig. 4 but with slightly more rapid cmr decay by200kHz.
Ben Duncan Research CMHV-1H AMPL(dBr) vs FREQ(Hz) 28 FEB 9418:08:18
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Fig. 10. Harris' HA5548 provides joint widest cmr bandwidth before decay.Compared to AMPO5 in Fig. 9, its cmr+n is about 3dB better.
Ben Duncan Research CM14-1B AMPL(dBr) vs FREQ(Hz) 06 MAR 94 21:18:01
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-80.00 .7-90.00 ___------"e.
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Fig. 5. For the LT1028, cmr degrades quite rapidly above 20kHz, while thenarrow -band plot echoes this three octaves lower.
Ben Duncan Research CMHV-1e AMPL(dB ) vs FREQ(Hz) 26 FEB 9419:15:12
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10
I
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Fig. 7. Burr -Brown's INA03 in -amp combines aspects of the ICs in Figs4 and 6.
Ben Duncan Research CMHV-1g AMPL(dBr) vs FREQ(Hz) 28 FEB 9417:41:18
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Fig. 9. The AMPO5 in -amp has current feedback, and along with Fig.10 displays joint widest cmr bandwidth before decay.
Ben Duncan Research CMHV-1j AMPL(dBr) vs FREQ(Hz) 28 FEB 9418:17:38
50.00
-60.03
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" -
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10 100 1k 10k 100k 200k
Fig. 11. One of the best combinations of low cmr+n and wide cmrejection bandwidth is provided by Harris's HA5137. The pair of hfvariations show the typical effect (upper) of imperfect trimmercapacitor setting.
All upper graph curves relate to wideband cm rejection (lOrlz to 200kHz). Figs 4-14All lower graph curves relate to narrowband cm rejection.(-100Hz to 22kHz).
July 1994 ELECTRONICS WORLD + WIRELESS WORI 543
COMPONENTS
Ben Duncan
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Research CMHV-1K AMPL(dB ) vs FREQ(Hz) 28 FEB 9418:25:36
-.-
100 1k 10k 100k 200k
Fig. 12. The AD829 is similar to the AD797 but its cmr+n is a fewdecibels better.
Ben Duncan
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10
Research CMHV-1N AMPL(dB ) vs FREQ(Hz) 28 FEB 94 20.20:27
. ......--'
- ------
100 1k 10k 100k 200k
Fig. 14. In terms of cmr bandwidth before decay, the AD818 issecond only to the HA2548 and AMP05. Its cmr+n on the other handis intermediate.
Ben Duncan
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Research CMHV-1r AMPL(dB ) vs FREQ(Hz) 28 FEB 94 21 02:56
B
A
100 1k 10k 100k 200k
Fig. 16. Test circuit Fig. 2 with AD829s for three settings of PR2, (a -c).Op -amp compensation is not used. Cancellation is oddlypoor at bothIf and hf.
Ben Duncan
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Research CMHV-3A AMPL(dBr) vs FREQ(Hz) 02 MAR 9418:59:41
A
,....,..
100 1k 10k 100k 200k
Fig. 18. Results from a Harris HA5137 with an SSM2017 in Fig. 3 testcircuit. Compared to Fig. 11, noise is about 3d8 lower, but cmr decaysearlier, as you would expect.
Ben Duncan
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Research CMHV-1m AMPL(dB ) vs FREQ(Hz) 28 FEB 94 20:09:55
----
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I
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Fig. 13. The sole current feedback op -amp, the AD811 has a small but unusualcmr decay step at about 8kHz in the wideband plot. The poor cmr+n isdegraded by noise as described in the text.
Ben Duncan Research CMHV-1p AMPL(dBr) vs FREQ(Hz) 28 FEB 94 20 34:26-50.00
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I
10 100 1k 10k 100k 200k
Fig. 15. Using AD797s in Fig. 2 test circuit, both narrow and wideband plotshave similar cmr+n characteristics. At If they are about 3d8 worse than thesingle AD797 in Fig. 4. Multiple plots with slightly varying trims of presetPRI are shown. The hf inflexion can vary widely with PR2 setting.
Ben Duncan Research CMHV-2B AMPL(dBr) vs FREQ(Hz 28 FEB 94 20:54:56-50.00
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,;-... -..y,..
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Fig. 17. Using HA2548s in Fig. 2 test circuit yields apoor cmr+n of only-60d8r (-26d8V). Two plots were made of the narrow -band response, whichis no better than the wideband, signifying high cm and low '+n'.
Ben Duncan Research CMHV-3A AMPL(dB) vs FREQ(Hz) 02 MAR 94 19:11 11-50.00
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B , . A-110.0
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10 100 1k 10k 100k 200k
Fig. 19. With an AD797 and SSM2017 in Fig. 3, the null became veryshallow. Narrow -band plot (A) is tangential to (B), the wideband. Noterapid cmr decay above 500Hz. In fact, cmr nulling was 'dulled' with theAD797, probably because of input parasitics. It remained so despiteretrials.
544 ELECTRONICS WORLD + WIRELESS WORLD July 1994
COMPONENTS
Ben Duncan Research CMHV-3F AMPL(dB ) vs FREQ(Hz 02 MAR 9419:20:51
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-110.0 A____.--------120.0
10 100 1k 10k 100k 200k
Fig. 20. An AD829 with an SSM2017 in Fig. 3 is a better combination.Changes compared to Fig. 12 mirror the HA5137 of Figs 11 and 18, butare even better. Topological noise is 8dB lower compared to Fig. 12.While bandwidth decay sets in at around 20kHz, it is barely an octavelower. The null is crisp -a good sign. Overall, results with this circuit arehighly dependent on ICI.
A probe for live placesMy interest in cm rejection stems from a need tomeasure millivolt signals on the mains. Figure 22shows points on an off-line psu that often needmeasuring. It includes the traditional, expensive,isolating transformer.Figure 23 shows an attenuator for reading high -voltage signals. This is all that is needed to readlarge differential signals with an existing instru-mentation or differential amplifier.
For small differential signals, irrespective of thecircuit's cm rejection, cm voltage must be atten-uated enough to prevent the active circuitryexperiencing a cmv beyond its limits. Saturationor malfunction from excessive cmv can be invis-ible on a oscilloscope, if dc or at some frequen-cy distant from the differential -mode signal.
For op -amps and in -amps operating on ±1 5Vsupplies, maximum cmv for normal, linear oper-ation is at least ±1 OV (see Table 1). Generallythe rating changes pro -rata with the supply. SoAnalog Devices' SSM2016, with its exceptionalmaximum ±36V supply capability, could handlecm voltages of up to ±24V.
While this is a worst case allowance, Fig. 24from Burr -Brown's INA03 in -amp data showshow cm voltage below positive and negativesupply rails at the op -amp inputs can reduce
Live
240 v rmsAC Mains
Neutral
ORO-1 R
SupplyEarth
Optional1:1 isolating
j-rso 1
O
Ben Duncan Research CMHV-APR AMPL(dBr) vs FREQ(Hz 02 MAR 9418:50:55
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4%..s...'........"
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e
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Fig. 21. Audio Precision test set receiver's own, transformer -aided cmrperformance. Wide (A) and narrow -band (B) modes have the same+16dBV cm test operating level, as Figs 10-20. All the test circuits aresuperior below 500Hz, and effectively as good or better above 10kHz- after considering their 41dB or 49dB higher noise gain. Fortunately,the test set's cmr performance does not restrict measurement results.Degraded cmr between 10-300Hz (A), is caused by the test set's dcblocking capacitors (see text).
headroom by subtracting from output swing.However, INA03 output gain can be increasedto alleviate the limitation; a unique feature.
For a 400V maximum cmv input, cm attenua-tion of about 35x or -31dB is therefore the bareminimum required to interface with op -amps orin -amps having ±15V supplies, Fig. 25. Sincecommon and differential -mode attenuationcome almost hand in hand when achieved resis-tively, attenuation should not be too generous. Ifit is, the differential -mode signal's noise andbandwidth will be needlessly degraded by theextra recovery gain required.
Figure 26 shows the complete circuit for inter-facing safely with the mains (obviously, youalways need to observe standard safety precau-tions when dealing with the mains - ed). It
replaces galvanically isolative but gain andband -limited transformer -coupled probes, asshown in Fig 22's lower rh corner. It can resolvea few mV to tens of volts on top of 400V ac ordc or cm voltage, from dc to 3MHz.
How much resolution?Current measurements may be made on typicalswitch -mode power equipment by readingacross a current sensing resistor such as points A
A liftChassis
HT.r - -F -
Diffi HT- probe
Fig. 22. Generic off-line supply connections and probe points. Optional, traditional safety isolatingtransformer connections are shown. Boxed resistors are milliohm current sensors. A smalldifferential voltage representing current can be read across them at A, B, C, D. Small voltages mayalso require probing, eg. transistor Vbe or Vim, or a fraction of the primary voltage at E, F, G.
to D in Fig. 22. To do this accurately, a com-mensurately low inductance shunt is needed.
Suitable components have resistances of10mf2 and below8. Resolving a minimum cur-rent of 1A then requires clean recovery of signalsat around 10mV. A gain of 20dB provides100mV/A - convenient for men:al arithmetic. Inpractice, a more modest gain like 10dB, with amore challenging 3 1.6mV/A scaling, may haveto be accepted
With a conventional ±15V supply, this at leastsets full-scale deflection at around 350A -enough headroom for most jobs. At this point,the design process begins to interact heavily withthe op -amp or in -amp chosen.
Defining rejectionIf common -mode rejection and noise ratio areinadequate, the smaller current signals just dis-cussed are the first to be lost in noise.
Fortunately, when reading switch -mode powersupply current, (points B, C, D in Fig. 22), thecm voltage is usually mainly dc. This can bevisually ignored, blocked and even nulled out.
Assume cm rejection is -65dB from dc to kilo-hertz, referred to OdBV. Current is 1A in 10mi2.With rectified 240V, cm voltage will be about
Secondaries
Signalisolating
Bal
Out toinstruments'
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 545
COMPONENTS
x
340V and 95% dc. At the output, there is
±323x0.00056, or ±180mV of dc offset. This isnot a problem, even though the current signal isonly 30 to 100mV rms.
If alternating at, say 50Hz, however, thisamount of cm voltage, would make oscilloscopeviewing difficult, even if an analyser could dis-criminate. A cm rejection ratio better than -65dBto as high a frequency as possible helps keep accm voltage at bay when viewing currents below1A, extending the instrument's versatility.
In practice, in a properly aligned direct cou-pled circuit, cm rejection ultimately degrades athf only. This can work out favourably, as thehigher frequency cm signals will often be thesmaller components of the total cm voltage.
Frequency response down to dc is the normwith in -amps, even if reading dc is unnecessary.This is because input dc blocking capacitorsdegrade both If and rf cm rejection, unlesshyper -matched and held at a constant tempera-ture, Fig 21. Beyond this, bandwidth limitationat hf depends mostly on the active device(s). Tobe useful in switching supply development, aresponse to at least 1MHz is a good target.
Slew rate of the device must be adequate forthe largest component's frequency. If not, it willnot have the full use of the active circuitry'sdynamic range in handling wanted and unwant-ed signals. For a bandwidth of 1MHz, slew ratewill need to be at least 100V/Ns. If the dominantcomponent is no more than 100kHz, then above10V/ps will be enough. Any devices working onrails of more than ±15V would benefit from apro -rata higher slew limit.
Extending bandwidthsSingle chip instrumentation amplifiers capable ofdc to 1GHz have yet to arrive. But very wide -
band op -amps - both current and voltage feed-back types - are increasingly prolific.
High-speed op -amps can be used instead onin -amps if the trade-offs can be justified. Inexchange for a ten or hundred fold increase inslew rate and high gain -bandwidth, maximumsupply is usually diminished, commonly tobetween ±5 to ±7V. Common -mode voltagecapability is reduced pro -rata. As a result, 7dB to10dB more cm voltage attenuation, and recoverygain, are required, using up gain bandwidth.
Testing these parameters when at their best isbeyond the scope of my test equipment. Butnoise, while commendably low at mid to high rf,
Current Sensing ProbeInsulated
Trin-as plg
Vge
Twin -ax
CMM=current monitoring modeSVS=small-signal voltage
FS
BTZ. 1400 V
R1
12 k 0.5
Fig. 23. Attenuatorfor 400V ac/dc hasbalanced format forsafely reading largevoltages, of sameorder as cmv. Largeresistances may beused since thermal -noise is not aproblem. Common -mode rejection isuncritical andresponse is flat to100kHz or more.
Live
To A or B
240 v rmsMains
To B or ANeutral
OR01.1R
- Earth
Caddock MS220100k, 2W
A 1 kVUAR
UAR00k, 2W
B 1 kV
can certainly be embarrassingly high at audioand frequencies less than 200kHz - especiallycompared with the latest conventional op -amps.
If useful response above 3MHz is essential,then the best of both worlds may be had by hav-ing a parallel vhf path and 'crossing over' atabout 1MHz. In Fig. 1, the high value of R6, andsimilarly R5 in Fig. 2 and Rg in Fig. 3, sets amore elementary limit on bandwidth.
Assume a 200k0 metal -film resistor with 0.3pFof parasitic shunt capacitance. Carefully laid -outpcb tracks add about 0.2pF. The sum of thesestrays is enough to subtract 3dB at 1.6MHz.
Replacing feedback resistor R6 with a T-net-work3 allows much lower ohmic values to beused, more in keeping with those recommendedfor best performance from current feedbackamplifiers. Premature bandwidth constriction isavoided accordingly, and wideband thermalvoltage noise' is also reduced.
References1. Linear Technology, LT1028 Data sheet,page 4, Fig. 4, LTC 1986.2. W. Jung and G. Erdi, Design notes, LinearTechnology, Newsletter No.25, Aug 1989.3. Mark Stitt, Amp provides 100V CM range,Burr -Brown, EDN, 10 Dec 1987.4. Walt Jung, System applications guide,Section 8, Analog Devices Inc., 1993, P.8:58-9.5. Walt Jung, IC op -amp Cookbook, 3rd ed.1986, Sams, P.346-7.6. Paul Horowitz and Winfield Hill, The art ofelectronics, 1st Ed, Cambridge UniversityPress, 1980, P.280-1.7. Gray & Meyer, Analysis and design ofanalogue ICs, 2nd ed., P.422-3, Wiley.8. Keith Billings, SMPS Handbook, Ch.13,McGraw-Hill, 1989.
10wBTZ. 2400 V
Panel CMRtrim
R3 PR. 112k. 0.5
10w S.0.7R4 D4
V-
5020 turn
Resistors: Ohms. Tol. Wattage InternalD1 -4 =11441B CMR trim
Zs (DM) = 2kAttn = 1/50
-4- Max Vo ±8V
Out
BNC
Hot select
22
16.5
11
5-5
0
Balancedreciever
input
R 11
Analyser
UnbalRx
input r
Scope I
Max common -mode voltagevs output voltage
5.5 11
Output Voltage (V)
16.5
Fig. 24. Common -mode voltage limitation. Howcmv subtracts from allowable output voltageswing. From Burr -Brown INA03 circuit data.
CMV
+1-400 v1AC/Dc max
UAR
It 1/35 (-31 dB)400 v=11.4 v320 v = 9.15 v
Sate voltageto In -amp input
CM<+/ -12 v
Fig. 25. Passive attenuation plan for interfacingwith cmr active devices working from ±15V orsimilar supplies.
R10.12 all 0.5%
487,1W R12
IC. 1
-15 V
SW. 1 Gain-30 (SVS)-20 (SVS)+18 (CMM)
Skt 2 SM. 3
51 BNC
R9661. 0.5%
Chassis
Fig. 26. Practical 400V -rated high common -mode
in -amp circuit example.High performance and
safety demands detailedattention to componentspacing, insulation, lead
dress and twist. But partscount and cost is low.
Resistor R6 is set -on -testfor a rough cmr null with
presets PR1,2 centred. Onetrimmer capacitor is usedto offset. Together, TCL2
have the same, lowtemperature coefficient. If
AD829 is used in IC,position, comp to pin 5
needs switching in for vhfstability in differential
small -voltage -signal -30demode.
22
546 July 1994 ELECTRONICS WORLD + WIRELESS WORLD
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CIRCLE NO. 107 ON REPLY CARD
VISAESTABLISHED
25 YEARS
AUDIO
Common -emitterpower amplifiers:a different perception?Low voltage audio poweramplifiers invariablydeliver the output signalfrom a collector ratherthan emitter circuit toallow a larger outputswing from a reducedsupply voltage. Does thisradical change in circuittopology affect thecrossover characteristics...Indeed, does thisrepresent a topologychange at all?Douglas Self examinesthe design issues.
When I read Michael William'sintriguing article Making a LinearDifference to Square -Law fetsl . I
was attracted by the prospect of applying it toan audio power output stage. I found thephrase "curvilinear class A" particularlyappealing.
The basic concept of the difference -of -squares is not new, as several correspondentsto EW+WW have pointed out.23 Another earlyreference (1949) to the quarter -squares prin-ciple can be found in the monumental MITRadiation Lab series on radar techniques.
Mr William's basic circuit is shown in Fig.1, and the first problem to overcome in apply-ing it for audio power is that the wanted out-put is the difference of two currents whereashard-bitten amplifier designers are more usedto a low impedance voltage output. Note thatwith the usual enhancement -mode power fets,if VI, V2 are ac sources only, and carry no dcbias, then Vb will have to establish point Msome volts below ground. No doubt some-thing could be done with industrial -sized cur-rent -mirrors, but it struck me that the circui
Fig. 2. Thei2 subtractioncarried out byinverting thepolarity of oneof the fets.Two biasvoltagegenerators arenow needed.
Fig. 1. The original Williams circuit;the output required is the differencebetween i1 and i2.
could be rearranged as Fig. 2, by making useof complementary devices. We now need twobias voltages Vb 1, Vb2, and the positioning ofthe two signal sources VI, V2 on opposite railslooks a little awkward, but at least the current -difference will be mathematically perfect, ifKirchhoff has anything to say on the matter.
So far so good. We now have a single cur-rent output lout. But is this any use for drivingloudspeakers? I am assuming that current -drive of speakers is not the final goal; I appre-ciate that this can be made to work, andpromises some tempting advantages in termsof reducing bass -unit distortion4. My imme-diate reaction to Fig. 2 was no, it can't work,because with a high impedance output, theoutput stage gain will vary wildly with loadimpedance making the amount of NFBapplied a highly variable quantity. It wouldalso appear that any capacitive loading of thishigh -impedance node would generate animmediate output pole that would make stablecompensation a waking nightmare.
However... just as I was discarding thenotion, it occurred to me that the structure inFig. 2 looks very much like the bipolar com-mon emitter (CE) stage in Fig. 3. This is wide-ly used in low voltage op amps because thelow saturation voltage allows a close approachto the rails5. The more usual emitter followertype of op amp output is usually called a CCor common -collector stage. It is highly prob-able that the widest application of these volt-age -efficient CE configurations is in the head-phone amplifiers of personal stereos.
At about the same time I encountered apaper by Cherry6 which pointed out that, solong as NFB is applied, the output impedanceof such a stage can be as low as for the usualvoltage follower type output. Cherry's paper isdauntingly mathematical, so I will summariseit thus. The vital point about using NFB toreduce the output impedance of an amplifier is
548 ELECTRONICS WORLD + WIRELESS WORLD July 1994
AUDIO
that the amount of NFB applied must be cal-culated assuming that the open -loop case isunloaded. This condition looks unfamiliar,because the average amplifier usually has afairly low output resistance even when open -loop, due to its output follower configuration,and so the loaded/unloaded distinction makesonly a negligible difference when calculatingthe reduction of output resistance by NFB.
Using this condition, Cherry shows that out-put impedance of a CE stage should be exact-ly equivalent to the usual CC stage, when theglobal NFB is applied. I appreciate that thisresult is counter -intuitive; it looks as thoughthe current output version must have a higheroutput impedance, even with NFB, but itappears not to be so. Doubters who areunafraid of matrix algebra should consultCherry's paper.
Topology to the testNonetheless, before reaching for the powerfets, I felt the need for further reassurance thata CE output stage was workable. There areseveral low voltage op amps that use the CEoutput topology, so it seemed instructive toprovoke one of these with some output capac-itance and see what happens. A suitable can-didate is the Analog Devices AD820, whichhas a BJT output stage looking like Fig. 3 andprovides all you need for CE experimentationin one 8 -pin package7.
My practical findings were that the op ampworks well, and while THD may not be up tothe very best standards, it was happy withvarying load resistances, proved stable withcapacitors hung directly on the output, andwas relaxed about rail decoupling. Once again,so far, so good.
By this stage, the quarter -squares principlewas slipping somewhat into the background.My attention was focusing on the possibilitiesof a BJT power output stage something like
Fig. 4, which shows the addition of driversand emitter resistors to make the circuit morepractical. A good output swing is facilitated bythe inward -facing driver arrangement. In aconventional emitter follower output the needto leave the drivers room to work in furtherreduces output swing.
Fig. 4 could be configured into somethinglike a normal Class -B amp, except that thenovel use of a CE output stage would allowgreater efficiency than usual because therewould be the low lice(sat) drops mentionedabove. Also the crossover behaviour wouldpresumably be different from a normal CCoutput, and quite possibly better, or at leastmore easily manipulated.
In a previous article8 I tried to demonstratethat for an amplifier in which all the easilymanipulated distortion mechanisms had beensuitably dealt with, the low frequency THDwas below the noise when driving an 8S2load... this without large global feedback fac-tors: 30dB at 20kHz is quite adequate.
At high frequencies (say above 2kHz) thedistortion is easily measurable, and almost allof it results from crossover effects in the out-put stage. Since NFB typically falls with fre-quency, these high -order harmonics receivemuch less linearisation. This is why any tech-nique that promises a reduction in basiccrossover nonlinearity is of immediate interestto those concerned with power amplifierdesign.
I began to think that Mr Williams hadopened up a whole new field of audio ampli-fication; each conventional CC output stagewould have its dual in CE topology, perhapswith new and exciting characteristics.
The next stage of the investigation was moresobering. There was a familiarity about CEoutput stages. Readers old enough to recallpaying 30 shillings for their first 0072 willrecognise Fig. 5 as the configuration used
almost universally for low power audio outputfor many years when there was no such thingas a complementary device. Transformers pro-vide one way to make a push-pull output. Atfirst sight bias voltage Vb looks as if it will befar too low but bear in mind these are germa-nium transistors. Note the upside-down formatof the circuit which is typical of the period.The circuit values are appropriate for an out-put of about 500mW.
While it is perhaps not obvious, this is theequivalent of Fig. 3. The need for an npn is
Fig. 3. The bipolar version of Fig. Z as used inmany low -voltage op amps and Walkmanoutput amplifiers.
Fig. 4. A practical circuit based on Fig. 3.Drivers and emitter -resistors have been added.
12V
Rioatl
OV
Fig. 5. A rather old-fashioned CE amplifier: thetransformers are expensive but avoid the needfor complementary devices.
Fig. 6. BIT Collector currents in Fig. 4 driving an8S2 load.
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 549
AUDIO
avoided by using phase inversions in the trans-formers. So clearly CE output stages were notas rare and specialised as I thought; howeverthey might still have handy distortion proper-ties that were not obvious in the long -gonedays of transformer coupling.
Adding Spice to the investigationThe next step was Spice simulation of thepractical BJT output circuit in Fig. 4: Fig. 6shows how the device currents vary in a rela-tionship that looks ominously like classicClass -B... Somehow I was expecting more
Fig. 8. Gain linearity of Fig. 4 for various bias voltages, load is 8Q. (BIT)
0.5V 1.0V
R L6Pti = 8S11 5V 2.0V
overlap of conduction. The linearity results arepresented in Fig. 7 as a plot of incrementalgain versus output voltage for varying loads,as in the Distortion In Power Amplifiersseries8.
The first obvious difference is that stagegain, instead of staying close to unity, varieshugely with load impedance - pretty muchwhat we expect from a CE stage operatingopen -loop. Note that the X-axis is VI (V2 =-V1 to induce push-pull operation) and so rep-resents the input voltage only rather than bothinput and output as before. Multiplying thisinput voltage by the gain taken from the Y-axis gives the peak output voltage swing. Thevertical gain drop-offs that indicate clippingmove inwards with higher load impedancesbecause of the greater output gain rather thanthrough any hidden limitation on outputswing.
Fig. 8 shows the effect of varying the bias,and hence quiescent current, for an 8 -Ohmload.
This circuit certainly works, but somehowthe linearity results seem depressingly famil-iar. There is the same gain -wobble atcrossover we have seen ad nauseam with CCoutput stages, and once again there is no biassetting that removes or significantly smooths itout. As before, the usual falling -with -fre-quency NFB will not deal with this sort ofhigh -order distortion very effectively, leadingto a rise in THD above the noise in the upperaudio band.
In fact, the characteristics look so suspi-ciously similar to the standard emitter -fol-lower CC stage, that it began to belatedlydawn on me they might actually be the samething...
Fig. 9 shows the final stages of this concep-tual hejira. 9a shows the simplified circuit ofFig. 3 with the power supplies V+, V- includ-ed; they no doubt come from a mains trans-former so we can float them at will, and itseems quite in order to pluck them from theirpresent position and put them in the collectorsof the output devices instead. All the othersupplies shown are equally without ties form-ing an independent unit with the associatedtransistor and emitter resistor Re. Thus theycannot effect device currents. Since there isonly one ground reference in the circuit, it isalso a legitimate gambit to put it wherever welike, which in this case is now the oppositeend of the load RI. (See reference 9 for anoth-er example of this manoeuvre). This gives usthe unlikely looking but functionally equiva-lent circuit in Fig. 9b.
A purely cosmetic rearrangement of 9b pro-duces 9c, which is topologically identical, andreveals that the new output stage is... a CCstage after all. Fig. 9d shows the standard out-put.
The only true difference between the "CE"stage and the traditional CC stage is thearrangement of the two bias voltages Vbi, Vb2.In a conventional CC stage, the output basesor gates are held apart by a single fixed volt -
Continued over page...
550 ELECTRONICS WORLD + WIRELESS WORLD July 1994
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Fig. 9. Showing how our experimental CE amplifier turns out to he a moreor less conventional CC amp when fumed inside out.
age, shown here as Vbl and Vb2 connectedtogether. This rigid "unit" can be regarded asdriven with respect to the output rail by thesignal source Vsig, representing the differencebetween input and output of the stage.Normally, of course, it is more useful toregard the earlier circuitry as generating a sig-nal voltage with respect to ground.
In contrast to Fig. 9d, Fig. 9c has two biasvoltage generators, and the consequence ofthis is that voltage drops in the emitter resis-tors Re are not coupled across to the oppositedevice by the bias voltage. This does not seemto offer immediately any magical stratagemsfor reducing the gain deviation aroundcrossover, and creates the need for two drivevoltages referenced about the output rail. Thisshould be fairly easy to contrive, but is boundto be more complex than the traditionalmethod.
Squaring the circleHaving gone through these manipulations, it istime to reconsider fets and the quarter -squaresapproach, knowing now that we are dealingwith something very close to a standardpower -amp configuration. To underline thepoint, Fig. 10 shows the gain characteristicsfor the circuit of Fig. 2, using 2SK135/2SJ50power fets. Note the very close resemblance toa conventional source follower8.
As Mr Williams points out, the Vgslid char-acteristic curve for power fets may follow asquare law at low currents, but it is more orless linear at high ones, and this appears torule out any simple approach to "curvilinearclass A". For the fets I used, the "square law-ish" region is actually tiny, being roughlybetween 0 to 80mA which is of limited use fora power stage. In so far as second -harmoniccancellation occurs at all, it is in the crossoverregion where, without this effect, the centralgain deviations would probably be greaterthan they are.
As I can see, the quarter -squares concept isalready in use in most fet power amplifiers inheavy disguise but only operational in thecrossover region. If this idea is to be pursued
Fig. 10. The gain linearity of the fet circuit in Fig. 2 for various bias voltages. This looks very similarto a conventional source -follower output stage.
further, we need a true square -law outputdevice. Since there is no such thing, it wouldneed to be realised by some kind of law -syn-thesis circuitry. If amplifier distortion needsreducing below the tiny levels possible withrelatively conventional techniques, there areprobably better avenues to explore.
References1. Williams, M, Making a linear difference tosquare -law fets EW+WW, Jan 94, p82.2. Brown, S F, Letters, EW+WW, March 94,p247.3. Owen, D, As 2.4. Mills & Hawksford, Transconductance
8 . OV
Power Amplifier Systems, Current -DrivenLoudspeakers. JAES Vol 37 #10, Oct 19895. Fonderie & Huijsing, Design of Low -VoltageBipolar Operational Amplifiers KluwerAcademic Publishers 1993 Chapter 3.6. Cherry & Cambrell, Output Resistance &Intermodulation Distortion of FeedbackAmplifiers JAES Vol 30 #4, April 827. Jung & Wong, High -Performance 1Cs inSingle -Supply Analog Circuits. AnalogDialogue #27-2 (1993) p16.8. Self, D Distortion in Power Amplifiers: Part4 EW+WW, Nov 93, p932.9. Baxandall, P Symmetry in Class B Letter,Wireless World Sept 1969, p416.
552 ELECTRONICS WORLD + WIRELESS WORLD July 1994
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Computerised data acquisition has neverbeen simpler, with all manner of plug-in data acquisition boards available for
the PC. Now, thanks to software packagesdesigned to make these cards easy to use, anew term has entered the vocabulary - name-ly virtual instrumentation. Separate digitalvoltmeters and oscilloscopes are no longerneeded. Sensors connect directly to the dataacquisition card and facsimiles of hardwareinstruments present the measurement resultson the vdu.
Virtual instruments are especially useful inlaboratory type environments, where sensorsare positioned within a few metres of the dataacquisition card in a relatively benign electri-cal environment. However they are less usefulin electrically noisy environments, such as afactory floor, where the sensor may be tens ifnot hundreds of metres from the computer.Used correctly, screened cables help, but theyare by no means a complete solution.
The major problem in getting data from aremote sensor to your data logging station orcomputer is noise. From a practical point ofview, noise can be divided into three ratherloosely defined categories. These categoriesare, pickup, impulse noise and random noise.
Pickup is usually a narrow band interferencemechanism. It is invariably due to ac powerline inductive coupling. Impulse noise consistsof very short duration, often very high ampli-tude spikes. These sometimes occur in bursts.Often these impulses are only microseconds induration, but of sufficient amplitude to play
By the time it reaches adata -acquisition system,the signal from a remotesensor can be almostindistinguishable fromthe noise it picked up enroute - particularly in anindustrial environment.Dave Robinson looks athow such signals can berecovered.
havoc with any naively designed digital equip-ment. Random noise is just that, an amor-phous mush that can completely swamp thesignal that you are trying to observe.
Invariably all three types of noise are presentto some degree. Basically, there are two waysof dealing with noise - one is to remove it, theother to avoid it. The first option includesalgorithms designed to recover your signalonce it has been contaminated with noise. Thisis obviously a not an ideal solution. Howeverthere are times when control of the noise is notin your hands.
lEarameter Variation]
Fig. 1. Reference waveform - before noise is added - used to illustrate the various techniques ofsignal recovery.
Noise removalAll noise removal techniques are a compro-mise. They rely on redundant data which isused to estimate the wanted signal. These esti-mates are then used to reduce the noise.
With Shannon rate sampling, where data issampled at the maximum theoretical rate,every sample represents new information.Thismakes noise removal techniques inappropriateand noise avoidance techniques are usedinstead.
It is however possible to obtain redundantinformation by over sampling the noisy sig-nal.The more the signal looks like a slowlydrifting dc level to your data acquisition sys-tem, the better chance you have of recoveringuseful information.
Basic statistics tell us that the signal-to-noiseratio can only be improved slowly. It goes upas the square root of the number of samplestaken. Thus four independent samples of thesame signal effectively halves the noise con-tamination, but 10,000 samples only reduces itby 100. From this basic rule of thumb you canroughly calculate the sample rate you willneed to produce the quality of signal given afixed degree of noise contamination.
Assume that you know that the maximumrate of signal you are looking for changes byan amount equivalent to the least -significantbit of your a -to -d converter in say T seconds.If your sample period is NxT, the maximumtheoretical improvement you can expect fromany algorithm is 'JN. From this approximateanalysis, and knowing the dynamic rangerequired by your control process, you canidentify the type of a -to -d converter your sys-tem requires, as described in the panel.
For demonstration purposes, the followingalgorithms are applied to the curve producedby a theoretical process Fig. 1. Before thealgorithms are applied, this ideal curve isburied in noise, as in Fig. 2. Time would prob-ably - but not compulsorily - be on the X axis.The Y axis could represent virtually any
554 ELECTRONICS WORLD + WIRELESS WORLD July 1994
DESIGN
parameter, for example voltage, temperatureor even sugar concentration.
Waveform averagingThe simplest, and perhaps the most intuitivemethod of signal recovery is to find the aver-age of a number of samples and use that as theestimate of the signal. Waveforms Fig. 3shows this process in action. Each sample inthese waveforms is simply the average of ablock of fixed number of preceding samples.
It is clear that as the block length increases,so the noise level decreases. At the longestblock length the data is almost as clean as theoriginal. Be cautious however. Compare thepure original signal with the cleaned up ver-sion, Fig. 4. Note how it has been distorted.Although the problem looks simply like delayand attenuation, it is mathematically morecomplicated than this. The distortion is math-ematically definable. It could be reversed, atleast in theory, but such techniques are beyondthe scope of this article.
Depending on the application, the distortionmay be tolerable. But be careful if you areusing the process within a feedback loop. Itsapparent delay, or lag, could result in the con-trol loop becoming unstable. This will result inthe complete system oscillating, and in somecircumstances lead to expensive damage toproduction machinery.
Although block averaging is fairly simple inconcept, building a real-time implementationof the algorithm might not be so straight for-ward. Do you redo the complete average pro-cess for each new input sample? Or do you tryto subtract the oldest value from the sum andadd in the newest value? In either case arecord has to be kept of the original block datasamples. This is not so easy if you are using asmall microcontroller with no external ram,particularly if you are trying to get a 100:1improvement in signal to noise ratio.
As an alternative to block averaging, a run-ning average can be used. Running averagesare easier to compute. Exponential smoothingis perhaps the most common running averagealgorithm. It is an iterative algorithm whichcomputes the following:
Yn+ 1 = Yn-1 nput)
Here Y,/ is the estimate for the latest value.Yn is the last sample estimate, variable input isthe current input sample and K is some con-stant which is less than 1. Why it is calledexponential smoothing when there is no expo-nential function in the equation can beexplained by simply considering its responseto be a step function. Assume that the originalinput has been zero, as is Yn, and the inputinstantaneously steps up to one and staysthere. Output from the algorithm for variousvalues of K is shown in Fig. 5.
The curves are true exponentials whose timeconstant is controlled directly from the Kvalue. Reducing the K value increases thetime constant. The procedure is analogous toconnecting a simple RC filter to a noisy elec-tronic node in order to remove the noise. This
algorithm is the simplest form of recursivedigital filter. Figure 6 shows results obtainedfrom applying simple exponential smoothingto Fig. 2.
PredictorsAveraging can be considered as a limitingcase of an algorithm known as a predictor.These use a block of data in order to predictwhat the next value will be. The averagermodels the data within its block as a simple dclevel. As a result, the next value will be theaverage of the previous data points.
Received signal after noise corruptionll
Predictors are classified in terms of orders.They attempt to model the data block in termsof a polynomial, and use a statistical mecha-nism such as least squares to find the best fit.The order of a predictor is simply the highestpower of polynomial being used to model thedata. Thus a linear fit y=nu+c is a first orderpredictor. An averager y=c is simply a zeroorder predictor.
Predictors do have problems. They have tobe tailored for a particular task. As the pre-dictor's order increases, so its ability toremove noise diminishes. This is illustrated by
Fig. 2. In passing from a remote sensor to a data acquisition board, the reference signal of Fig. 1would pick up noise. Before the signal can be analysed on computer, it needs to be recovered fromthe noise.
Freraged over 4 samples
Averaged over 16 samples I
-- ,
Let:reraged over 64 samples I
Fig. 3. Using averaging to recover a signal from noise, apparent quality of the recovered signalimproves as the number of samples increases. But the results can be misleading.
averaging Distortionl
Raw data --74 -Averaged data
Fig. 4. Although the signal recovered using averaging and a high sample rate looks clean, it suffersfrom distortions that can cause problems, for example, if the measurements are used to determinefeedback in a control loop.
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 555
DESIGN
considering, say, a 16th order pre-dictor running with a block of 16previous data values. An exactpolynomial fit can be made to thedata, noise and all - which is use-less.
The higher the predictor's order,the more independent parametersthe predictor is trying to estimatefrom the same data. An averager isonly producing one value - theaverage - whereas a first order pre-dictor needs to determine the offsetand slope from the same data. Theresult must be inherently morenoisy.
Predictors offer an advantage inthat the data being extracted fromthe noise is probably going to bemoving. This means that a polyno-mial model is likely to be a closer fit than amodel that suggests that the data is a simple dclevel. Consequently the apparent phase shiftshown by an averager is a good deal lessnoticeable using a higher order predictor, andit is less susceptible to closed control looposcillation.
More powerful statistics can be used toenhance the signal-to-noise ratio. For examplethe value of slope and offset computed at eachnew data sample can be averaged. Predictorscan be made to react almost instantaneously todrastic changes in input signal. This is accom-plished using statistical decision theory.
If you have calculated the optimum param-eters for your model using data within thebuffer, you can also calculate how far eachdata point is adrift from that model. In otherwords you have a measure of the local signal-to-noise ratio. By comparing the current pre-dicted value with the latest sample, a decisioncan be made as to whether the current datapoint belongs to the rest of the distributionwithin the buffer. If it is, the prediction is out-put, maintaining the smoothed data output. Ifnot, the actual value is output, and the contentsof the predictor buffer can be deleted since the
Demonstrations of exponential smoothingusing various values of K
Original edge/
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////
Fig. 5. In an averaging signal recovery filter withexponential smoothing, quantity K control thetime constant directly.
previous value is no longer valid, and a dis-continuity has occurred. The signal-to-noiseratio will return to its raw state until the pre-dictor has gained sufficient data to be able tostart making sensible estimates once more.
Figure 7 shows results from a simple firstorder predictor, using a 64 sample buffer andboth slope and offset smoothing, applied to thesample noisy waveform. Note that the result-ing waveform is not as smooth as the straightforward averager of similar buffer length.However the fit to the raw data is far better.
A priori knowledgeMethods described so far are recommended ifand when you have no information regardingthe distribution of the incoming data stream. Ifcertain aspects of the data's distribution areknown, they can be used to produce remark-able signal recoveries. What form this knowl-edge is in, or how it is best used, depends onthe situation.
LRwtniitg average K=1/161r
For example, suppose that thewaveform being recovered isrepetitive. Ideally its repetitionfrequency is known. It is not nec-essary to know the actual phaseinformation. If you take a sampleat a given time after the encodersynchronisation pulse, then youcan expect to get the same valueat the same point after the nextpulse. Any discrepancy is due tothe noise corruption on the signal.
Imagine setting up a number ofaveragers, or exponentialsmoothers evenly distributedthroughout the repeat cycle. Thesewould simply average out thenoise and find the true value ofthe signal at that phase position.By sequentially interrogating
these averagers, you can build up a very goodpicture of the underlying waveform.
Figure 8 shows how effective techniqueslike this can be. The signal is as used previ-ously, but this time replicated to form therepeating waveform. It is buried in far morenoise than was used in the previous examples,so much so that the underlying waveform isundistinguishable.
Each cycle is split into 256 points, and eachpoint is equipped with its own exponentialsmoother with weight K=1/64. After runningthe system for a short time its output settlesdown to an equilibrium position as shown.The original waveform is almost completelyrecovered.
In this particular example we have twopieces of information, namely that the wave-form is repetitive and its repetition frequency.Even if the repetition frequency is not known,all is not lost. There are signal processingtechniques, such as auto -correlation, whichallow you to determine repetition frequency,enabling the previous technique to be used.
A word of warningInvariably, corruption of data by noise is mod-
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Fig. 7. Compared with an equivalent averaging filter, the simple first -order predictor produces a less smooth output but the overall fit with the originalsignal is much better.
556 ELECTRONICS WORLD + WIRELESS WORLD July 1994
DESIGN
elled as a linear process. The noise and thesignal are viewed as two separate entities andare combined by arithmetical addition. Underthese circumstances the processes describedabove work well.
However beware of multiplicative noise cor-ruption. This is where noise and the signal aremultiplied together. Under these circum-stances the techniques mentioned no longerwork. Multiplicative noise corruption canoccur in many places. In data -acquisition sys-tems, the most common sources are noisy illu-mination systems in optical sensors. Here, out-put from the sensor is the product of thereflectance of the object multiplied by the illu-mination. Similarly noisy excitation of resis-tive sensors can be a problem.
Output voltage from such sensors is theproduct of device resistance and excitationcurrent. Removing the effect of such corrup-tion is not easy, so make sure that these nodesare given the respect they deserve.
Next month, David discusses thealternative to noise removal techniques,namely noise avoidance.
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Analogue -to -digital conversionTransducers monitoring real world parameters, forexample temperature or strain, invariably producean analogue output. In order to process such asignal digitally, it needs to be converted into aform that can be handled by a computer by ananalogue to digital converter.
An analogue to digital converter, or ADC, isdesigned to produce a digital numberapproximating to the analogue input. Imaginetaking a reading from a temperature sensorcovering the 0 to 100°C. In theory, thisthermometer could monitor any temperaturewithin its range.
However the ADC splits the range into a finitenumber of steps. Combined, the thermometer andADC are only capable of measuring discretequantities, or quantization levels. It is thedesigner's task to ensure that the number ofquantization levels provides adequate dynamicrange for whatever their required task demands.
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As is usual, trade offs have to be made. When desigr inganalogue -to -digital converters, desirable parameters are highresolution, i.e. lots of quantization levels, high sampling rateand low cost.
There are several types of ADC. These include flasi, halfflash, successive approximation and charge integration types.The chart below shows how the important parameters arebalanced for these four converter technologies.
Note how the number of quantization levels, or rripe.conventionally the number of bits, is inversely related todigitisation rate. Commercially, ultra fast converters arenormally only available with limited dynamic range.Similarly very accurate converters are only available withlimited conversion speeds.
The question of conversion rate bears heavily on F ow theconverter is connected to the input signal. Very fastconverters only need a fast high quality amplifier. The speedof conversion is such that the input signal will have barely
Fig. 9. Analogue -to -digital converters used for data acquisaion are acompromise between resolution cost and sampling rate capability.
moved curing conversion.For slower converters, this is no longer true. Input voltage
needs to be frozen cluing th= conversion period, otlerwisethe input signal may change appreciably during theconversion process. This wastes any advantage gained in theincreasep dynamic range of the slower converter.
A solu-ion to this problem is to use a sample and -oldcircuit. The simplest form of sample and hold configurationcomprises an RC circuit corrected to the input signal viasome form of switch. Wher the switch is closed, thecapacitcr rapidly charges u: to the voltage at the input.When tFe switch is open, tFe voltage on the capacitorremains fixed while the con/ersion is completed, e.,enthough the input signal may change significantly.
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 557
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July 1994 ELECTRONICS WORLD+WIRELESS WORLD
PCENGINEERING
Graph plotting inWindowsGraphs are essential tools forconveying engineering andscientific information butproducing them is tedious andtime consuming. Not so, saysAllen Brown, with this newplotting package.
Plotting data has never been easier than with PCsrunning under Windows. It is now common inengineering environments to see PCs with high
resolution colour monitors, linked to laser printers. Thesestandard tools, together with suitable software, makeplotting an almost pleasant task.
The attractive features of Windows are its universalacceptance and dynamic linking facilities. In addition, itscommon user interface makes all Windows software lookthe same.
Most engineers now use word processors from time totime. Although many word processors include graph -plotting facilities, they tend to be rather limited in scope.This can result in the user wasting valuable time trying tofashion the supplied standard graphs into an acceptableformat.
The alternative is to use a specialised graph plottingpackage that allows graphs to be imported into yourfavourite word processor.
A new graph plotting software package for Windows hasrecently been released by MicroCal Software ofMassachusetts. Entitled Origin, it is a fully comprehensivegraph plotting utility capable of producing both two andthree-dimensional plots.
A remarkable feature of Origin is its high degree ofcontrol over the many display formats granted to the user.Also, the ease with which control can be exercised overthe plotting formats is appealing.
User input is carried out via dialogue boxes that provideconsiderable choice of positioning, fonts, colour, scaling
MicroCal Origin DAOFIGINWAMWW_7Elie Edit Column Data convert Wisdow
Pie Chart 9 9.012 33./112Polar Plot Phol 10 10.432 37.1142
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Plot selected region as line graph
and plotting styles. Whatever feature is selected on a plot,a click with the mouse's right-hand button evokes thedialogue box associated with that feature. Each dialoguebox contains numerous options for adjustment and display.
Part of the Origin package is a tutorial that willparticularly benefit the new user in that it provides a goodunderstanding of the mechanics of the software. OnceOrigin has been installed -a very easy task - the new userwill find the Getting started section in the tutorial veryuseful. The tutorial exercises are well thought out, takingthe new user through the majority of the features which thepackage has to offer.
One immediate feature which is very useful is the easewith which ascii data files can be imported. Even with filesonly having y axis data, the user is offered the choice ofdefining the x axis data and prompted for both startingpoint and increment. This is especially useful if the rawdata has been obtained from an expansion card that onlyprovides y data streams or batches.
Fig. 2. From eachworksheet, graphscan be createdindividually ordisplayed on thesame graph.
Fig. 3. Origin offersa wide choice of
curve fittingsoptions. Most usethe least -squares
method
Fig. 4. A typical 3Dtrajectorygenerated fromOrigin - not overlyimpressive.
Dynamic linkingData can be brought into the Origin window via theWindows dynamic linking facility from other concurrentsoftware packages such as the spreadsheet Excel. Thisoffers some exciting possibilities when using other dataacquisition software.
An interesting feature of Origin is its error -barcapability. Scientists use error bars on their graphs butengineers rarely do. Including error bars has always been aproblem for software displaying data graphically. WithOrigin however, error bars are very easily added to graphs.This is thanks to Origin's worksheet format.
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WorksheetsWhen Origin starts up, a defaultworksheet is generated. It looks likea spreadsheet design with an array ofcells. As data is imported intoOrigin it fills up the columns in theworksheet.
Graphs can be generated directlyfrom the worksheet data. When errorbars are needed, an extra column isproduced - via a drop -down menuoption. This column is dedicated toerror bar, which are plotted at thesame time as the worksheet data, Fig.1. This display also shows theplotting options offered in the PLOT
drop -down menu.Imported data can be loaded
directly into a worksheet or into agraph. From each worksheet,individual graphs can be created oralternatively the data can bedisplayed on the same graph asillustrated in Fig. 2.
By accessing the DATA option from the drop -down menuit is possible to generate a column of linearly increasingvalues. If need be these can be used to form the x axis.You can place, with ease, as many data columns in thesame worksheet and they can be plotted as required.
Even if data is not available from an outside source itcan be generated within Origin from the function -plotoption. This can be displayed in either Cartesian or polarformats. Some elementary statistical processing can alsobe applied to each column or row.
This can provide information such as mean deviation,standard deviation and the result of t -testing. A furtherinteresting feature of Origin is its ability to put severaldata plots in layers on top of each other and display themalltogether. In addition, different axis limits can beattached to the top and right hand side of the graphs toshow alternative scaling.
Several worksheets can be open at any one time. Byusing the Windows clipboard, data can be exchangebetween worksheets very easily. The worksheet alsoallows editing of the data values in each column - so -
560 ELECTRONICS WORLD + WIRELESS WORLD July 1994
PC ENGINEERING
called data massaging. This feature should instantly endearOrigin to statisticians working in the Treasury orEmployment Department.
TemplatesMany engineering and scientific tasks that need largeamounts of data logging and plotting tend to be repetitive.With this in mind, Origin allows users to constructgraphical templates.
Major features of templates - for example axis limits,scaling and labelling - remain fixed. Only the data plottingand possibly the legend will change from graph to graph.
This design feature would be very useful for proprietarygraphs showing for example calibration and systemperformance for quality checking. A system performancegraph can incorporate a tolerance envelope as part of thetemplate. The actual performance curve, i.e. the data, isthen inserted into the template graph. By looking at theresulting plot, an inspector can immediately determinewhether the system under test conforms to expectation bystaying within the tolerance envelope.
Curve fittingHaving imported a batch of data into Origin, you canexercise a variety of curve fitting options on the resultingcurve. Some of the options are shown in Fig. 3 in the drop -down menu. Also shown in this shot is an example forfitting an eighth -order polynomial to a data batch. As thecurve fit is in progress another window is opened to showthe results of the calculations and to display thecoefficients and the correlation values. This provides ameasure of how well the polynomial fits the data.
Most curve fitting techniques use the least -squaresmethod. When this is applied to an eighth -orderpolynomial, an 8 -by -8 matrix is generated that has to beinverted. This requires a reasonable amount ofcomputation.
Speed of the maths calculations in Origin whileperforming curve fits is remarkably quick.
3D and contour plottingThree-dimensional plotting is the second part of Origin. Itappears to be an addition to the Origin package proper.Contour plotting is quite impressive, particularly theautomatic labelling.
I don't have the same enthusiasm for the 3D plottinghowever. Although it is easier to use than many othergraphics packages, its range of options is small and itdoesn't behave as you would expect.
For example, consider an unstable oscillator where timeis along the z axis and velocity and displacement along they and x axes respectively. You would expect to see anexpanding helix along the z axis. Figure 4 shows what youactually get even when you specify a trajectory plot - notvery impressive.
However the surface plots are acceptable, as you can seefrom Fig. 5, and colour grading is easy. Surface plots areproduced by importing matrices into Origin, which is now
a common practice for plotting surfaces.There is however a long wait for the redraw of the
surfaces each time a slight change is made. This can bequite irritating after a while. Although the value of surfaceplots is sometimes questionable, they are quite usefulwhen illustrating the significance of poles and zeros in theS -domain.
LabTalkFor really enthusiastic users who want to design customgraph formats, Origin comes with its own commandlanguage. This language, LabTalk, can also be used todetermine how data is read into its associated worksheet.
LabTalk is a programming language providing access tothe majority of Origin functions. These include the user -designed dynamic data links , or DLLs, for MicrosoftWindows linking.
Syntax of LabTalk is not unlike that of dos batchcommands, with operators, control flow and the customarystructuring options. LabTalk is actually an interpreter thatprocesses its native script or source code language.
The fact that LabTalk is an interpreter is useful if you
Fig. 5. Everyone likeslooking at surfaceplots but are theyreally useful?
Fig. 6. With a littleimagination and lotof time someinteresting displayscan be designedusing LabTalk.
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July 1994 ELECTRONICS WORLD + WIRELESS WORLD 561
PC ENGINEERING
need to design a custom product with plotting features.However it is not the sort of feature that the casual user ofOrigin would use. An example of what can be achieved isshown in Fig. 6.
Reference manualThere are in four manuals with Origin -a tutorial guide, areference manual, LabTalk's user manual and a3D/Contour supplement.
The tutorial guide is well written and is aimed at thegeneral user. It provides a number of good examplesillustrating Origin's salient features. In addition it hasmany screen dumps and all the examples work accordingto the guide -a pleasant surprise.
As expected the reference manual contains all thefunctions of Origin and complements the screen helpfacilities provided in the software.
Round upOrigin is a package that I like very much. It is easy to useand its operation is logical. The range of 2D plottingoptions is most impressive. Above all, the flexibilityafforded to the user makes it very attractive.
The learning curve needed is gradual. In no time, I wasable to exercise a lot of control over plotting formatswithout having to cover all the features offered by theproduct. This is the sort of package that you can use a partof, quite competently, without having to worry about therest of it.
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plotting. You would not be able to plot a Lorentz Attractorand make any sense of it. However if you need no 3Dplotting, then you should find Origin a treat to use.
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Coherer-based radioFollowing its introductiona century ago, the cohererelectromagnetic wavedetector helped radioevolve from being acuriosity to a practicalcommunication tool.George Pickworth hasbeen studying earlydesigns and has evenexperimented with work-ing transmitter/receiverscapable of communicat-ing at up to 1 km.
Fig. 1. Sensitivity of the coherer. Althoughsensitivity is important, it makes the cohererprone to false triggering due to naturaldischarges if too high.
The coherer can be seen as a very fast,self latching relay. When triggered by apulse induced in the receiver antenna, a
local dc source of typically I .5V operates apaper -tape Morse register, via an auxiliaryrelay. This provides a permanent record of thereceived signal.
The coherer was the first practical Hertzianwave detector. During its life, from about1895 to 1905, it turned radio from a possibil-ity into a practicality. History of the devicewas comprehensively covered by LeonidKryhanovsk} in his article (The coherer,EW+WW March 1992), but as he said, itsphysical mechanism was not fully understood.
As a tecrmical historian, I am particularlyinterested in the sensitivity of the coherer,as no meaningful information could be foundin the literature, I decided to make a replica ofa circa 1900 coherer and conduct my ownresearch.
PulsesMy research showed that the coherer is actu-ally a vo'tage-pulse triggered device. Thepulse causes the coherer's resistance to drop toa level determined by the peak potential of thepulse. In a practical radio system, the pulsemust be large enough to lower resistance to acertain threshold. If not, there will be insuffi-cient current flow from the dc energiser circuitto operate the auxiliary relays and Morse reg-ister. Fig. 1.
The coherer can be triggered by a single uni-directional pulse, as may occur with naturaldischarges, or by the first negative or positive -going half cycle of current induced in theantenna by a train of exponentially decliningHertzian waves. However, multiple triggeringcan occur with pear-shaped wave trains duringthe incremental increase in the amplitude ofsuccessive half cycles.
You can see from Fig. 1 that a pulse with apeak potential in the order of volts is neededto cause the coherer's resistance to drop to afew hundred ohms. Polarity of the pulses rel-ative to the 1.5V dc energising source wasimmaterial above the 3V threshold.
Working pointThe threshold at which the system began oper-ating would have depended upon the sensitiv-
VAIVimmivw.
Fig. 2. Current induced in an antenna by anexponentially declining wave train. Triggeringof the coherer occurs on the first half cyclepulse: remaining pulses are redundant.
Fig. 3. Current induced in the antenna by apear-shaped wave train. Successive pulseslead up to the final pulse at the peak. As withFig. 2, subsequent pulses serve no purpose.
ity of the auxiliary relays. Reliable operationseems to start at the knee of the curve, and isbest above the saturation level of 9V. Whilemy research shows sensitivity of the replicacoherer, overall receiver sensitivity would byinfluenced by sensitivity of the relays and thisrequires further research.
It appears that pulses with a peak potentialin the order of volts would be needed for reli-able working. At first sight, an induced pulsepresenting a potential of this order seemedinconceivable. However I then realized thatearly spark transmitters packed an enormousamount of energy in the first wave of an expo -
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 563
HISTORY
Fig. 4. Current induced in antenna byrepetitive wave trains. Coherer triggeringoccurs on the first half cycle of each train.The period between triggering is long enoughfor operation of Morse register and restorer -typically 50 to 200ms.
TelegraphMOM
To telegraphinstruments
Overhead line
Copperfilings
GND
Fig. 5. Varley's lightning protector compriseda glass tube loosely filled with copper filings.Provided the lightning wasn't a direct hit, theprotector could be restored by gentlevibration.
80% steel and20% nickel (10p coin) filings
200mm
3mm
Plastic tube from ball-point pen
Fig. 6. My prototype experimental cohererhad a plastic tube and could easily betriggered by esd. Replacing the tube with aglass alternative reduced this effect.
Glass tube2.5mm ID
Silver electrodes
1.0mm
Sealed afterevacuation of
air
'1/
96% nickel / 4% silver30(tm granules
Fig. 7. In the Slaby Arco coherer,performance consistency was improved byhaving uniform granules.
nentially declining train. Much of this energywas present in the first half wave.
Moreover, the coherer presents a high resis-tance, typically 5001S2. I saw no reason whythe first wave should not induce a potential inthe order of volts across the coherer at normalworking range. Unfortunately, early sparktransmitters cannot be replicated. As a result,direct measurements of currents induced in anantenna by waves propagating through spacecannot be made.
However, thanks to co-operation of the DTI,experiments with a replica of Marconi's earlyvhf transmitter were made underground in adisused railway tunnel and substantiated mea-surements made on the bench and outdoors, asdiscussed later.
My experiments showed that once thecoherer is triggered by a pulse of given ampli-tude, successive pulses of lesser amplitudehave no further effect on resistance; thisapplies to exponentially declining trains, Fig.2.
I found that if the magnitude of the pulsesincreases incrementally, as would occur withpear-shaped wave trains, the coherer is suc-cessively triggered as the wave train builds upto maximum amplitude; this of courseassumes that lowering resistance of the coher-er does not unduly load the pulse source.Thereafter resistance remains steady, Fig. 3.
StaticI demonstrated the fact that the coherer ispulse activated by rubbing a screwdriveragainst my pullover and touching its tip on acoherer terminal. It triggered instantly.Resistance drop was roughly proportional tocharge on the screwdriver, so the coherer maywell be adapted as an electrometer
This triggering mode was substantiated byexperiments with a pulse/spike generator.Surprisingly, I found no reference in the liter-ature to the coherer being triggered by a staticcharge, and concluded that it was caused byusing plastic tube for my replica instead of theglass alternative used by the pioneers.Changing the tube material to glass dramati-cally reduced so the effect may not have beenobserved by the pioneers.
It has long been known that the coherer wassusceptible to triggering by natural discharges.Both Popoff and Tesla used the coherer tostudy atmospheric electricity before it wasapplied as a detector of Hertzian waves.
For maximum range with a coherer receiver,energy should ideally be radiated as electro-magnetic (em) pulses. True pulses howeverare untunable so syntony (oscillations pro-gressively built up in a receiver by virtue ofresonance) would be out of the question. Earlyspark transmitters radiated energy in trainscontaining very few waves, not unlike a light-ning discharge. While well suited to the coher-er, they precluded syntony, Fig. 4.
The coherer/Morse register was slow. In thequest for syntony and a higher signallingspeed, the coherer was superseded by detec-tors better suited to the longer wave trains thatwere vital for syntony. These later detectors -
which include Marconi's magnetic detector,Fessenden's electrolytic detector andDeForest's audio - produced an audible soundin a telephone earpiece that corresponded toMorse code characters.
EvolutionThe coherer had its roots in Varley's telegraph'lightning protector'. This consisted of a glasstube loosely filled with copper filings, con-nected between an earth plate and the over-head line where it entered the building. In theirloose state, the filings presented a high resis-tance and therefore did not significantly inter-fere with signalling, Fig.5.
A pulse induced in the line by a lightningdischarge caused the filings to cohere with adramatic drop in resistance; this was so rapidthat the pulse was shunted to earth before itcould damage equipment. Moreover, unlessthe strike was very close, in which case the fil-ings fused together, the protector could berestored to its original high resistance state bygentle vibration.
Branley seems to have been first to applyVarley's device to detecting Hertzian wavesand it is named after him. But like many radioinnovations, the coherer evolved throughempirical experiments by a number of pio-neers. It was applied to receiving Hertzianwaves by Marconi and Popoff at around 1895.The name 'coherer' was invented by Lodgeand aptly describes the device.
Throughout its life, the coherer graduallyimproved in sensitivity and operating consis-tency, culminating with the Slaby-Arco coher-er in 1903. However, sensitivity was not theprimary concern. If too sensitive, the cohererwas susceptible to triggering by natural dis-charges. Consistency of operation was perhapsmore important factor.ConstructionMy experimenter's coherer consisted of aglass tube about 30mm long and 5mm insidediameter with a brass plug inserted in eachend. The plugs served as electrodes and wereseparated by a 3mm gap at the centre of thetube. this gap was loosely filled with metal fil-ings, typically steel with a small proportion ofnickel.
I made four versions of coherer, each havingdifferent proportions of iron and nickel filings.In all cases the filings were sifted to removetine particles. As explained in the main article,I used the plastic case of an old ball point peninstead of a glass tube, Fig. 6. All were phys-ically the same size so that they clipped into amodified fuse holder.
I found 80% steel and 20% nickel (10pcoin), as recommended by some early writers,gave best results. This article is based on dataobtained with this version. All coherers areunique, but I believe the characteristics of myreplica are similar to those used by earlyexperimenters.
Setting up and preliminary adjustmentinvolved gently forcing the electrodes into thetube until resistance fell to about 1052. Theelectrodes were then eased apart, while gentlytapping the tube, until resistance increased to
564 ELECTRONICS WORLD + WIRELESS WORLD July 1994
HISTORY
about 500ka To ensure maximum sensitivity,final adjustment was made with the aid of abuzzer type signal generator as described inearly literature.
The Slaby-Arco coherer and other highquality coherers had silver electrodes and care-fully graded metal granules. These were typi-cally 5% silver and 95% nickel of the order50pm in diameter. Air was removed and theelectrodes sealed in the glass tube, Fig. 5.
Size of the granules determined sensitivity:the smaller the granules, the greater the sensi-tivity. Consistency of operation depended pri-marily on the uniformity of the granules. Fig.
7.Regarding sensitivity, I doubt that early
experimenters' coherers were inferior to theSlaby-Arco coherer. Experimenters couldincrease sensitivity by reducing the size of thefilings. But with all coherers there is a limit tohow far this can be taken and experimentersdevices most probably approached this limit.However, the Slaby-Arco coherer wouldundoubtedly have operated more consistently.
Coherers have only two terminals so chok-ing coils were necessary to isolate trigger puls-es from the dc energising circuit. In somedesigns the relays served as choking coils, Fig.
8a. The antenna circuit must not present a dcpath across the terminals.
RestoringOnce triggered, the coherer would remain inits low -resistance state indefinitely. In a prac-tical signalling system, it had to be restored toits high resistance state in readiness for thenext wave train. This was achieved by gentlytapping the coherer with a device similar tothe hammer of an electric bell: this operationwas synchronized with the Morse register, Fig.7a, but some systems had only one relay.
For my experiments it was more convenientto restore the coherer by gently tapping it witha pencil. Only the slightest vibration wasrequired and some early experimenters sug-gested that it could be used as a seismometer.
Signalling was by transmitting short or longgroups of wave trains representing a 'dot' or`dash' of Morse code. Each train caused theMorse register to make a discrete mark on thepaper tape. Successive wave trains caused themarks to merge, thus forming a continuousline. Length of the line corresponded to theduration of the group of wave trains.
Very fastVarley's lightning protector had shown thatcoherence was very fast. I found that withpulses having a rise of 1 ms, coherenceoccurred before the pulse reached maximumpotential. There was no further drop in resis-tance as potential increased. Moreover, oncetriggered, the protector's resistance falls, load-ing on the source increases and this mayinhibit a further rise in the pulse's potential.
Furthermore, pulse rise time must be soshort that the choke coils are able isolate thepulse from the dc energising circuit. So, forgreatest resistance drop, the pulse mustapproach maximum potential faster than
Exponentially decliningwavetrain
Coherer
Restorerelectromagnet
GND
Morse register relay
II
Paper tape
Morse registerelectromagnet
Restorer relay
Energy stored in antenna,
Interrupter
Induction coil
Spark gap
Fig. 8. In the 'untuned' coherer receiver, a hammer similar to the one on an electric bell providedthe vibration needed to restore the coherer each time a pulse was received via the antenna. In theso-called untuned transmitter, b), length, capacity and resistance of the antenna actually set theoperating wavelength.
Exponentially declining wavetrain
Energy stored in capacitor
-r
\l/ Capacitor series -tunedjigger secondary winding
Choke coils
To pointsX and Y, Fig. 7a
Fig. 9. Early tuned transmitter, a) and Marconi experimental jigger with dc blocking capacitor b).
coherence. For this reason, the coherer waswell adapted to Marconi's early vhf system.
Coherence is generally accepted as being aphysical effect. As a result, less energy wouldbe required to overcome the inertia of smallfilings/granules. The effect is therefore fasterthan with larger filings/granules.
Untuned systemsWith early vhf systems, it was logical to insertthe coherer at the centre of a dipole antennawhere it avoided shorting the coherer. Thiswas adopted by Marconi. With later long -wave systems, employing Marconi type anten-nas, the coherer was inserted between theearth plate and the base of the antenna, Fig.8a.
Similarly, the transmitter had its spark gapbetween earth and the antenna base: thisbecame known as an untuned system, Fig. 8b.The term `untuned' was in fact a misnomer.The length, capacity and resistance of the
transmitter antenna set the operating wave-length. Because the antenna was a very effi-cient radiator, the amplitude of the waves ineach train declined steeply.
With large spark coils, ship -to -ship and ship -to -shore signalling over of 50km or more wasachieved. Experimenters' manuals fromaround 1895 suggest that a transmitter usingan induction coil comparable with a modemautomotive spark coil and a 10m elevatedantenna should have a range of about I km.
Tuned transmittersSecond generation transmitters had inductorsand capacitors and became known as tunedtransmitters. Energy was still radiated as wavetrains but each contained a greater number ofsignificant waves than with the untuned' sys-tem.
Generally, transmitters employing one tunedstage, Fig. 9a, radiated exponentially decliningwave trains while those having an inductively-
GND
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 565
HISTORY
Fig. 10. Transmitterin a) had two tunedstages, and the \l/complementaryjigger in b) had twosecondary windings.
Inductance/capacity tuners were not wellsuited to exponentially declining waves. Thepulse induced by the first half -wave simplyshocked the tuner into generating a train ofoscillations with a magnitude much less thanthe original pulse. So, it was logical to con-
Antenna variometer
Capacitors fitted to later versionsconverted jigger configuration
into a tuned configuration
Isolator choke coils
To points X and Y,Fig. 7a
tinue to connect the coherer directly to theantenna in the 'untuned' mode.
On the other hand, the gradual increase inamplitude of pear-shaped wave trains reducedthe incidence of shocking the tuner in -.0 oscil-lation. But there were still too few trains, ccn-taining too few waves for a significant buildup of voltage in an LC tuner by virtue of res-
onance. Syntony was minimal, but some volt-age gain seems to have been achieved throughstanding waves.
Standing wavesNotwithstanding syntony, trains radiated byeven the earliest 'untuned' transmitters con-tained more than one significant wave.Theoretically. a transient standing wave coulddevelop in an antenna cut to an appropriatelength.
There is of course, some voltage gain at avoltage antinode, but this was likely to havebeen insignificant with early Marconi untunedsystems. What is more, diagrams from thetime show the coherer inserted at a pointwhere a voltage node could be expected tooccur.
During experiments with my replica ofMarconi's vhf system, which radiated veryshort trains, it made very little differencewhere the coherer was inserted. More remark-ably, the actual length of the antenna made lit-tle difference either.
Standing waves were apparently very sig-
Coherer experiments
My first attempts to measure pulsepotential against drop in resistance werecarried out by incrementally charging alow -inductance capacitor of 1 nF. It wasthen discharged it through the coherervia a high speed electronic switch.
For the experiments, the relays weresubstituted by an analogue ohmmeter. Inall experiments, restoring was carriedout by gently tapping the coherer with apencil.
For the next measurement, a squarewave generator was connected via acapacitorin parallel with a 5001d2resistor. This component substituted forthe coherer in its high resistance state,producing spikes.
Peak potential of the spikes wasmeasured via an oscilloscope with thesignal generator calibrated to producespikes with increments of 1V. Next, theresistor was replaced by the coherer.Finally, resistance was plotted againstthe peak potential of the spikes.
In the tunnel. Experiments with thereplica of Marconi's vhf transmitter weremade without the reflectors. Theantenna received only a few mJ, soenergy in each wave train was minimal.
The experiment began with thetransmitter operated manually so as toradiate single wave trains. Resistancewas measured and plotted againstdistance as the receiver was movedaway from the transmitter in lm steps.
The coherer was then substituted by aresistor and the above exercise repeatedwith the transmitter set to automaticallyradiate wave trains with a repetition rateof 1 kHz. Peak voltage across the resistorwas measured by my 'magic eye'voltmeter. This related to resistance drcpat a given distance from the transmitter
Open country. Following theexperiments conducted in the tunnel, Iconducted open -country trials with theHertz type transmitter radiating
individual wave trains, Fig. 11. Pressingand quickly releasing the key generallycaused a single discharge and a singlewave train. Although a crudearrangement, it proved to be adequatefor experimentation. I estimate thatenergy stored in the antenna was only inthe order of a few mJ.
The receiver is shown in Fig. 12. Youcan see that instead of connecting thecoherer to the centre of the dipole, itwas offset to where a voltage antinodeshould theoretically exist. In practice itmade little difference where the cohererwas inserted. As with the tunnelexperiments, the resistor was used inconjunction with my 'magic eye'voltmeter. Range for the abovetransmitter/receiver is shown in Fig. 13.
Having conducted the aboveexperiments, the DTI kindly allowed meto radiate a few more wave trains toreplicate Marconi's 'untuned' systemand to compare the sensitivity of my
1 Om
180mml
Capacityplates Choking
coil
Auto spark coil (12V)
Set up for individual wave trains
Fig. 12.Representation ofa very low -powerreplica of aHertz -typetransmitter.
Telescopicantenna
25mm
To ohmmeterOr
'Magic eye'voltmeter
Fig. 13. Cohererreceiver used inconjunctionwith the low -power Hertztransmitter, Fig.12.
566 ELECTRONICS WORLD + WIRELESS WORLD July 1994
HISTORY
nificant with later transmitters radiating pear-shaped wave trains. A voltage antinode wasthe logical place to insert the coherer. WithMarconi type antennas however, the voltageantinode was at the top of the antenna where itwas impractical to insert the coherer. TheSlaby-Arco system overcame this problem byusing a quarter -wave matching section raised3m above the ground, Fig. 11.
Marconi developed transformers to step upthe voltage, which he called 'jiggers'. Thesewere inserted at a voltage node occurring atthe base of a Marconi type antenna. Couplingthe jigger to the coherer however presented aproblem. Direct -current resistance of its sec-ondary winding was far less than that of thecoherer.
If the jigger was connected directly acrossthe coherer terminals it would simply haveshunted both the coherer and the dc energisingcircuit. So a dc blocking capacitor was insert-ed between the secondary winding and thecoherer. But as the coherer had a highimpedance, this proved unsatisfactory becauseit series -tuned the secondary winding, Fig. 9b.
coherer with data from the archives.Transmitter details are shown in Fig.
14. The hand cranked magneto chargedthe capacitor to 100V, which was then
Voltageantinodel
AC=BD.1/4X
B Coherer
Voncenode \C i3m
To relays:points X and Y Fig. 7a
Voltageantipode
D
Marconi laser developed a jigger with a pair ofisolated secondary windings, which apparent-ly was successful.
Ultimately, each secondary winding wasparallel tuned by a fixed capacitor which con-verted it into a pre-set tuned transformer, Fig.10b. This arrangement seems to have beensuccessful, probably because of the successivetriggering. Furthermore, it partially reconciledthe conflicting requirements of syntony andthe coherer. It was used by Marconi until
was discharged through the primarywinding o- the induction coil via athryristor. The sloping antenna wasattached to the apex of a farm building.
Cohererresistanceaftertrigerring
100k -
10k _
1.0k
500
200
100 _50
20
Fig 14. In open country experiments with acoherer-based Hertzian transmitter running atvery low -power produced these results.Experiments with the larger transmittershowed that the transmitter/receivercombination still worked at 1km.
Distance fromTx 2
Est. peak potentialof induced current
I II I I I
4 6 8 10 12 14 16 18
10V
Full waverectifier
5V
Automotiveigni ioncoil
100Vdc
Sparc gap1.5rrrn
GND
3V
20 metes
Fig. 15. In thesingle -wave -traintransmitter, ahand -crankedmagneto
8 Om charged thecapacitor to100V beforebeingdischargedthrough thetransformerprimary.
Fig. 11. In Marconi designs, thebest place to insert the cohererwas also the most impractical -i.e. in the voltage antinode atthe top. Slaby Arco antennasovercame this problem.
1906, when the coherer was ultimately super-seded.
In conclusion, my research has shown thecoherer to be something of an enigma andmuch remains to be learnt. Nevertheless, Ihope that this discussion has tilled a few gapsin our knowledge of the device.
I owe thanks to the DTI. NorthamptonshireCouniy Council, and to farm owner MrThomas for their co-operation in my experi-ments
Fig.: 6. Receiver arrangement used with theunto -red transmitter in open -countryexperiments.
The receiver arrangement as shown inFig. 13, but in this case the antenna wasattached to a convenient tree.
Triads were made at distances ofapprcx 500m and Ikm. At 500m thecoheier's resistance dropped to 500 andto about 5000 at 1 km. The curveobtained with the Hertz type transmitterindicates lkm approaches the maximumwork ng range for equipment of thispower. This agrees with data fromexpelimenters working around the turnof the century.
Rar ge would undoubtedly nave beenincreased by experimenting withdifferent spark gaps and using a longermore efficient antenna system, i.e. onewith greater capacity to earb.Remarkably, the coherer receiverseemed imune to triggering by powerfulradic
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 567
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CIRCLE NO. 114 ON REPLY CARD
568 July 1994 ELECTRONICS WORLD+WIRELESS WORLD
INTERFACINGWITH C
by
HOWARD HUTCHINGS
Interfacing with C can be obtained from Lorraine Spindler, RoomL333, Quadrant House, The Quadrant, Sutton, Surrey SM5 2AS.
Please .make cheques ;or £14.95 (which includes postage andpacking) payable to Reed Business Publishing Group.
Alternatively, you can telephone your order, quoting acredit card number. Telephone 081-652 3614.
A disk containing all the example listings used in this book isavailable at £29.96. Please specify size required.
C HERE!If you have followed ourseries on the use of the Cprogramming language, thenyou will recognise its valueto the practising engineer.
But, rather than turning upold issues of the journal tocheck your design for adigital filter, why not have allthe articles collectedtogether in one book,Interfacing with C?
The book is a storehouse ofinformation that will be oflasting value to anyoneinvolved in the design offilters, A -to -D conversion,convolution, Fourier andmany other applications,with not a soldering iron insight.
To complement thepublished series, HowardHutchings has writtenadditional chapters on D -to -A and A -to -D conversion,waveform synthesis andaudio special effects,including echo andreverberation. An appendixprovides a "getting started"introduction to the runningof the many programsscattered throughout thebook.
This is a practical &uide toreal-time programming, theprograms provided havingbeen tested and proved. It isa distillation of the teachingof computer -assistedengineering at HumbersidePolytechnic, at which DrHutchings is a seniorlecturer.
Source code listings for theprograms described in thebook are available on disk.
RF ENGINEERING
New waveMICROWAVES
Active devices fall into three groups: signal gen-eration such as oscillators and amplifiers: sig-nal reception using diode detection and mix-
ing: signal control for attenuating, phase shifting,switching, modulating. limiting.
The silicon bipolar junction transistor (BJT) workswell at the lower end of the microwave bands and isthe preferred device for mobile phone transmitters, forreasons of its high output power and efficiency. Powerlevels of 100W or more are available from a singletransistor operating around IGHz and efficiencies inexcess of 35% can he obtained. It also exhibits verylow phase noise.
However, the BJT is a transit time device, in that itsfrequency of operation is ultimately limited by thetime taken for electrons to travel from the base -emitterjunction to the collector. In practice, this means thatthe BJT is restricted (with a few exceptions) to fre-quencies below about 4GHz. Above this frequencyand through into the millimetre wave bands above30GHz, the majority of amplifier and certain oscillatorapplications have become dominated by the n -typeGaAs mesfet.
The metal -semiconductor junction is preferred forthis and, as we shall see later. for other devicesbecause of the virtual elimination of minority carrier
charge storage effects. N -type material is used becauseof the higher mobility of the electron as a majority car-rier. A derivative of the mesfet, the high electron -
mobility transistor (hemt), has revolutionised low -
noise receiver design in the last few years and can givenoise figures previously only attainable by cryogenicreceivers. For example, noise figures of less than0.4dB at 10GHz and 2.5dB at 60GHz are available atroom temperature from hemt chips. Further improve-ments in noise figure and operating frequency areavailable in the pseudomorphic hemt (Phemt).
However, as often happens, a dominating progress inone technology stimulates older processes and this hasbeen the case with the bipolar transistor. Fet technol-ogy is a surface -orientated process. with performancelimitations being set by pattern definition capability -0.1pm lithography is now called for in millimetricdevices which affects suitability for power generation.The response has been the GaAs heterojunction bipo-lar transistor (HBT). This device is likely to replacethe fet in power applications, initially up to aboutI OGHz, and possibly up to millimetric frequencies.Advantages include non -critical lithography due to the'vertical' bipolar process, leading to medium levels ofoutput power (..,1W) and power -added efficiency of50% or more.
4: active devices for millimetre waves
Most millimetrewave active devices
are either unique to,or specially adapted
for, this region of thespectrum.Mike Hosking
describes the
specialities and theirapplications.
*Mike Hosking is a lecturer intelecommunications andmicrowaves at the University ofPortsmouth.
;.0 ELECTRONICS WORLD + WIRELESS WORLD July 1994
RF ENGINEERING
In addition, the circuit designer can easilyimplement class B or C operation, togetherwith common base or cascode configurations.In effect, the GaAs HBT possesses the power,efficiency and spectral noise advantages of thelower frequency Si BJT, but translated to thehigher frequency bands.
Substantial development work is also takingplace in using indium phosphide as a replace-ment for GaAs in certain areas to improvepower and frequency performance. Howeverthe final outcome is unclear and investmentcosts are high.
Two terminal semiconductorsThere are classes of device not applicable tolower frequencies. Gunn -effect (or transferredelectron) device and the Impatt (impactavalanche and transit time) diode have beenthe mainstay of solid state microwave powergeneration and, although becoming super-seded by the transistor below about 30GHz,have wide application through the millimetrewave bands. Both are used as fundamentaloscillators, as their inherent principles of oper-ation give them a negative resistance charac-teristic, but they can also be designed intoreflection amplifier circuits.
The Gunn device has traditionally been usedin low-cost, high volume applications such asspeed or intruder motion detectors and as thelocal oscillator in radar receivers. CW outputpowers of 0.5W or more are possible and
operating frequencies up to about 140GHz;pulsed devices can deliver 40W or more ofpeak power.
Impatt diodes are the highest power solidstate devices at millimetre wavelengths; outputpower is measured in 100's of mW, with sev-eral watts being possible at lOGHz. Operatingfrequency can be throughout the millimetrebands (to 300GHz). New applications areopening up for these devices in the 38 and50GHz PCS bands, as well as the 60 and77GHz bands for vehicle communicationapplications.
There are, of course, other solid state meansof generating microwave signals, i.e. up -con-version, frequency multiplication, harmonicgeneration, and there are specialised, but little -used derivatives of some of the above devices.All systems raise questions about maintenanceof frequency stability and tuning. These arebest answered by examining practical circuits.
Gunn -effect deviceNamed after its inventor, J B Gunn of IBM,this represents a class of semiconductorsknown as transferred electron devices (TED).They are transit time devices, in that their fre-quency of operation is dependent upon thetime taken for charge carriers to traverse theactive region. The Gunn effect relies for itsoperation on a particular energy band structurefound in certain III -V compounds: especiallyGaAs and InP, with GaAs being by far themost common material; Si and Ge cannot beused.
Basically, the device consists of an n -typeactive region sandwiched between two epi-
Fig. 1. Doping profile of a lowpower GaAs Gunn device (notto scale) showing a typicalvariation of carrier density. Theproduct n.L is used characterisemodes of operation.
Fig. 2. Detail of the energyband structure of GaAs.Electrons transfer from thevalence band to the highmobility lower band andthence to the higher energy,but lower mobility upper band.
Fig. 3. DC bias curve for GaAsshowing the gradual departurefrom the Ohm's law straightline and the Gunn effectnegative resistance after thethreshold field has beenexceeded.
upper valleyn = 150cm2V-Is-,
10.36eV
taxially grown n+ ohmic contacts, as shown inFig. 1.
Important parameters are the doping density(charge carriers per cm3), the active layerlength, L. and the cross-sectional area. Figure2 shows schematically a detail of the GaAsenergy band structure as a function of the elec-tron momentum as it drifts through the semi-conductor.
The main features of this structure are thetwo regions of the conduction band close inenergy to the valence band and separated fromeach other by an energy gap of 0.36eV. (Anelectron at room temperature has a thermalenergy of about 0.026eV). In each of these
bands, the electrons have an effective mass meand a mobility p (same symbol as, but not tobe confused with, permeability). Mobility hasthe units of m2y-ls-1 (colloquially cm2v-Is-I)and is a measure of electron speed in anapplied electric field, i.e. p=velocity/E-field.The unusual situation in GaAs is that electronsin the lower energy band have a low mass andhigh mobility (8000cm2v-I s -I), whereas thosein the higher energy band have a high massbut a low mobility (150cm2v-Is-1). Thus.higher energy electrons actually travel moreslowly in the material.
If a small voltage is now applied across the
Metal
Metal
lower valley= 8000crn2V-ls-1
Forbidden gap = 1 43eV
Valence band
ET=3.2kVcm-I
Momentum
Negative resistanceregion.
Electric field, E ( ).
Gunn device and steadily increased, the resul-tant electric field and the electron velocity (i.e.
current) will also increase; linearly at first, inaccordance with Ohm's law. However, asshown in Fig. 3, as the voltage (E -field)increases, there is a departure from linearity,corresponding to electron transfer to the upperband.
Eventually, a threshold value, ET, of about3.2kVcrrrl is reached, at which point the greatmajority of electrons transfer to the upperband. However, in this band, the physical lawsmust be obeyed: the mobility is low and thuselectrons slow down, even though they havemore energy. The result is an electron 'trafficjam' at the cathode ohmic contact, a rapidbuild-up of charge called a domain. Thus, asthe applied voltage is increasing, the electroncurrent (proportional to velocity) is actuallydecreasing, giving rise to a region of negativeresistance.
The domain continues to grow rapidly, cre-ating its own E -field at the expense of the fieldacross the rest of the device. The applied volt-age, though, is still present and causes the
domain to drift across the active region at aconstant velocity (called the saturation veloc-ity). On arrival at the anode contact, thedomain will disappear as a current pulse, the
July 1994 ELECTRONICS WORLD + WIRELESS WORLD571
RF ENGINEERING
E -field will rise again and the whole processwill repeat itself.
The frequency of these current pulsesdepends upon the transit time of the domainacross the active region which, for a constantvelocity, depends upon the length L only andcan be made to occur at microwave frequen-cies. Bias requirements for the Gunn deviceare simple and require a constant voltagesource supplying, for example, typically 4.5Vat 1.5 A for a 200mW output at 60GHz. Alow power motion sensing device giving10mW at I0.7GHz would require about 7V at100 mA. It can be seen that the dc to rf con-version efficiency is low, typically 1.5% to4.5% for standard commercially availabledevices, although values up to 12% are possi-ble.
As described so far, the Gunn device hasbeen treated as an unpackaged chip and can besimply represented by a series combination ofnegative resistance -RD and a capacitance CD.These parameters are functions of operatingfrequency, power output and temperature andare more complicated to determine than nor-mal static values, as they are formed by thedynamic situation of growing and collapsingdomains. However, a typical range of values is-4 Q to -15 Q for RD and 0.5pF to 2pF for CDFor this and other microwave power devices,it is usual to encapsulate the chip on an inte-gral heat sink and there are a wide variety ofpackage styles available for 2 -terminaldevices. Fig. 4a shows two such packages, thesmaller being used more at millimetre wave-lengths and Fig. 4b indicates an approximateequivalent circuit of the package alone, withtypical element values.
The disadvantage is that the package intro -
Fixed transit time butvariable frequency?
If Gunn frequency is determined by the fixedwidth of the active region, then how may thisfrequency be changed?
The answer is that the external resonant cir-cuit into which the Gunn device is mountedhas its own loaded Q -factor and its own res-onant frequency (which may be differentfrom the transit frequency) and can be tunedindependently.
When the Q -factor is sufficiently high, thenthe rf voltage swing across the Gunn devicecan affect the time at which the domainforms and may even suppress its formationfor a time. This leads to modes of operationcalled the delayed mode and quenchedmode, the frequencies of which are dictatedby the external circuit and thus may be var-ied.
Within each of these three modes, a rela-tively small frequency control is possible byvarying the bias voltage (called frequencypushing) as the electron transit time is a func-tion of electric field. However, output powerand mode stability are also affected and thetechnique is not often used.
duces small parasitic inductance and capaci-tance, the reactances of which are extremelysignificant at microwave frequencies and mustbe accounted for. Finally, in order to effi-ciently extract microwave power and to obtaina single frequency spectral output, the Gunndevice must be embedded into a suitable res-onant circuit.
At microwave frequencies, a resonant circuitmay be simply produced from a length oftransmission line, which appears as a dis-tributed RLC circuit. For example, a length oftransmission line, short-circuited at both ends,becomes resonant and can be represented by aparallel RLC network when its length in thedirection of propagation is 1/2 wavelength.
For 2 -terminal Gunn and Impatt devices, themost popular resonant structure is a length ofrectangular waveguide, short-circuited at one
Fig. 4. Typicalpackages used for twoterminal Gunn and!moat devices whichrequire good heatsinking. The penaltypaid is the parasiticcomponents shown inthe equivalent circuitof the package alone.
( b )
LP
end and with the active device mounted acrossthe guide on a metallic post. Waveguide ispreferred to coaxial line and to planar circuitsof microstrip or coplanar waveguide due to itshigher Q -factor, leading to a better frequencystability and lower fm noise. Heat sinking anddc bias connections are also readily imple-mented. Furthermore, as one enters the mil-limetre wave region, the physical size andweight of such resonators is not great. Ka -
band waveguide, for example, which supportsthe frequency range 26.5-40GHz has internaldimensions of only 7.1x 3.6mm. A 1/2X in theguide at 30GHz is 7mm.
There must, of course, also be a means ofcoupling the microwave signal out of the res-onator and three different techniques areshown in Fig. 5.
In version (a), the resonator is formed
Gunn device-1mm dia.
3.48 UNC
chip
( a )
cp ;: Ci
fa)
( b )
Fig. 5. Various forms of waveguide mounting for Gunn oscillators.a. Resonator formed by a short-circuited length of guide;b. Resonator formed by post and iris;c. Coaxial probe coupling to the guide.
1.6mm dia.
bond wires
ceramicbody
gold contacts
Cp = package capacitance0.18-0.3 pF
Lp = package inductance0.1-0.4 nH
Cf = fringing capacitancedepends on mount, - 0.2 pF
SMAconnector
( c )
572 ELECTRONICS WORLD + WIRELESS WORLD July 1994
RF ENGINEERING
Xc
IIxc
9 - cp
Lp
TCo
_R.
XL
Fig. 6. Overall equivalent circuit of a waveguidemounted oscillator including the post, activedevice, packaging, resonator and loadimpedances.
DC reverse bias
- N P intrinsic drift region
active length L
avalanche breakdownoccurs at this abruptjunction.
Fig. 7. Classical doping profile for the Si impattdiode. In practice, a double drift region is usedin which domains of both electron and holescontribute to the output current.
between the short circuit and the device -postcombination, with the output load impedancebeing that of the waveguide itself. In version(b), a thin metal diaphragm with a small cou-pling hole or slot cut in it (called an iris) formsthe output. The short length of line betweenpost and short circuit forms part of theimpedance tuning. Version (c) uses the sameprinciple as (a), but with a coaxial output. TheE -field in the waveguide is parallel to theprobe formed by the centre conductor of the
coaxial line and will, therefore, couple to it.The adjacent short circuit position adds alength of line for impedance matching.
Figure 6 gives an overall equivalent circuitof this type of oscillator where the activedevice elements, -R9 and CD are modified bythe package parasitics Lp and Cp. The postitself appears largely inductive to the field inthe waveguide and is represented by the reac-tance XL. Additional capacitive reactances Xeaccount for the finite diameter of the post.Capacitance Cg accounts for the gap in thepost and fringing fields. The impedance ZR isthat of the short circuited length, P. of waveg-uide of characteristic impedance Z0 which, aswe saw in Part 2 is given by Z1 = jZo tan BP;B=2rcap. Impedance ZL is the output trans-mission line impedance as transformed to orseen at the device terminals by the output cou-pling structure. ZL itself may this be quitecomplicated and the total oscillator designserves to illustrate the varied electrical effectswhich changes in physical structure cause atthese frequencies.
Impatt diodeThis specialised microwave device alsobehaves as a negative resistance and, like theGunn device, can be used as a directly oscil-lating source without the need for feedbackcircuits. The mechanism for generating thenegative resistance is completely different,although the Impatt is still a transit timedevice. Choice of semiconductor is notrestricted to the III -V compounds although, inpractice, only Si and GaAs are used, withdevelopmental devices available in InP.
Impatt operation is based on a controlledavalanche breakdown process in a reversebiased semiconductor and depends upon thedoping profile.
Figure 7 shows the simplified structure inwhich an intrinsic region is sandwichedbetween heavily doped n+ and p+ regions with
Gunn characteristics
In a semiconductor, the average electrondrift velocity in the direction of an appliedfield does not continue to increase withincreasing field strength, as in a conductor.Instead, even though the electrons becomemore energetic, they are scattered by thesemiconductor lattice and graduallyapproach a limiting average velocity in thedirection of the external field. In GaAs atnormal Gunn operating voltages, thissaturation velocity, vs, is approximately105ms-1. If we take the type of Gunn deviceused in intruder detectors, radar speedindicators and automatic door openers,then an operating frequency in the region of10GHz is required. Thus, the active length,L, in Fig. 1 would be given byL=105x10-1°m or 10pm for a transit modecycle time at 10GHz. The 10-10quantityrepresents the period in seconds of one
signal cyc e at the operating frequency.The threshold field in GaAs is 3 2kVcm-1
and so, fo- a 10pm device, the thresholdvoltage would be 3.2V.
Typically, the bias voltage would beabout 7V fo- a 20mW device at a supplycurrent of 125mA, giving a dc to ifefficiency of 2.3%.
The curent density, 1, in the device canbe estimated from the relationship J=nevs,where n i> tie carrier density and e is theelectron charge. In our example,r1.2x1015cm-3, e=1.6x10-19C aindvs=107crr s-1. Hence, J=2000A/cm2.
With the actual size of the GaAs chiptypically oeing less than 100pm square and,at 2.3% effizient, with nearly 1W beingdissipated, ]eat sinking is vital, especiallyas devices delivering more than nn timesthis power are readily available.
TotalVoltageAcrossDiode.
Rate of DomainBuild-up.
Output CurrentInduced
microwave voltage
bias voltage
0
R/2
wt
0
0
2Ir
I 2R
wt = 0.74n
Fig. 8. The voltage and current relationships asthe avalanche domain forms and then driftsacross the active region of the impatt diode,creating an effective negative resistance.
the key profile being the abrupt n+p interfaceand the narrow p -region.
As the reverse bias voltage is increased, theresulting electric field is sufficient to sweepthe region between n+ and p+ dear of carriersto form a depletion layer. Thus at the abruptn+p interface a high electric field is formed.When this field reaches about 350kV/cm-1,avalanche breakdown occurs and electron -holepairs are generated: once above this fieldvalue, the rate of charge build-up becomesexponential.
The electrons enter the n+ region in this par-ticular structure and can be neglected, whilethe charge of holes enters the depletion region.Electric field in this layer is very much lessthan the avalanche field: several thousandvolts per cm and the charge carrier saturationvelocity, due to scattering effects, occurring atabout 5 kV/cm-I in silicon, is about 107cm/s-1.This means that the time taken for the chargecarriers to cross the depletion region can bemade independent of bias voltage and dependsonly upon the length of this region.
To explain the Impatt mechanism, assumethat the bias voltage is increased until the elec-tric field intensity is just below that requiredfor avalanche breakdown. At this point therewill be sufficient energy in one of the ever-present, random noise carriers to trigger offthe avalanche process. For clarity, Fig. 8assumes the steady-state condition whereoscillations have already built up.
During the first half of the ac cycle, the fieldis increased, avalanche multiplication com-mences and charge carriers build up at anexponential rate. When the alternating voltagefalls below zero, the total field is less than theavalanche value and the process decays expo-nentially.
wt
wt
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 573
RF ENGINEERING
Gunning for intruders
As an application example of the Gunndevice, the Philips CL8960 series dopplerradar module, Fig. 9, has been around formany years for motion sensing equipmentsuch as intruder alarms and automatic dooropeners. This component works as ahomodyne radar transceiver and antennamodule along the lines shown in Fig. 9b.
A microwave CW signal is transmitted andthe reflected signal is detected by a singlediode mixer which uses a sample of thetransmit power as the local oscillator. Just aswith the acoustic doppler effect caused by amoving sound source, the microwave signalreflected from a moving object will be shiftedin frequency. This 'doppler shift' fp dependsupon the relative velocity between movingobject and detector and is given by:
relative velocityto - 2 wavelength
With low-pass filtering at the mixer output,just the intermediate frequency is selected;which will be zero for stationary object. Withmovement present, the IF will be:
(transmit frequency ±6)-LO frequency
which, as transmit and LO frequencies are thesame, results in a mixer IF of 6. In the alarmapplications, it is not necessary to measurefo; the very existence of a non -zero IF impliesmovement.
The actual module shown in the pictureuses a 10mW Gunn device, post -mountedacross the left-hand section of rectangularwaveguide, short-circuited at approximately a
Gunnoscillator
(b)
Antenna
half wavelength from the post.Operating frequency, for an indoor
application, is 10.687GHz ± 12MHz, hencethe advantage of the higher -Q waveguideform of resonator. The mixer is a single diodein a relatively large package that fitsconveniently across the right hand guide andis impedance matched by positioning about aquarter wavelength away from anotherterminating short circuit. Both transmitter anddetector couple to free space via the smalltapered section of guide, which behaves asan antenna having approximately 5dBi ofgain. There is, however, a deliberate slightmis-match associated with this couplingwhich causes spill over of the transmit signalinto the mixer, thereby providing the LOinput. A dielectric cover over the end (i.e. thewall of a plastic box) can be used to adjustthis spill -over as well. Power supplyrequirements are 7V at about 140mA.
With these parameters, the dopplerfrequency generated is about 71.2Hz perms -1 or 32Hz per miles per hour.
A variation on this type of radar is used intemporary traffic light systems where it isnecessary to sense the actual direction ofmotion. This can be done by adding a seconddetector diode, suitably positioned andcomparing the phase of the two outputs.Finally, of course, we must not forget thepolice radar speed indicator application!
Although mainly used as oscillators, bothdevices may also be designed as reflectionamplifiers. With a load resistance greater thanthe negative resistance, the device will notoscillate and a low power incident signal canbe reflected back out, but with amplification.
Fig. 9. A microwave signal reflected from amoving object will undergo a doppler shift infrequency and a simple motion sensing radar (a)comprising a transmitter/detector/antenna canbe made using the Gunn device. Signal pathprocessing is shown below.
coupled power from oscillator+power reflected
doppler amplifer and filter.
fp output to signalprocessing.
The result is shown in Fig. 8 where thecharge density is seen to be a sharply definedspike and, in particular. the peak charge 11014'lags the peak alternating voltage by 90°.Under the influence of the dc bias, this bunchof charge now drifts across the depletionregion at constant velocity and thereforeinduces a constant current in the external cir-cuit. If the diode depletion length is such thatthe carrier transit time corresponds to one half-
cycle of the alternating voltage, then theinduced current will he 180° out of phase withthe voltage. Hence, negative resistance is pro-duced and the diode will generate microwavepower when incorporated into a resonant cir-cuit with output coupling.
In fact, the maximum value of negativeresistance occurs when the transit time of thedomain t is such that an=0.741[ (called thetransit angle) where co is the angular frequen-cy of operation.
Thus, the frequency of oscillation is approx-imately r./2L, where vs is the saturated carriervelocity of about 105ms-I and L is the deple-tion length. For a frequency of 10GHz,
Dimension L=5x10-3cm, i.e. half that of theGunn effect device. Also, at this frequency,the junction area is about 5x10-4cm2 givingrise to bias current densities of about10,000A/cm2. Thus, as with the Gunn device,good heat sinking is also essential and dia-mond heat sinks, within the package, are com-monly used for millimetric operation. Theoverall equivalent circuit is the same as that ofthe Gunn device, but with RD typically -0.9 51and CD 0.25pF fora millimetric power device.
The simple doping profile of Fig. 7 was theoriginal structure proposed by W.T. Read ofBell Systems but, in practice, has been large-ly superseded by a double -drift profile. Theprinciple of operation remains the same, butboth hole and electron domains form and addto the output current. Efficiency is increased:values greater than 20% are possible, togetherwith an increase in output power.
For example, IOW to 20W of peak power ataround 10GHz and 1W at 100GHz would betypical, with slightly lower CW power avail-able. One particular application has been inportable, outside broadcast communicationlinks; much effort has been put into combiningthe outputs of many diodes to produce outputwattage in the hundreds.
The Impatt requires a higher bias voltagethan the Gunn device, but a proportionallylower current, from a current-stabilisedsource. For example, a 3W pulsed device ataround 30GHz would require peak supply val-ues of some 35V at 0.5A.
Next month: devices such as the hemt, HBTand step -recovery diode, together withmethods of oscillator tuning such as YIG andvaractor and stabilising using the dielectricresonator.
574 ELECTRONICS WORLD + WIRELESS WORLD July 1994
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ELECTRONICS WORLD+WIRELESS WORLD July1994 575
COMPONENTS
Applying Hall to good effectIntegrated Hall -effect sensors have a vast range of uses, from limitswitches to current monitors. Martin Eccles looks at some of theapplications for both digital and analogue-output devices.
Free Hall -effectsamplesA device pack comprising a choiceof either a 3503 ratiometric linearsensor or a 3121 Hall -effect switchand data pack will be sent free ofcharge to the first 500 readersreturning the special reply cardlocated between pages 584 and585 of this issue. Please note thatthis offer only applies to readers inthe UK and Eire and that allenquiries relating to the offershould be directed to AmbarCascom, whose details appear atthe end of this article.
AHall element is simply a small sheet ofsemiconductor material. A constantbias current flows through it and the
output -a voltage measured across the widthof the sheet - reads near zero provided thatthere is no magnetic field present. If the biasedHall sensor is placed in a magnetic field atright angles to the Hall current, the voltageoutput is directly proportional to the strengthof the magnetic field. This is the Hall effect,discovered by E. H. Hall in 1879.
Integrated devices incorporating the Hallelement together with amplifiers, regulators,drivers and schmitt comparators are now usedwidely: ignition distributors, motor speed con-trols, security systems, alignment mechanisms,micrometers, mechanical limit switches, com-puter peripherals, machine tools, key -switch-es and push buttons.
Linear senor applicationsRotation detection. Normally, a linear Hallsensor's output is capacitively coupled to anamplifier that boosts the output above the mil-livolt level, as in Fig 1.
In two applications shown in Fig 2, a per-manent bias magnet is attached with epoxyglue to the back of the epoxy package.
Fig. 2. By attaching a magnet to the packaging,linear Hall sensors can be used to senserotational speed. When a ferrous material passesthe face of the Hall device opposite the magnet,flux is concentrated and the device outputvoltage changes proportionally.
Presence of ferrous material at the face of thepackage acts as a flux concentrator.
The south pole of a magnet is attached to theback of the package if the Hall effect IC is tosense the presence of ferrous material. If thedevice is to sense the absence of ferrous mate-rial the north pole of a magnet is attached tothe back surface.
Calibrated linear Hall devices - useful for
Magnet+V
Load
2N5812
Load
Fig. 1. When used forsensing ferrous metals,detecting notches in adisk or teeth on a spurgear for example,linear Hall sensors arenormally ac coupled.Circuit componentsneed to be alteredslightly depending onwhether theconfiguration is being
2N5812 used to detect thepresence or absence ofa ferrous metal.
Fig. 3. Magnets fastened to a disc can be usedto trigger a Hall -effect detector to senserotation. This configuration however, inwhich a ferrous vane interrupts flux from afixed magnet, offers benefits in manyapplications. These assemblies can be usedfor precision switching over largetemperature ranges.
576 ELECTRONICS WORLD + WIRELESS WORLD July 1994
COMPONENTS
measuring heads and determining flux densi-ties during the design stage - are available.
Since a Hall -effect sensor is triggered bymagnetism, the obvious way to sense rotationis to fix magnets to the rotor. In many appli-cations however, there are significant benefitsto from having a fixed magnet and fixed sen-sor, as shown in Fig. 3.
With this arrangement, the magnet needs tobe powerful enough to turn the sensor oppo-site on while unobstructed. When a blade ofthe ferromagnetic vane passes between the
magnet and sensor, flux is shunted and thesensor turns off.
Movable vanes are a practical way to switchHall devices. The sensor and magnet can bemoulded together to eliminate alignmentproblems and produce a rugged switchingassembly. The ferrous vane or vanes that inter-rupt the flux can move linearly, or rotate as inan automotive distributor. Ferrous vaneassemblies, due to the steep flux density/dis-tance curves that can be achieved, are oftenused where precision switching over a large
Switching Hall sensorsIntegrated Hall -effect switches are easy touse, bounce -free, economical and reli-able since they have no moving parts.Unaffected by dirt and light, they canalso be used in harsh environments andthey are fast - capable of cycling at up to100kHz.
A Hall sensor is activated by a magnet-ic field created by either electro or per-manent magnets. Magnetic fields havetwo important characteristics: magnitudeand orientation. In the absence of anymagnetic field, most common Hall -effectdigital switches are designed to be off,i.e. open circuit at their output. They willturn on only if subjected to a magneticfield that is strong enough and of the cor-rect polarity.
If an approaching magnetic south polecauses switching action of a digital sen-sor, the approach of the north poleshould have no effect. In practice, a closeapproach by the south pole of a magnetwill cause the output transistor to turn on.
The plot below shows transfer charac-teristics of input versus output. Hall effectswitches have hysteresis, typically 20G.This hysteresis ensures that even if
mechanical vibration or electrical noise ispresent, the switch output is fast, clean,and occurs only once per thresholdcrossing.
Detecting a thresholdOutput from a Hall -effect element is lin-ear. But in many applications a switchingoutput representing whether magneticfield strength is above or below a giventhreshold is more appropriate. Examplesof these applications are angular velocitydetectors and end -of -travel indicators onslides.
Due to the Hall element's inherentlysmall output, the best place for the com-parator circuitry needed to turn the linearoutput into a reliable on -off signal is asclose as possible to the sensor and its lin-ear amplifier. Integrating a comparatorinto the Hall sensor also reduces inter-facing costs.
Integrated Hall -effect switches like the3 /xx series from Allegro are temperature
stable and stress -resistant. Three newparts with enhanced temperature stabili-ty have recently been added to the range,namely the 3121, 3122 and 3123. Thesehave typical switch -on points of 350, 340and 345G respectively but are otherwiseidentical.
In addition to a Hall element, linearamplifier and schmitt trigger, the devicesinclude open -collector output bufferingwith 25mA capability. There is also built-in temperature compensation and a reg-ulator capable of operating from any sup-ply between 4.5 and 24V.
Standard parts are capable of operatingin temperatures between -40 and 85°Cbut there are also L -suffix parts capable ofoperating at up to 150°C. Since thedevices have unipolar switching charac-teristics they can be sued with simple baror rod magnets. The devices are bestused in applications that provide steepmagnetic slopes and low residual levelsof magnetic flux density.
Output of the devices switches lowwhen magnetic field at the Hall sensorexceeds the operate point threshold. Atthis point, the output voltage is the satu-ration voltage of the output transistor,which is typically 140mV.
When the magnetic field is reduced tobelow the release point threshold, thedevice output goes high. The differencein the magnetic operate and releasepoints is hysteresis, of typically 105G.This built-in hysteresis allows cleanswitching of the output even in the pres-ence of external mechanical vibrationand electrical noise.
Features- Good temperature stability- 4.5 V to 24 V unregulated supply- Open -collector 25 mA output,
compatible with digital logic- Reverse Battery Protection
Activate with small, commerciallyavailable permanent magnets
- No moving parts- Small size
Resistant to physical stress
temperature range is required.
Linear motion. Most magnet/sensor combi-nations produce a non-linear flux -distancerelationship. The push -push configuration inFig. 4 however produces an almost linearcurve, as Fig. 5 illustrates.
Suitable for use with either linear or switch-ing sensors, this arrangement produces a bipo-lar field with a fairly steep slope. While thesensor is in the centre of the space between thetwo magnets, flux is cancelled. With a ratio -
400
300
100
0
50 .25 .0 25 50 75 100 125 150Ambient temperature in °C
Operate and release points of 3120 -seriesintegrated Hall -effect switches remainconstant over a wide temperature range.
Switch points
Operate point
Release point
Vcc = 12 V
12L
9
6
..G
cL 3
00
Off
R.P.
O.P.
On
0 100 200 300 400 500 600
Magnitude flux density (gauss)
Transfer characteristic of a typical Hall -effectswitch. Hysteresis is built into the device -inthis case about 90G. This ensures cleanswitching even in the presence of mechanicalvibration or electrical noise.
Vcc
Witbin an integrated Hall -effect switch such asthe 3121 are a Hall voltage generator,temperature compensation, a small -signalamplifier and schmitt trigger. In addition, anemitter follower provides 25mA outputcapability while a regulator extends supply -voltage capability to a range 4.5 to 24V.
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 577
COMPONENTS
Fig. 4. Linear Hall -effect devices can beused to detect small displacements withhigh resolution using dual magnets in apush -push configuration.
B = 6 G/A
500
300
100
0
300
-500-0 06 -0 04 -0 02 0 0.02 0.04
Magnet assembly travel (inches)
Push -push head-on, alnico 8, 0.212" D x 0.187"
0.205"
8.44 G MIL
0.06
Fig. 5. In a push -push configuration, fluxseen by the sensor is linearly proportionalwith displacement. In the middle of thetravel, flux is zero since fields from thetwo magnets cancel each other.
Fig. 6. When 25A or more is involved, alinear Hall -effect sensor in the gap of atoroidal ferrite can be to measure currentin a conductor simply passed through thetoroid.
metric sensor such as the 3503, moving thesensor towards one magnet reduces outputvoltage while moving it towards the otherincreases output. Polarity depends on whichway the sensor is facing.
Current monitoring. Hall effect devices
make excellent current limiting or measuringsensors. Their response bandwidth rangesfrom dc to kilohertz. For very high -currentapplications, detection can simply be a matterof placing the sensor in the gap of a slottedtoroidal ferrite material wrapped around theconductor, as illustrated in Fig. 6.
Linear output Hall deviceLinear Hall -effect linear sensors are usedprimarily to sense relatively smallchanges in magnetic fields - changes toosmall to operate a Hall -effect digitalswitch. They can detect the motion, posi-tion, or change in field strength of anelectromagnet, a permanent magnet, or aferromagnetic material with an appliedmagnetic bias.
Hall effect sensors like Allegro'sUGN3503 not only cheaper but alsomore efficient and effective than inductiveor optoelectronic sensors in many appli-cations. Their power consumption is lowand their output is temperature stable.
Linear sensors are useful as front -endsin flux measuring equipment and fordetection motion. In addition, they canbe used to measure current with negligi-ble system loading while providing iso-lation from contaminated and electrical-ly noisy environments.
Between 0 and 900G, the 3503's sen-sitivity is typically 1.3mV/G. Linear Halleffect integrated circuits include a Hallsensing element, linear amplifier, andemitter -follower output stages. Problems
associated with handling very low levelanalogue signals are minimised by havingthe Hall cell and amplifier on the samechip.
Rated for operation over the range of-20 to +85°C, the 3503U is a ratiometricdetector, i.e. output voltage depends notonly on field strength detected but also bypower supply fluctuations. For applica-tions where ratiometric output is notappropriate, there is also a linear sensorwith full internal supply regulation -3501.
Response of the 3503 is flat to 23kHz,making the it useful for ac as well as dcmeasurement. When no magnetic field issensed, output null voltage is nominallyone-half the supply voltage. A south mag-netic pole at the part -marked face of thesensor drives the output higher than thenull voltage level. A north magnetic polewill drive the output below the null.
Greatest sensitivity is obtained with asupply voltage of 6V, but at the cost ofincreased supply current and a slight lossof output symmetry. Minimum supplyvoltage is 4.5V.
In finding the flux reaching the sensor,radius r in inches from the centre of the con-ductor to the centre of the sensor is important.With r at 0.5in, a current of 1000A produces159G at the Hall device in the toroid's gap.This is because B in gauss is approximatelyequal to current in amps divided by 4pr, wherer is in inches. Minimising the air gap betweenthe ferrite and sensor generally improves per-formance.
Current sensing capability is increased bywrapping the conductor around the toroidalferrite, as shown in Fig. 7. Each additionalturn multiplies the gauss -per -ampere intensityseen at the sensor, i.e. ten turns increase theintensity tenfold. Main concerns are that thecore retains minimal field when the current isreduced to zero and that the flux density in theair gap is a linear function of current.Consideration also needs to be given to thefact that the air gap changes with temperature.
Designing with Hall switchesElectrical interfacing. Hall -effect switcheslike those in the 312x series have an open -col-lector output transistor that can drive up to25mA. As a result, many loads such as smalllamps and relays can be driven without anyadditional components.
Since the output driver transistor has a satu-ration rating of typically 140mV - combinedwith nanovolt-level leakage - interfacing tonearly all common logic technologies rarelyrequires more than a pull-up resistor.
Driving low -voltage, high -current DC loadsvia a Hall effect switch requires few additionalcomponents. In many applications, an emitterfollower will provide the necessary boost with
Features- High sensitivity- Flat response to 23kHz- Low output noise- 4.5 to 6V supply
vcc
Integrated linear Hall -effect devices like the3503 from Allegro incorporate a Hall cell,linear amplifier and emitter follower. Supplyto the dc amplifier is regulated but the hallfeed is not. As a result, this ratiometricdevice tracks supply voltage.
Fig. 8. For loads over 20mA, 3120 Hall -effect switches need buffering.With this configuration, loads of up to 4A can be switched. The firsttransistor is necessary not only for amplification but also for inversionto ensure that the load switch turns on rather than off when magneticflux rises above the Hall -device threshold.
a slight loss in efficiency. As Fig. 8 shows.switching efficiency can be increased by usingan inverter amplifier - the 2N5812 - togetherwith a low-cost 2N3055 driver.
Using the 2N58/2 intermediate stage pro-vides inversion as well as amplification. Itensures that the load is switched on when thesensor sees magnetic field and off when thefield is removed.
Figure 9 demonstrates how easy it is to
Magnetic materialsMaterials most commonly used to pro-vide flux in Hall -effect systems are vari-ous Alnicos, Ceramic 1 and barium fer-rite in a rubber or plastic matrixmaterials. Manufacturers often havestock sizes, including cylindrical typeswith various numbers of pole pairs.
Alnico is the name given to numberof aluminum nickel -cobalt alloys thathave a fairly wide range of magneticproperties. In general, Alnico ring mag-nets have the highest flux densities, thesmallest changes in field strength withchanges in temperature, and the high-est cost.
They are generally too hard to shapeexcept by grinding and are fairly brittlewhich complicates the mounting ofbearings or arbor. Ceramic 1 ring mag-nets, with trade names like Indox,Lodex, have somewhat lower flux den-sities (field strength) than Alnicos, andtheir field strength changes more withtemperature. They are however consid-erably cheaper and are highly resistantto demagnetisation by external magnet-ic fields.
Ceramic materials are resistant tomost chemicals and have high electri-cal resistivity. Like Alnico, they canwithstand temperatures well above thatof Hall switches and other semiconduc-tors and must be ground if reshaping ortrimming is needed.
Rubber and plastic barium ferrite ringmagnets are roughly comparable toCeramic 1 in cost, flux density, and
adapt the digital Hall -effect device to mainsswitching applications. The triac needs 80mAof drive but the Hall IC provides up to 25mA.Adding the n -p -n emitter follower solves theproblem.
Limit detection. Even with a simple bar orrod magnet, there are several possible pathsfor motion detection. The magnetic pole canmove perpendicularly straight at the active
face of the Hall device. Known as head-onmode, this method is simple, works well, andis relatively insensitive to lateral motion. Adrawback is that if the slide carrying the mag-net travels too far, the sensor could be dam-aged.
Flux density plots for a typical head-on sys-tems show that the magnetic slope is quiteshallow for low values of flux density -a dis-advantage that generally requires extreme
MaterialMaximum energy
productinducijn(gauss -oersted)
Resicial
(galls)Coercive brce
(oerstecs)Twnperature
,oefficientCost 7omments
R.E. Cobalt 16 x 106 8.1 x 103 7.9 x 103 - 0.05%/e HighestStrongest, snallest. resistsdemagnetizing best
Alnico 1, 2.2. 4 1.3 - 1.7 x 106 5.5 -7 5 x 103 0.42 - 0.72 x 103--4.000260Do
Medium Non-onentec
Alnico 5. 6.1-7 4.0 - 7.5 x 106 10.5 - 12.5 x 103 0.64 - 0.7E x 103-' 02%r C to
-0 03°/orCMedium -
highOriented
Alnico 8 5.0 - 6.0 x 106 7- 9.2 x 103 1,5 - 1.9 x 103 -4.0164/7C to-0,01%.7C
Medium-high
Oriented. hich coercive force.best temperature coefficient
Alnico 9 10 x 106 10.5 x 1(3 1,6 5( 103 -0.02%/"C High Oriented, hic hest energy product
Ceramic 1 1,0 x 106 2.2 10: 1.8 x 103 -0.2%re LowNon-onented. high coercive force.hard, brittle, non-conductor
Ceramic 2. ; . 4 6 1.8 - 2.6 x 106 2.9 - 3.3 x 103 2.3 - 2.8 x 103 -0.2%TCrhLeodwa,-,,, roarcrteiallt),raordrieh,rt,eht,vheoryhhcighhdcuocteordive
Ceramic 5. 7. 8 2.8 - 3.5 x 106 3.5 - 31 x 103 2,5 - 3.3 x 103 -0 2%,'-C MediumFully. oriented.ha.d,h hvieery hoenorcoc rucal voer
Cunite 1.4 x 106 5,5 x 10- 0.53.103 Medium Ductile, can cold form and machine
Fe-Cr 5.25 x 106 13.5 x 113 060.103 Medium-high
Can machine prior tofinal aging treatment
Plastic 0.2 - 1.2 x 106 1.4 -3 > 103 0 45 - 1.4 x 103 -0.2 %/°C Lowest Can be molded, stamped. machined
Rubber 0.35 - 1.11 x 106 1.3 - 2.; .i 103 1 - 1.8 x 103 -0.2% /"C Lowest Flexible
Neodymium 7 - 15 x 106 6.4 - 11 75 c 103 5.3 - 6.5 > 103-4.1517962t,/`cC to Mehdr - Non -oriented
There is a wide variety of magnetic materials eo choose from when applying Hall -effectdevices, ranging from hard, brink ceramics tc rubbe.
temperature coefficient. Unlike ceram-ics however, they are soft enough toshape using conventional methods. It isalso possi3le to mould or press themonto a shaft for some applications.Rubber and plastic magnets do havetemperatt..re limitations ranging from70°C to 130°C depending on the par-ticular material, and their field strengthchanges nore with temperature thanAlnico or Ceramic 1.
Regardless of material, ring magnets
have limitations on the accuracy ofpole Jlacement and uniformity of polestrength. In turn, this limits the preci-sion of the output waveform.EvalLations have shown that poleplacement in rubber, plastic andceramic magnets usually falls within 2or 3° of target, but 5° errors have beenmeasured. Variations in flux densityfrom pole to pole will commonly be±5% although variations of up to±30% can occur.
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 579
COMPONENTS
115/230 VAC
Common
Fig. 9. Since Hall -effect switches in the 3120 range have a 25mA output capability, veryfew components are needed to control heavy loads. In this circuit, an intermediate n -p -ntransistor boosts current to the 80mA or so needed to switch mains loads via a triac.
mechanism travel and extreme sensitivity toflux changes in operate and release points ofthe Hall switch. This problem can be over-come by selecting Hall switches with higheroperate and release properties.
A safer option is to move the magnet infrom the side of the Hall device, past its face -slide -by mode. Strong magnets and/or ferrousflux concentrators in well -designed slide -bymagnetic circuits allow better sensing preci-
sion with smaller magnet travel than for head-on mode. This method is, however, however,very sensitive to lateral play, as the flux den-sity varies dramatically with changes in the airgap.
Because the active area of a Hall switch isclose to the branded face of the package, it isusually operated by approaching this face withmagnetic south pole. It is also possible tooperate a Hall switch by applying a magnetic
north pole to the back side of the package.While a north pole alone is seldom used, thepush-pull configuration - simultaneous appli-cation of a south pole to the branded side anda north pole to the back side - can give muchgreater field strengths than are possible withany single magnet. Perhaps more important,push-pull arrangements are relatively insensi-tive to lateral motion and are worth consider-ing if a loosely fitting mechanism is involved.
Another possibility is the push -pusharrangement described earlier, Fig. 4. A natu-ral extension of this is to use two oppositelypolarised magnets in slide -by mode, movingacross the face of a sensor
Hall sensor sourceIntegrated Hall sensors mentioned inthis article - plus others - areavailable in the UK via AmbarCascom Ltd, Rabans Close,Aylesbury, Buckinghamshire HP193RS. Tel. 0296 434141, fax 029629670. Applications literature, uponwhich this article was based, is alsoavailable.
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580 ELECTRONICS WORLD + WIRELESS WORLD July 1994
COMPUTER ICS8742 1 SHOT £8 8742 WIPED £5 "NEWTMS320 £5 TMS320 1 SHOT £3 **NEWAM27CO20-125L1 SURFACE MOUNT EPROM USED/WIPED £1.50 "NEWMM16450 UART CHIP £5 ea "NEWMM16550 UART CHIP few only El 2 ea **NEWP8271 BBC DISC CONTROLLER CHIP EX EQPT £20SAA5050 TELETEXT CHIP EX EQPT £52817A-20 (2K x 8) EEPROM ex eqpt. £2D41256C-15 25610(1 PULLS 9 FOR £580C31 MICRO £2P8749H MICRO £5D8751-8 NEW £10MK48Z02-20 ZERO POWER RAM EQUIV 6116LP £4NEW 4164-15 £1USED 41256-15 £1USED 4164-15 60pBBC VIDEO ULA £108051 MICRO £1.25KS82C55-250 SAMSUNG 89/90 1100 AVAILABLE £39 x 41256-15 SIMM £108 x 4164 SIP MODULE NEW £8FLOPPY DISC CONTROLLER CHIPS 1771 £16FLOPPY DISC CONTROLLER CHIPS 1772 £17.5068000-8 PROCESSOR NEW £6HD6384-8 £5ALL USED EPROMS ERASED AND BLANK CHECKED2716-45 USED £2100/£12732-45 USED £2100/£12764-30 USED £2100/£1.6027C256-30 USED £227C512 USED £3.501702 EPROM EX EQPT £52114 EX EQPT 50p 4116 EX EQPT 70p6264-15 8k STATIC RAM £2GR281 NON VOLATILE RAM EQUIV 6116 f5Z80A S10-0 £1.2580387-16 CO PROCESSOR (OK WITH 25MHz 386) £3571263/ DIGIT LCD DRIVER CHIP £2 ea2816A-30 HOUSE MARKED £2IBM PART NO. 68X6271 PANASONIC PART NO.MN4B40512S85 512K X 40TMS9000NL PROCESSOR £20TMS9901NL £10TMS9902/3NL, TIM9904NL f5 eaHM6167LP-8 65pM27C4001-15 £868000-10 PROCESSOR £6
REGULATORSLM338K £6LM323K 5V 3A PLASTIC £2LM323K 5VA METAL £3SANKEN STR451 USED IN AMSTRAD MONITORS £578H12ASC 12V 5A f578M05 5V 0.5A 7/£1LM317H T05 CAN £1LM317T PLASTIC T0220 variable £1LM317 METAL £2.207812 METAL 12V 1 A £17805/12/15/24 25p7905/12/15/24 25pCA3085 TO99 variable reg 2/£1
POWER TRANSISTORS0C29 f1.35 eaP POWER FET IRF9531 8A 60V 3/£1N POWER FET IRF531 8A 60V 2/£12SC1520 sim 8E259 3/£1 100/£22TIP 141/2 £1 ea TIP 112/428 2/£1SE9301 100V 1DA DARL SIM TIP121 2/£1PLASTIC 3055 OR 2955 equiv 50p 100/£35BUZ31 POWER FET TO -220 200V 12.5A 2/£1
TEXTOOL ZIF SOCKETS28 PIN USED £3 40 PIN NEW £10SINGLE IN LINE 32 WAY CAN BE GANGED FOR USE WITHANY DUAL IN LINE DEVICES . . . COUPLING SUPPLIED 2/£1.50
QUARTZ HALOGEN LAMPS12V 50watt LAMP TYPE M312 £1 ea HOLDERS 60p ea24V 150 WATTS LAMP TYPE A1/215 £2.50 each
ALPS MOTORISED DUAL 47K LOG pots with spindle, works on6v -12v £1.50 eaTL071 LO NOISE OP AMP 5 for £1 **NEW47000u 25v SPRAGUE 36D £3.50 (£2) "NEW12 way dil sw £3 for £1 "NEW100nF 63V X7R PHILIPS SURFACE MOUNT 30K available
£1BT PLUG +LEAD 3/£113A MOULDED PLUG 2m lead £1MIN. TOGGLE SWITCH 1 POLE Go PCB type 5/£1LCD MODULE sim. LM018 but needs 150 to 250V AC for display40x2 characters 182 x 35 x 13mm £10TL431 2.5 to 36V TO92 ADJ. SHUNT REG 2/£16-32 UNC 5'16 POZI PAN SCREWS £1/100
NUTS £1.25/100PUSH SWITCH CHANGEOVER 2/£1RS232 SERIAL CABLE D25 WAY MALE CONNECTORS
INMAC LIST PRICE £30LCD DISPLAY sim Hitachi LM016L £6.50AMERICAN 2/3 PIN CHASSIS SOCKET 2/C1WIRE ENDED FUSES 0.25A 30/£1NEW ULTRASONIC TRANSDUCERS 32kHz £2/prAlso available 28 slot van -bus backplane same size +Price NEWPOWERFUL SMALL CYLINDRICAL MAGNE S 3/E1BNC 500HM SCREENED CHASSIS SOCKE- 2/E1SMALL MICROWAVE DIODES AE1 0C1026A 2/E1D.I.L. SWITCHES 10 -WAY £1 8 -WAY 80p 4/56 -WAY 80p180VOLT 1WATT ZENERS also 12V 8 75V 20/£1MIN GLASS NEONS 10/£1RELAY 5V 2 -pole changeover looks like RS 3.55-741 markedSTC 47WBDst £1 eaMINIATURE CO -AX FREE PLUG RS 456-071 2/£1MINIATURE CO -AX PCB SKT RS 456-093 .._ 2/£1PCB WITH 2N2646 UNIJUNCTION WITH 12\ 4 -POLE RELAY
El400 MEGAOHM THICK FILM RESISTORS 4/£1STRAIN GAUGES 40 ohm Foil type polyester backed balco gridalloy E1.50 ea 10+ £1ELECTRET MICROPHONE INSERT £0.90Linear Hall effect IC Micro Switch no 613 SS4 sim RS 304-267
£2.50 100+ £1.50HALL EFFECT IC UGS3040 + magnet £1OSCILLOSCOPE PROBE SWITCHED x 1 x 0 £121 pole 12 -way rotary switch 4/E1AUDIO ICS LM380 LM386 TDA 2003 £1 ea555 TIMERS £1741 OP AMP 6/E1ZN414 AM RADIO CHIP .. 80pCOAX PLUGS nice ones 4/£1COAX BACK TO BACK JOINERS 3/£14 x 4 MEMBRANE KEYBOARD £1.50INDUCTOR 20pH 1.5A 5/£11.25" PANEL FUSEHOLDERS 3/£1CHROMED STEEL HINGES 14.5 x 1" OPEN fl each12V 1.2W small w/e lamps fit most modern ca -s 10/£1STEREO CASSETTE HEAD £2MONO CASS. HEAD El ERASE HEAD 50pTHERMAL CUT OUTS 50 77 85 120"C £1 eaTHERMAL FUSES 220°C/121°C 240V 15A . 5/£1TRANSIS-OR MOUNTING PADS TO-5/TO- 8 £3/1000TO -3 TRANSISTOR COVERS 10/£1PCB PINS FIT 0.1" VERO 200/E1TO -220 m cas + bushes 10/50p 100/£2TO -3 micas + bushes 15/£1Large Sea: shrink sleeving pack E2IEC chassis plug fitter 10A £3POTS SHORT SPINDLES 2K5 10K 25K 1M 2M5 4/£140k U/S TRANSDUCERS EX-EQPT NO DA -A £1/ prLM335Z 13MV/derlee C £1
£1BNC TO 4MM BINDING POST SIM RS 455-961 £1MIN PCB COWER RELAYS 10.5v COIL 6A CONTACTS 1 poleGo £1AVEL-LINDBERG MOULDED TRANSFORMER TYPE OB1015+15V 10VA QTY. AVAILABLE E2 eaBANDOLIERED COMPONENTS ASSORTED Rs, Cs, ZENERS
f5/1000LCD MODULE 16 CHAR. X 1 LINE (SIMILAR TO HITACHILM10) £5KYNAR WIRE WRAP WIRE El/REELOPI1264A 10kV OPTO ISOLATOR £1.35 ea 100+ El ea'LOVE STORY' CLOCKWORK MUSICAL BOX MECHANISMMADE BY SANKYO El eaTelephone cable clips with hardened pins 500/£2
1N5401 3A 100V 10/E1BA158 lA 400V fast recovery 100/£3BY127 1200V 1.2A 10/E1BY254 800V 3A 8/C1BY255 1300V 3A 6/£16A 100VSIMILAR MR751 4/£11 A 600V BRIDGE RECTIFIER 4/C14A 100V BRIDGE 3/£16A 100V BRIDGE 2/£110A 200V BRIDGE £1.5025A 200 V BRIDGE £2 10/£1825A 400V BRIDGE £2.50 10/022KBP02 IN LINE 2A 200V BRIDGE REC 8/£1
CONNECTORSD25 IDC PLUG OR SOCKET £134 -way card edge IDCCONNECTOR (disk drive type) £1.25CENTRONICS 36 WAY IDC PLUG £2.50CENTRONICS 36 WAY IDC SKT £4.00BBC TO CENTRONICS PRINTER LEAD 1.5M £3CENTRONICS 36 WAY PLUG SOLDER TYPE £4USED CENTRONICS 36W PLUG+ SKT £314 WAY IOC BLOCK HEADER SKT. 5/£1
PHOTO DEVICESHI BRICHTNESS LEDS CQ)C24 RED 5/£1SLOTT iD OPTO-SWITCH OPCOA OPB815 £1.302N5777. 50pTIL81 PHOTO TRANSISTOR £1TIL38 INFRA RED LED 5/£14N25, CP12252 OPTO ISOLATOR 50pPHOTC DIODE 50P 6/£2MEL12 :PHOTO DARLINGTON BASE n/c) 50pLED's F ED 3 or 5mm 12/£1 100/£6LED's GREEN OR YELLOW 10/£1 100/£6FLASH NG RED OR GREEN LED 5mm sop 100/E40HIGH PEED MEDIUM AREA PHOTODIODE RS651-995 £10 ea
STC NTC BEAD THERMISTORSG22 20R, G13 1K, G23 2K, G24 20K, G54 50K, G25 200K,RES 2C'C DIRECTLY HEATED TYPE £1 eaFS2213`V NTC BEAD INSIDE END OF 1" GLASS PROBE RES20°C 29OR £1 eaA13 DI lECTLY HEATED BEAD THERMISTOR 1k res. ideal foraudio Wien Bridge Oscillator £2 ea
IC SOCKETS14/16/' 8/20/24/28/40 -WAY DIL SKTS £1 per TUBE8 -WAY DIL SKITS £2 per TUBE32 -WAY TURNED PIN SKIS. 7k available 3 for £1SIMM SOCKET FOR 2 x 30 -way SIMMS El
POLYESTER/POLYCARB CAPS330nF 10% 250V AC X2 RATED PHILIPS TYPE 330.... £20/100100n -20n 63V 5mm 20/£1 100/£3ln/3nF5n6/8n2/10n 1% 63V 10mm 100/£510n/15:1/22n/33n/47n/66n 10mm rad 100/£3.50100n 250V radial 1 Omm 100/£3100n 00V Sprague axial 10/£1 100/£6 (£1)2p2 leov rad 22mm, 2112 100V rad 15mm 100/£1010n/3' 11/47n 250V AC x rated 15mm1p 60CV MIXED DIELECTRIC1p0 103V rad 15mm, 1p0 22mm rad
10/£150p ea100/£6
RF BITSSAW FILTERS SW662/SW661 PLESSEY SIGNALTECH JOLOGY 379.5 MHZ £1,50 ea **NEWFX3286 FERRITE RING (ON CX25) ID 5mm OD 10mm 10 for£1 **PEWASTE3 UM1233 UHF VIDEO MODULATORS (NO SOUND)1250 STOCK £1.50 **NEWMARCONI MICROWAVE DIODES TYPES DC2929, DC2962,DC4239F1/F2XTAL =ILTERS 21M4 55M0 £2 eaALL TRIMMERS 3 for 50pVIOLET 5-105pFYELLOW 5-65pF RED 10-110pF GREY 5-25pFSMAL_ MULLARD 2 to 22pF 3 FOR 50p £10/100TRANSISTORS 2N4427, 2N3866, 2N5109 80p
ea.CERAMIC FILTERS 4M5/6M/9M/10M7 60p eaFEED THRU' CERAMIC CAPS 1000pF 10/£1SL610 £56 VOLT TELEDYNE RELAYS 2 POLE CHANGEOVER £2(BEY.51 TRANSISTOR CAN SIZE)2N2222 METAL 5/£1P2N2222A PLASTIC 10/£12N2369A 5/£1VNIOKM 4/£1
',twin. toroidal II alISIMIIICTS 225VA 10 la -0-10.5 Sun Ian fight gun terminated with a jack plug andprimary 0-260-285 secondary i29.95 PPS clip gives a signal when pointed at 50hz
LEDs 3mm or 5mm, red or green 6p each flickering light with output wave formYellow I 1p each chart £3.95I ligh intensity red, gteen or yellow 5mm .-. 30 each DC -DC convertor Reliability model V 12P5 12v in 5vCable ties, 1 p each. £5.95 per 1000, £49.50 per 200ma out 300v input to output Isolation with
10.000 data...£.4.95 each or pack of 10 £39.50High quality photo resist copper clad epoxy glass Hour counter used 7 digit 240v ac 50 Hz £1.45
-boards QWERTY keyboard 58 key good quality switchesDimensions single sided double sided new £5.003x4 inches £1.09 £1.23 Airp. A82903 -C large steppMg motor 14v 7 5' step4x8 inches £2.75 £2.99 27ohm 68mm dia body 6.3mm shaft...£8 95 orfix 12 inches £620 - £200.00 for a box of 3012x12 inches £12.25 - Polyester capacitors box type 22.5malead Mud, 'Rechargeable batteries 0.9uf 250vdc 18p each 14p...100+ 9p...1000+
( H P 7) AA 500mAH with solder I uf 250Vdc 20p each 158...100+ 10 .'1'000+500mAH £0.99 tags £1.55 2.2uf 250vdc (27.5mm pitch).... 30p each 20p 100+
AA 70OrnAH £1.75 C(HP1 I) 1.8AH £2.20 15p...1000+( l 2A H with solder D(HP2) 1.2 AH £2.60 3.3uf 100vdc... 30p each 20p...100+ 15p...1000+
D IITH with soll2de60r P P?lOrnAH8 . 4 V I uf 50v bipolar electrolytic axial leads 15p
£4.95 each 7.5p...1000+1271
with solder4.Su bra Cs with solg; 0.221u0f02,50v polyester axial leads 15p each, 7.5p gd
£1.55 1/3 AA with tags (Philips Polypropylene luf 400vdc (Wirna MICE10) 27.5mmA A T (HP1 6) CTV) £1.95 pitch 32x29x17rtirn case 75p each 60p 100+
180mAH £1.75 Philips 123 series solid aluminium axial leads - 33ufStandard charger charges 4 AA cells in 5 hours or 10v & 2.2uf 40v 40p each 25p 100+
4Cs or Ds in 12-14 hours+ laPP3 (I, 2, 3 or 4 cells Philips 108 series 22uf 63v axial 30pmay be charged at a time) £5.95 each 15p...1000+
high power charger as above but charges the Cs and Multilayer AVX ceramic capacitors all 5mm pitchDs in 5 hours. AAs, Cs and Ds must be charged in 1005 100pf, 150pf, 220pf, 10.000pf (10n) 10p2s or 4s £1 0.95 each 5p...100+ 3.5p...1000+
Nickel Metal Hydryde AA cells high capacity with no 500pf compression trimmer 60pmemory. 1000mAH £3.85 1200mAH £4.40 40 uf 370vac motor start capacitor (dialectrol type
Special offers, please check for availability. containing no pcbs) £5.95 or £49.50 for 1042 x 16mrn dia 1.2v £1.45 Welwyn W23 9W 120ohm 35p each 20p 100+Stick of 4 17Immx16mm dia with red & black leads 680 ohm 2W metal film resistor 4p 100+ 2p 1000+
38000uf 20v £2.50 each 15p each 100+8 7 0 0 0 u f I 0 v ... £ 1 . 9 5 6 8 0 0 0 u f We have a range of 0.25w 0.5w lw and 2w solid
15v...£2.95 I 0000uf 16v...£1.50 58000uf carbon resistors, please send SAE for list60v £4.95 P.C. 400W PSU (Intel part 201035-001) with stan
7 segment common anode led display 12mm £0.45 dard motherboard and 5 disk drive connectors,1..M293 I AT5.0 low drop our 5v regulator T0220 fans andns inlet/outlet connectors on backmains
package £0.85 and switch on the side (top for tower case) dims7812 and 7912 12v IA regulators £26.00 per 100 212x149x149mm excluding switch. £26.00 eachI.M337k TO3 case variable regulator £1.95(£1.44 £138.00 for 6
100+) MX 180 Digital multimeter 17 ranges I000vdcGaAs FET low leakage current S8873 £12.95 each 750vac 2Mohm 200mA transistor life 9v and
(£9.95 10+, £7.95 100+) 1.5v battery test £12.9585250 P channel mosfet...£0.45 BC559 AMD 27256-3 Eproms £2.00 each £1.25-100+
74LS05 hex invertor £10.00 per 100 Used 8748 Disk drive boxes for 5.25 disk drive with mom for aMicrocontroller £3.50 power supply, light grey plastic,
SL952 UHF Limiting. amplifier LC 16 surface 67x268x247mm £7.95 £49.50 for 10mounting package with data sheet £1.95 Hand held ultrasonic remote control £3.95
A M 2 7 S 0 2 . . . £ 1 . 2 5 each 9 0 p I 0 0+ CV2486 gas relay. 30x lOrnm dia with 3 wire termi-CD4007UB 10p nals, will also work as a neon light 20p
100+(6p. 1000+) each £7.50 per 100A23 12v battery for car alarms or lighters 75p
each £50.00 per 100
All products advertised are new and unused unless otherwise stated.Wide range of CMOS TIT 7411C 74F Linear Transistors kits. Rechargeable batteries..raparitors. tools etc
always in stock. Please add £1.95 towards p&p. VAT included in all prices.
Electron tubes: Transmitting,Industrial, Microwave, Audio,
Receiving, Display, etc, etc. For Maintenance, Spares or
Production. Semiconductors: Transistors,
Thyristors, Diodes, RF, Power I/C's,etc.
We have one of the largest stocksin the U.K.
* TRY US! *
FAX, PHONE. POST OR TELEX YOUR REQUIREMENTS
1 30 NEW LONDON ROAD, CHELMSFORD,ESSEX CM2 ORG, ENGLANDTelephone: (0245) 3 55296/265865
Telex: 995398 SEEVEE G Fax: (0245) 490064
MEGAPROM &vim programmer. EPROMS, E2PROMS, and FLASH memories from 2k (2716) to8 Meg (27C080). Runs on IBM PC via the centronies port using standard printer cable. Works on allPC compatibles, laptops, and notebooks. No special port requirements.
Uses approved programming algorithms. Very fast program and verify 27C512(64K Bytes) in 45 seconds.
Full screen editor software supports Bin, Intel Hex, motorola S and Asc formats. Only £99.95
Top quality components used throughout including production ZIF socket.
Requires external power supply 18-25v AC or DC @ 250ma. (optional extra (£6.50)
PICPROG Programs Picl6C54-5556-57-71414. Centronics port interface same as Megaprom.Powerful editing software to Read, write & copy Pic devices including data memory in Pic16014.
Unit suipplied with IBM software & 12 months parts & labour guarantee. Only £69.95
Requires external power 15-20v AC or DC @ 250ma. (optional extra £6.50).
EPROM EMULATOR Works on ANY computer with centronics printer port. Data sent to theprinter appears in the target board Eprom socket. Emulates from I k to 32k Byte (27C256) roms,board switchable. Power supplied from target Rom socket (less than 10ma ). Very fast download.
Software supplied for IBM PC to convert and send Intel Hex, Motorola S, ASCand Bin files. Only £49.95Board supplied with software and 12 months parts and labour guarantee.
PC SCOPE Convert your IBM PC into a Storage Oscilloscope with our A/D converter. Simply pluginto the printer port (no power required). Sample rate 10k to 30k per second.
Software supplied for Scope and Voltmeter. AID source to write your ownprograms.
DEVELOPMENT SOFTWAREDevelop software on your IBM PC for other Microprocessors, Controllers, Pic's etc. Software hasfully integrated Text Editor, Assembler, Disassembler and Simulator.
The Simulator displays all registers along with disassembled code program counter, Condition codsregister. The user can single-step, go with breakpoints, watch memory etc. change any/all registers/memory locations at any time (on the fly).
Code can be Saved to disk and/or downloaded directly to our EPROM Emulator. All softwaresupplied with sample ASM files and user documentation.
Very powerful software as supplied to universities, colleges 1TECS and Industry.
Available for the following:-
MC88051/52/552 series Software /19.95 MCS8048/49 series Software £19.95P1C16C54/5/6/7 Software £29.95 PIC16C71/84 Software £29.9511D63/6809 Software £49.95
LOW COST PIC ICE (In -Circuit Emulator)Plus into the printer port and runs in conjunction with the PIC development simulator software.Appears to the target system as a normal Pic device including 05C2 and RTCC in/out. Runs in realtime from the IBM PC changes made to File registers reflected on target.Supplied with Software of your choice Pic54-57 or Pic 71/84 Only £89.95
All hardware carries a 12 months parts and labour Guarantee. No VAT payable.Please add £1 .50 for Carriage. SAE or TEL for further details.
Only £29.95
JOHN MORRISON DEPT WW4 Rein Gardens, Tingley
West Yorkshire imuitTel (or Fax): 0532 537507 VISA
CIRCLE NO. 121 ON REPLY CARD
582
CIRCLE NO. 122 ON REPLY CARD
July 1994 ELECTRONICS WORLD+WIRELESS WORLD
APPLICATIONSPlease mention Electronics World + Wireless World when seeking further information.
Battery -powered circuit measures down to ptS2This simple battery -powered adapterconverts an ordinary digital voltmeter
into a four -wire milliohm meter. It is said toaccurately measure the resistance of wiring,motor coils, solenoids, high -currentinductors and meter shunts. It can also beused for locating short circuits in a powersupply or a printed circuit board.
With components shown, the circuitshown is about ±2% accurate. For higheraccuracy, you can make componentadjustments described later.
The circuit applies 1A, 100mA, or 10mAto the unknown resistance via two test leads,depending on the range -switch setting. Next,the DVM is set to its 2V range andconnected via two more test leads. Thisforms a four -wire connection to theresistance being measured.
Indications on the DVM are presenteddirectly in ohms on pressing the momentary -on power switch. A 1.00052 resistance, forexample, reads 1.000V on the circuit's lArange, so one millivolt corresponds to onemilliohm. Four and five -digit DVMsfrequently have lmV sensitivity, providingresolutions of lma
Because the output is a current source, theunknown resistance of the connections andtest leads does not cause measurementerrors. Accuracy depends on the DVM, theop amp's input -offset voltage - which is±70mV maximum for the device shown -and the tolerance of resistors R1-6
To set up the circuit, first trim the 1 Arange by selecting R4 or by adding atrimming potentiometer between R1 and R2.
Next, trim the 100mA range and then the10mA range by adjusting the highest -valuedresistors in the R5 and R6 networks.
Si
- 91,
Power -fail and resetfor PCs
Anumber of power management functionshave been integrated into one chip by
Dallas Semiconductor. This chip - the DS1632- produces the real-time clock reference, acontrolled reset signal, power -source switchingand power -fail indication.
Many PC chip sets already provide a real-time clock. For those that do not, or forapplications where the existing RTC is notaccurate enough, the DS1632 provides a stable32.763kHz reference. Tuning is provided onchip so no additional oscillator components areneeded. Using a 6pF-load crystal such as theDaiwa DT26S or Seiko DS -VT -200, timing
2
MA X8725
R1
50M
R2
100k
10
R6. 10 100tk
MAX 80
R3
1k
R7
1k
821 5V+1
-OUT
01
1RFM0
N -CHANNEL
1A (1m L)/mV)
100mA (10m (/mV)
10mA (100m Lamy)
S2
ORANGE
Added on to a digital multimeter, this circuit accurately measures resistances down to micro -ohmsand can be used to detect shorts on PCBs.
Pressing the push-button turns on themicropower reference, which produces2.500V. Resistors R1 and R2 divide thatoutput to 0.1V, and the op -amp forces 0.IVat the source of the moOet. This actioncreates a current source that develops 0.IVacross R4, R5, and R6.
The range switch selects a current of 1A,100mA, or 10mA in the loop formed by theresistors, the unknown resistance, the 1.5Vbattery, and the mosfet
Note that releasing S1, or disconnectingthe adapter, eliminates all current drain fromthe 1.5V battery. As a result, an alkaline 'ID'cell can produce thousands of measurements- even on the 1 A range, if the push button isused sparingly. The 9V battery can last foryears because its load is less than 30µA.
To search for a shorted component or a
PUSHBUTTON
0 0
32766 kHz
veal
DS1632
short between tracks on a pcb, first connectthe two adapter leads, one to each of thetracks in question. Connect a DVM lead tothe same point as one adaptor lead, and usethe other DVM lead to probe along thetracks.
Location of the short is revealed by thehighest reading on one track and the lowestreading on the other. Constant readingsindicate no adapter current flowing in thatsection of the track, so that section can beeliminated from the search.
The design is taken from Maxim'sEngineering Journal number 14.
Low -power consumption portable PCs need sensing circuitry tosignal when to switch over to the backup battery and when to shutdown altogether if the battery fails. This IC provides those featurestogether with properly timed resets and a stable 32.768kHz crystaloscillator for a real-time clock.
MICROPROCESSOR
314RESET, RESET
vvcc
CHIPSET
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 583
APPLICATIONS
accuracy is two minutes per month.A reset signal for a microprocessor must
be triggerable form a number of sources.Most important of these sources are powerfail, power -up, and user demanded systemresets. To provide these in discrete logicneeds a fair number of chips, as shown. Thislogic however is built into the DS1632.
In addition to power -fail outputs signallingan out -of -tolerance supply voltage, thedevice can be used to switch between a mainpower source and a backup. Uninterruptedoperation is ensured by window comparatorcircuitry. It switches the power fail linewithout causing reset when supply voltagefalls enough to warn of impending failurebut not enough to cause incorrect operationof the circuits fed by the power supply.
Further circuitry provides a signal givingwarning when battery voltage becomes lowso that the system can be shut down in anorderly fashion.
To provide power -on,power -up and user -initiated resets fora PCneeds 5 -bit and 8 -bitcounters, 2-3 nand gates,an octal latch, an octalinverter, a single inverterand a 1ms clock. Thesefunctions are part of theDS1632 chip.
1 MEI
According to Dallas Application Note 64which includes further details on thecircuitry described here, the DS1632 one -chip solution costs $2.45 as opposed to$5.75 for an equivalent discrete solution.There is also specific information on
Programmable oscillator is easy to useNormally, oscillator ICs designed to workwith crystals need additional passive
components selected for the specific crystalfrequency. The HA7210 from Harris can beexternally programmed for any crystalbetween 10kHz and 10MHz by simplyconnecting two programming pins to logicone or zero. Apart from the crystal, it needsno additional components.
Operating from a single supply rail
V
8ENABLE II
Do
1.4V
Voty. 2.2V -.
VD, - 3.0V -...
VDD 3'83
Ibis,
Freq 1 M--
7Frog 2
between 2 and 7V, the 7210 is a low powerdevice needing 130pA at 1MHz and only5p A at 32kHz. As the device data sheetdescribes, it will drive two cmos loads.
Applications of the oscillator includebattery powered circuits, remote meteringsystems and palm -top notebook PCs. The7210 also has a disable mode that switchesthe output to a high impedance state. Thisfeature is useful for minimising power
EN
E
ON
10
- 20>
8(-11PL)loo
- 2C4>OFF
R
0
mux
0
mux
O
interfacing the device to Intel's 386SL andthe Chips Technologies/Siemens 82C206.
dissipation during standby and whenmultiple oscillator circuits are used. Thehigh impedance output provides a highresistance path to ground to avoid floatingcmos inputs.
All other models available -all oscilloscopes supplied wth 2 probes
BRUEL & ILIOER Vibration bolter System Consisting of miter control1047. Power Amp 2708 & Exciter Body 4802 (up to 178ON - 4001b0
OTHER DU EQUIPMENT AVAILABLEBLACK STAR EQUIPMENT (P&P all writs 6)
APOLLO 10-100MHz Counter 11rner Rato/Perodlirne intent., etc £222
APOLLO 100-10061111 (As above with more functions, 0375
METEOR 100 FREQUENCY COUNTER 100MHz [1 19
METEOR 600 FREQUENCY COUNTER 600W; 045METEOR 1000 FREQUENCY COUNTER IN! 6189
JUNIOR 500 FUNCTION GEN 0 Dix 500kHz SineSci In 0119
ORION COLOUR BAR GENERATOR Pal/74410n 0779
Ail other Black Star Equipment available
SPECTRUM ANALYSERSHP 1411 with 8555A & IF Plug in I OMHz-18511, C2000HP 141T with 85540& 85528 5o0kMMH 1250MH] Li 300
HP :401 with 855418 8552A 5009112- 1250MHz 41000HP 1111 with 85569 & 85525 20Hr- 30001 £1000HP 1401 with 85531 & 8552A 191-1z 110MHz UNMARCONI 132170305! 110MHz E1500HP I821 with 85580 100012 150061,17 £1500HP 05870 0 0252 25 51017 IMO
OSCILLOSCOPE PROBES SwItchable x I m 10 (P&P 01 E17
Used Equipment - GUARANTEED. Manuals supplied If possible.This is a VERY SMALL SAMPLE OF STOCK. SAE or Telephone for lists. Please check availabliity befure ordering.
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TWIN TWIN PPM
Comprising two PPM9 boards, featuring inherent stability withlaw under micro -processor control, the unit gives simultaneousmonitoring of A/B on red/green and M/S on white/yellowpointers. Together these provide complete information aboutstereo signals. Manufaotured under licence from the BBC.
PPM10 In Vision PPM and Chart Recorder generates a highquality colour video display emulating the well known coaxialtwin movements, long Tegarded as a most satisfactory way ofmonitoring stereo audio levels and mono compatibility. Theeye can judge the level displayed, at a glance, from the angleof pointers, without needing to refer to scale markings. Also asexpansion board for Acorn computers.
*Advanced Active Aerial 4kHz.30MHz* Stabilizers and FixedShift Circuit Boards for howl reduction *10 Outlet DistributionAmplifier 4 *Stereo Variable Emphasis Limiter 3 `Stereo DiscAmplifier *Peak Deviation Meter *PPM5 hybrid and PPM8 IEC/DIN -50/+6dB drives and movements *Broadcast StereoCoders. *Broadcast Monitor Receiver 150kHz-30mHz
Fig. la. Basic bipolartransistor Hartleyoscillator circuit.b) Loop gain (Y axis)vesus amplitude (Xaxis) of an oscillatorwhich may fail to starti), and of a reliable rfoscillator circuit
x
RIEF
The ins and outs ofoscillator actionCertain electronic circuits are taken for granted.Ian Hickman has explored the detailedfunctioning of the LC oscillator to revealunsuspected sophistication to its operation.
Ioften wondered why it was that, in many respects,valve oscillators were so much better than thetransistorised versions that replaced them. Clearly it
had to do with the differences between a valve and atransistor. Comparing the grounded emitter circuitwith the grounded cathode, the latter has a very highinput impedance when, as is usual, the grid is negativewith respect to the cathode, while the base inputimpedance of a transistor is by comparison, distinctlymiddling.
Comparing the collector and anode circuits, at dcand low frequencies the transistor presents a highoutput slope resistance rather like a pentode, althoughconsidering internal feedback via inter -electrodecapacitances, the transistor is more like a triode.
And there is one other major difference betweencollector and anode circuits. When the voltage at theanode of a valve swings below the cathode voltage,the anode simply ceases to draw current. By contrast,when the voltage at the collector of an npn transistorswings below that of the base, the collector/basejunction becomes forward biased and when it swingsbelow even the emitter voltage, the transistor works inthe inverted mode where the collector acts as anemitter and vice versa.
At one time, symmetrical transistors weremanufactured, for use as crosspoint switches. Havingidentical emitter and collector structures, thesedevices worked equally well in either direction,although perhaps "equally badly" would have been abetter description. But modem transistors have veryasymmetric emitter and collector structures and, beingoptimised for operation in the normal mode, they
xl
(b)
perform very badly in the inverted mode. In thatmode, they present an impedance which mightperhaps be described as a soggy mess, inflicting (in anoscillator) heavy resultant damping on the collectortuned circuit. There is no reason why a diode in serieswith the collector could not be fabricated on the die.But it never is, at least not in small signal or rftransistors.
The basic circuitNow a typical transistor oscillator circuit, such as theHartley oscillator of Fig. la, is designed with a small -
signal loop -gain well in excess of unity, Fig. 1 b. Thisguarantees that, when switched on, it will start tooscillate: nothing is more infuriating - and less useful- than an RF oscillator which works very well whenrunning, but sometimes fails to get started at switch-
on. But the excess loop gain at start-up has to bereduced somehow to a loop gain of just unity whenrunning. In this type of single transistor circuit (asdistinct from some other types of rf oscillator, Ref. 1),this is usually brought about by the collector voltagefalling below that of the base. As a result, thecollector/base junction thus becomes a forward biaseddiode connected directly across the tuned circuit,imposing heavy damping upon it and reducing theloop gain by lowering the tuned circuit's effectivedynamic resistance Rd. At the same time, thetransistor, operating in the inverted mode, clamps thecollector to ground, adding to the harmonic distortionin the output.
By contrast, a valve oscillator limits its amplitude inan entirely different way. Fig. 2a shows a valveHartley oscillator and the anode voltage and cathodecurrent waveforms, Fig. 2b, from so lightly coupledthat the circuit barely oscillates, to heavily coupledwith lots of excess loop gain. The valve works in classC and generates its own negative grid bias. As theloop gain is increased, the peak cathode currentincreases and the peak to peak anode voltage swingrises until the valve bottoms on negative -going peaks.At this point, the cathode current cannot rise any
586 ELECTRONICS WORLD + WIRELESS WORLD July 1994
DESIGN BRIEF
Fig. 2a. Valve Hartley oscillatorcircuit, above.b) Anode voltage and cathodecurrent waveforms for varyingdegrees of loop gain, right.
Anode VoltageV
OV
Anode current
ImA
OmAl
(i) Very light coupling(K tapping near G)
further, however positive the grid becomes, but thecurrent just either side of the negative peak can stillincrease somewhat.
With heavy coupling, the anode voltage can swingbelow ground but the points of the cycle where thevalve feeds energy to the tuned circuit to maintain theincreased swing are confined to the two regions eitherside of the negative peak, where the grid voltage is stillnear its positive peak but the anode is not bottomed.The anode current breaks up into two completelyseparated pulses, being zero in between.
With further increase in amplitude, the anode swingsfurther and further below ground and the two currentpulses move further apart. They thus occur at a part ofthe cycle where the rate of change of anode voltage isgreater; hence the time from grid voltage rising abovecutoff to anode voltage falling below ground becomesshorter, strangling off the current pulses to a narrowerwidth. This reduces the component at the fundamentalavailable to make up the tank circuit losses, leading toan equilibrium at a particular amplitude.
Some years ago I made up a test circuit, to see if itwere possible to simulate some of the features of avalve in a transistor oscillator circuit. Having only themost rudimentary equipment at the time, a lowoperating frequency, 20kHz, was chosen, enablingcircuit operation to be easily viewed.
Twin peaksStarting with the circuit of Fig. la, a resistor was addedto the base circuit, to raise the device's input impedanceto something nearer that of a valve's grid when forwardbiased. Then, a diode was connected in series with thetransistor's collector to prevent it conducting when itspotential fell below that of the base. The completedcircuit, Fig. 3, drew 30mA from the supply andproduced what appeared on an oscilloscope to be aperfect sinewave, swinging many volts below ground atthe collector, despite the undoubtedly low Q of the coil(the Rd of the tank circuit was probably only of theorder of 5000). Some small distortion was howeverobservable on the smaller waveform at the base end ofthe tank circuit.
Being now better equipped, I decided to repeat theexperiment at a higher frequency, but not so high that itwould be impossible to observe the narrow currentpulses expected. Also, to use a tunable oscillator to seehow much the output amplitude varied across the tuningrange. A tank circuit of 10pH (nominal) tuned by a365pF (maximum) variable capacitor was chosen,giving a lowest frequency of 2.5MHz. Note that over anoctave tuning range, the Rd of the tank circuit will vary
D1 HP5082-2301
Tr1
BC182
x10Scopeprobe
L\ AA AA(ii) Light coupling (ii) Medium coupling (iv) Heavy coupling
(K tapping nearercentre of coil)
+6V
C247n(Bypass)
OV
10y
2100n
L1 = 10µH nom.7mm dia. former with slug
47k 500 co -axto spectrumanalyser
365pmax.
x = Probe points
by about 2:1, and so therefore, to a first approximation,will the loop gain. If the collector current were constant,then a 2:1 variation in output amplitude could beexpected.
The intention was to use a jfet in place of a bipolartransistor, since the gate characteristic of this deviceresembles a valve, in that it normally draws no current,only conducting when driven above the sourcepotential. A J310 n -channel depletion vhf/uhf amplifierlet was used. Incidentally, this device has a typicalequivalent short-circuit input noise voltage of just lOnVat 100Hz. While this may be not too relevant in an rfamplifier, it is a definite plus point for an oscillatortransistor, where the device's lif noise producesmodulation sidebands about the output frequency,determining the level of the oscillator's very -close -innoise.
Testing problemsAll attempts to use this device at the planned frequencywere complicated by the J310's implacable resolve tooscillate at several frequencies simultaneously in the
Fig. 3. Circuit of a lowdistortion 20kHz LC valveoscillator look alike, usinga transistor (see text).
Fig. 4 . Circuit of the2.5-5MHz 'valve style'oscillator. The 47ki2connection to thespectrum analyser wasremoved when not inuse.
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 587
DESIGN BRIEF
Fig. 5a, left. Tank circuitwaveform with tuningcapacitor set to max,
Fig. 4 at 2.5MHz.Vertical 10dB/div, ref.level -10rIBm, span 0-20MHz, IF bandwidth
100kHz, video filterswitched on.
b) Waveform at thecollector (cathode ofthe diode) at 2.5MHz
(upper rh trace, 5V/div)and the base (lower
trace, 1V/div), OV leveltwo divisions below
centreline, 10Ons/div.
11111111
range 50-500 MHz, as well as performing (at firstsight) as expected over a 2.5-5MHz tuning range.Parasitic stoppers only proved a partial answer.
A bipolar device was pressed into service. This wasthe BC182, with a minimum fr of 150MHz, theparticular sample used having an hFE of 240. As withthe J310, the circuit was constructed over a groundplane consisting of a sheet of copper -clad laminate, towhich the frame of the tuning capacitor was firmlyfixed. To permit grounding of the frame of the tuningcapacitor, the Hartley circuit was modified to a tunedcollector circuit with base feedback winding. A 4.70resistor was placed in series with the transistor'semitter, to permit current monitoring.
Initially, the inductor was grounded and the 4.70emitter resistor was connected to a locally decouplednegative rail. However, it proved impossible tomeasure the small drop across this resistor due toimperfect negative rail decoupling and other causes,so the circuit was modified to use a positive supply asin Fig. 4. From this it will be seen that in view of thehigher operating frequency, the series resistor in thebase circuit has been omitted as it would not wellsimulate the higher impedance of a valve grid circuit.
Fig. 5a with its 100ns/div timebase shows thevoltage at the anode of the diode at maximum tuningcapacitance, a shade over 2.5MHz. With the 10Vcollector supply voltage, the 25V peak -to -peakvoltage across the tank circuit results in the anode ofthe diode swinging well below the base voltage andindeed well below ground - OV ground is twodivisions below the centreline, the upper trace at5V/division. Both traces are dc coupled.
The other trace, at 50mV/div, is the voltage acrossthe 4.70 emitter current sensing resistor, and itproved quite difficult to measure. The magnetic field
from the coil coupled into the probe's ground lead,wherever it was placed. In the end, the probe groundlead was removed entirely and the probe's tip andearth ring strapped across the resistor body asindicated in Fig. 4.
As in a valve oscillator, the collector current hassplit, in this case due to the presence of the diode, intotwo separate pulses, each flowing only while the baseis forward biased and collector voltage above thetransistor's bottoming voltage. The ringing on thesetwo pulses is possibly due to the inductance of the4R7 resistor, and doubtless other circuit parasitics alsosuggesting the wisdom of not attempting theexperiment at too high a frequency.
A case of conduction angleFigure 5b shows the same picture, but with the circuittuned to oscillate at 5MHz. Bearing in mind that thereactance of the inductor at 5MHz will have doubledrelative to 2.5MHz and constant Q unchanged (onlyapproximately true), the tank circuit's dynamicresistance would have doubled. Yet the amplitude ofoscillation has increased by only a few percent. Thereason is that the collector current pulses are now verymuch narrower, not only in absolute terms but as afraction of a cycle. Thus the total conduction angle isreduced, and with it both the mean collector currentand the component at the 5MHz fundamental. Whilethe peak amplitude of the pulses is little changed, theyare now only a few nanoseconds wide. With the 15i.i Abase current supplied and the device's hFE of 240, thecollector current drawn when the base feedback wasremoved, stopping the oscillation, was 3.6mA. At2.5MHz it fell to 1.6mA reducing to 1.3mA at 5MHz.The mean base current was of course unchanged, theexcess being spilled through the base circuit during
588 ELECTRONICS WORLD + WIRELESS WORLD July 1994
DESIGN BRIEF
the period when the collector current was zero due tothe diode being reversed biased.
Figure 6a shows the output spectrum at 2.5MHz(span 0-20MHz), that at 5MHz being the same, exceptthat the second harmonic rose to -32dBc. Harmonicshigher than the fifth were negligible in both cases.The spectrum analyser's reference level (top ofscreen) is -I0dBm, but due to the 1000:1 attenuationintroduced by the 471(52 resistor, it corresponds to+50dBm - at least in terms of volts, though not interms of power of course, as the tank circuitimpedance is much higher than 50Q.
Figure 6b shows the base voltage waveform at2.5MHz, (lower trace, 1V/div ) and a waveform(upper trace, 5V/div) which could not be seen in thecorresponding valve oscillator. This is the waveformat the cathode of the diode. The collector can be seento be firmly clamped to ground at the negative peak(when the diode is reverse biased), subsequentlyrising to the positive peak of the tank circuit voltage.It remains there until the transistor turns on again, atthe first of the two current pulses surrounding thefollowing negative peak.
Figure 7a shows the tank circuit/collector voltagewhen the diode is short circuited, to give conventionaltransistor LC oscillator operation. Here, the negativepeak is brutally clamped to ground: compare this withFig. 5b, where the tank circuit voltage is free to swing5V below ground. The extra damping has reduced theswing from 28V to 25Vp-p. The neat snipping off ofthe negative tip of the waveform does not affect thelow order distortion greatly, but as Fig. 7b (span 0-100MHz) shows, the significant harmonics nowextend to a much higher order. Incidentally, theemitter current also breaks up into two pulses in thiscircuit, but for an entirely different reason from the
case where the diode is present.Nothing shows the difference between a
conventional transistor LC oscillator and the 'pseudovalve' circuit better than Fig. 8. The base voltagewaveform of the pseudo valve circuit at 2.5MHz (at0.5V/div) and the emitter current pulses monitoredacross the 4.7Q resistor (at 50mV/div). Note that thebase voltage stays positive during the period betweencurrent pulses, when the tank circuit voltage isnegative. This is in complete contrast to theconventional circuit without the diode. (Fig. 8b).Here, when the collector tries to swing below ground,the base -collector diode turns on, dragging the basek oltage down with it. This reverse biases the base -emitter junction, interrupting the emitter current andsplitting it into two separate pulses. In this circuit, theexcess base bias current is shunted into the collectorcircuit while the emitter current is off. In the pseudovalve circuit, it goes into the emitter circuit, while thecollector current is cut off.
The differences between a conventional transistorLC oscillator and the 'pseudo valve' circuit shownhere, can be expected to apply to the two circuitswhen operating at much higher frequencies. Some ofthe effects, such as the ringing on the emitter currentpulses would not be present in a practical application.Given its advantages, the 'pseudo valve' oscillatorcould be seriously considered for applications atsubstantially higher frequencies.
References1 Design Brief, Oscillator tails off lamely? IanHickman EW+WW Feb 1992.
Fig. 7a, left. Waveform atthe collector (tank circuit)with the diode shortcircuited, at 2.5MHz(10V/div), OV level twodivisions below centreline,10Ons/div, left-hand photo.Tank circuit voltage cannotswing below ground.b) Spectrum of a). Vertical10dB/div, ref. level-10dBm, span 0-100MHz,IF bandwidth 1MHz, videofilter on.
Fig. 8a. Pseudo valvecircuit. Base circuitwaveform with tuningcapacitor set to max,2.5MHz (larger trace,0.5V/div) and emittercurrent waveform (smallertrace, 50mV/div). Groundlevel 2 divisions belowcentreline, 10Ons/divhorizontal.b) Conventional circuit.2.5MHz. Traces and scopesettings as a).
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 589
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snip price of f12, Order Ref: 12P19.
Telephone Extension Wire 4 core correctly colour coded,ntended for permanent extensions, 25m coil, £2, Order Ref.2P339.High Power Switch Mode PSU. Normal mains input, 3outputs: +12V at 4A, +5V at 16A and -12V at 1/2A.Completely enclosed in plated steel case. Brand new. Ourspecial offer price of £9.50, Order Ref: 9.5P1.Philips 9" High Resolution Monitor. Black and white inmetal frame for easy mounting. Brand new, still in maker'spacking, offered at less than price of tube alone, only £15,Order Ref: 15P1.High Current AC Mains Relay This has a 230v coil andchangeover switch rated at 15A with PCB mounting withclear plastic cover. £1, Order Ref. 965.
Ultra Thin Drills, actually 0.3mm. To buy these regularcosts a fortune. However, these are packed in half dozensand the price to you is £1 per pack, Order Ref: 797B.You Can Stand On It! Made to house GPO telephoneequipment, this box is extremely tough and would be idealfor keeping your small tools in, internal size approx.100/2"x41/2"x6" high. Complete with carrying strap, price £2,Order Ref: 2P283B.Ultra Sonic Transducers. Two metal cased units, onetransmits, one receives. Built to operate around 40kHz.Price £1.50 the pair, Order Ref: 1.5P/4.Power Supply with Extras. Mains input is fused and filteredand the 12V DC output is voltage regulated. Intended forhigh class equipment, this is mounted on a PCB and, alsomounted on the board but easily removed, are two 12Vrelays and Piezo sounder,£3, Order Ref: 3P80B.Insulation Tester with Multimeter. Internally generatesvoltages which enable you to read insulation directly inmegohms. The multimeter has four ranges, AC/DC volts, 3ranges DC milliamps, 3 ranges resistance and 5 amp range.These instruments are ex -British Telecom but in very goodcondition, tested and guaranteed OK, probably cost at least£50, yours for only £7.50 with leads, carrying case £2 extra,Order Ref: 7.5P/4.Mains Isolation Transformer. Stops you getting "to earth"shocks. 230V in and 230V out. 150 watt, £7.50, Order Ref:7.5P/5 and a 250W version is £10, Order Ref: 10P97.Mains 230V Fan. Best make "PAPST", 41/2" square, metalblades, £8, Order Ref: 8P8.2MW Laser. Helium neon by Philips, full spec. £30, OrderRef: 30P1. Power supply for this in kit form with case is £15,Order Ref: 15P16, or in larger case to house tube as well£18, Order Ref: 18P2. The larger unit, made up, tested andready to use, complete with laser tube £69, Order Ref: 69P1.12v Bohm speaker, only £1.50 and waterproof.Solar Charger. Holds 4AA nicads and recharges these in 8hours, in very neat plastic case £6, Order Ref: 6P3.Ferrite Aerial Rod. 8" long x 3/8" diameter, made by Multard.Complete with two coils, 2 for £1, Order Ref: 832P.Air Spaced Trimmer Caps. 2-20pf, ideal for precisiontuning UHF circuits, 4 for £1, Order Ref: 818B.Modem Amstrad FM240 As new condition but customerreturn, so you may need to fault find, £6, Order Ref. 6P34.Amstrad Power Unit. 13.5V at 1.9A or 12V at 2A encasedand with leads and output plug, normal mains input £6,Order Ref: 6P23.80W Mains Transformer. Two available, good quality, bothwith normal primaries and upright mounting, one is 20V 4A,Order Ref: 3P106, the'other 40V 2A, Order Ref: 3P107, only£3 each.Project Box. Size approx. 8"x4"x41/2" metal, sprayed grey,louvred ends for ventilation otherwise undrilled. Made forGPO so best quality, only £3 each, Order Ref: 3P74.Sentinel Component Board Amongst hundred of otherparts, this has 15 ICs, all plug in so do not need soldering.Cost well over £100, yours for £4, Order Ref. 4P67.Sinclair 9V 2.1A Power Supply Made to operate the 138KSpectrum Plus 2, cased with input and output leads.Originally listed at around £15, are brand new, our price isonly £3, Order Ref. 3P151.Experimenting with Valves. Don't spend a fortune on amains transformer, we can supply one with standard mainsinput and secs. of 250-0-250V at 75mA and 6.3V at 3A, £5,Order Ref: 5P167.15W 8 Ohm 8" Speaker & 3" Tweeter. Made for adiscontinued high quality music centre, gives real hi-fi andonly £4 per pair, Order Ref: 4P57.Water Pump. Very powerful, mains operated, £10, OrderRef: 10P74.0-1mA Full Vision Panel Meter. 23/4" square, scaled 0-100but scale easily removed for re -writing, ft each, Order Ref:756.VU Meter. Illuminate this from behind becomes on/offindicator as well, 11/2" square, 75 each, Order Ret: 366.Amstrad Keyboard Model KB5 This is a most comprehen-sive keyboard, having over 100 keys including, of course,full numerical and qwerty. Brand new, still in maker'spacking, £5, Order Ref. 5P202.1 RPM Motor. This is only 2W so will not cost much to run.Speed is ideal for revolving mirrors or lights. £2, Order Ref.2P328.Unusual Solenoid. Solenoids normally have to be energi-sed to pull in and hold the core, this is a disadvantage wherethe appliance is left on for most of the time. We now havemagnetic solenoids which hold the core until a voltage isapplied to release it. £2, Order Ref. 2P327.Mains Filter. Resin impregnated, nicely cased, pcb mount-ing. £2, Order Ref. 2P315.200VA Mains Transformer. Secondary voltages 8v -0-8v.So you could have 16v at 12A or 8v at 25A. Could be idealfor car starter charger, soil heating, spot welding, carbon rodwelding or driving high powered amplifiers etc. £15, OrderRef. 15P51.Prices include VAT. Send cheque/postal order or ringand quote credit card number. Add £3 post and packing.Orders over £25 post free.
M&B ELECTRICALSUPPLIES LTD
Pilgrim Works (Dept. WW),Stairbridge Lane, Bolney,
Sussex RH17 5PATelephone (0444) 881965 -
phone for FaxCallers to 12 Boundary Road,
Hove, Sussex
590
CIRCLE NO. 126 ON REPLY CARD
July 1994 ELECTRONICS WORLD+WIRELESS WORLD
NEW PRODUCTS CLASSIFIED
ACTIVEAsics143MHz PLD. The Cypress CY7C371is a complex programmable logicdevice with a 143MHz performanceand better than 8.5ns propagationdelay, the device offering bothelectrical erasure and reprogramming.It has a programmable interconnectmatrix and product term matrix, whichallows product terms to be routed tomacrocells individually without'stranding' adjacent macrocells orintroducing extra delay. Pinassignments are selectable so thatlogic changes do not affect the pinout.Ambar Components Ltd. Tel., 0844261144; fax, 0844 261789.
10,000 -gate FPGA. Already availablefrom Actel are the 1500 -gate A1415Aand the 4000 -gate A1440A field -programmable gate arrays; the10,000 -gate A14100A to be releasedin June. These devices extend theACT 3 range which includes 2500 -gate and 6000 -gate types. Newfeatures are 167MHz counters anddata paths and 7.5ns clock -to -outdelays. Actel Europe Ltd. Tel., 025629209; fax, 0256 55420.
A -to -D and D -to -AconvertersLowest -power A -to -D. Harris'sHI5813 is a 3-6V single -supply, 12 -bitconverter that uses only 9mWmaximum at full speed over theindustrial temperature range. Itincludes an on -chip track -and -holdamplifier and the input bandwidth is1MHz; conversion time is 25ps, giving40ksample/s. Total error, due to non -linearity, offsets and full-scale errorbefore calibration, is 9LSB. HarrisSemiconductor UK. Tel., 0276686886; fax, 0276 682323.
Discrete active devices9GHz transistor. With a typical fT of9GHz at 25mA, Zetex's ZGF300F isintended for use in cellulartelephones, CATV and radionetworking at frequencies over2.5GHz. Noise figure at 10mA and1GHz is 1.9dB and gain at 2GHz is7dB and 12dB at 1GHz; unilateralpower gain at 1GHz is 13dB.Collector/base capacitance is lessthan 0.5pF. Zetex plc. Tel., 061-6275105; fax, 061-627 5467.
Low -noise hemt. Low -noise InGaAshigh electron -mobility transistors fromMitsubishi, the MGF4710A are meantfor C -band first and second stage
LNB use in the 3.7-4.2GHz band andin K band amplifiers. They areintended for microstrip circuitry,providing a 1dB noise figure and 9dBgain at 12GHz. Gate/drain andgate/source voltage is -4V with adrain current of 60mA. MitsubishiElectric UK Ltd. Tel., 0707 276100;fax, 0707 278692.
Schottky barrier diode. The BAS85silicon Schottky barrier diode by ITThas a reverse breakdown voltage of30V and forward voltages of 0.24V at0.1mA to 0.8V at 100mA. Leakage is2pA at 25V reverse voltage andreverse recovery time is 5ns. Powerdissipation at 65°C is 250mW. ITTSemiconductors. Tel., 0932 336116;fax, 0932 33148
High -voltage mosfet. Zetex'sZVN4424 is a 240V, medium -powermosfet with a typical on resistance of40 and a threshold voltage of 1.8Vmaximum, so that it interfaces directlywith low -power logic. The deviceswitches up to 260mA continuous or1A in pulses, rise and fall times being5ns and 16ns at 250mA drain current.Input capacitance is around 110pF.Zetex plc. Tel., 061-627 5105; fax,061-627 5467.
Bipolar switches. Temic Telefunkenhas a new series of high blocking -capability bipolar switchingtransistors, BUD 87/620 and TD13003/13005, in Dpaks. Typicalapplication is in the contactlessswitching of electronic fluorescentlamp ballasts. All types switch 30Wloads and block up to 1 kV at 4Acollector currents. Operating
Stereo/dual sound processorsPhilips is offering three Newsound processors fortelevision receivers and videorecorders which have or -chipdigital pHs, synchroncusdetectors and digitalintegrators to give relbbleidentification of the stereo/dualsound pilot modulation.TDA9840 provides leveladjustment, stereo ba antecontrol and signal -sourceswitching for I2C-bus-controlled tvs and vas,TDA9845 gives simple logiccontrol of signal switching inlow-cost VCRs and TDA3847complex main/auxiliary Inputswitching for equipment withScart connectors. PhilipsSemiconductors (Eindhoven).Tel., 01031 40 722091; fax,01031 40 724825.
frequency is up to 100kHz. TD13005is also made with a free -wheelingdiode. Tem c Telefunken GmbH. Tel.,01049 7131 672747; fax, 01049 7131993342.
Linear integratedcircuitsMultiplexed-i/p video amplifiers.Two or four input multiplexed videoamplifiers in the EL4400 series byElantec provide 8ns switching and70dB channel isolation. Bandwidth atgains of 1 or 2 is 80MHz with gainerror of 0.2% even with low -impedance loads. Two of the devicesare two -input types with commoninverting inputs, two have four inputswith all four taken to a commonfeedback line and a further two arefour -input versions with positive andnegative inputs separate.Microelectronics Technology Ltd. Tel.,9844 278781; fax, 0844 278746.
Precision dual op -amp. Micro Callhas a dual op -amp which draws amaximum supply current of 20pA peramplifier at 5V. Features include aninput offset voltage of 1801.Nmaximum with 0.6pV/°C drift andinput offset current 350pA maximum.Peak -to -peak current noise is 1.5pAand voltage noise 0.9pVpk-pk from0.1Hz to 10Hz. Input range goes300mV below ground and the npnoutput swings to within a few mV ofground, sinking current without put-down resistors. Micro Call Ltd. Tel.,0844 261939; fax, 0844 261678.
500MHz mixer. AD comes to the RFarea with a mixer giving low distortion(third -order intercept +23dBm) andonly -10dBm local oscillator powerover the 500MHz bandwidth. Local -oscillator driver and low -noise outputamplifier are integrated with the mixercore in one 20 -pin PLCC. RF, IF andLO ports can all be dc -coupled whenthe voltage rail is ±5V or ac -coupledwhen 9V is used. IF output is eithersingle -ended or differential and cancome directly from the mixer. AnalogDevices Ltd. Tel, 0932 253320; fax,0932 247401.
Low -voltage mosfets. Sificonixannounces three more Little Footsurface -mounted mosfets: Si9925DY,Si9434DY and Si9928DY with onresistances of 40-80m0 and 12Vbreakdown, being designed for 3.3Vor 5V logic. The 9925 is for use inlithium-ior battery psus, in which the2.5V end -of -charge voltage ismatched with the mosfet's 80m0resistance at 2.5V gate voltage.Complementary 9928s in the outputstage of a voltage converter provide
Crystal oscillator. Using anSC -cut crystal with a heaterdirectly depositec on the crystal,the Sematron DXCO providesthe performance 3f an ovenoscillator with small size, lowweight less than 1W of power.Frequency coverage is 7-20MHzat a frequency stability of 2x10 1over -20°C to 70°C. Ageing is1x10-7 per year. The directheating gives rapid warm-up,low phase noise and relativeinvulnerability to vibrationcompared with some ovenoscillators that are larger in size.Sematron UK Ltd. Tel., 0734819970; fax, 0734 819786.
60m0 and 130mft (p -channel); andfor load switching, the 9434 gives40m0 on resistance at 4.5V and 1pAdrain/source leakage. Siliconix/TemicMarketing. Tel., 0344 485757; fax,0344 427371.
Analogue switches. Maxim'sMAX391/2/3 are quad single -throw,single -pole analogue switches, thosein the 391 being normally closed, inthe 393 normally open and in the 393two of each. All are for 5V or ±5Vworking and offer 250 on resistance,<20 matching between channels andwithin 30 flatness over the signalrange. Since the switches are of thebreak -before -make characteristic,they are suitable for multiplexers andmultiple outputs can be connectedwith no risk of interchannel shorting.Maxim Integrated Products UK Ltd.Tel., 0734 845255; fax, 0734 845240.
GaAs fet bias generator.MAX850/1/2/3 from Maxim supply afixed -4.1V or variable output at 5mAand under 2mVpk-pk ripple to biasGaAs fet RF power amplifiers incellular telephones and othercommunications equipment. Theytake up less than 0.1in2 of boardspace and need only three 1pF
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 591
NEW PRODUCTS CLASSIFIED
Please quote "Electronics World + Wireless World" when seeking further information
capacitors and one 10pF one. Supplyrange is 4.5-10y at 3mA or 1pAquiescent. MAX852 takes anoscillator signal to allowsynchronisation in noise -sensitivesystems. Maxim Integrated ProductsUK Ltd. Tel., 0734 845255; fax, 0734845240.
RF video drivers. Motorola'sCR2428 and CR3428 are hybrid RFamplifiers for use in high and veryhigh resolution CRT monitors.Bandwidth of the 2428/3428 is130/115MHz and rise and fall times2.5/2.7ns. Motorola Inc. Tel., 0908614614; fax, 0908 618650.
Voltage regulators. As a secondsource to Linear Technology,Semtech offers a series of lowdropout regulators with outputcurrents of 1.5A (L1086), 3A (L1085),5A (L1084) and 7.5A (L1083) at fixedvoltages of 3.3V, 5V and 12V, oneversion having adjustable outputdown to 1.2V. Regulation andstabilisation are 0.01% and 0.015%.Current limiting and thermal shutdownare provided. Semtech Ltd. Tel., 0592773520; fax, 0592 774781.
Logic building blocks24 -bit video mixer. Raytheon'sTMC22080 video mixer is designed tomix graphics and live video, forlapping between two video sourcesand for fading and wiping. It mixes atspeeds of up to 26 millionpixels/second and is controlled by a9 -bit alpha -channel input. The devicesupports 24 -bit RGB, YCbCr444, 16 -bit YCbCr422 component videosources and the A channel alsoaccepts 8 -bit colour -indexed pixeldata which addresses the threebypassable 256 by 8 -bit colour look-up tables with a 15 -colour overlaypalette. Interpolation filters and thecolour space conversion matrices areused when different pixel formats arein use. TMC22080 is microprocessor -
3.3V programmable logic. AMD hasits first 3.3V PLD family. PALLV16V8-10 is a low -voltage cmos device thatinterfaces with 3.3V and 5V logic,having a maximum 1Ons delay andtaking an 83MHz clock.PALLV22V10Z-25 takes 15pAstandby current and has 10macrocells programmable asregistered or combinatorial and activehigh or low. MACHLV210-15/20 is thefirst 3.3V MACH device, with 1800gates and 64 macrocells, and handlesa 50MHz clock. All are supported bythe Palasm design software.Advanced Micro Devices (UK) Ltd.Tel., 0483 740440; fax, 0483 756196.
Active SCSI terminator. Claimed tobe the industry's lowest -capacitance,9 -line SCSI active terminator,Unitrode's UC5613 has only 3pFchannel capacitance, providesimproved impedance matching andeliminates transmission problemsfound in some other passive andactive terminators. A special featuredisconnects all lines and disables the400mA sink/source regulator, thedevice drawing less than 10nA in thissleep mode and all channels being ina high -impedance state. Unitrode(UK) Ltd. Tel., 081 318 1431; fax, 081318 2549.
Microprocessors andcontrollersBigger-rom micros. Hitachi'sH8/3837 and H*/3836 8 -bitmicrocontrollers are 2.7V devicestaking 0.5mA in an intermediatespeed mode and having 40Kbyte(3837) or 48Kbyte of program rom.Both have an lcd controller/driver for160 segments and other on -chipfeatures include 2Kbyte of ram, fivetimers, a 12 -channel 8 -bit a -to -dconverter and three serial interface
600V mosfet driver. IR's IR2155 600V chip has everything needed tocontrol and drive power mosfets in electronic lighting ballast, with aclean waveform that virtually eliminates mosfet losses. Parts countis reduced by virtue of the high -side driver dispensing withtransformer gate drives; by the on -chip oscillator; and by generatingthe IC supply voltage internally. Internal 1.2ps dead time iscompatible with dv/dt snubbed circuits to 100kHz. Polar Electronics.Tel., 0525 377093; fax, 0525 378367.
DJ D,akI I hx,41Jr 715'
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channels. Minimum instruction time is4ps. Hitachi Europe Ltd. Tel., 0628585000; fax, 0628 585200.
133MHz Orion 64 -but R4600. The133MHz version of IDT's Orion R4600risc processor is claimed to be thefirst offering the requiredperformance, dynamic powermanagement and low price forWindows NT and high -end embeddedapplications. IDT says it performsbetter than the Pentium at 486DXprices. It is a full 64 -bitimplementation of the MIPS IIIinstruction set architecture in theearlier R4000PC and R4400PCdevices but with a five -stage pipelineto reduce stalls and therefore improveperformance. There is also the cache:1616Kbyte for instructions and1616Kbyte for data. Integrated DeviceTechnology. Tel., 0372 363734; fax,0372 378851.
Comms processor. Ruby is anadvanced communications processorchip from VLSI, which uses an ARM32 -bit risc processor core with acomprehensive set of commsperipherals, power management and2.7V -5.5V operation. It contains aPCMCIA/ISA interface supportingdirect memory, attribute space andcomms port modes, a uart, serialcomms controller, PIO and a serialport controller. The ASRM FSB coregives up to 20Mips. Sleep andstopped modes are provided, in whichpower dissipation is 3mW and200pW. VLSI Technology Ltd. Tel.,0908 667595; fax, 0908 670027.
Mixed -signal ICsLan chipset. Regatta 100 local areanetwork chipset by AT&T allows theaddition of multimedia services suchas video and sound to Ethernet orToken -Ring wiring at 100Mb/s. Theset conforms to IEEE 802.12 100VG-AnyLAN, the first siliconimplementation to do so. Its highbandwidth is achieved by means of anew quartet signalling scheme usingfour pairs of UTP wiring. AT&TMicroelectronics. Tel., 0732 742999;fax, 0732 741221.
RDS frequency synthesiser. Philips'TSA6060 low -power PLL frequencysynthesiser IC for AM and fm isintended for use in rds car radios,providing on -chip loop amplifiers and2ms frequency locking, although theplls can be switched between highgain for fast lock and lower gain forfrequency stability. The only externalsneeded are two passive feedbacknetworks for the loop time constant.Philips Semiconductors (Eindhoven).Tel., 01031 40 722091; fax, 01031 40724825.
Optical devicesSingle -chip camera. A cmos single -chip camera by WL, the 1070, isclaimed to be the first commerciallyavailable image sensor with a built-ina -to -d converter. It integrates a 160by 120 pixel array with all theelectronics needed for an auto -exposure camera in a windowed 44 -
pin PQFP. Current consumption is30mA and there is to be a range oflenses with differing fields of view.VLSI Vision Ltd. Tel., 031-539 7111;fax, 031-539 7140.
Photo -IC coupler. Toshiba's TLP251photocoupler drives low -power IGBTsdirectly, maintaining gate isolation. AGaAIA5 led is the light source, a p -nphotodiode, a high-speed, high -gainamplifier and output circuitry,comprising the photo -IC which is usedas the detector. Operating voltage is35V and an 8mA input produces apeak output of 100mA with a 1pspropagation delay. ToshibaElectronics (UK) Ltd. Tel., 0276694600; fax, 0276 691583.
OscillatorsLF crystal oscillators. Crystaloscillators from GPS work atfrequencies down to 1.5kHz. TheQC6109 oscillator will drive loads ofup to 50pF (HCMOS) and theQC6110 up to 10 TTL gates, bothhaving rise and fall times of 1Ons for6-30MHz versions or 15ns for the Iftypes. Start-up time is 4ms. Twotemperature ranges are available:-40°C to 85°C with a frequencytolerance of ±5Oppm; and -55°C to125°C with a tolerance of ±100ppm.GEC Plessey Semiconductors Ltd.Tel., 0793 518510; fax, 0793 518582.
Power semiconductorsHorizontal crt deflection. Powerdissipation in horizontal deflectioncircuitry is reduced by short switchingtimes and low power loss of PhilipsBU2522AF and BU2527AF n -p -npower transistors. These are intendedfor 14-17in high -resolution monitorsscanning at up to 64kHz. Both are1500V devices operating at 5-7A (DCpeak ratings 10A and 25A for the2522 and 12A/30 for the 2527). Whenswitching 6A in a 64kHz circuit,maximum charge storage time is 2ps,collector turn-off times being 0.25psand 0.2ps. Philips Semiconductors(Eindhoven). Tel., 01031 40 722091;fax, 01031 40 724825.
PASSIVEPassive componentsFeed -through capacitors. Re -engineering of Cambion's 560-3265series of feed -through capacitors hastrebled the range of values to 220pF-1500pF in ±20% tolerance. They arescrew -mounted and plated in 0.55pmgold, although other styles andplatings can be made. Insulationresistance is over 105M11 anddissipation factor less than 2% at1kHz. Interconnection Products Ltd.Tel., 0433 621555; fax, 0433 621290.
Wirewound resistors. Neohm CWP,CWU and CWL ranges of high -powerwirewounds, in moulded chippackaging, use temperature sensingto achieve standard temperaturecoefficients down to 1-3ppm/°C. TypeCWP are down to 2.4 by 3.2mm in
592 ELECTRONICS WORLD + WIRELESS WORLD July 1994
NEW PRODUCTS CLASSIFIED
size and offer resistance ranges of0.112-1.4k12, 0.111-51(12, 0.111-18k12and 0.112-45k11 in tolerances of±0.1% to ±5% and 0.75W to 4.5Wpower ratings. CWU resistors havestandard tolerance down to 0.005% at0.5W, while CWLs offer low values of0.00512-0.512 at less than 7nHinductance. Surtech InterconnectionLtd. Tel., 0256 51221; fax, 0256471180.
Transient suppressor. Giving board -level ESD protection in a 1.3mm2package, the AVX Transguard 0603version transient voltage suppressorclamps at 10\/, 15.5V, 30V or 40V.Energy rating is 0.1j and peakcurrents up to 30A in eight 20pspulses can be accepted, responsetime meeting the European EMCDirective. AVX Ltd. Tel., 0252336868; fax, 0252 346643.
Transformers. Electrospeed hasadded new isolating transformers byRoxburgh and pulse types fromNewport to its catalogue. Roxburgh'sTT81 range are of split -bobbinconstruction with a metal -shroudedcoil in ratings of 25-1000VA withinputs from 0 to 415V. Newport's 766series are ferrite -cored and meant fordigital and data processing use, whilethe 1600 series are data isolators with5ps pulse width capability at high rep.rates. Electrospeed. Tel., 0703644555; fax, 0703 610282.
Ceramic resonators. Fuji's newceramic resonators now operate up to12MHz, with an initial tolerance of±0.3% or ±0.5%, depending onfrequency, anti -resonant resistancebeing over 50k12. Stability is ±0.3%from -20°C to 80°C and theresonators age at ±0.5% over 10years. They come in plastic cases orepoxy -encapsulated versions from190kHz to 830kHz, while higher -frequency types are in an epoxydipped finish. Advanced CrystalTechnology. Tel., 0635 528520; fax,0635 528443.
Chip inductors. Three chip inductorsby Murata are meant for EMI filteringin surface -mounted power suppliesand DC converters at currents up to6A. At 100MHz, the 1A BLM41P01has a typical impedance of 8012, the3A BLM41P02 7012 and the 6ABLM41P03 6011. At 1GHz, all threeretain an impedance above 700.Murata Electronics (UK) Ltd. Tel.,0252 811666; fax, 0252 811777.
Sealed rotary switch. Wasp's newDR 12 -position rotary switches aresealed at both ends and can be flow -soldered. The 12.5mm switches havestandard contact arrangements of 1,2, 3 and 4 -pole bcd and bcdcomplement, gold -flashed silvercontacts being rated at 5V dc and10V ac and 2A. The spindle is sealedto a maximum leakage of 1m1/h.Wessex Advanced SwitchingProducts Ltd. Tel., 0705 453711; fax,0705 473918.
Dielectric filter. AVX announces thePDFC series of dielectric filters meantfor use in telecomms, particularly in
Please quote "Electronics World + Wireless World" when seeking further information
Toroidal transformers. X. new series of toroidal mains transformersnow being made by Willesden covers the 30VA-2000VA powerrange. Primaries are ' 1C/120V in parallel or 220/240V in series,secondaries being connected in series or parallel to obtain therequired voltage. Flerib e leads or tags are provided and insulationis Class B; finish is Melinex. Willesden Transformer Co. Ltd. Tel.,0920 821385; fax, 0923 f 22795.
the DECT sector. Frequency range is1.8-2GHz, insertion loss 3dB and, forcompatibility with the newestequipment, size is 6.5 by 5.5 by 3mm.Filters to provide lower insertion lossand improved stop -band attenuationare available to order. AVX Ltd. Tel.,0252 336868; fax, 0252 346643.
DisplaysMulticolour leds. Dialight 552-3511is a three -leaded led circuit -boardindicator, offering true multicolouroperation with less drive circuitry thanis needed for the two -lead type. Ituses two GaP led chips in a 5mmpackage, producing red, green,amber and a range of colours inbetween red and green. The red ledprovides 5mcd at 10mA at 2.1V andthe green one 8mcd at 10mA and2.3V, the drive coming from standardICs with current -limiting resistors.Dialight. Tel., 0638 665161; fax, 0638660718.
FiltersSwitched -capacitor filter. LinearTechnology's LTC1066 14 -bit dcaccurate, clock -tunable low-pass filteris meant particularly for dataacquisition at up to 14 -bit accuracyand rates up to 200kHz. To form an8th -order elliptic or linear low-passfilter, an external RC circuit is neededfor dc accurate working, but no activecomponents. Input/output impedanceis 500M0./0.112 and the outputhandles 40mA. For frequencies up to0.7f,o, pass -band ripple is ±0.15dB,gain at fcc, is -1dB and stop -bandattenuation is 80dB at 2.36. MicroCall Ltd. Tel., 0844 261939; fax, 0844261678.
InstrumentationProgrammable functions. TTI'sTG1304 programmable functiongenerator is digitally controlled,generating complex waveshapes atfrequencies up to 13MHz and using
digital measure -and -correcttechniques to achieve frequencystability to within 0.01%.Theinstrument produces, as well as theusual sine, square and triangularshapes, unpolar pulses and dc levels;variable -symmetry start/stop phaseallows more exotic shapes. fm andsweep control come from an auxiliary5mHz-50kHz generator, as do AM,linear vca and log VCA. ThurlbyThandar Instruments Ltd. Tel., 0480412451; fax, 0480 450409.
Level measurement. LM311, whichis a level measuring test set fromSeaward for voice band telecomms, isavailable in an improved version.There is now a multi -frequency,precise -output oscillator with variablefrequency and level and a level metermeasuring frequency and level indBm. LM311 also measuresresistance and voltage and has artaudio output and smoothing filter.Seaward Electronic Ltd. Tel., 091 5863511; fax, 091 586 0227.
LiteratureAmplicon. Amplicon Liveline's 1994catalogue is now available. Additionsto the range of products includeautomatic data switches, optical -fibrelinks/repeaters, optical RS232modems, Combios for Windows, 3.3Vdc -to -dc converters, more DAP dataacquisition boards and multifunctiondpms. There is a glossary of technicalterms. Arrplicon Liveline Ltd. Tel.,0800 525 335 (free); fax, 0273570215.
Data access arrangements. AT&TMicroelec:ronics has a free 12 -pagebooklet showing a variety of dataaccess arrangements. These areused to connect voice or datasignalling circuits to the telephone linein modems, answering machines, etc.It is illustrated with circuit and blockdiagrains. with information on usingsolid-state relays to implement on/offhook control, ring detection and loop -
current sensing. AT&TMicroelectronics. Tel., 0732 742999;fax, 0732 741221.
Power supplies. Astec StandardPower's short catalogue describes arange of products from 4.5W dc -to -dcconverters to switching supplies up tothe kW range. It also details a further -information service, by means ofwhich engineers receive data sheetson their fax, anywhere in the world,simply by dialling a number andproduct code. Astec Standard PowerEurope. Tel., 0384 440044; fax, 0384440777.
Ceramic EMI filters. Miniatureceramic filters in the form of C, LL,LC, pi and T circuits are described byMPE in a new brochure. Thepublication contains applicationinformation and there is an EMCHelpline on 051 548 6525. MPE Ltd.Tel., 098 122481; fax. 098 122223.
RF semiconductors. Toshiba's newrange of semiconductors for rf work isdescribed in a new catalogue andcomprises single and dual gatemosfets, jfets, bipolar transistors, pindiodes, Schottky diodes and tuningVaricaps. Other devices integrate hfdevices and passive components ona single chip. Toshiba Electronics(UK) Ltd. Tel., 0276 694600; fax,0276 691583.
Lithium batteries. A brochure fromBatteryhigh-energy lithium/thionyl chloridebatteries; electrochemical systems,cell construction and characteristics.Battery Engineering Inc. Tel., (USA)0101 617 361-7555; fax, 0101 617361-1835.
SMD selection guide. A completerange of surface -mounted devices forpower control is described in theInternational Rectifier short guide,including Hexfets, diodes, igbts andmos-gate driver ICs. InternationalRectifier. Tel., 0883 713215; fax,0883 714234.
Digital radio testing. 2050series signal generators byMarconi Instruments testmany of the world's emergingdigital radio systems withcomplex modulation. Digitaland vector modulation allowsreceiver testing on systemsincluding the new systemsfrom North America and theFar East, as well as theTerrestrial Flight TelephoneSystem (TFTS). This requiresthe generation of quaternaryamplitude modulation, phase -shift keying, broadband AMand spread -spectrum signals;with extra equipment, theinstrument can also generatePersonal Handiphone(Japanese) and DECT signals.Marconi Instruments Ltd. Tel.,0727 859292; fax, 0727 857481.
July 1 994 ELECTRONICS WORLD + WIRELESS WORLD 593
NEW PRODUCTS CLASSIFIED
Please quote "Electronics World + Wireless World" when seeking further information
Power supplies20W dc -to -dc converter. SemtechMP9600 series 20W voltageconverters produce pwm-regulatedsingle or dual outputs of 5, 12, 15, 24,t5, t12, t15 and t24V to within t5%and at a typical efficiency of 70%. Themodules measure 0.83in high forboard mounting. Inputs of 12, 15, 24and 48V dc can be accepted andoutput currents of 800mA to 4A areavailable. Regulation and stabilisationare t5% and ripple 200mVpk-pk.Semtech Ltd. Tel., 0592 773520; fax,0592 774781.
200W dc -to -dc converters.Veropower 200 series voltageconverters by BICC-Vero are 200Wtypes with input ranges of 40-60V, 36-75V and 200-400V DC, giving at theoutputs 3.3V, 5V, 12V, 15V, 24V and48V, depending on the version. The200-400V type is powered by rectifiedand filtered mains and can beconfigured to accommodate complexsupply needs. A 700kHz switchingfrequency gives conversionefficiencies of over 80% andregulation and stabilisation of betterthan 0.1%. BICC-Vero ElectronicsLtd. Tel., 0489 780078; fax, 0703264159.
Wide -range dc -to -dc converter.Operating from a variety of inputvoltages, the Calex LV dc -to -dcconverters provide a 6W output atfixed voltages of 5V, 12V and 15Vfrom 4.8-12V input. Ground loops areeliminated by 700V dc isolation andnoise levels are less than 50mVpk-pkover 20MHz - less with a specifiedexternal circuit. Regulation andstabilisation are both 0.1%. CalexElectronics Ltd. Tel., 0525 373178;fax, 0525 851319.
3.3V dc -to -dc converters. To caterfor the increasing numbers of low -voltage ICs, Amplicon has introduceda series of dc -to -dc converters, the Z
series, providing a regulated 3.3Voutput from 9-18V, 18-36V or 36-72Vinputs at 16W. Features include 500VDC input/output isolation, 78%efficiency, continuous short-circuitprotection and 1%pk-pk ripple andnoise. All the devices have remoteon/off and an input pi filter. AmpliconLiveline Ltd. Tel., 0800 525 335 (free);fax, 0273 570215.
Radio communicationsproductsMiniature mixer. ZP-11A is a mixerby Mini -Circuits Europe, accepting1400-1900MHz rf and local oscillatorinput and producing a 40-500MHz IF.Conversion loss of 4.5dB is flat towithin 0.6dB and compression 1dB,1dBm typical. Mini -Circuits Europe.Tel., 0252 835094; fax, 0252 837010.
Power splitter. Mini -Circuits Europeoffers the SCP-4-4 surface -mounted,four-way power splitter for telecomms,radio and remote -control application.Bandwidth is 800-1000MHz andfeatures include 24dB isolation, 0.9dBinsertion loss, input VSWR 1.3:1 and1.15:1 at the output. Power ratingsare 0.5W input and 0.125W internaldissipation. Mini -Circuits Europe. Tel.,0252 835094; fax, 0252 837010.
Microwave resonator materials.New electroceramic materials byMorgan Matroc are intended toreplace metals used in the
Dielectric constants from 19 to 90allow selection of the ideal size ofresonator to balance ease ofconstruction against miniaturisation.Barium-zinc-tantalate has a Q of11000 and is meant for puckresonators from 5GHz to 26GHz. A10GHz puck using material with adielectric constant of 29.5, forexample, measures 6mm in diameterand 3mm thick. Barium -neodymiumhas a constant of 87 for pucks in the400MHz-8GHz range and
Bespoke power supplies. Gresham XG and XF series powersupplies have one 5V output at 60A or 70A and up to three otherregulated, adjustable and isolated outputs as additional modules, inany combination. These provide 2-6V at 15A, 5-15V at 12A or 15-36Vat 7A. Stabilisation is t0.2% over the input range and regulation0.2%, zero to full load. Outputs are filtered to VDE and FCC Class Aand optionally to Class B. Remote inhibit and sense are providedand the units are fully thermally, voltage and current protected.Gresham Power Electronics Ltd. Tel., 0722 413060; fax, 0722 413034.
Programmer/emulator. Stag announces its new Orbit 32 battery-
powered, hand-held programmer, which it claims is the smalleststand-alone portable programmer available. It will program epromsto 8Mbit, eepron-,s and flash devices. Some cmos proms and serialeeproms in 0.3in and 0.6in dips also fit the 32 -pin wide -blade zifsocket. Orbit 32 has a high-speed emulator to allow connection tothe target, so that there is no need to program devices until code isoptimised. All device libraries are resident in non-volatile memory.Stag Programmers Ltd. Tel., 0707 332148; fax, 0707 371503.
magnesium-calcium-titanate at 19.5 isfor coaxial resonators from 2GHz to5GHz. Morgan Matroc Ltd. Tel., 0978810456; fax, 0978 824303.
Transducers andsensorsInductive sensors. Colvern's Type94 range of non -contact sensors areinductive types intended for rotation
COMPUTERComputer board -levelproductsPC -based waveforms generator.AWG7223PC is a 50MHz arbitrarywaveform generator by TTI that plugsinto most ISA and EISA extension busslots. Two output channels generateseparate waveforms of up to 32Klength, but the memory can bearranged to to produce waveforms upto 100 gigapoints in length. Resolutionof the nine different standardwaveforms (sine, triangle, sawtooth,square, pulse, sine x/x, Gaussianpulse, exponential rise/decay pulse,pseudo -random noise and DC) is 12bits from 100mV to 12Vpk-pk into500, each channel having five filterscutting off at frequencies between50Hz and 10MHz. Software includes ados driver and Borland C++ libraryand optional WaveCAD. ThurlbyThandar Instruments Ltd. Tel., 0480412451; fax, 0480 450409.
EISA 488.2 controller. An IEEE 488.2interface board by National for EISAcomputers, the EISA-GPIB uses theTNT4882C controller chip and HS488protocol for transfer rates up to8Mbyte/s for both read and write. Itincludes NI -488.2 dos and Windowssoftware that is compatible with
speed measurement and positionsensing for engine management,automatic braking, motor speed andignition timing. In 13 standard andseveral specially designed forms, thedevices consist of a magnet andtoothed wheel varying the pathreluctance and therefore producing asignal in the coil. Zero -crossingdetection is incorporated. Colvern Ltd.Tel., 0708 762222; fax, 0708 762981.
Lan View, LabWindows andLabWindows/CVI. Hardware baseaddress, interrupt and dma settingsare all software -configured; nojumpers or switches are needed.National Instruments UK. Tel., 0635523545; fax, 0635 523154.
50MHz C40 products. LSI is the firstsupplier to use the Texas Instruments50MHz C40 digital signal processor inproduction equipment. Modules usingthe C40 include memory, processorand i/o units, with sram and dram -equipped modules and application -specific TIM -40s. As an example,LSI's MDC4OT is the first to use twoC40s and allows PC or VME boardsoffering eight processors giving400Mflops and 2.2Gflops; this isclaimed to be the fastest DSP board inthe world. Loughborough SoundImages Ltd. Tel., 0509 231843; fax,0509 262433.
Computer systemsIntelDX4 motherboard. TheSV2/GX4 PC motherboard from SPDuses the new 100MHz IntelDX4processor and power -managementfeatures. On the Norton SI V6 index,the IntelDX4 shows a 50% gain inperformance over its 66MHz
594 ELECTRON CS WORLD + WIRELESS WORLD July 1994
NEW PRODUCTS CLASSIFIED Field Electric Ltd.
predecessor, the 486DX2. There areseven VL and ISA bus slots on theboard, which has 256Kbyte of cache asstandard, expandable to 1Mbyte, eight72 -pin simm slots allowing 1Mbyte to64Mbyte main system memoryexpansion. As well as the DX4, the zifprocessor socket accepts 486DX2, DXand SX devices and 487SX, Intel 486and Pentium Overdrive chips. SpecialProducts Distribution Ltd. Tel., 0420563588; fax, 0420 562206.
Blue Lightning motherboards. BlueMicro has available PC motherboardsbased on Blue Lightning processors.First to appear are Cobalt Baby ATboards, which use the 75MHz clock -tripled version, 100MHz types soonbeing available. There is a 16K cpucache and up to 512K external write -back cache can be fitted, four 72 -pinsimms allowing the installation of up to64Mb of dram. The board has a mathsco -processor and a local -bus IDEdriver handles two hard disks; i/oincludes two serial ports, a bi-directional parallel port and support fortwo floppy drives. Blue MicroElectronics. Tel., 0604 603310; fax,0604 603320.
Tough PC. For the type of workplacewhere even a rack -mounted pc is notwell enough protected and in whichemc/rfi needs to be avoided, the BlueChip ICON PC range meets EN55022for interference radiation and mainsterminal voltage, and IEC 801-3 forimmunity to EM interference. Thelockableplated steel and is thereby protectedagainst liquids, dust and, the companysays, collisions. A 14 -slot PC ATbackplane is used that leaves at least13 slots free, and processors up toP24 Pentium overdrive with local busvideo and VESA expansion areavailable. Four drive bays areincluded. Blue Chip Technology. Tel.,0244 520222; fax, 0244 531043.
Data communicationsModem kit. A modem designers' kit,the MDK from RCS, assists engineersto develop new modems andapplications quickly and easily. Itenables a single board layout tobecome the foundation for a family ofmodems, from 2400 -baud data -onlytypes to a 28-Kbaud V.Fast Classmodem with data, fax and voice. MDKis a serially configured modemcomplete with power supply, UKBABT-certified line interface, externalmicrophone and speaker, demosoftware, firmware and documentation.RCS Microsystems Ltd. Tel., 081 9792204; fax, 081 979 6910.
Development andevaluationBackground debugger. FlashDesigns' Universal MDS fordevelopers of embedded programshas what the company claim is theworld's smallest background debuggerat 100-150byte, which allows on -the -fly viewing and editing of allmicroprocessor registers, stack,memory and i/o ports. It is non -intrusive and lets the code run in realtime. Debuggers are available for
8031/51, 68HC11, H8, Z-80 and other4/8 -bit devices. Flash Designs Ltd.Tel. and fax, 0293 551229.
Computer peripheralsPCMCIA hard drive. Seagate'sST7050P is a 42.7Mb hard drive on aPCMCIA card for use in notebooks anddesktops, as well as data collection andinstrumentation systems. The driveincorporates the most popularoperating systems, including dos andWindows and is compatible with allsystems complying with PCMCIArelease 2.1 or higher. A software driveron disk is provided to ensuredrive/PCMCIA compatibility, but if thedrive is integrated under the 68 -pinATA standard, the drive uses s:andardAT Bios support without the softwaredriver support. There is a kit to ease thedevelopment of new equipmen: usingthe drive. Ambar Components Ltd. Tel.,0844 261144; fax, 0844 261789.
SoftwareTransient data capture. AdeptScientific announces the Flash/SP,which combines the Strawberry TreeFlash -12 Model 1 data-acquisotionboard with Dadisp, the data -analysissoftware package. A software driverdeveloped by Adept allows collecteddata to be taken directly to a Dadispworksheet for reduction and analysisat sampling rates up to 1Msample/s.The Flash/SP hardware driver moduleallows the Flash -12 board to becontrolled from Dadisp, the systemaccepting inputs between 350mV and
points (1 million points with an optionaldaughter board). Adept ScientificMicro Systems Ltd. Tel., 0462 480055;fax, 0462 480213.
Windows psu characterisation.Powerstar Characterisation Module isnow part of the Intepro (Schaffner)Windows -based system for therepetitive test of power supplies incharacterisation -a process normallynecessitating thousands ofmeasurements in a variety ofconditions and needing a number oftest instruments. The system's librarycontains over 100 standard tests andthe characterisation procedure is ableto measure many more test pointsthan in the manual case. Results canbe saved to disk and analysed by thePowerstar data analysis package.Scahffner EMC Ltd. Tel., 0734770070; fax, 0734 792969.
Windows pcb design. Pentica'sTangoPRO Schematic Lite and PCBLite form an entry-level version of itsTango circuit design and board layoutsoftware, giving an upgrade path fromits already workstation -class EDAsoftware to the highest specificationversion. These tolls run underWindows and offer features suitablefor most modern pcb designs.Schematic Lite has powerfulplacement and editing tools, keyboardshortcuts and instantaneous netlistgeneration, with over 20,000 librarycomponents. There intelligent wiresand buses and automatic junction andbus entry placing. PCB Lite includesCut/Copy/Paste and design errorindication. Pentica Systems Ltd. Tel.,0734 792101; fax, 0734 774081.
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JJ Inst XY Chart Recorder PL4Apple II GS and Apple colour monitor etc1.44Mb Laptop floppy disk doves new72 pin Simms for PS2 Compaq Dell etcParallel & Serial data switches up to 8 ways - Ring for detailsCompaq enhanced at keyboards (no cable)PC power supplies up to 600w, in stock - Prices start fromIBM 336.3 optical disk drive102 key AT enhanced keyboarc with PS2 type plug
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TEAC 5.25" BBC compatible F.D. dnves 340K/720K refurbs £8.95 C/P £3.7516 bit hard disk/F. disk controller card £12.00 C/P £3SCSI ha'd disk dnve s new CDC 344Mb £250.00 C/P mooNew anc Coxed 286/16 Motherboards, on board, hard and floppy cont. serial'para ports on board VGA etc.takes Simms £21.00 C/P £4.00Vuasa maintenance -free rechargeable batery NP7-12 12v 7.0,4131506.409.2 £12 C/P £4.50Rose die-cast box 17.505.607.8 new £4.25 C/P £1.80Sony r colour monitor KTX-900OUB 2403AC input with manual: inbuilt modern, needs to be converted toRGB etc £85 C/P £16.00386 5016 CPU (Intel) motherboard with Phonix Bios 6016 slots: 2x8 bit slot. Takes dram or Simm memory:310mm0215mm386 5015 CPU (Intel) motherboard without Bios etc £1425 incnc // PP
TEST AND MEASUREMENT EQUIPMENTHP portable p11.6 computer wth LCD screen, lmbMEM drawer. software drawer etc C75Tektronix standard arnpIrtude calibrator 047-502 C100.00Fluke 8010A digital muarneter C105EH microwave swept oscillator- model 574-1.7-12.4 GI-lz C450Systron (toner pulse gen, 103c C95
Compla senes 7000 digitizer tablet with Complotsenes 7033 ciagrtzer £600Hydrostatic stability indicator -ISM-400 P1 f:800Astec SA 30/1306, new and boxed PSU 240V acinput, 5V at 2a r 15v at 1 Eta - 15v at 8.3a C12.50HP 722IA plotter £150HP 1332 x -Y display wan opt3ns 215/300 315/570/631 £150Hughes model 639 scan conversion memory £300JJ Inst. PL4 recorder £75Sorensen SRL 40-12.0-40 VDC 0-126 metered115 VAC input £125KSM SCT-200 15 power supply 0-200V 0-15A
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£195Fluke 335A DC voltage standard differentialvoltmeter null detector £350Parnell 830/20 0.30VDC (a' 206 £250AEI Gauss meter FB22 form with probe £117HP 331A distortion analyzer £150FMI Rotary attenuate 27111 POAHP Fniquency meter X5326 POAHP 1740A 100MHZ osaloscope. Dual CHN wrth3rd CHN, tngger view etc £325AS Eltek switch mode vanable PSU 250vAC input.0.60vDC 25A max metered 17012.505" velhmanual £325Inmac 300VA Batt: Back up & fine condrbonermodel HO 300VA C95
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595
LETTERS
More distortion...I would like to thank EIV-I-WW andDouglas Self for an educational andinteresting series on distortion inpower amplifiers, articles which Ithoroughly enjoyed. I do not wish todetract from the series but wouldlike to propose an extra distortionmechanism to add to Mr Self's list:output (voltage) clipping throughinsufficient output current capabilitywhen driving loudspeakers insteadof resistors.
I know of only one set ofpublished measurements ofloudspeaker current, cited by BenDuncan in an EW+WW article sometime ago, and peaks of sixty ampswere recorded, using realloudspeakers and a music signal.
This may be an extreme case, but itmakes the point. Five minutes with acalculator is enough to conclude thatthe load impedance (as opposed toresistance) must have been far fromAO and highly reactive. The outputcurrent capability of Mr Self'sdesigns, class A and B, indicatesthat he (in common with many otheresteemed designers) may not haveaddressed this problem.
All of his published data on outputstage performance used a resistiveload - normally 812, sometimes 41- unless I am mistaken.
Resistive -load measurements andsimulations may be useful duringdevelopment, but I suggest that theyare all but irrelevant to the finalproduct, expected to drive
Military optionThe UK once had a strong electronics industry. It became involved inarmsequipment manufacture and is now virtually dead. How strange then thatyou should conclude: "It is... certain that we would not have an indigenouselectronics industry if it were not for military spending" (Comment, April).
I believe such involvement has been a bad thing, and would go so far asto say it is the single most significant factor contributing to the demise ofthe industry.
In the early 60s, when I started in electronics, the industry was strong,innovative and fiercely competitive. Domestic consumer choice was vast,and dozens of manufacturers produced radios, tape recorders, tvs andaudio. The industry was not without its faults but it was certainly wellplaced to take on any foreign competition. Ferranti, GEC, Marconi, Ultra,Decca, Pye, Cossor, Bush Murphy, Ekco, and many more I could mentionwere all supplied by an equally vigorous and diverse component supplyindustry: names such as Mullard, Mazda, Ferranti, Brimar being active inthe new and rapidly changing semiconductor field.
It is popular to blame the Japanese for the decline. But the early Japaneseimports were plain rubbish (I well remember fixing batches of Sony radiosand tape recorders before they could be offered for sale, a good 50% beingu/s some beyond economic repair).No don't blame the Japanese, they just moved in on a market that was
being vacated by its home industry, and vacated with unseemly haste attimes.
The reason for the decline was the MoD with its highly irresponsiblecost-plus contracting. A seemingly inexhaustible supply of taxpayers'money could be used to divert the industry into military equipment supply.
Now the industry is being ditched with the same cynicism with which itwas acquired. Unfortunately the companies that remain are no longercapable of operating in the domestic market. The management structuresencouraged by the military market actively works against the efficient re-organisation such a move would require.
Was it not General Eisenhower who warned "...beware the military-
industrial complex"? That a once proud UK electronics company shouldnow be reduced to using timed -out government ministers to set up sordidlittle deals with dubious foreign governments is wholly consistent withsuch an alliance. That the once proud Wireless World should endorse thoseactivities is just sad. Very very sad.RM BurfootAvon
I agree totally that military contracts have been disastrous for thecompetitiveness and diversity of the UK electronics industry. Howeverthey now represent our only legacy - diminished and sad though they maybe. Rebuild from them by all means. But don't ignore them.Frank Ogden
loudspeakers with a music signal.Many highly regarded amplifiers
can deliver more output current thanmight he expected if a resistive loadis assumed. I'm not just referring toAmerican monster amps here - theNAD3020 is a perfect example.Many thousands of consumers weresufficiently impressed to vote withtheir wallets.
Of course. I cannot prove that itshigh output current was responsiblefor its sound quality, but it's athought...
Finally, the gibes against thesubjective community which appearhere and there do not sit well withan otherwise professionalpresentation. They are unworthy ofMr Self, and highly subjective innature - and I would hate to have todescribe Mr Self as a subjectivist.
There is high -end equipment thatdoes not measure well (ref. part I).But if - and only if - it reproducesmusic better than competingequipment, then this is sufficient.The only purpose for audio poweramplifiers is reproduction of music.'Hills music reproduction must bethe primary criterion for judging thesuccess of a design. Measurementsare, at best, an indirect estimate ofmusical performance.
There arc those who advise cautionwhen applying techniques to reducedistortion, lest the cure be worsethan the disease. Mr Self pointed outseveral examples of this, helpingdesigners to avoid problems. Tointerpret such warnings to mean thatlow distortion is immoral (part 8) isa cheap debating trick, presumablyintended to discredit those who donot share Mr Self's views.Stephen MerrickCheshire
...clearly the bestThe difference of opinion betweenDouglas Self and Ben Duncan(Letters, May) would have moresignificance for practical audio fansif we had an amplifier constructionproject of Ben's that we couldcompare with Douglas' amplifier(Distortion in power amplifiers: pt7, February, 1994. pp.137-142).
All electronics ends up at the endof a soldering iron and in audio whatcounts is the sound from thespeakers - regardless of thesemantics involved.
Offer of an excellent pcb for theclass B amp is greatly appreciated asis the down-to-earth concepts usingstandard components fromestablished UK sources. Thiscontrasts with many offerings duringthe past decade from other UK and
foreign journals specifying parts thatcan only be obtained from foreignsuppliers.
Ben will be well aware thatexisting UK construction kits havedegenerated, in some instances, intovalue-added enterprises withcomponent applications that are nowstratospheric in price.
Douglas has brought us back toearth (sic). And about time too.Hugh HainesSunderland
Ears and knowsLittle did I think that my simpledescription of my use of listening inthe development of audio -relatedproducts (Letters, EW+WW,November 1993) would embroil mein "subjectivist wars" with DouglasSelf and elicit accusations of voodoopractices from Alan Dyke (bothLetters, June 1994).
The fact is that audio electronicscircuits are built and sold to belistened to. This basic andintractable truth should bejustification enough for designers touse their own ears somewhere alongthe way. Yet it is one that I have yetto see Douglas Self address or evenacknowledge.
The research I cited in my lastletter - which shows that customersin the professional audio industrylisten to competing products beforemaking purchasing decisions - is myown. It is culled from a careerspanning 25 years of talking andlistening to customers in thebroadcasting, sound recording, livesound and music markets around theworld. They are all professionallisteners in the sense that they maketheir living from the creative use ofaudio electronics.
Experienced sales and marketingpeople from any other audioequipment manufacturer ordistributor would tell Douglas Selfthe same thing and indeed, in thecase of the company for which heworks, probably already have.
Whether or not he wishes to hearit, believe it or act upon it, the dataexists.
Alan Dyke doubts that I wouldtake part in the sort of independentlistening tests suggested by AlanThomas. Why should he doubt it? Iwill quite happily accept thatchallenge - as might a number ofmy colleagues - if in doing so wecould help to move the study of thecorrelation of hearing andmeasurement beyond the limitationand self -defeatism of entrenchedprejudice and selective study.
As to technique,and assuming that
596 ELECTRONICS WORLD + WIRELESS WORLD July 1994
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ELECTRONICS WORI D+WIRI I [ SS WORLD July1994
LETTERS
I would be required to heardifferences between two unseenpower amplifiers I would want tonominate the other components inthe listening chain and choose myown source material and listeninglevels. I would then want to spend aslong as I felt necessary listening toeach amplifier. Once I was happyand relaxed (on the assumption thatSelf would not count theserequirements as "fatal flaws" in mymethodology), the two amplifierscould then be A/Bd until the cowscame home and I would hear thedifference every single time.Jerry MeadHerts
Charge build upHaving worked for the past 30 yearsas a capacitor engineer, both indesign and applications, I eagerlyread the article by Tony Wong onChoosing Capacitors (EW+WW,April, pp.327-329).
Unfortunately the article has anumber of typographical errorswhich could confuse a user, and alsomakes fundamental mistakes -especially concerning electrolyticcapacitors.
The most serious - "... If connectedincorrectly [reversed], the insulatingoxide film is not formed and there isno capacitance" - is incorrect.
Manufacture of non -solidaluminium electrolytic capacitorsstarts with rolls of pure aluminiumfoil etched to increase surface area.They are then electrolytically formedto produce the dielectric oxide byapplying a positive voltage, typically20% greater than rated voltage, in abath of weak acid.
After slitting to width and windinginto a capacitor, the cut edges are re-formed by applying voltage atelevated temperature and usingoxygen available from the capacitorelectrolyte. This, oxide film, usedwith chemically suitable electrolytes,is inert. Indeed were this not so, thecapacitor would fail in storage.
Consequently, every aluminiumelectrolytic capacitor contains thisdielectric oxide film from day one.
Application of reverse voltage doesnot, in the short term, remove thisoxide and the capacitance value isessentially unchanged. IndeedCECC-30-300 clause 4.15 requireschange of capacitance to be less than10% of initial value when subjectedto IV reverse, then rated voltage,each for I25h at upper categorytemperature.
A capacitor requires two foils eachcovered with dielectric oxide formedto the same (non -polarised) ordifferent (polarised) voltages.
Given a polarised construction, thesecond foil (cathode) will haveatmospheric oxide equivalent to 2-3V electrical. Both foils'capacitances are dependent on
formation voltage and surface area.Assuming the cathode foil is
2000p F and the anode foil is 615pFand has been formed to 8V, theresulting 470p F capacitor could bemodelled as two capacitors of theabove values in series, each having aparallel zener diode of 2-3V and 8Vrespectively.C BatemanNorfolk
Mixing itMany readers may have seen atelevision programme in the series'From A to B' (BBC2) whichexplored the obsessive relationshipbetween travelling sales reps andtheir motor cars. What was mostworrying was that the obsessionseemed to have spread from the repsto their customers. It appears thatwhen you take delivery of yourpretty new mixing desk, the sliderpots are unlikely to have beenselected on a careful calculation ofprice versus performance andreliability - they were very probablybought from the supplier whosesales reps arrived in the car with thefanciest logo on its rear end.
Is it any wonder that Britishmanufacturing industry is vanishingbefore our eyes?MT HawkinsHants
Science frictionAll strength to EW+WW forallowing open debate in its letterscolumn on many 'heretical' subjects,something which few other technicaljournals have the courage to do.
There exists an academic andmedia mafiosi which attempt todiscourage individuals who evenstart to show an interest in'heterodox ideas'.
Michael Williams' attack on me(Letters, May, 1994) employedname calling, ridicule and humour -just a few of the 28 deceptivestratagems used by those who have aweak scientific case; (see appendix 4of Science versus Evolution,Malcolm Bowden, 1991).
Organised pressure groups,chicanery, sharp practice, andzealous histrionics abound in thescientific establishment, all gearedto prevent and discredit any researchand experimentation that threatensthe establishment status quo or isagainst 'informed opinion'. This isespecially so in the areas of today'sthree sacred cows of evolution,relativity and heliocentricity. See
Researchers like ImmanuelVelikovsky (catastrophist), HaltonArp (anti -Big Bang), StefanMarinov (anti -relativist), Pons andFleischmann (cold fusion), RobertGentry (pleochroic halos), RichardMilton (anti -evolution), BarrySetterfield (decrease in speed oflight), Walter van der Ramp
(geocentrist).They have all been shown to have
strong cases, or evert to besubstantially correct. Yet they wereall initially greeted as stupid or evenharmless fruitcake. Conspiratorialattempts could then be made tosilence them at the hoghest levels, inblatant disrespect of the pursuit ofnovel human knowledge.Amnon GoldbergLondon
Vision thingThe trouble with John de Rivas'virtual travel idea (Letters, May) isthat, unlike VisionRing, it cannoteasily be adapted as a massbroadcast medium.
VisionRing allows unlimitednumbers of viewers to jump betweenone or more fixed VR pods, eachsupplying up to 360° of independenthorizontal picture control withstereo vision.
Every VisionRing pod isessentially a weatherproofcylindrical caddy with a magazine of(typically nine or ten) cheapreplaceable semi -pro video camerasat one end, trained on an outward -pointing ring of wide-angle lenses atthe other via mirrors.
The multi -core feed from the podis patched straight into the cablenetwork (via a switcher box forcommercial breaks) using onechannel per camera. The homeviewer uses head position to selectwhich pair of consecutive channelsis to be fed into the VR headset froma two -channel decoder.
A normal tv set could be fed by thedecoder at the same time. For anoutlay of a few thousand pounds perpod, a cable tv company can add alow -maintenance VR supplement toits live broadcasts, with no extracamera crew or productionpersonnel: if a particular viewbecomes boring, the viewer cansimply 'look away', jump to anotherpod's channels (if available), orswitch back to the standard(monovisual) broadcast.
Viewers without special equipmentcan still 'channel hop' betweenindividual views, and hotels or pubscould run multiple channels onseparate tv sets to produce animpressive multi -view backdropduring sporting events.
Between major sporting featuresand the like, a VR pod could be lefton-line for all live studio output, andwhen suitable programming is notavailable, the network could patch inlive VR 'test cards' frompermanently installed pods at, say,the Grand Canyon, a nice stretch ofbeach, or the top of the Empire StateBuilding (live panoramic 3D sunsetsover New York from arty angle,anyone?).
The final commercial attraction ofVisionRing is a little more painful.
While you can watch the Superbowlor the World Cup live in VR, youwon't be able to videotape theexperience on a domestic machine.So you will not be able to avoid theVR Coca Cola adverts . Sorry,everyone.Eric BairdMiddlesex
Virtual intercourseI was interested to read John deRivas' letter (Letters, May)concerning virtual travel and thepaying of virtual visits.
The system he envisages wouldcertainly be possible, although Idoubt if the data streams could everbe compressed enough to be sentdown an ordinary twisted pair. Ithink the scheme would have to waituntil we all have optical fibre laid toour houses.
Also, until the technology exists tosequence DNA in real time and tore -synthesise it at the other end ofthe link there will remain someinteractions that cannot take place invirtual reality.IS LinfootOxford
Theoretical limitsI agree with Mr Goldberg's view(Letters, April 1994) that thefoundations of theoretical physicsare in just as poor shape as ever. Iam quite familiar with the argumentthat physicists' perception of thespeed of light is monotonicallydecreasing since first measured byGalileo (who found it to beWhen I was studying engineeringphysics fifteen years ago, myteachers told me that the effect wasdue to technological advancementand the fact that early measurementdepended on astronomical constants- such as the length of the solar year- which are now recognised toindeed vary.
Mr Goldberg points out that thefundamental constants are inter-related so that a new electron massgives a different Planck's constantand so forth. But it is ludicrous tosay that: "the change is not due tolimitations of equipment".
Dane Ole Romer, a contemporaryof Hamlet, deduced from watchingthe stars that it takes a certain timebefore the light reaches Earth and tosay that his vintage calculations areon an equal footing with thosenewfangled atomic clocks is toodamned conservative.Extrapolations of laboratory realitysuch as determination of the age ofthe Universe are entirely thescraping of horns of the big ramsconcerning correct application ofobserved laws and need not be takenseriously.Michael WilliamsBeth Shemesh
598 ELECTRONICS WORLD + WIRELESS WORLD July 1994
INTRODUCING THE
v 1WAT TI1VC GOING' °N211mErfV;
4ffMETER TMFor Installation and Maintenance of:
POWER DISTRIBUTION SYSTEMS
VARIABLE SPEED MOTORCONTROLLERS
PROCESS CONTROL EQUIPMENT
SECURITY & OTHER VIDEOSYSTEMS
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HO', CO RESET Mr,1:4"f4
122.8auunimn
.'31=JV-AC
MA`:
if,e EN,
f-", ITO
Large LCD Display gives clear indicationincluding Max, Min and Max -Min values.
1-911 bilt :;ELECT = PI I
H250 I lot0
Dual channel opera ion allows relEtiyetiming of signals to be observed.
RuLDER =1E. . 74rnSREO .7 H
NUu,P5 GE
-r, FI H
Display of signal shape lets you findtl:aults that DMM can not show.
Today the Digital MultiMeter (DMM) is not always
enough! Modern electronics permeates our lives
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CIRCUIT IDEAS SEND YOUR CIRCUIT IDEAS TO THE EDITOR, ELECTRONICS WORLD,
QUADRANT HOUSE, THE QUADRANT, SUTTON, SURREY SM2 SAS
Do you have an original circuit idea for publication? We are giving £100 cashfor the month's top design. Other authors will receive £25 cash for each circuitidea published. We are looking for ingenuity in the use of modern components.
Digital sinewave generatorA s an alternative to using a look -up table,
rlan analogue -to -digital converter and afixed filter, this circuit possesses theadvantage that the frequency of theprogrammable output filter variesautomatically.
The clock input drives the MAX29.v filterand, via a divide -by -10 counter, a seconddivide by 10 counter that develops a voltageacross R proportional to the count. Outputfrequency is f,,,/100.Lee SzymanskiStamfordLincolnshire
Clock input
Sinusoid generator of1,1°,11100 in which outputfilter tracks automaticallywith input frequency.
Spare inverter converts 5V to ±15VIf you have only a 5V rail and need a dual 15V supply, use thiscircuit to generate it cheaply.A spare Schmitt inverter from, say, a 7414 operates as a free-
running multivibrator at a frequency of about 100kHz using aresistor and capacitor with the values shown. As the transistor isdriven on and off by the square wave from the oscillator, spikes ofabout four times the supply voltage develop across the 1mHprimary of the 1:1 pulse transformer. Diode D2 rectifies the spikes,which are filtered and regulated to give +15V, the current suppliedbeing determined by the capabilities of the 5V supply and the wiregauge of the transformer. Diode DI rectifies the transformeroutput to form a -15V rail.V LahkshminarayananCentre for Development of TelematicsBangalore India
On C HON, AlsIAI I/
72.
YAW got,.
EDO mum.Digital output
\11,11'
2k2 100n
Effect ofR and C
Instead of using a DC -to -DC converter or a 555 oscillator, use aspare Schmitt gate as an oscillator in this 5V to t 15V converter.
YOU COULD BE USING A 1GHzSPECTRUM ANALYSER ADAPTOR!Got a good idea? Then this Thurlby-Thandar InstrumentsTSA1000 spectrum analyser adaptor could be yours.
Covering the frequency range 400kHz to over 1GHz with alogarithmic display range of 70dB ±1.5dB, it turns a basicoscilloscope into a precision spectrum analyser with digital readoutcalibration.
Recognising the importance of good design, TTI will be givingaway one of these excellent instruments every six months tothe best circuit idea published in the preceding period until furthernotice. This incentive will be in addition to our £100 monthlystar author's fee together with £25 for all other ideas published.
Our judging criteria are ingenuity and originality in the use ofmodern components with simplicity particularly valued.
600 ELECTRONICS WORLD + WIRELESS WORLD July 1994
CIRCUIT IDEAS
Square waves from a 555In the usual 555 astable oscillator, the timing capacitor charges
through two resistors and discharges through one of them, the twotime constants therefore being unequal. In this circuit thecharge/discharge paths are similar, giving a 50:50 mark:space ratio.
The capacitor C1 charges and discharges via VR1 and R2 and it isnecessary to ensure that Di and Trl base/emitter diodes are similar toavoid timing errors. Charging takes place when pin 7 is high, turningTr' on; when it is low, the capacitor discharges through the diode.To obtain accurate square waves, the 5 -turn potentiometer VR2varies the comparator control voltage. Either mos or bipolar 555swork in the circuit shown, but the bipolar version gives a lowermaximum frequency; the 555CN works up to 2MHz.
To set the waveshape at very low frequencies, temporarily replacea large C1 with a small one, set VR2 to obtain unity M/S ratio andreplace the larger Ci.I C RohslerHa rbomeBirmingham
Inrush current limiterMost of the methods of dealing with theinrush current into large smoothing
capacitors have their disadvantages, whetherthey are to do with inconvenience,performance, reliability, size or cost. Thiscircuit uses the high -impedance control andlarge switching safe -operating area ofmosfets to do the job, with none of theabove drawbacks.
It does not suffer from dv/dt limitationsand works from zero current up to designedlimits, it needs a small hold current and isproof against shorts if R12 is a positivetemperature -coefficient type or has one inseries. Under test without a PTC resistor,Tr4 survived a short but R12 blew.
Resistor R12 determines the inrush currentand Rio sets the maximum peak currentallowed in steady-state conditions - about4.5A with these values. A smaller maximumcurrent would allow the use of a smallermosfet, but would call for a higher -valueresistor and more heat, so a small R10 ispreferable.
In a switching supply, the four RGP3OMdiodes could be part of the diode bridge, thewhole circuit preceding the smoothingcapacitors.Kristen EllegArdOsloNorway
Inrush current limiter has none of the drawbacksof conventional solutions, such as relays,
thermistors or thyristors, and can be made partof the diode bridge in a switching supply.
Crcuitaround Tr1ensures thatCl chargesanddischargesat the samerate, givingaccuratesquarewaves up to2MHz.
0-0-0
0
R1210
D5RPG3OM
3
PTC
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.y D6RPG3OM
F 1 4
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BC558B
R11
100k/WV'
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R8
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1k
R4D. Tr3 4k7
BC49OB1N4148
R5 R6
4k7 4R7
eR3
10k
100k
Dt
BA159
Tr2BC489B
D3
10V
Ci0+ 4117
R2100<vw
D2112V
D8RPG3OM
0
July 1994 ELECTRONICS WORLD + WIRELESS WORLD 601
CIRCUIT IDEAS
High -torque position servoDarallel-connected power mosfets in an HI bridge, driven by an SG3731N pulse -width modulator, form a simple, high -torqueservo driver for a I2V, 380W DC motor.
Pairs of BUZ1/A and RFP30P05complementary mosfets are common drainconnected to simplify gate driving and inparallel to obtain the necessary current. Allthe circuitry is supplied by two 6V, 100Ahlead -acid batteries.
As the motor turns, it drives the 5142 servopotentiometer, from which a voltage is takento one input of the PWM, where it iscompared with the reference input. Forclockwise rotation, the SG3731N maintainsmosfets 3 in conduction, while switchingmosfets 1 and 2 on and off. For the otherdirection, mosfets 2 are on and mosfets 3and 4 go on and off. The gain of the PWM'sdifference amplifier can be altered by
RFP30P05*
selecting new values for R1,2 to suit differentgeared motors.
Capacitors C2,3 reduce the effects of leadinductances and should be kept close to themosfets, as should the back-to-back zenersacross the motor, which absorb high -voltagespikes.M T lqbalRutherford Appleton LaboratoriesDidcot
RFP30P05*
C,6[100n
A'BZX85C11
11v
1OR g
10R
s
d g s
Aug
gbirg d
Z.10R
lOR
11V
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CO °6801.1
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2k8
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12 1OR--AINNV- 1 1 2V, 38W
2k
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11 +10k
10mil
2200µ 6V,fi I lOR
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4 1000 5680µ
+6V
Ri10k
I-.100k 1OR
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099
1OR
T.11V
5k BUZ11A BUZ11A*Reference
2position 10k
Power MOS on heatsinks with 6 = 1.16*C/W
PWM IC controls mosfet H -bridge in a high -torque position servo driving a 12V,380W DC geared motor.
Monitor shows three-phase sequence-r wo of the phases in a three-phase supply have a 60° phase
I difference with respect to the third, but in an unknown order.The monitor shown indicates this phase sequence, needing noneutral point and few components.
If V 1 goes high, V2 being low, Trl remains cut off and Tr2draws base current through R4. After 60°, phase 3 goes high andTr2, already conducting, holds Tr I off and led 2 lights during the120° overlap to show the L1 -L2 -L3 sequence. In the reversecondition, V2 goes high while V1 is low and led 1 lights to showL1 -L3 -L2.Cyril W W PalihawadanaSana'aRepublic of Yemen
2
ZiBZX7.5
v,
V,
60' 180'240' 360'
+
5k Servo potentiometer
1N4006
R1
100k(1W)
/.5V
TI LEDforwarddrop
D2
1144006
R6
100k(1W)
z2BZX7.5
40A
100Ahd acid
I
100Ahacid
40A
+6V
-6V
602ELECTRONICS WORLD + WIRELESS WORLD July 1994
CIRCUIT IDEAS
Electronic fuseH:tying a voltage range of 10-36V andhandling currents up to 1A, this circuit
disconnects a load in a time variable up to100ms by changing a capacitor. Muchgreater currents and voltages can be handledby the same design with changed componentvalues. It simply goes in series with load.
Most of the voltage drop across the circuit,VAB, which is proportional to the DC loadcurrent and less than 2V, is across R11.12. Atswitch on, all the supply voltage is acrossthe fuse and Tr3 conducts, its base currentbeing supplied by R4 and its collectorcurrent set by D3 and R8 according to /0 =(VD3-Vbe3)/R8. Base current of Tr4 istherefore stabilised, Tr4 conducting andturning on Tr5. Delay determined by C1prevents premature interruption of Tr3 basecurrent.
If load current increases excessively, thevoltage dropped across R12 begins to turnTr2 on, reducing the collector current ofTr'3,4.5 and increasing the terminal voltage tomore than 2V. When it exceeds 4.5V, Diavalanches, Tr1 conducts and the cut-off ofthe three output transistors is cumulative,current through the fuse now being a fewmilliamps. Capacitor C1 determines the timedelay to cope with motor inrush currents orfilament lamps and C2 handles voltage
100n
T
Ri27k
R4
Di 15k
3.3V
D21 N4148
R2100
Tr'E..BC451
R3
27k
R5
56k
D3
10mA
1N4148
Tr22N3107
R66k2
R7
20R
C.Tr4BD140
Tr32N3107
R3
2R2
R8 R1020 360
R12OR62
A
nilR43 Load
Tr5 C22N5192 100r
spikes. Diode D2 prevents CI dischargingthrough the load when VAB is almost zero.
With component changes, the circuitshould be able to operate with currents from10mA to 40A and on voltages from 6V to500V. It can also be used as an AC fuse, asseen in Fig. 2.
To re-establish the circuit after aninterruption, switch off for a short time.
N I LavrentievKaliningradMoscow RegionRussia
PCBs for Douglas Self's
power amplifier seriesCircuit boards for Douglas Self's high-performancepower amplifier are now available via EW+WW.
Detailed on page 139 of the February issue, DouglasSelf's state-of-the-art power amplifier Is theculmination of ideas from one of the most detailedstudies of power amplifier design ever published in amonthly magazine. Capable of delivering up to 100Winto 852, the amplifier features a distortion figure of0.0015% at 50W and is designed around a newapproach to feedback.
Designed by Douglas himself, the fibreglass boardshave silk-screened component IDs and solder maskingto minimise the possibility of shorts. Sold in pairs, theboards are supplied with additional detailedconstructional notes.
Each board pair costs £45. which includes VAT andpostage, UK and overseas. Credit card orders can beplaced 24 hours on 081-652 8956. Alternatively, senda postal order or cheque made payab,e to ReedBusiness Publishing to EW+WW, The Quadrant.Sutton, Surrey SM2 5AS.
R13TR14
July 1994 ELECTRONICS WORLD + WIRELESS WORLD
Powersource
Fig.1. Circuit acting as a fuse for voltagesfrom 10V to 36V and currents up to 1A, withvalues shown.
Fig.2. Same circuit operating in AC circuit.
R19
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CIRCUIT IDEAS
Two -wire switch status detectionne central control determines the stateof up to eight remote switches, using
only two wires.Figure 1 is the control unit, in which /CI is
a 4094 latched shift register, driven by /C2, a4060 14 -stage binary counter/oscillator.Signals from /CI also drive the base of thepower transistor Tr], which applies 12V tothe signal bus at each positive excursion ofthe base drive.
Remote units derive power from the bus,as shown in Fig. 2, and send pulses to thebus when the associated switch is off. Whenpower is on the bus. C3 charges to 5Vthrough D10 and D12 and supplies power tothe 4093 /C3 when the bus is off. CapacitorC2 also charges from the bus.
After eight clock periods, Tr] turns the busoff and C2 discharges through R16,12. /C3aoutput goes high, this change being differen-tiated and passed to the bus as a square pulsewhose width is set by the values of C4R18and after a delay determined by R16.17. If theswitch is on, no pulse passes lC3b.
When pulses arrive on the bus at Tr2, the
IC1 clock
ICI OE 7
IC1 STR
Signal bus
IC1 D
+0
'Ai Di o6V2
Dit1N4148
NDi 21N4001
C3220µ10V
C2CI
R1622k
R171M
14
C34
7
CD4093
CD40938
9 IC3C
Signal bus
c2
IC3Aoutput
ICso output
D131N4148
R2o2k2
Fig. 2. One of the remote switches (S1) and its associated pulse -formingcircuitry. A return pulsepasses to the signal bus when the switch is off.
4094 D input goes low and the clock shiftsthe 4094 state. Delay time after bus powerloss is set to a different period in eachremote unit, so that the return pulse isdetected at different clock times and thestate of each remote switch is shifted in the
1 2 3 4 5 6 7 8
PI
IC2
04050607Qs
09Q10Q12
CD4060 013
Q14
PO
/PO
L
Ri -198
L4k7
D1- D8
R14100k
,./WV`
CiF150µ
Fig. 1. Control unit of remote switchstate indicator for up to eight switches,using only two wires.
01
02CLK 03
0405
I01 0607
CD4094 08
Os/Os
OE
STR
4094. On the eigth pulse, the combinedstates are latched in the 4094 and illuminat-ed leds indicate off switches.Yongping XiaTorranceCalifornia USA
Isolated I2C bus interfaceWbile the 12C bus, which consists of abidirectional data bus and a
unidirectional clock, has many attractions, itis not easy to use it across an isolationharrier. This circuit performs that function at400kHz.
In Fig.1, the data transmission circuit isseen to be symmetrical to allow truebidirectional working. When data from themaster is high, cutting Try off, Tr.i's basedraws current through R8, Opto 2 conducts,
R9 R10
10k 10k
Master°data
Tr6
BC182
Master OV
7r3 cuts off and the slave data bus is pulledhigh by R,. A low from the master causesthe opposite state, Di conducts and the slavedata bus is low.
Since Tri base is reverse biased, Tr2conducts, Opto 1 conducts and Tr6 is off, sothat it does not affect operation: Tri.5 areneeded to prevent the circuit locking upwhen the master data line goes low, pullingthe slave low. which would keep the masterdata line low and stop anything more
Slaveclock
Slave +5V Master +5V
BC182
Tr'
BC182
0 o3
Al10k
4E10 Masterclock
R,3560
lave OV Master OV
Fig.2. Simpler circuit for unidirectional clocksignal transmission.
happening. When the slave transmits, theopposite to all the above takes place.
Since clock transmission is unidirectional,the simpler circuit of Fig.2 is sufficient.
As the couplers are in base circuits ofbuffer transistors, the coupler transistors seeconstant -current loads and, since the basesignal is only 0.6V, even slow 4N25couplers work well.CM ClarksonBrownhills, West Midlands
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July 1994 ELECTRONICS WORLD + WIRELESS WORLD 605
RF ENGINEERING
USING RF TRANSISTORSTransforming wideband circuits
Multi -octave impedancematching is almostexclusively carried outusing transformers. NormDye and Helge Granbergexplain how differenttransformers work andindicate how to choosethe most appropriatetype.From the book RF
Norm Dye is Motorola's productplanning manager in the SemiconductorProducts Sector, and Helge Granberg isMember of Technical Staff, RadioFrequency Power Group(Semiconductor Products) at Motorola.Their rf transistors book includespractical examples from the frequencyspectrum from 2MHz to microwaves,with special emphasis on the uhffrequencies .
RF Transistors: Principles and practicalapplications is available by postalapplication to room L333 EW+WW,Quadrant House, The Quadrant,Sutton, Surrey, SM2 SAS.
Cheques made payable to Reed BooksServices. Credit card orders accepted byphone (081 652 3614).
The dependence of device impedances onfrequency means that any type of wide-
band impedance matching naturallycompromises amplifier performance. Also,low impedance rf transformer -impedanceratios can only be realised with integers suchas I:1, 1:4, 1:9 etc. Other ratios are possible,but the structures usually become complexand bandwidth is lost through the increasedleakage inductance coming from the numerousinterconnections.
The effect of compromises in the input is toreduce power gain and increase return -lossand vswr. In the output the results are reducedefficiency, lowered stability against load mis-matches and poorer linearity.
But RLC networks inserted between thedevice input and the matching transformer cancompensate for the impedance versus fre-quency slope, as well as for the gain vs fre-quency slope. Corrective networks, with neg-ative feedback and associated additionalnetworks, can allow amplifiers to be designedthat cover up to five or six octaves, from lowband to vhf - or even uhf.
In the output, very little can be done to com-pensate for the output impedance/frequencyslope, due to excessive power loss.
Fortunately, output -impedance variationwith frequency, using both mosfets and bjts, isusually much smaller than that of the input.Sometimes a low value inductance or amicrostrip between the device output andmatching transformer considerably improvesefficiency at the high end of the frequencyrange, by providing compensation for thedevice's output capacitance. Normally only`over -compensation' of the output transformerwill do an adequate job, calling for addedcapacitance across the transformer primaryand in some cases also across the secondary.
Wideband operationA wideband rf transformer performs one or a
Rather than using their primary -to -secondaryturns ratios, transformers are most oftenreferred to by their impedance ratios (turns -
ratio, squared). In these applications, we aremostly interested in manipulating impedancerather than voltage or current.
RF transformers can, in basic terms, be com-pared to low frequency transformers - exceptthat with increasing frequency a parametercalled leakage inductance becomes an impor-tant factor.
To extend coverage to the low end of thefrequency band, some type of magnetic core isrequired. Either powdered iron or ferrite coresare acceptable depending on the frequencyrange, with ferrites being the most common.
A general formula for calculating the maxi-mum flux density of a ferrite core is:
Bmax=Wmax/(27yAn)1102
where Bmax is the maximum flux density(gauss), Vina, is peak voltage across the wind-ing, f is frequency in MHz, A is core cross-sectional area in cm2 and n is number of turns.
Either the primary or secondary can be usedfor the Bmax calculations, although the 500side - if applicable - is commonly used forconvenience and standardisation. ThenVmax=\1(2PR) where P is rf power level and Ris resistance (5052).
For example, if:
V, = 50V,f=2.0MHz, A=1.0cm2 and n=4.
then
Bmax(50/50.2)( IO2)= 99.6gauss.
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In certain types of transmission line trans-formers the rf voltage (1,,,,ax) used in the Bmaxcalculations is lower than the value obtainedfrom the 1/,,,a, formula given above. This isbecause the maximum voltage across thewinding(s) must be divided by the number ofline segments connected in series in the trans-former configuration in question.
The same result can also be reached usingthe formula if the full voltage across the 5052terminals is used for Vmax as the numerator,and n is multiplied by the number of line seg-ments in series.
Since high permeability ferrites tend to sat-urate sooner than low permeability ones, goodpractice is to limit their maximum flux densi-ties as follows:
Bmax of 40-60 gauss/cm2 of cross-sectionalarea for ferrites with p at 40000.
Bmax of 60-90 gauss/cm2 of cross-sectionalarea for ferrites with µ at 100-400.
Brna, of 90-120 gauss/cm2 of cross-sectionalarea for ferrites with p at < 100.
In the Brna, versusµ figures, the magneticpath is assumed to be solid: eg without airgaps such as in toroids and balun cores.
Importance of leakage inductanceAt low frequencies, leakage inductance is vir-tually unknown and most designers areunaware of such a term. But in rf transformersit is the parameter that limits high frequencyresponse.
Performance becomes more critical at lowimpedance levels, where tight couplingbetween the windings is of utmost importance.Leakage inductance is a product of the cou-pling between the primary and secondary andany exposed area in either winding. It is alsoaffected by interconnection lead lengths andmutual coupling.
Leakage inductance (or reactance) is diffi-cult to calculate. But it can be measured foreach individual case with a vector impedancemeter, vector voltmeter, or network analyser.Ideally, when one winding is shorted with alow inductance path, measurement in the otherwinding should show essentially zero R andphase angle. In practice this is never the case.
Deviation from zero in the value of the resis-tive component and phase angle can be usedto calculate the leakage inductance (or ratherthe high frequency performance of the trans-former).
Relating leakage inductance directly to Ifperformance of a transformer is difficultbecause it is impedance -level dependent.
At vlf (50-500kHz), where high p cores arerequired, a problem may appear which looksinexplicable. It is called magnetostriction, andis a magnetic resonance of the ferrite corewhich can cause chattering, leading to disin-tegration of the core.
There are many resonant modes such as lon-gitudinal and torsional, etc and the only cure isto select a physical core size and shape which
Fig. 1. Equivalent circuit for a conventionaldiscrete -winding rf transformer. lip is leakageprimary, Lpp is parallel L primary, 45 is leakageL secondary and Lps is parallel L secondary.
has resonances outside the critical frequencyspectrum.
Conventional transformersThe simplest design of rf transformer is a con-ventional type - spanning several differentkinds - some of which are more suitable forcertain applications than others.
But in all, the basic principle is roughly thesame (Fig. 1): that low frequency couplingbetween the primary and the secondary is pro-vided through the flux of magnetic media(core): as in audio transformers.
At high frequencies tight capacitive couplingbetween the windings is essential and themagnetic core has little effect except in theform of dielectric losses. So the quality ofmagnetic media employed is a very importantfactor in design. There is also the question ofwhether to use higher permeability core mate-rial and suffer high frequency losses; or designaround the losses from the increased straycapacitances caused by additional turns in thewindings required when using low perme-ability cores. A few tenths of a dB of unnec-essary power loss in an output transformer canmean a significant increase in power con-sumption and device dissipation.
Conventional transformers are inferior inperformance to transmission line transformers,with the differences mainly in power handlingcapability, loss factor and bandwidth. Butconventional rf transformers can be con-structed for a wider range of impedance ratiosthan transmission line types. Some ratios willhave wider bandwidths than others due to thenumber of turns required to achieve thedesired turns ratio. There are no fractionalturns - as in all transformers - and if the wirepasses through the core, one full turn is com-pleted.
In Fig. 1, stray capacitances have been omit-ted since a relatively low impedance case isassumed and the capacitive reactance arisingfrom applicable construction techniques rarelybecomes appreciable in comparison to the lowvalues of resistances involved.
Figure 2 shows a conventional if trans -
Fig. 2. Simplest form of conventionaltransformer. The windings are usually randomlywound one on top of the other. It finds use athigh impedance levels, 20052 and up, whichdictates the frequency response of the unit.
former that finds wide usage at highimpedance levels (200SI and higher) in lowpower designs. One winding is simply woundon top of the other, usually providing goodenough coupling at these impedance levels upto uhf. The most convenient core shape is atwo -hole balun, although toroids can be seenin some designs if a sufficient number of turnsis provided on the periphery for the couplingrequired.
As in all rf transformers, wire size also hasan effect on the coupling between the primaryand secondary. The heavier the wire size, thetighter the coupling will be. This increases themutual winding capacitance, again resulting incompromise.
The capacitance can be lowered by using ahigh p magnetic core, but core losses wouldbe higher. Since the mutual winding capaci-tance has a larger effect at higher impedancelevels, designers must determine whichapproach is most beneficial for a specificapplication.
One -turn advantagesThe most popular conventional type of rftransformer is probably that (Fig. 3) with theone turn winding consisting of metal tubesgoing through sleeves or stacks of toroids ofsuitable magnetic material. The tubes are elec-trically connected together at one end of thestructure and separated at the opposite end,where connections to the one turn winding aremade.
Fig. 3. The most common conventional type ofrf transformer. One winding consists of metaltubes shorted at one end, thus forming only oneturn. This limits the impedance ratios to integers1:1, 4:1 9:1 etc. It is fairly efficient at impedancelevels down to 2-3Q if properly constructed andmay have a bandwidth up to 50MHz.
In practice, connections are usually madewith pieces of single -sided metal -clad lami-nate with proper patterns etched in the metal.
The construction also produces a physically -sturdy structure with all its components intact.To make up a transformer, the required num-ber of turns of wire is threaded through thetwo tubes to form a continuous multi -turnwinding. The resulting tight coupling betweenthe two windings has relatively low mutualwinding capacitance, and so permits use atvery low impedance levels.
The wire ends of the multi -turn winding canbe taken out from either end of the trans-former, whichever is physically most conve-nient. The usual arrangement is to have theprimary and secondary terminals at oppositeends (Fig. 3).
The disadvantage of this type is that its one -turn winding allows only integer -squaredimpedance ratios such as 4:1, 9:1, 16:1, etc...
Fractional integers look to be possible by
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Fig. 4. Another form of conventional typetransformer. a and b are segments of coaxialcable which, in practice, are bent to get theterminals of the low impedance winding closetogether (see Fig. 5).
threading the winding wire through one tubeone more time than the other. But this offsetsthe balance and the transformer will not func-tion properly. Bandwidth is actually deter-mined by the impedance ratio, and a 9:1impedance ratio transformer will be usable upto 50-60MHz. But higher impedance ratiosreduce the bandwidth rapidly, because of theincreasing leakage inductance. A 25:1 trans-former will perform poorly at 30MHz, and a36:1 unit is usable only to 15-20MHz.
The form factor - the length -to -width ratio -is important. If the transformer structure isshort, the coupling between the windings islowered and the leakage inductance isincreased. At the other extreme, if the unit islong, the mutual winding capacitance isincreased and the physical length of the multi -turn winding may produce resonances withinthe desired spectrum.
Another disadvantage with these transform-ers is that when used in an amplifier output,the one -turn winding makes the magnetic coresaturate at a low flux density. But despite allthese drawbacks, one -turn transformers arewidely used in both input and output matchingin the 2-30MHz frequency range and at powerlevels up to 100-150W, and as input matchingtransformers up to even higher frequencies.
A clear advantage is the transformer's sim-
CD CD
"I" Core
"E" Cor
Fig. 6. Transformer shown in Figs. 4 and 5provided with a magnetic core (E and I) tobroaden its low frequency response. The arrowsindicated points where epoxy can be applied tomake the unit a solid structure.
HIGH IMPEDANCE
WINDINGS
CENTER
TAP
4:1
IMPEDANCE
RATIO
9:1
IMPEDANCE
RATIO
CONNECTIONS
TO LOW IMPEDANCE
WINDINGS
Fig. 5. One possible physical realisation of the transformer described. Note the height of the segmentstacks with increasing impedance ratios. This produces a delay from the connection points of the lowimpedance winding to the uppermost segment.
ple construction, making it inexpensive andeasily mass -producible.
Parallel winding connectionsIn other variations of the conventional trans-former (Figs. 4-6), impedance transformationis obtained by connecting in parallel a numberof windings on one side, and in series on theother.
For the most common type (Fig. 3), one turnin the low impedance winding, limits possibleimpedance ratios to full integers. Windings aremade of segments of coaxial cable and thestructure is formed into a shape of a 'CY or acircle (Figs. 5 and 6). Leakage inductance islower than with most other conventional trans-formers making it usable up to 200-300MHz.
The high frequency end is limited by phys-ical size of the structure because, to avoidmajor resonances, the length of the high -
impedance winding should usually be keptbelow 1/8 wave -length at the highest frequen-cy of operation.
e So physical length of a U-shaped 4:1 unit islimited to about 3.5cm and a 9:1 unit to 2.5cmfor operation up to 200MHz.
The characteristic impedance of the coaxialcable determines the coupling coefficientbetween the windings, and the optimumclosely follows the line impedances calculat-ed for transmission line transformers. If cableimpedance is too high, bandwidth is reduced:if too low, the maximum bandwidth can berealised, but at a cost of capacitive reactanceand reduced efficiency of output matching.
Transformer segments can be made fromsemi -rigid coaxial cable with all outer con-ductors tied together to form the lowimpedance side. The inner conductor willautomatically make up the high impedancewinding (Fig. 5).
With a U-shaped design, the bending radius
should be as small as possible, though limitedby the recommended minimum for the spe-cific cable used.
Spot welding would be the best way to con-nect the inner conductor segments together,but soldering (preferably with high tempera-ture solder) is adequate. Some commerciallyavailable units use tiny pc boards at the frontend of the cores to make the connections.
A typical 3cm-long coaxial cable trans-former has a low frequency response ofaround 100MHz without a magnetic core.
With an E and I core of material (Fig. 6)having 1.4 equal to 125, for example, theresponse will be lowered to 3-10MHz depend-ing on impedance ratio.
Only a physical constraint limits the highestpractical impedance ratio. If too many linesegments are stacked, the structure becomeshigh and it is difficult to make the electricalconnections to all segments without introduc-ing excessive phase delay to the uppermostones. The effect depends on the cable diame-ter, but for a power level of 200-300W a cablediameter of 2.3mm (standard with most man-ufacturers) can be considered a minimum andthe highest practical impedance ratio would be9:1. If 16:1 or higher is needed, a smallerdiameter cable must be used, and the powerhandling capability lowered.
Twisted wire transformersA unique and versatile rf transformer can berealised with twisted wires. Enamelled magnetwire is commonly used since it has a thin, butgood, temperature -resistant insulation. It isalso available with Teflon insulation for veryhigh temperature applications.
Characteristic impedance of a twisted wiretransmission line is determined by wire size,dielectric constant of the insulation and thenumber of twists per unit length. Twists/length
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has the least effect on the line impedance(assuming the wires do not separate from eachother in the winding process). A simplemethod of approximating line impedance is bymeasuring its capacitance per unit length andcomparing it against a line of knownimpedance.
The most common twisted -wire transmis-sion line is a single pair of wires. For a wiresize of #28 AWG, the characteristicimpedance will be approximately 50g. Lowerline impedances are possible by using heaviergauge wire or by replacing each single wirewith a multiple of smaller gauge wires.
In those cases where multiple numbers ofsmaller gauge wires are used to form a twist-ed -wire transmission line, location of the wireswith respect to each other should maintain asymmetry (Figs. l la and 11 b discussed later ).
Versatile solutionsThe twisted wire transformers discussed heredo not have a defined line impedance - exceptfor Fig. 7d. They are versatile (Figs. 7a and7b) and many more odd impedance ratios arepossible.
Figure 7a is a normal 1:1 balun with a mag-netising winding added (centre). If the balun'sload is balanced - feeding fet gates in a push-pull amplifier for example - the magnetisationcurrent flows through only one winding andonly one half of the load. The effect causesundesirable phase and amplitude unbalance inthe balun, restricting bandwidth. But balancecan be restored with a third or tertiary windingto shunt the magnetisation current around theload.
Figure 7d is a standard 4:1 transmission linetransformer where the required line impedanceis RLx2 or 2552 for RL-12.50. Two twistedpairs of #28 AWG magnet wire are the bestway to achieve the result, with each pair con-nected in parallel by shorting at both ends.Both pairs are twisted together to form the lowimpedance transmission line. (It is customaryto locate the pairs with respect to each other asshown in Fig. 11).
In the twisted wire transformers we are con-sidering (Figs. 7a, 7c and 8a -d) as stated ear-lier, there are no defined line impedances.Without data, a designer should experimentand make measurements with various inter-connection combinations of the twisted wires.Although not shown in the figure, all terminalsare referenced to ground.
Another example of the versatility of twist-ed wire transformers is that they can also beconnected in balanced -to -balanced, and evenin isolated primary and secondary configura-tions, providing several impedance ratios(Figs. 8a -c). Many other fractional integerimpedance ratios are also possible with morewires.
The units make compact interstage matchingelements in push-pull circuits and are espe-cially suitable when dc isolation between thestages is required.
Figure 8c can be considered to represent atransmission line transformer if the lineimpedance is correct (2552 in this case), which
Fig. 7. Conventional rftransformers usingmultiple twisted wires.A wide variety ofimpedance ratios arepossible depending onthe number of wiresused and connectionconfigurations.Although not shown,terminals arereferenced to ground.
1:1
is also the case with the ones shown in Figs 7aand 7d.
Twisted wire transformers have bandwidthshigher than most other conventional trans-formers, and up to seven octaves have beenmeasured at 500 and lower impedance levels;and at least one octave higher when theimpedance levels are higher and the transformratios low.
Advantages of these transformers are theirversatility for odd impedance ratios.
RL (a)
RL
(b)
(f)
Disadvantages are their limited power -hand-ling capability and, in some cases, difficulty ofconstruction due to all the multiple intercon-nections.
Although the single wire transformer (Fig.8d) is obviously not a twisted wire type, itsdescription fits better here than with other con-ventional transformers since it uses capacitivecoupling to a larger degree than magnetic cou-pling. The design represents a unique concept,where several 2-3 turn low impedance wind -
The attraction of ferrites
Ferrites a -e the most commonmagnetic materials used for 1.
transfo-rrers.The two basic types are nickel-
manga -iEse with high permeebilities(pr=relative permeability) used in lowfrequency applications; and nickel -zinc fe-ri:es. These have lower high-frequenci losses, but with Curie pointsas low as 130°, they only can bemanufactured with ps of less thanapproximately 1000. (Curie point is thetemperature where magnetic materialloses its magnetic properties.)
Low ur ferrites usually have highervolume resistivity than high pr ones,meaning lower eddy current losses.Detailed information on the behaviourof ferries at rf is rarely available fromferrite -nanufacturers.
Core eddy current losses andwindir g dielectric losses heat up thecore and its temperature must be heldwell below the Curie point or themagnetic properties of the material willbe permanently altered.
To avoid saturating the core,operat onal flux densities mast be kept
well within the linear portion of thematerial's B -H curve. Saturationmainly occurs at low frequencies,where most of the coupling is throughthe core, producing non-linearoperation, heat and harmonics. Thearea inside the B -H curve normallyrepresents the relative loss and sonarrow curves are preferred for lowloss designs. But the situation isconfused since the curves are usuallycreated under dc conditions and theydo npt really give the data needed foran rf designer.
High p ferrites, though having highersaturation flux densities than low ones,saturate easier under rf conditions.One reason is that high p cores requirea smaller number of turns to satisfy theminimum magnetising indLctancerequirement. So use a ferrite core withrelat vely low p and added turns in thewinc ings - at least to the extent thatthe added inter -winding capacitancecan Je tolerated at higher frequencies.
As a rule, the winding reactanceshoLld be at least twice the impedanceacross it.
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(a)RL
RL (b)
ings are connected in parallel and interlacedbetween the turns of the high impedancewinding. Heavy gauge enamelled wire (#18-16 AWG) increases the capacitive couplingbetween the windings and makes the unit aself supporting structure.
The windings are wound on a cylindricalcore such as a length of ferrite rod (Fig 7d,photo) and all the winding connections aremade when the transformer is mounted to aPC board.
Multiple impedance ratios are possibledepending on the number of turns in the low-
impedance windings.These transformers have been in commercial
use in equipment operating up to I75MHz andat power levels of 100-120W. Variations suchas flat ribbon wound units have been experi-mented with, but their fabrication is more dif-ficult and no significant improvement in per-formance has been found. Obvious advantagesof the single wire transformer are its extreme-ly compact size versus power handling capa-bility and the dc isolation between the prima-ry and secondary.
Transmission line transformersTransmission line transformers are quite dif-ferent from conventional ones in many ways:
to take advantage of optimum performance,line impedance must be correct for the typeof transformer in question;
at high frequencies, the series reactancecombines with the inter -windingcapacitance and the circuit behaves as atransmission line, greatly extending thehigh frequency response;
IRL (c)
power transferred from input to output isnot coupled through the magnetic core,except at very low frequencies, but throughthe dielectric medium separating the lineconductors. This is an important pointregarding the transmission line transformerprinciple;
from the above point it follows that arelatively small cross-sectional magneticcore can operate unsaturated at very highpower levels.
In practice, transmission line transformers canbe realised with twisted enamelled wires,coaxial cables, paralleled flat ribbons (sepa-rated by a dielectric medium), or a microstripon a two-sided substrate. Practicality and con-venience in each case depends on the exactapplication and frequency spectrum.
The simplest transmission line transformer isa quarter wavelength line whose characteristicimpedance (Z0) is chosen to give the correctimpedance transformation. It is a relativelynarrow -band device and valid only at fre-quencies for which the line is an odd multipleof a quarter wavelength.
In a 1:1 balun (Fig. 9a), with line impedance(Zo)=RL, low frequency performance is limit-ed by the amount of impedance offered tocommon mode currents. It should be at leasttwice the load impedance and can be increasedwith a core of suitable magnetic material.
Inductance of a conductor is in direct pro-portion to its relative permeability. As linelength limits the high frequency response,these two factors seem to be in direct conflict- we should remember the 1/8 wavelength rulediscussed earlier.
Fig. 8. Conventionaltransformers, providingbalanced -to -balancedfunction and isolatedprimaries and secondaries. a)to c) are twisted wire types,whiled is a unique single wiretransformer with its parallellow impedance windingsinterlaced between the turnsof the high impedancewinding. Number of turns inwinding d of the single wiretransformer should equala+b+c-1 not to have extrauncoupled turns to windingsa, b and c. The schematic forthe 2.25:1 balancedtransformer as left in thephoto c) is not shown.
The most commonly used material for trans-mission lines in these transformers is coaxialcable with Teflon dielectric. Cable can beeither semi -rigid or flexible, of which bothhave equal velocity propagations, at least intheory.
For calculating the maximum line lengthallowable, the velocity factor must be known.Multiplier for the velocity factor is obtainedas: vr=1/4e where ea is the relative dielectricconstant of the insulating medium. For Tefloncable, with its cp=2.5, the velocity factor mul-tiplier is 0.633.
Unlike a microstrip line, where two dielec-tric materials (air and the main substrate) formthe medium and the width -height ratio is avariable, coaxial cable has a constant velocityfactor as a function of characteristicimpedance.
Connecting points a and b in the I:1 balun(Fig. 9a) as in Fig. 9b, produces an unbal-anced 4:1 design. For minimal leakage induc-tance, connection must be kept short by bend-ing the line to get the connection points closetogether. In this case the line 4 should be thegeometric mean of the input and outputimpedances or 4(50x12.5) or 250.
The same is true of other impedance ratiotransformers. Derivations are shown in Figs.9c and 9e, of a balanced -to -balanced config-uration, using two or four lines. A commonmagnetic core can be used for both if the cou-pling between the two can be kept minimal.But separate cores are usually recommended.Since this transformer has a 4:1 impedanceratio, the optimum line impedance is again25g. If the 'centre tap' is left floating, dc canbe fed through it - eg not by-passed to ground- and a balun normally seen to provide a bal-
610 ELECTRONICS WORLD + WIRELESS WORLD July 1994
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RL
0
RL/4
a
AL (c)
anted -to -unbalanced function can be omitted.Otherwise, another dc feed method must bechosen.
This also applies to the 16:1 ratio trans-former (Fig. 9e), which employs two 4:1transformers in series, where the same rulesare in effect.
Line impedance of the high -impedance 4:1segment is 250, which was previously deter-mined to be the required value. The lineimpedance of the second section would be\i(25x3.12)=6.2552, making its design some-what impracticable as line impedances of sucha low value are difficult to achieve. But itwould be possible to parallel two 12.552 coax-ial cables, for example, which is standardpractice.
Coaxial cables with impedances of 12.5,16.7, and 2512 are becoming standard itemsfor cable manufacturers today. For manyapplications however, the line impedance isnot critical provided that some bandwidthdegradation is acceptable.
Figure 9d shows a 9:1 balanced -to -balancedtransformer. Performance can be good if theinterconnections can be kept short - but this ismore difficult than with the 4:1 transformersince there are more interconnections and theimpedance levels are lower. Here the optimumline impedance is 1.1(50x5.55) or 16.652.
Unlike the 4:I unit, the balanced 9:1 trans-former always requires a balun in the end thatis to be terminated with an unbalanced sourceor load. It also does not have a balanced pointto allow dc feeding through the lines.
RL 9
RI_ 16
2
(f)
R[ (d)
Overcoming limitationsAs mentioned earlier, a limitation of squaredinteger transformation ratios is the biggest dis-advantage of the transmission line transformer.There are ways to get around this, but thedesigns are complex and bulky, and call foradditional lines and connections betweenthem, greatly reducing bandwidths in somecases.
One such design for three different config-urations is shown in Fig. 9f (in simplifiedform in Fig. 9f3 to make analysing its opera-tion easier than using configuration Fig. 9f2for example). An analysis of the current dis-tribution between each winding reveals a ratioof 1.5:1 between the primary and the sec-ondary, equalling the turns ratio and resultingin an impedance ratio of 1.52 or 2.25:1.
Assuming RL=5011 (in which case thesource would be 112.50), optimum lineimpedance is 50/1.5 or 3311. This transformerhas a balanced -to -balanced circuit configura-tion, requiring a balun if interfaced with anunbalanced source or load in either a step-upor step-down mode.
Equal delay transmission linetransformersIn normal 4:1 transmission line transformers,the high frequency response is limited byphase errors introduced between the intercon-nection points (such as a -b in Figs. 9, 10a and10b
If the connection from a to b were madewith a transmission line of equal impedance
3
Fig. 9. Some examples oftransmission linetransformers. Forsimplicity, most areshown without magneticcores and can be used assuch in many vhf and uhfapplications. All the linesmust be formed into aphysical shape whichminimises the lengths ofthe interconnection forreduced leakageinductance. The photo atg) shows a uhf push-pullamplifier usingtransmission linetransformers in its inputand output matching. Theinput at the left uses a 4:1as shown in c) and theoutput at the right uses a1:9 transformer as shownas d).
and length as the main line, the phase dif lea -ence between the input and output would beeliminated. The transformer topology wouldremain the same, except that the a -b connec-tion would have the same phase delay as themain transformer line.
Such a transformer can be viewed as twocoaxial lines with their input terminals inseries and output terminals connected in par-allel. Where one line is always used only toprovide a delay of a controlled amount, it isalso the case with equal delay transformers ofany other impedance ratio.
For this reason, the sub -class is called equaldelay transmission line transformers, servingapplications from 1MHz to at least 500MHzdepending on the impedance levels involved.
Transformer input and output connectionscan be physically separated - an advantage inmany cases.
Figure 10b is a pictorial and schematic rep-resentation of a 4:1 equal delay transformer. Ifa third line is added to the 4:1 design (Fig.
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4RL (a)
(b)
(c)
10c), a 9:1 impedance transformer results.Similarly, four lines will produce a 16:1 trans-former (Fig. 10d) and so on.
Wideband requirementsWideband operation demands that most of thetransmission lines must be surrounded bymagnetic material, generally in the form oftoroids or sleeves. The amount of magneticmaterial required in each line depends on thelevel of the impedance transformation. Theline impedances are equal, but the highestimpedance transform line requires one unit ofmagnetic material, the next one two, the fol-lowing one three and so on. By unit we meana measure of cross-sectional area of similarmagnetic material.
All these designs are unbalanced -to -unbal-anced transformers - though baluns (Figs.10f2 and 10f3) can be added to obtain a bal-anced interface.
Suppose we add a magnetic core to the bot-tom line of a 4:1 transformer. Now we candisconnect the grounds of the parallel con-nected lines (still keeping the shields con-nected) and add a balanced, floating loadbetween the centre conductors and the shieldsto form a 4:1 balun.
Stray capacitances to ground can be bal-anced by connecting the centre conductor ofone coax to the shield of the other and a trans-former as in Fig. 9c) would be formed. Inequal delay transformers of any impedanceratio, the last line only provides delay and hasno external fields. It requires no magneticcore, but the presence of magnetic materialwill not affect its performance. The line char-acteristic impedance (Z0) requirements are the
(d)
(e)
same as for standard transmission line trans-formers - eg Z0 equals the ratio of voltage to
where N=-V(ZIN/ZouT).Equal delay transformers have the full inte-
ger limitations of the standard transmissionline networks. But their physical configura-tions make it is easier to create fractional inte-ger impedance ratios with equal delay trans-formers by using subgroups of additional lines(Fig. 10e).
If we describe group A (Fig. 10a) as themain transformer, providing the full integersof impedance transformation, adding group B(Fig. 10b) lines with their low impedancesides connected to the high impedance side ofgroup A results in fractional impedance trans-form ratios. The resulting impedance ratioscan be calculated as N=(n A4-1/nB), where nA isthe impedance ratio of group A, i.e. the maintransformer, and ng is the impedance ratio ofgroup B.
For example, if group A has one line andgroup B has two, the transform ratio is 2.25:1.Further, if A=2, B=4, N=5.0625:1; and A=2,B=2, N=6.25:1.
Line impedances are dictated by the trans-form ratio and the impedances required for themain transformer (group A).
How much improvement in bandwidth theequal delay transformer gives compared withthe standard transmission line transformerdepends largely on mechanical factors. Alsoeven if both are correctly compensated, theinsertion loss of the equal delay transformercan be at least 0.1dB less than the standardtransmission line transformer in the frequencyregion up to 500MHz.
Fig. 10. Equal delay transformers. a) is abasic standard transmission line typeshown as a comparison against b). b), c)and d) are basic configurations, wherease) uses a sub -group of lines to provide afractional integer impedance ratio. 0 is a4:1 unit with baluns (c and d) added forbalanced interface.
(a) (b)
Fig. 11. Cross section of a correctly arrangedtwisted wire with two pairs of wires a) and fourpairs of wires b). 0 represents one conductor ofthe line and X the other.
612 ELECTRONICS WORLD + WIRELESS WORLD July 1994
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BILLINGTON EXPORT LTDlE GILLMANS IND EST, BILLINGSHURST, SUSSEX RH14 9EZ
CALLERS STRICTLY BY APPOINTMENT ONLYTEL: 0403 784961 FAX: 0403 783519
MINIMUM ORDER £50.00 PLUS VAT
TURN YOUR SURPLUSTRANSISTORS, ICS ETC, INTO CASH
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complete factory clearance.Contact
COLES-HARDING & CO. 103 South BrinkWisbech, Cambs PE14 ORJ.
ESTABLISHED OVER 15 YEARSBuyers of Surplus Inventory
Tel: 0945 584188 Fax: 0945 475216
TOP PRICES PAIDFor all your valves, tubes,semi conductors and IC's.
Langrex Supp ies Ltd,1, Mayo Road, Croydon,
Surrey, CRO 20PTEL; 081 684 1166FAX 081 684 3356
ARTICLES FOR SALE
Cooke internationalSUPPLIER OF QUALITY USED
TEST INSTRUMENTSANALYSERS, BRIDGES, CALIBRATORS,
VOLTMETERS, GENERATORS, OSCILLOSCOPES,POWER METERS, ETC. ALWAYS AVAILABLE
ORIGINAL SERVICE MANUALS FOR SALECOPIES ALSO AVAILABLE
EXPORT, TRADE AND U.K. ENQUIRIES WELCOME,SEND LARGE "A3" S.A.E. + 50P POSTAGE FOR LISTS
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OPEN MONDAY -FRIDAY 9AM-5PM
Cooke InternationalELECTRONIC TEST & MEASURING INSTRUMENTSUnit Four, Fordingbridge Site, Main Road, Barnham,
ENGINEERSThe ASSET team of Philips Electronics is currently seeking to recruittwo Senior Acoustics Engineers. ASSET (Acoustics Support andService Team) is a design centre for sound reproduction systemsand is located in Dendermonde, Belgium. Projects are executed forother Philips' business units and for non -Philips companies.The team is active in very different markets: hifi, audio systems,portable audio, TV, car radio, multimedia, sound reinforcement.Recently ASSET was involved in the design of Philips' DSS 930digital loudspeaker, a real breakthrough in speaker technology.
PROFILEBecause of the highly professional environment, candidates requireindepth knowledge and experience in the design of acoustics systems.An understanding of analogue and digital audio processing is a distinctadvantage. Fluent communicative skills are vital for day-to-daycustomer contact, target specifications, planning and costs.If you are intrested in this challenging position, you can addressyour application (letter and C.V.) to: PHILIPS N.V.Flor Boeckx - Hoogveld, 50 - 9200 Dendermonde - Belgium
For more information on this position, please contactLuc Auwaerts, Manager Asset Team - tel.: 32.52. 261 405
1 OR 2 YEAR CONTRACT, NO FEES.FAX DETAILED CV/RESUME TO
KEN BEAMTEL: 966-3-894-6909
RECEIVER DEVELOPMENT ENGINEERA British Company are about to start an exciting new projectto develop a state of the art HF communications receiver tocompete in the World market. A vacancy exists for a topgrade engineer to take charge of this project. The successfulcandidate will probably have several years previous experi-ence of receiver design, be aware of the best of currenttechnology in the field, and be conversant with digital signalprocessing techniques.
The salary and benefits package offered will be commensuratewith the importance of the project, and maximum freedomwill be given to the individual to exercise their own creativity.
Please reply in confidenceCIRCLE NO. 134 ON REPLY CARD
FREE CLASSIFIEDWIRELESS WORLD 1976-1992 1 or pricelist S.A.E. Teleyuipment 054-10MhzDual Trace £1151 or exchange with Fre-quency Counter. S. 20, Cite -vertu!) Road, London N19 3AY. Tel:071-272 7139.
DRANETZ 305C. Phasemeter for sale. 2Hz to 700 KHz. 11,111 degrees resolution,fully working with plug -ins £3611 ono. Askfor Mike after 7pm. 0483 457159.SPEEDWIRE TERMINALS, reels ofWOO, Vero part number 244-262193 150each. 0234 219756.
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All advertisements must be received five weeks prior to publication date.All cancellations must be received by eight weeks prior to publication date. Afterthat no advertisement can be cancelled.Please send to Electronics World & Wireless World, Classified, 3rd Floor,Quadrant House, The Quadrant, Sutton, Surrey SM2 5AS. Tel: Malcolm Wells on081-652-3620.
ELECTRONIC UPDATEContact Pat Bunce on
081-652 8339
zAGI's/ 1Pws!E 13=Tr$4:415.FLA.S.H. E whaks,s and OW'S, MP tp 610
The system 2000 is an idealprogrammer for the produc-tion environment. Fast prog-ramming results in highthroughput and rigorous veri-fication leads to improvedquality control. Single keyfunctions and checks againstmisoperation facilitates itsuse by unskilled staff.
OLSON ELECTRONICS LIMITED isa leading manufacturer in the field ofmains distribution panels of everyshape and size to suit a variety ofneeds. For use in Broadcasting,Computing, Data Communications,Defence, Education, Finance,Health etc. All panels aremanufactured to BS5733. BRITISHAMERICAN, FRENCH, GERMANCEE22/IEC and many othersockets. Most countries catered for.
All panels are available ex -stock andcan be bought direct from OLSON.
The new 230 page 1994 PC -LABcatalogue covers an extensive rangeof PC -based data acquisition, mea-surement, control, and interfaceplug-in cards plus supporting soft-ware packages for engineering &scientific applications. Also inclu-des 19" rack mounting industrialPCS, custom OEM PC chassis andassociated sub -systems.Please contact integrated measure-ment systems for a free cataloguecopy.
Tel: (0703) 771143Fax: (0703) 704301
INDUSTRIAL PCsArcom's PCbus range is expresslydeveloped for embedded control anddata acquisition, providing high integ-rity industrial solutions with:* full range of CPU and 110 functions* industrial EMC enclosures mezza-nine bus expansion " industry stan-dard signal conditioning * Windows 1/0 drivers with predictable perform-ance.Arcom Control Systems makes plug -together PC solutions for industry areality!Please forward all enquiries to AlanTimmins at: Arcom Control SystemsLtd, Units 8-10 Clifton Road,
A regular advertising feature enablingreaders to obtain more informationon companies' products or services.
LabWindows/CVIBrochure
The LabWindows/CVI Brochure,from National Instruments,explains how users can buildinstrumentation applications onWindows PCs and Sun SPARCsta-tions using the ANSI C program-ming language and LabWindows/CVI data acquisition, analysis, andpresentation libraries.
NATIONAL INSTRUMENTSFor further information
FREEPHONE 0800 289877
CIRCLE NO. 146 ON REPLY CARD
SPICE A/D Simulation
;da
1111[0,11. DIVIDE BY 2 ClaClIr [MIKE
S00 500
Mixed Analogue and Digital All SPICE 2G6 analyses Behavioural Modelling Graphical post -processor FREE 10 transistor version 640K version £395
32 bit extd. mem. ver. £695 Schematic front-end £149
To receive your FREE working evaluation version just send a 1.44MBHD 3.5in disk to: EW+WW Otter, CRaG Systems, 8 Shakespeare Rd,Thatcham, Newbury, BerksRG13 4DG, Tel (0635) 873670 CIRCLE NO. 147 ON REPLY CARD
2nd EDITION TOKO RFCATALOGUE
Cirkit have just published the 2ndEdition of the Toko RF Catalogue,featuring details of Tokos' extensiverange of RF coils, inductors, filtersand comms ICs.
The 128 page catalogue includesmany new products such as;Surface mount high currentinductors, surface mount multilayerinductors, helical filters at 2.5GHzand a new section of push buttonand tact switches.Cirkit Distribution Ltd, Park Lane,Broxbourne, Herts, EN107NOTel: (0992) 441306Fax: (0992) 441306
CIRCLE NO. 148 ON REPLY CARD
High Speed EPROM & FLASHProgramming from your PCO Programs EPROMs to 4 Mbits/
32 -pins Superfast 8, 16 & 32 -bit
programming Approved algorithmsO Menu driven software included Sophisticated editor functions Easy file managementO FREE demo disk available
MARCONI INSTRUMENTS2019 AM/FM synthesized signal generator 80kHz-1GHz
2019A as above, improved spec
2828A/2829 digital simulatorianalyser
2830 multiplex tester
6059A signal source 12-18GHz
C1000
C1500
£750
6460/6420 power meter 10MHz - 12.4GHz 0.3uW - 10mW
6460/6423 power meter 10MHz - 12.4 G Hz 0.3m W- 3W
67008 sweep oscillator 8 1 2.4G Hz & 12.4 - 8GHz
6912 power sensor 30kHz - 4.2G Hz for above series
8935 audio power meter
0A2805A PCM regenerator test set
Tr 2910/4 non-linear distortion (video) analyser
TF2914A TV Insertion signal analyser
TF2910 TV interval timer
£1750
£1950
DISTRIBUZIONE E ASSISTE ITALY: TLC RADIO, ROMA, 106 71 90254
TEST EQUIPMENTANRITSU ME518A PCM portable error rate test setBRUEL & KJAER 2511 vibration meter set/1621 filter
BRUEL& KJAER 2307 level recorder
BRUEL & KJAER 2317 portable level recorder
BRUEL & KJAER 1618 band bass filter
BRUEL& KJAER 3513 portable vibration analyser
BRUEL &KJAER 2515 vbration analyser
AVORM2151-2 insulation & breakdown tester
DATRON 1065 digital mubmeter
DRANETZ 626 mains disturbance analyser/2 x PA6001
DRANETZ 606-3 line disturbance analyser
KEITHLEY 192 programmable dmm
MAURY MICROWAVE 8650E TNC-calibration kit
NAG RA IV -SJ tape recorder
£2500
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f1000£1850
£750
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0400
C1503
20130
TEKTRONIC CSA803A COMMUNICATIONS SIGNAL ANALYSER
As new, supplied with IxS022 head f22000 eachTEKTRONIX 1503013/4/5/6 tdrcable tester £3250
MUCH MORE, FULLY RE -FURBISHED, FULLY GUARANTEED TESTEQ U IPM ENT AVAILABLE FROM STOCK. PLEASE REQUEST OU R
CURRENT LISTINGS. WE CAN FAX LISTS & SHIP GOODS WORLD-WIDE. HIGH -END EQUIPMENT ALWAYS WANTED FOR STOCK
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£350
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0500
RACAL 9008 automatic modulation meter £325.9009
RACAL 9082 synthesized AM/FM sig' gen' 5- 520MHz
RACAL 9300 RMS voltmeter - 80dB to +50db
RACAL 9341 LCR datattidge component tester
RACAL -DANA 9302 RF milli -voltmeter 1.5GHz
RACAL -DANA 9303 level meter, digital
ROBERTS& ARMSTRONG fb-cableend-eut measure unit
TEKTRONIXJ16 digital photometer
TEKTRONIX 1503C/03/04/05/06 TDR cable tester
WAVETEX 2000 0 -1400MHz sweep generator
WAYNE KERR B905 automatic precision bridge
£300
£500
£325
£350
£450
£1000
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£3250
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£150
-. :
50:
11111 i a
331A distortion meter
339A distortion meter
3457A digital multimeter
3335A synthesizer8evelgenerator with option 01
33364 level generator
3552A transmission test set
3586A selective level meter
415E swr meter
4274A multi -frequency (100Hz-100kHz)LCR component meter
4275A multi -frequency LCR component meter
432A1478A microwave power meter 10MHz-1OGHz
432NR486A uwave power meter 26.5-40GHz (waveguide)
50058 signature multi -meter, programmable
54501A digitising oscilloscope 100MHz 10MS/s
6253A dual power supply 0-20V 0-3A twice
6825A bOolar power supply/amp -20 to +20vdc 0-1A
70300A tracking generator plug-in unit
70907A external mixer for 70000-ser spectrum analyser
7035B X -Y single pen analogue chart recorder
8011A pulse generator 0.1Hz-20MHz
816A slotted line 1.8-I I3GHz with carnage 8090 & 447B
8350B sweep generator main-frame
8405A vector voltmeter, voltage & phase to 1000MHz
8620C sweep generator. many plug-in units available
8671 A synthesized signal generator 2 6.2GHz
8153C eh 8504£4 NETWORK ANALYSERS
wttA S-PillAMETEll 1S1 SET as new, calibrated. 822503
£200
£1500
C1250
02500
£2000
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£225
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PLEASENOTEALLOUR EQUIPMENT IS NOW OPERATIONVERIFICATION
TESTEDBEFORE DESPATCH BY INDEPENDENT LABORATORY
We would be pleased to handle all grades of calibration or NAMAS certification
by same laboratory at cost pnce. All items covered by our 90 -day parts and labour
guarantee and 7 -day 'Right to Refuse (money.back) warranty.
ALL PRICES SUBJECT TO ADDITIONAL VAT AND C ARRIAGE
CIRCLE NO. 131 ON REPLY CARD
INDEX TO ADVERTISERS
Anchor Surplus Ltd
BK ElectronicsBull Electrical
Chelmar ValveCitadel Products Ltd
Dataman DesignsDisplay Electronics Ltd
Field Electric Ltd
Halcyon Electronics Ltd
Ice Technology Ltd
John MorrisonJohn's RadioJohn's RadioJPG Electronics
Kestral ElectronicsKeytronics
Lab Center
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582
IFC
OBC547
595
Langrex
M & B ElectricalM B Radio (Leeds)MQP Electronics
Number One Systems
Powerware
Ralfe ElectronicsRemote Imaging Group
595 Seetrax LtdSmart CommunicationsSmart CommunicationsStewart of ReadingSurrey Electronics
539
582
530
535
582TektronixTelnet
582 Those Engineers Ltd581 Tsien Ltd
558 Ultimate Technology
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616 July 1994 ELECTRONICS WORLD+WIRELESS WORLD
FROM CONCEPT TO ARTWORK IN 1 DAY
INIULTlboard;ULTIcap evaluation system: all features of the bigger versions full set of manuals design capacity 350 pins
Price incl. S & H, excl. VAT:
Purchase price is 100% credited when upgrading toa bigger version. Also suitable tole/ & hobby
'sign ideas are quickly cgtured using the ULTIcap schematic design Tool. ULTIcap usesf)ME checks to prevent logic errors. Schematic editing is painless: simply click your start and endInd ULTIcap automatically wires them for you. ULTicap's auto snap to pin and auto junction
features ensure your netlist is cc mplete. thereby relieving you of tedious netlist checking.
ULTIsh011.1he integrated user interface, makes sure allyour deign information is transferred correctly fromULTIcajito ULTlboard. Good manual placement tools arevital to the progress of your design. therefore ULTlboardgives you a powerful suite of REAL-TIME functions suchas, FORCE VECTORS, RATS NEST RECONNECT andDENSITY HISTOGRAMS. Pin and gate swapping allowsyou to further optimise your layout.
" -=1.
4 :
, Y
you can quickly route your critical tracks.LTIboard's REAL-TIME DESIGN RULE CHECK
,,,i1,1nc allow you to make illegal connections orviolate your design rules. ULTlboard's powerfulTRACE SHOVE, and REROUTE -WHILE -MOVEalgorithms guarantee that any manual trackediting is flawless. Blind and buried vias andsurface mount designs are fully supported.
If you need partial ground planes, thenwith the Dos extended board systems youcan automatically create copper polygonssimply by drawing the outline. The polygonis then filled with copper of the desired net.all correct pins are connected to thepolygon with thermal relief connectionsand user defined gaps are respectedaround all other pads and tracks.
ULTlboard's autorouter allows you tocontrol which parts of your board areautorouted, either selected nets, or acomponent. or a window of the board, orthe whole board. ULTlboard's intelligentrouter uses copper sharing techniques tominimise route lengths. Automatic viaminimisation reduces the number of vias todecrease production costs. The autorouterwill handle up to 32 layers, as well assingle sided routing.
ULTlboard's backannotation automaticallyupdates your ULTIcap schematic with any pinand gate swaps or component renumbering.Finally, your design is post processed to generatepen / photo plots, dot matrix/laser or postscriptprints and custom drill files.
L EPROMg 16 -BIT EPROM*g EEPROMCSI SERIAL EEPROM*CI FLASHg PIC*08751*I EMULATION
C1 FREE UPGRADES_I TOTALLY HANDHELD'g 3 YEAR GUARANTEEg AVAILABLE TODAY!
'Requires optional modules.
A 32 pin ZIF socket programs a huge library ofEPROMs. EEPROMs and FLASH devices upto 8Mbit. And our unique user loadableLibrary means that new parts can be addedquickly. and at no cost. All software upgradesare free and available for 24hr download fromour high speed bulletin boards.
EmulationSee your code running before committing yourselfto an EPROM. With S4's powerful and easy -to -use internal emulation system, download yourcode to S4, press 'EMULATE', and your targetsystem runs in real time as if an EPROM wasplugged in to the socket. Use S4's 'EDITcommand to make minor alterations to your codeand see the changes happen immediately - justone reason why S4 is used by the world's carmanufacturers to develop advanced enginemanagement systems in real time! With S4emulation there's no need for trailing cables orexternal power sources; earth loop problems area thing of the past. S4 even emulates RAM.
Remote ControlAs well as being totally stand alone and selfcontained, S4 can be operated remotely via it'sserial port at speeds up to 115,200 Baud. Wesupply you with a FREE disk containing customterminal software and a pop-up TSR communica-tions utility.
The CompanyDataman has been designing and selling
innovative programmers world-wide for over 15
years. As well as havingsales and support offices inboth the UK and the USA, wesupply the world demand for ourproducts via a network of approvecdealers stretching from Norway toAustralia.
The PackageS4 comes complete with mains charger,emulation leads, comprehensive manual,PC software and a spare library ROM;there are no hidden extras to buy.Upgrading S4's device library is free, doesnot involve costly internal ROM upgradesand technical support is free for life. OnlyS4 comes with a three year guarantee.
Availability
S4 is always in stock and we ship worldwide on adaily basis. Call now for delivery TOMORROW.
Bona -fide UK customers can try S4 for thirty dayswithout risk. 16,000 users can't be wrong!
Size:186 x 111 1 46mmWeight: 515g
Dataman Programmers Ltd
Credit card hotline:0300 320719for same -day dispatch
