ANALOG ELECTRONIC CIRCUIT DESIGN (15 EC 2103 · PDF file · 2016-07-30ANALOG...

ANALOGELECTRONICCIRCUITDESIGN(15EC2103)

Dr.M.Durga.PrakashAssociateProfessor

Dept.ofECE

CourseOverviewandinformaKon

OUTLINEOFSYLLABUS

u Part-1:P-NJuncKons

u Part-2:Transistorbiasing&stability

u Part-3:OperaKonalamplifiers

u Part-4:Feedbackamplifier&Oscillators

P-1:P-N JuncKons:Diode theory, forwardandreverse-biased juncDons,reverse-biasbreakdown, loadlineanalysis,diodeapplicaDons-Limiters,clippers,clampers,voltagemulDpliers,halfwave&fullwaverecDficaDon,Capacitor filters, π-secDon filter, ripple factor, Special purpose diodes -Zener diode, Varactor, light emiPng diodes, Laser diodes. Regulators:Series and shunt voltage regulator, percentage regulaDon, Concept ofSMPS.

P-2: Transistor biasing& stability: Q point, Self-Bias-CE, CompensaDontechniques, h-model of Transistor, Expression of voltage gain, currentgain, input&output impedance,Trans-resistance&Trans-conductance,EmiWer follower circuits, High frequency model of Transistor, FETfundamentals, ConfiguraDons, current-voltage characterisDcs,parameters of JFET, Biasing of JFET, Biasing of MOSFET.Transistoramplifiers:RCcoupledamplifier,FuncDonofallcomponents,Equivalentcircuit, derivaDon of voltage gain, Current gain, Input impedance &output impedance, Frequency response characterisDcs, Lower & upperfrequencies,Bandwidth,ConceptofWidebandamplifier,FETsmallsignalmodel,CommondraincommongateconfiguraDons.

P-3: OperaKonal amplifiers: Ideal OPAMP, DifferenDal amplifier,Constantcurrentsource,CMRR,Open&closedloopcircuits,importanceof feedback loop (posiDve & negaDve), inverDng & non-inverDngamplifiers, Voltage follower circuits. ApplicaDon of OperaDonalamplifiers: Adder, Integrator & DifferenDator, Comparator,SchmiWTrigger, InstrumentaDon Amplifier, Log & AnDlog amplifier, Trans-conductancemulDplier,Precision recDfier,Voltage tocurrent&Currenttovoltageconverter.FilterCircuits:AnalysisofLowpass,Highpass,Bandpass, Band reject, All pass filters (first and second order only) usingoperaDonalamplifier.

P-4:Feedbackamplifier&Oscillators:ConceptofFeedback,NegaDve&PosiDvefeedback,Voltage/Current,Series/Shuntfeedback,Barkhausen’scriterion, ColpiW’s, Hartley’s, Phase shia, Wien Bridge, & Crystaloscillators. Power amplifiers: Class A, B, AB, C, Conversion efficiency,DistorDon. MulDvibrators: Monostable, Bistable mulDvibrators,Monostable & Astable operaDon using 555 Dmer. Special funcDoncircuits:VCO&PLL

KLUDr.M.DurgaPrakash

CourseObjecKve

•  TofamiliarizewiththetheoreDcalandmathemaDcalaspectsofElectronicsystems

•  To design Electronic systems and resolve Designorientedproblems


DesiredOutcome•  AnalyzingvariousdiodebasedcircuitsanddemonstraDngworking

principlesofBJTandJFET.

•  DesignofBJTamplifer.

•  DemonstraDngtheLinear&Non-linearapplicaDonsofOPAMPs.

•  Design of the concepts of feedback amplifiers, oscillators andpoweramplifiers.

•  DesignandTesDngofAnalogcircuits


OtherRelevantInformaKon

•  Prior knowledge required: Some basic Knowledge ofSemiconductorPhysics

•  Levelofdifficulty:Medium

•  MathemaKcs:Simple


EvoluKonSchemeEvaluation Component

Weightage/Marks Date Duration CO1 CO2 CO3 CO4 CO5

Marks

COI Number COI-1 COI-2 COI-1 COI-2 COI-1 COI-2 COI-1 COI-2 COI

BTL 2 3 2 3 2 3 2 3

Test 1 Weightage (6%)

1.5 hr

1.2% 4.8% 6M

Max

Marks(30) 6M 24M


1.5 hr

1.2% 4.8% 6M

Max

Marks(30) 6M 24M


1.5 hr

1.2% 4.8% 6M

Max

Marks(30) 6M 24M

Active Learning

Weightage (15%)

15M

Max

Marks(25)

Attendance Weightage (5%) 5M

Lab Continuous Evaluation

Weightage (5%)

5M

Max Marks(20)

Project

Weightage (7%)

7M

Max Marks(20)

SE Lab Exam

Weightage (5%)

3 hrs

5M

Max Marks(20)

SE Project

Weightage (5%)

5M

Max Marks(30)

Semester End Exam

Weightage (40%)

3 hrs

1.6% 6.4% 1.6% 6.4% 1.6% 6.4% 3.2% 12.8%

40M Max Marks(50) 2M 8M 2M 8M 2M 8M 4M 16M

Question Number

1a 1b 2a 2b 3a 3b 4a & 5a 4b & 5b

TOTAL 100M


Reference

TextsBooks1.   MuhammadH.Rashid,“MicroelectronicCircuitsAnalysisandDesign”,2nd

ediKon,CengageLearning.

2.   Sedra&Smith,“Micro-ElectronicCircuitstheoryandapplicaKons”,OxfordPress

ReferenceBooks1.   JacobMillman&ChristosC.Halkias,“IntegratedElectronics”,Tata-

McGrawHill,2ndEdiKon,(2010).

2.   RobertL.BoylestadandLouisNashelsky,“ElectronicDevicesandCircuitTheory”,PHI.9thEdiKon


HaveQuesKons?

LocaKon:C–Block,RoomNo:C016

E-Mail:[email protected]


Lecture:1 Topics

IntroducDon

Diodetheory:operaDon,forwardandreverse-bias,V-I

characterisDcs.

DiodeequaDon,smallsignalandlargesignalequivalentcircuits.


IntroducDon

•  Thediode is thesimplestandmost fundamentalnonlinearcircuitelement.

•  Justlikeresistor,ithastwoterminals.

•  Unlikeresistor,ithasanonlinearcurrent-voltagecharacterisDcs.

•  Its use in recDfiers is the most commonapplicaDon.


PhysicalStructure

Themostimportantregion,whichiscalledpnjuncDon,istheboundarybetweenn-typeandp-typesemiconductor.


SymbolandCharacterisDcfortheIdealDiode

(a)diodecircuitsymbol;(b)i–vcharacterisDc;(c)equivalentcircuitinthereversedirecDon;(d)equivalentcircuitintheforwarddirecDon.


CharacterisDcs

•  ConducDng in one direcDon and not in theotheristheI-VcharacterisDcofthediode.

•  The arrowlike circuit symbol shows thedirecDonofconducDngcurrent.

•  Forwardbiasingvoltagemakesitturnon.

•  Reversebiasingvoltagemakesitturnoff.


BasicSemiconductorConcepts

•  IntrinsicSemiconductor•  DopedSemiconductor•  Carriersmovement


IntrinsicSemiconductor

•  DefiniDonAcrystalofpureandregularla4cestructureiscalledintrinsicsemiconductor.

•  MaterialsØ Silicon---today’sICtechnologyisbasedenDrelyonsilicon

Ø Germanium---earlyusedØ Galliumarsenide---usedformicrowavecircuits


IntrinsicSemiconductor(cont’d)

²  Two-dimensionalrepresentaDonofthesiliconcrystal.

²  The circles represent the innercore of silicon atoms, with +4indicaDng its posiDve charge of+4q,whichisneutralizedbythecharge of the four valenceelectrons.

²  Observe how the covalentbondsare formedby sharingofthevalenceelectrons.

²  At 0 K, all bonds are intact andno free electrons are availableforcurrentconducDon.



²  At room temperature,some of the covalentbonds are broken bythermalionizaDon.

²  Each broken bond givesrise to a free electron anda hole, both of whichbecome avai lable forcurrentconducDon.


•  ThermalionizaDonØ Valenceelectron---eachsiliconatomhasfourvalenceelectrons

Ø Covalentbond---twovalenceelectronsfromdifferenttwosiliconatomsformthecovalentbond§  Beintactatsufficientlylowtemperature§  Bebrokenatroomtemperature

Ø Freeelectron---producedbythermalionizaDon,movefreelyinthelaPcestructure.

Ø Hole---emptyposiDoninbrokencovalentbond,canbefilledbyfreeelectron,posiDvecharge





•  CarriersAfreeelectronisnegaDvechargeandaholeisposiDvecharge.Bothofthemcanmoveinthecrystalstructure.Theycanconductelectriccircuit.


•  RecombinaDonSomefreeelectronsfillingtheholesresultsinthedisappearanceoffreeelectronsandholes.

•  ThermalequilibriumAtacertaintemperature,therecombinaDonrateisequaltotheionizaDonrate.SotheconcentraDonofthecarriersisabletobecalculated.



•  CarrierconcentraDoninthermalequilibrium

•  Atroomtemperature(T=300K)

carriers/cm3

inpn ==kTE

iGeBTn −= 32

10105.1 ×≅in



Importantnotes:•  hasastrongfuncDonoftemperature.Thehighthe

temperatureis,thedramaDcallygreatthecarrierconcentraDonis.

•  Atroomtemperatureonlyoneofeverybillionatomsisionized.

•  Silicon’sconducDvityisbetweenthatofconductorsandinsulators.ActuallythecharacterisDcofintrinsicsiliconapproachestoinsulators.

in


DopedSemiconductor

•  Dopedsemiconductorsarematerialsinwhichcarriersofonekindpredominate.

•  Onlytwotypesofdopedsemiconductorsareavailable.

•  ConducDvityofdopedsemiconductorismuchgreaterthantheoneofintrinsicsemiconductor.

•  ThepnjuncDonisformedbydopedsemiconductor.


DopedSemiconductor(cont’d)

ntypesemiconductor•  Concept

Doped silicon in which the majority of charge carriers are thenega>velychargedelectronsiscalledntypesemiconductor.

•  Terminology

Ø  Donor---impurityprovidesfreeelectrons,usuallyenDrelyionized.

Ø  Posi>ve bound charge---impurity atom donaDng electron givesrisetoposiDveboundcharge

Ø  carriers•  Freeelectron---majority,generatedmostlyby ionizedandslightlybythermalionizaDon.

•  Hole---minority,onlygeneratedbythermalionizaDon.



²  Asiliconcrystaldopedbyapentavalentelement.

²  Each dopant atomdonatesa free electron and is thuscalledadonor.

²  The doped semiconductorbecomesntype.



ptypesemiconductor•  Concept

Dopedsiliconinwhichthemajorityofchargecarriersaretheposi>velychargedholesiscalledptypesemiconductor.

•  Terminology

Ø  acceptor---impurityprovidesholes,usuallyenDrelyionized.

Ø  nega>velyboundcharge---impurityatomaccepDngholegiverisetonegaDveboundcharge

Ø  carriers•  Hole---majority,generatedgeneratedmostlybyionizedandslightlybythermalionizaDon.

•  Freeelectron---minority,onlygeneratedbythermalionizaDon.



²  A silicon crystal dopedwithatrivalentimpurity.

²  Each dopant atom givesrise to a hole, and thesemiconductor becomesptype.



CarrierconcentraDonforntypea)  ThermalequilibriumequaDon

b)  ElectricneutralequaDon

200 inn npn =⋅

nn0 = pn0 + ND



CarrierconcentraDonforptypea)  ThermalequilibriumequaDon

b)  ElectricneutralequaDon

200 ipp nnp =⋅

App Nnp += 00



Becausethemajorityismuchgreatthantheminority,wecangettheapproximateequaDonsshownbelow:

forntypeforptype

⎪⎩

⎪⎨

⎧

≈

≈

D

in

Dno

Nnp

Nn2

0 ⎪⎩

⎪⎨

⎧

≈

≈

A

ip

Ap

Nnn

Np2

0

0



•  ConclusionØ Majoritycarrier isonlydeterminedbythe impurity,butindependentoftemperature.

Ø Minoritycarrierisstronglyaffectedbytemperature.

Ø Ifthetemperatureishighenough,characterisDcsofdoped semiconductor will decline to the one ofintrinsicsemiconductor.



•  DopingcompensaDon² n type semiconductor is generated by

donordiffusion,theninjecDngacceptorintothespecificarea(assuming )formsptypesemiconductor.

² The boundary between n and p typesemiconductoristhepnjuncDon.

² This is the basic step for VLSIfabricaDontechnology.

ND

NA

DA NN >>


CarriersMovement

Therearetwomechanismsbywhichholesandfreeelectronsmovethroughasiliconcrystal.

•  Drig--- The carrier moDon is generated by the electrical fieldacrossapieceofsilicon.ThismoDonwillproducedriacurrent.

•  Diffusion--- The carrier moDon is generated by the differentconcentraDonofcarrierinapieceofsilicon.ThediffusedmoDon,usually carriers diffuse from high concentraDon to lowconcentraDon,willgiverisetodiffusioncurrent.


DriaandDriaCurrent

•  DriaØ DriavelociDes

Ø DriacurrentdensiDes

⎪⎩

⎪⎨⎧

−=

=

EvEv

ndrift

pdrift

µ

µnp µµ ,

Jn−drift = (−qn) ⋅ (−µnE) = qnµnEJp−drift = qp ⋅µpE

WherearetheconstantscalledmobilityofholesandelectronsrespecDvely.


DriaandDriaCurrent

•  Totaldriacurrentdensity

•  ResisDvity

EpnqJ pndrift )µµ＋（=

)(1

pn pnq µµρ＋

=


DriaandDriaCurrent

•  ResisDviDesfordopedsemiconductor

*Resis@vi@esareinverselypropor@onaltotheconcentra@onof

dopedimpuri@es.•  Temperaturecoefficient(TC)TCforresisDvityofdopedsemiconductorisposiDveduetonegaDveTCofmobility

⎪⎩

⎪⎨

⎧

=+=

pA

nD

pnqN

qNpnq

µ

µµµρ

1

1

)(1 Forntype

Forptype


DriaandDriaCurrent

•  ResisDvityforintrinsicsemiconductor

*Resis@vityisinverselypropor@onaltothecarrierconcentra@on

ofintrinsicsemiconductor.

•  Temperaturecoefficient(TC)TCforresisDvityofintrinsicsemiconductorisnegaDveduetoposiDveTCof.

)(1

)(1

pnipn qnpnq µµµµρ +=+=

in


DiffusionandDiffusionCurrent

•  Diffusion

Abarofintrinsicsilicon(a)inwhichtheholeconcentraDonprofileshownin(b)hasbeencreatedalongthex-axisbysomeunspecifiedmechanism.


DiffusionandDiffusionCurrent

wherearethediffusionconstantsordiffusiviDesforholeandelectronrespecDvely.

*Thediffusioncurrentdensityispropor@onaltotheslopeof the the concentra@on curve, or the concentra@ongradient.

dxxdnqDJ

dxxdpqDJ

nn

pp

)(

)(

⋅=

⋅−=

np DD ,


EinsteinRelaDonship

Einstein relaDonship exists between the carrierdiffusivityandmobility:

WhereVTisThermalvoltage.

Atroomtemperature，

qkTV

DDT

p

p

n

n ===µµ

mvVT 25=


pnJuncDon

•  ThepnjuncDonunderopen-circuitcondiDon

•  I-VcharacterisDcofpnjuncDon

Ø TerminalcharacterisDcofjuncDondiode.Ø PhysicaloperaDonofdiode.

•  JuncDoncapacitance


pnJuncDonUnderOpen-CircuitCondiDon

•  UsuallythepnjuncDonisasymmetric,therearep+nandpn+.

•  Thesuperscript“+”denotestheregionismoreheavilydopedthantheotherregion.


pnJuncDonUnderOpen-CircuitCondiDon

Fig (a) shows thepn juncDonwith no applied voltage(open-circuitedterminals).

Fig.(b) shows the potenDaldistribuDon along an axisperpendiculartothejuncDon.


ProcedureofFormingpnJuncDon

The procedure of forming pn the dynamic equilibrium ofdriaanddiffusionmovementsforcarriers inthesilicon. Indetail,thereare4steps:

a)  Diffusionb)  Spacechargeregion

c)  Driad)  Equilibrium



•  DiffusionØ Both the majority carriers diffuse across theboundary between p-type and n-typesemiconductor.

Ø ThedirecDonofdiffusioncurrentisfrompsidetonside.



•  SpacechargeregionØ Majority carriers recombining with minority carriersresultsinthedisappearanceofmajoritycarriers.

Ø Bound charges, which will no longer be neutralized bymajoritycarriersareuncovered.

Ø There isaregionclosetothe juncDonthat isdepletedofmajoritycarriersandcontainsuncoveredboundcharges.

Ø This region is called carrier-depleDon region or spacechargeregion.



•  DriaØ Electricfieldisestablishedacrossthespacechargeregion.

Ø DirecDonofelectronicfieldisfromnsidetopside.

Ø It helps minority carriers dria through the juncDon. ThedirecDonofdriacurrentisfromnsidetopside.

Ø Itactsasabarrierformajoritycarrierstodiffusion.



•  EquilibriumØ TwooppositecurrentsacrossthejuncDonisequalinmagnitude.

Ø NonetcurrentflowsacrossthepnjuncDon.

Ø Equilibrium conducDon is maintained by thebarriervoltage.


JuncDonBuilt-InVoltage

TheJuncDonBuilt-InVoltage

Ø ItdependsondopingconcentraDonandtemperature

Ø ItsTCisnegaDve.

2lni

DATo n

NNVV =


WidthoftheDepleDonRegion

WidthoftheDepleDonRegion:

Ø DepleDonregionexistsalmostenDrelyontheslightlydopedside.

Ø WidthdependsonthevoltageacrossthejuncDon.

oDA

depo VNNq

W )11(2+=

ε

))11(2 VVNNq

W oDA

dep －（+=ε


I-VCharacterisDcs

Thediodei–vrelaDonshipwithsomescalesexpandedandotherscompressedinordertorevealdetails


I-VCharacterisDcCurve

TerminalCharacterisDcofJuncDonDiodes

•  TheForward-BiasRegion,determinedby

•  TheReverse-BiasRegion,determinedby

•  TheBreakdownRegion,determinedby

ov >

0<<− vVZKZKVv −<


ThepnJuncDonUnderForward-BiasCondiDons

Ø ThepnjuncDonexcitedbyaconstant-current sourcesupplying a current I in theforwarddirecDon.

Ø ThedepleDonlayernarrowsand the barrier voltagedecreases by V volts, whichappearsasanexternalvoltageintheforwarddirecDon.



Minority-carrierdistribuDoninaforward-biasedpnjuncDon.Itisassumedthatthepregionismoreheavilydopedthanthenregion;NA>>ND.



ExcessminoritycarrierconcentraDon:

Ø ExponenDalrelaDonshipØ SmallvoltageincrementalgiverisetogreatincrementalofexcessminoritycarrierconcentraDon.

T

T

Vv

ppp

Vv

nnn

enxn

epxp

0

0

)(

)(

=−

=



DistribuDonofexcessminorityconcentraDon:Where

arecalledexcess-minority-carrierlifeDme.

np

pn

Lxx

ppppp

Lxx

nnnnon

enxnnxn

epxppxp)(

00

)(

0

])([)(

])([)(＋

－

−−+=

−+=−

nnn

ppp

DL

DL

τ

τ

=

=

pn ττ ,



Thetotalcurrentcanbeobtainedbythediffusioncurrentofmajoritycarriers.

)1)((

)()((

)(

00 −+=

+−=

+=

+=

−==

T

pn

VV

n

pn

p

np

xxxx

nDpD

nDpD

eLnD

LpD

Aq

dxxdnq

dxxdpqA

JJAIII

）



ThesaturaDoncurrentisgivenby:

)(

)(

2

00

An

n

Dp

pi

n

pn

p

nps

nLD

nLD

qAn

LnD

LpD

qAI

+=

+=



I-VcharacterisDcequaDon:Diodecurrent

•  ExponenDalrelaDonship,nonlinear.•  IsiscalledsaturaDoncurrent,stronglydepends

ontemperature.•  or2，ingeneral•  VTisthermalvoltage.

)1−= TnVv

s eIi （

1=n 1=n



assumingV1atI1andV2atI2then:

* For a decade changes in current, the diodevoltage drop changes by 60mv (for n=1) or120mv(forn=2).

1

2

1

212 lg3.2ln I

InVIInVVV TT ==−



•  Turn-onvoltageAconducDondiodehasapproximatelyaconstantvoltagedropacrossit.It’scalledturn-onvoltage.

•  DiodeswithdifferentcurrentraDngwillexhibittheturn-onvoltageatdifferentcurrents.

•  NegaDveTC,

VVVV

onD

onD

25.0

7.0

)(

)(

=

= Forsilicon

Forgermanium

CmvTC !/2−=


ThepnJuncDonUnderReverse-BiasCondiDons

Ø The pn juncDon excited by aconstant-current source I in thereversedirecDon.

Ø To avoid breakdown, I is keptsmallerthanIS.

Ø Note that the depleDon layerwidens and the barrier voltageincreases by VR volts, whichappears between the terminals asareversevoltage.


ThepnJuncDonUnderReverse-BiasCondiDons

I-VcharacterisDcequaDon:WhereIsisthesaturaDoncurrent,itisproporDonaltoni2whichisastrongfuncDonoftemperature.

sIi =

)(

)(

2

00

An

n

Dp

pi

n

pn

p

nps

nLD

nLD

qAn

LnD

LpD

qAI

+=

+=

Independentofvoltage。


ThepnJuncDonIntheBreakdownRegion

ThepnjuncDonexcitedbyareverse-currentsourceI,whereI>IS.ThejuncDonbreaksdown,andavoltageVZ,withthepolarityindicated,developsacrossthe

juncDon.


ThepnJuncDonIntheBreakdownRegion

•  Supposing,thecurrentsourcewillmoveholesfromptonthroughtheexternalcircuit.

•  ThefreeelectronsmovethroughoppositedirecDon.

•  This result in the increase of barrier voltage anddecreasealmostzeroofdiffusioncurrent.

•  Toachievedtheequilibrium,anewmechanismsetsinto supply the charge carriers needed to support thecurrentI.

sII >>


Lecture:2 Topics

Recap- Diode theory, Diode equation, small signal and large

signal equivalent circuits.

Breakdown:ZenerandAvalanchemechanisms.

Loadlineanalysis

Conclusion&Summary–Breakdown,loadlineanalysis.


BreakdownMechanisms

•  ZenereffectØ OccursinheavilydopingsemiconductorØ  Breakdownvoltageislessthan5v.Ø  Carriersgeneratedbyelectricfield---fieldionizaDon.Ø  TCisnegaDve.

•  Avalancheeffect.Ø OccursinslightlydopingsemiconductorØ  Breakdownvoltageismorethan7v.Ø  Carriersgeneratedbycollision.Ø  TCisposiDve.


BreakdownMechanisms

Remember: pn junc@on breakdown is not a destruc@veprocess,providedthatthemaximumspecifiedpowerdissipa@onisnotexceeded.


ZenerDiode

Circuitsymbol

Thediodei–vcharacterisDcwiththebreakdownregionshowninsomedetail.


JuncDonCapacitance

•  DiffusionCapacitanceØ  Chargestoredinbulkregionchangeswiththechangeofvoltage

acrosspnjuncDongivesrisetocapaciDveeffect.

Ø  Small-signaldiffusioncapacitance

•  DepleDoncapacitanceØ  ChargestoredindepleDonlayerchangeswiththechangeofvoltage

acrosspnjuncDongivesrisetocapaciDveeffect.

Ø  Small-signaldepleDoncapacitance


DiffusionCapacitance

AccordingtothedefiniDon:Thechargestoredinbulkregionisobtainedfrombelow

equaDons:

Qd dVdQC =

pp

pnonn

x nonp

ILpxpAq

dxpxpAqQn

τ=

⋅−×=

−×= ∫∞

])([

])([

nnn IQ τ=


DiffusionCapacitance

Theexpressionfordiffusioncapacitance:

Forward-bias,linearrelaDonship

Reverse-bias,almostinexistence⎪⎩

⎪⎨

⎧≈

=

=

0

)(

)(

][

QT

T

QT

T

VV

sTd

IV

IV

eIdVdC T

τ

τ

τ


DepleDonCapacitance

AccordingtothedefiniDon:Actuallythiscapacitanceissimilartoparallelplate

capacitance.

QR VVRj dVdQC

=

=

)1(

))(11(2[

0

0

o

R

j

RBA

depj

VVC

vVNNq

AWAC

+=

++

=ε

εε＝


DepleDonCapacitance

•  AmoregeneralformulafordepleDoncapacitanceis:

•  Wheremiscalledgradingcoefficient.•  IftheconcentraDonchangessharply,•  Forward-biascondiDon,•  Reverse-biascondiDon,

mR

jj V

CC

)V1(0

0

+=

21~

31

=m

21

=m

02 jj CC ≈

dj CC <<


JuncDonCapacitance

Remember:a)  Diffusion and deple@on capacitances are

incremental capacitances, only are applied underthesmall-signalcircuitcondi@on.

b)  Theyarenotconstants,theyhaverela@onshipwiththevoltageacrossthepnjunc@on.


AnalysisofDiodeCircuit

•  ModelsØ MathemaDcmodelØ Circuitmodel

•  MethodsofanalysisØ GraphicalanalysisØ IteraDveanalysisØ Modelinganalysis


TheDiodeModels

MathemaDcModel：

ThecircuitmodelsarederivedfromapproximaDngthecurveintopiecewise-line.

⎪⎩

⎪⎨⎧

−≈

−=

s

nVv

s

nVv

s

IeI

eIi

T

T )1(

Forwardbiased

Reversebiased


TheDiodeModels

CircuitModela)  Simplifieddiodemodel

b)  Theconstant-voltage-dropmodel

c)  Small-signalmodel

d)  High-frequencymodel

e)  ZenerDiodeModel


SimplifiedDiodeModel

Piecewise-linearmodelofthediodeforwardcharacterisDcanditsequivalentcircuitrepresentaDon.


TheConstant-Voltage-DropModel

Theconstant-voltage-dropmodelofthediodeforwardcharacterisDcsanditsequivalent-circuitrepresentaDon.


Small-SignalModel

SymbolconvenDon:Ø Lowercasesymbol,uppercasesubscriptstandsfortotalinstantaneousqualiDes.

Ø Uppercasesymbol,uppercasesubscriptstandsfordccomponent.

Ø Lowercasesymbol,lowercasesubscriptstandsforaccomponentorincrementalsignalqualiDes.

Ø Uppercasesymbol,lowercasesubscriptstandsfortherms(root-mean-square)ofac.

)(tId

)(tid

DI

)(tiD


Small-SignalModel

Developmentofthediodesmall-signalmodel.Notethatthenumericalvaluesshownareforadiodewithn=2.


Small-SignalModel(cont’d)

Incrementalresistance:

*The signal amplitude sufficiently small suchthat the excursionatQalong the i-v curve islimitedtoashort,almostlinearsegment.

DQ

Td IVr =


High-FrequencyModel

Highfrequencymodel

rd

rs

cj


ZenerDiodeModel

ZZZZ rIVV += 0


MethodofAnalysis

Ø LoadlineØ DiodecharacterisDcØ QistheintersectpointØ VisualizaDon


Lecture:3 Topics

Recap-Breakdown,loadlineanalysis

Workingofclippers&clampers

WorkingofLimiters&voltagemulDpliers

Conclusion&Summary–Workingofclampers,clippers,Limiters

&voltagemulDpliers.


Clippers

²  Clippers or diode limiting is a diode network that have the ability to “clip” off a portion on the i/p signal without distorting the remaining part of the alternating waveform.

²  Clippers are used to eliminate amplitude noise or to

fabricate new waveforms from an existing signal.

²  2 general of clippers: a) Series clippers b) Parallel clippers

Clippers


²  The series configuraDon is defined as onewherethediodeisinserieswiththeload.

²  A half-wave recDfier is the simplest formofdiodeclipper-oneresistoranddiode.

SeriesClippers

+

-Vi RL Vo

-

+


The diode “clips” any voltage that does not put it in forward bias. That would be a reverse biasing polarity and a voltage less than 0.7V for a silicon diode.

ClipperDiodeCircuit


Vm

Vi

t0 T/2 T

+

-Vi

V

RL Vo-

+

²  The half-wave rectifier with addition of dc supply is shown in following figure. The cct known as biased series clipper.

² The dc supply have pronounced effect on the o/p of a clipper.

Biased series clipper KLUDr.M.DurgaPrakash

ClipperDiodeCircuit

•  +ve region turn the diode ON. •  -ve region turn the diode OFF. •  Vi > V to turn ON the diode •  In general diode is open cct (OFF state) and short cct (ON state) •  For Vi > V the Vo = Vi – V •  For Vi = V the Vo= 0 V •  The complete cct shown above

Vm

Vi

t0 T/2 T

+

-Vi=Vm

V

RL Vo

-

++ -

T/20

Vo

tT

Vm-V

Vi=V (diodes change state)


ClipperDiodeCircuit

² The diode connection is in parallel configuration with the o/p.

²  Diode is ideal

+

RL

Vo-

+

-

Vi

ParallelClippers


By taking the output across the diode, the output is now the voltage when the diode is not conducting. A DC source can also be added to change the diode’s required forward bias voltage.

ChangingOutputPerspecKve


ClipperCircuitsSummary



ClipperCircuitsSummarySimpleShuntclipper(IdealDiodes)

ClipperCircuitsSummary


Clampers

²  The clamping network is to “clamp” a signal to a different dc level. Also known as dc restorers. The clamping cct is often used in TV receivers as a dc restorer.

²  The network consists of: a) Capacitor b) Diode c) Resistive element d) Independent dc supply (option)

²  The magnitude of R and C must be chosen such that the time constant

²  τ = RC is large enough to ensure that the voltage across the capacitor does not discharge significantly during the interval the diode is nonconducting.

²  Our analysis basis that all capacitor is fully charge and discharge in 5 time constant.

Clampers


+R Vo

-

+

-

Vi

Vi

t0 T/2 T

V

-V


Clamper

+ ve region

+

R Vo

-

+-

Vi

C •  0 - T/2: Diode is ON state (short-cct equivalent) •  Assume RC time is small and capacitor charge to V volts very quickly •  Vo=0 V (ideal diode)

- ve region

•  T/2 - T: Diode is OFF state (open-cct equivalent) •  Both for the stored voltage across capacitor and applied signal current through cathode to anode •  KVL: - V- V- Vo = 0 and Vo = -2V

+

R Vo

-

+-

V

C

Vo

-

+V

Vi

t0 T/2 T

V

-V

OperaKonofclamper


Tips : Clamping network Total swing o/p signal = the total swing i/p signal


SummaryofClamperCircuits


VoltageMulKpliers

WhatisaVoltageMulDplier?

² Voltage mulDpliers are AC-to-DC power conversiondevices, comprised of diodes and capacitors, thatproduce a high potenDal DC voltage from a lowervoltageACsource.MulDpliersaremadeupofmulDplestages. Each stage is comprisedof onediode andonecapacitor.

Depending on the output voltage, mulDplierscanbeofdifferenttypes

Ø VoltagedoublersØ VoltageDpplersØ Voltagequadrupler

TypesofvoltagemulDplier

AVoltagedoublerproducesad.c.voltagealmosttwicethermsvalueoftheinputa.c.voltage.

Voltagedoublercanbeoftwotypes;v Halfwavevoltagedoublerv Fullwavevoltagedoubler

Voltagedoublers

CircuitDiagram

HalfwavevoltageDoubler

The circuit for a half wave voltage doubler. During the positive half cycle of the secondary voltage diode D1 conducts and D2 is cut off. Now capacitor C1 charges to the peak rectified voltage Vm, with polarity shown in the figure. During the negative half cycle, the secondary voltage comes in series with voltage across the capacitor C1.

HalfwavevoltageDoubler

Thus C2 will try to charge towards 2Vm(Vm of the input and Vm of the capacitor C1. After few cycles the voltage across the capacitor C2 will be equal to 2Vm Since diode D2 acts as a short during the negative half-cycle (and diode D1 is open), we can sum the voltages around the outside loop. i.e;

−𝑉𝑚 − 𝑉𝐶1−𝑉𝐶2=0 (or) −𝑉𝑚 − 𝑉𝑚 −𝑉𝐶2=0from which, 𝑉𝐶2=2𝑉𝑚

In the circuit capacitor C1 will discharge in the negative half cycle. Again in the positive half cycle, it starts charging. Thus the half wave voltage doubler supplies the voltage to the load in one half cycles. Therefore regulation of the half wave voltage doubler is poor.

²  Another voltage doubler circuit called full wave voltage doubler isshowninfig.

²  During the posiDve half cycle of the secondary voltage diode D1conducts, charging the capacitor the capacitor C1to the peak voltageVm.

²  AtthisDmediodeD2isnon-conducDng.

²  During negaDve half cycle diode D2conducts, charging capacitor C2toVm,withpolarityasmarked,whilediodeD2isnon-conducDng.

²  SincebothcapacitorsC1andC2areinseries,thefinaloutputvoltageisapproximately2Vm.

²  This circuit is called full wave voltage doubler because one of theoutput capacitor is being charged during each half cycle of the inputvoltage

Fullwavevoltagedoubler

Circuitdiagram

Fullwavevoltagedoubler

•  Thevoltagetriplerarrangementaddsanotherdiode/capacitorset.

•  +half-cycle:C1chargestoVpthroughD1,•  -half-cycle:C2chargesto2VpthroughC2,•  Next + half-cycle: C3 charges to 2Vp throughC3.

•  OutputisacrossC1&C3.

VoltageTripler

Circuitdiagram

VoltageTripler

•  Thevoltagetriplerarrangementaddsanotherdiode/capacitorset.

•  +half-cycle:C1chargestoVpthroughD1,•  -half-cycle:C2chargesto2VpthroughC2,•  Next+half-cycle:C3chargesto2VpthroughC3.•  Next-half-cycle:C4chargesto2VpthroughC4•  QuadrupleOutputisacrossC2&C4.

VoltageQuadruplers

Circuitdiagram

VoltageQuadruplers

Originally used for television CRT's, voltagemulDpliersarenowusedfor lasers, x-raysystems,travelingwavetubes (TWT's), photomulDplier tubes, ion pumps,electrostaDc systems, copymachines, andmany otherapplicaDonsthatuDlizehighvoltageDC.

CommonMulDplierApplicaDons

Lecture:4 Topics

Recap-Workingofclampers,clippers,Limiters&voltage

mulDpliers

WorkingofHWR,FWR&BridgeRecDfier

WorkingofFWR&BridgeRecDfier

Conclusion&Summary–WorkingofHWR,FWR&BridgeRecDfier


ApplicaDonofDiodeCircuits

•  RecDfiercircuitsØ Half-waverecDfierØ Full-waverecDfier•  Transformerwithacenter-tappedsecondarywinding• BridgerecDfier

Ø ThepeakrecDfier


RecKfier•  Rectifiers convert ac into dc

•  Some commercial rectifiers

(Usedtochargebajeries)

BlockdiagramofPowerSupply

RecKfier•  AcircuitthatconvertsacvoltageofmainsupplyintopulsaDngdcvoltageusingoneormorepnjuncDondiodes.

•  HalfWaveRecDfier•  FullWaveRecDfier

•  CenterTapRecDfier•  BridgeRecDfier

Half-WaveRecDfier


CircuitDiagram

OperaKonofHalfWaveRecKfier

WaveformofHalfWaveRecKfier

AverageDCloadCurrent(IDC)

AverageDCvoltage(Edc)

RMSLoadCurrent(Irms)

RMSLoadVoltage(Erms)

DCPowerDeliveredtotheload

ACinputpowerfromtransformersecondary

HoweffecKvelyarecKfierconvertsacintodc:

•  RecDfierEfficiency(η)

•  RippleFactor(r)

RecKfierEfficiency(η)Tellsusthepercentageoftotalinputacpowerthatisconvertedintousefuldcoutputpower.

η=40.6%

UnderbestcondiDons(nodiodeloss)only40.6%oftheacinputpowerisconvertedintodcpower.

Therestremainsastheacpowerintheload

RippleFactorMeasureofpurityofthedcoutputofarecDfier

DefinedastheraDoofaccomponentoftheoutputwavetothedccomponentinthewave

RippleFactor

Thisindicatesthattheripplecontentintheoutputare1.211Dmesthedccomponent.

i.e.121.1%ofdccomponent.

Theripplefactorisveryhigh.

ThereforeahalfwaverecDfierisapoorconverterofactodc.

TheripplefactorisminimizedusingfiltercircuitsalongwiththerecDfier.

PeakInverseVoltage(PIV)

PIV=Em

DiodemustbeselectedbasedonthePIVraDngandthecircuitspecificaDon.

DisadvantageofHWR

²  TheripplefactorofhalfwaverecDfieris1.21,whichisquitehigh.

²  Theoutputcontainslotofripples²  ThemaximumtheoreDcalefficiencyis40%.²  ThepracDcalvaluewillbequitelessthanthis.²  ThisindicatesthatHWRisquiteinefficient.

Full-WaveRecDfier


WorkingofCenterTapRecDfierCurrentFlowduringtheposiDvehalfoftheinputcycle

CurrentFlowduringthenegaDvehalfoftheinputcycle

Waveforms

AverageDCcurrent

Average(DC)Voltage

RMSLoadCurrent(Irms)

RMSLoadVoltage

DCOutputPower

ACinputpower(Pac)

RecKfierEfficiency(η)

RippleFactor

Thisindicatesthattheripplecontentsintheoutputare48%ofthedc component whichismuchlessthanthatforthehalfwaverecDfier.

PeakInverseVoltage

AdvantagesofFullWaveRecKfier

•  Efficiencyishigher.•  Thelargedcpoweroutput•  Theripplefactorisless

DisadvantagesofFullWaveRecKfier

•  PIVraDngofdiodeishigher.•  HigherPIVdiodesarelargerinsizeandcostlier.•  Thecostofcentertaptransformerishigh.

TheBridgeRecDfier


WorkingofBridgeRecKfier

WaveformsofBridgeRecKfier

Parameters:

AdvantagesofBridgeRecKfier

²  Itdoesnotneedcentertaptransformersecondary.

²  The transformer secondaryvoltageofCT recDfier is2Vm,whereas inBridgethetransformersecondarymusthaveapeakvoltageofVm.Thatis the transformer secondary of CT recDfier must have double thenumberofturns.Suchtransformersarecostlier.

²  Ifsteppinguporsteppingdownofvoltageisnotneeded,wemayevendoawaywithouttransformer.

²  Each diode in center tap has a PIV raDng of 2Vm,whereas diodes inbridge recDfierneedsaPIV raDngofVm.Hence thediodes foruse incentertaprecDfierarecostlierthanmeantforbridgerecDfier.

DisadvantagesofBridgeRecKfier

² It requires four diodes, two of which conduct inalternatehalfcycles.Thiscreatesatotalvoltagedropof1.4V(ifSidiodesareused).

² Therefore this creates a problem if low dc voltage isrequired.

² The secondary voltage is low and two diode voltagedropof1.4Vbecomessignificant.

SummaryThemainperformanceparametersdefinedforthethreeconfiguraDons

PeakRecDfier

Ø VoltageandcurrentwaveformsinthepeakrecDfiercircuitwith.

Ø Thediodeisassumedideal.

TCR >>


Lecture:5 Topics

Recap-WorkingofHWR,FWR&BridgeRecDfier.

WorkingofCapacitor&π-secDonfilter

WorkingofCapacitor&π-secDonfilter

Conclusion&Summary–WorkingofCapacitor&π-secDonfilter.


Lecture:6 Topics

Recap-WorkingofCapacitorfilters&π-secDonfilter.

Specialpurposediodes-Zenerdiode

Q&ASessionVaractor,lightemiPngdiodes,Laserdiodes.

Q&ASession

Conclusion&Summary–Specialpurposediodes


Lecture:7 Topics

Recap-Specialpurposediodes

Seriesandshuntvoltageregulator

Q&ASessionPercentageregulaDon,ConceptofSMPS.

Q&ASessionConclusion&Summary–Seriesandshuntvoltageregulator,

SMPS


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