PULSE EEWeb.comIssue 10

September 6, 2011

Dr. TaufikElectric Power Institute

Electrical Engineering Community

EEWeb

Contact Us For Advertising Opportunities

1.800.574.2791advertising@eeweb.com

www.eeweb.com/advertising

Electrical Engineering CommunityEEWeb

Digi-Key is an authorized distributor for all supplier partners. New products added daily. © 2011 Digi-Key Corporation, 701 Brooks Ave. South, Thief River Falls, MN 56701, USADigi-Key is an authorized distributor for all supplier partners. New products added daily.

www.digikey.com/techxchange

It’s all about connections.

The user-to-user forum is for everyone, from design engineers to hobbyists, to discuss technology, products, designs and more. Join the discussions that match your interest or offer your expertise to others.

Join the discussion now at:

discussions

hobbyists

engineers

industry experts

resourceslinks

technical documentswhite papers

reference designs

application notes

community

power

microcontroller

lighting

wireless

sensor

students

EEWeb | Electrical Engineering Community Visit www.eeweb.com 3

TABLE O

F CO

NTEN

TSTABLE OF CONTENTS

Dr. Taufik 4DIRECTOR, ELECTRIC POWER INSTITUTEInterview with Dr. Taufik - Professor of Electrical Engineering at Cal Poly State University

The DC House Project: Providing Access 8to Electricity for the Less Fortunate BY DR. TAUFIK

HD, 3D Service Aggregation Drives 10Bandwidth in Professional Video BY JUAN GARZA WITH VITESSE

The Taylor Expansion for RF Mixers 13BY CHRISTOPHER MARKI WITH MARKI MICROWAVE

RTZ - Return to Zero Comic 16

The DC House Project’s engineers aim to operate a house solely on DC power from renewable and sustainable energy sources.

The arrival of 3G HDTV, 3D HDTV, 4K2K, and Super Hi-Vision (Ultra HD) has brought much attention to multi-gigabit switching performance and associated routing infrastructure.

Marki points out flaws and issues with the Taylor Expansion approach to explaining and understanding mixers.

EEWeb | Electrical Engineering Community Visit www.eeweb.com 4

INTERVIEWFEA

TURED IN

TERVIEW

Electric Power Institute

How did you get into electronics/engineering and when did you start?It wasn’t until my senior year in high school. Back then I lived near the seaport district of Jakarta known as Tanjung Priok and went to this public high school called SMA 13. As part of the high school curriculum at the time, we were introduced to basic circuit components and analysis. I hope they are still doing this these days because that was what really got me interested in engineering. As for the electronics, I was very much interested in the subject, but the coverage was scant, which motivated me to choose electrical engineering as my major when

Dr. Taufik - Professor of Electrical Engineering at Cal Poly State University

I came to the U.S. to study. Now I have been teaching electrical engineering at Cal Poly since 1999, and it has been an honor and great pleasure to be able to teach the very subject that I am passionate about.

What are your favorite hardware tools that you use?I like to use the Frequency Response Analyzer which is a great tool for analysis, measurement, and design of feedback loops in dc-dc converters. The one I have in the power electronics lab at Cal Poly State University is the Venable Frequency Response Analyzer which has been used to help students’ understanding in

feedback compensator design.

What are your favorite software tools that you use?MathCAD. It is an awesome tool for design calculations. I’ve used it in all my consulting work and in design and problem examples I have in my lecture notes. The software really helps streamline long and complex design calculations, and its handling of units provides a convenient way to quickly troubleshoot your design equations. As for circuit simulation, I’ve come to like LTSpice developed by Linear Technology Corporation. It is completely free to download and extremely fast when simulating switching regulators compared to normal Spice simulators.

What is the hardest/trickiest bug you have ever fixed?Minimizing noises in high-frequency switching dc-dc converter circuits have always been tricky to me.

What is on your bookshelf? Being a faculty in a primarily undergraduate institution, I have been assigned to teach various electrical engineering courses (lectures and labs). However, courses that I mainly teach almost every year are circuits, control systems, power electronics, power systems, and machines. As a result, my bookshelf is filled with textbooks and my own lecture notes on these subjects. Although since my main interest is in power electronics, two rows of my

Dr. Taufik

EEWeb | Electrical Engineering Community Visit www.eeweb.com 5

INTERVIEWFEA

TURED IN

TERVIEW

bookshelf are actually filled with text and reference books on power electronics. My bookshelf is also where I stock up on quite a few selections of power components such as power MOSFETs, diodes, inductors, and pwm controller chips. These components come in handy for my students to conduct their senior design and master’s thesis projects.

Do you have any tricks up your sleeve?Not tricks, but perhaps teaching undergraduate students a simpler way to analyze and perform basic design of dc-dc converter circuits. This is what I hope to share some day in the near future through an undergraduate level textbook on power electronics, which I have been planning to write.

What has been your favorite project?Several years ago my students and I were involved in the investigation and development of new topologies for Voltage Regulator Modules (VRMs) to power future microprocessors. As the number of transistors on a microprocessor increases, the power supply to these microprocessors, VRMs, must be able to supply the increase in current demand while maintaining their high efficiency. This becomes especially challenging considering the relatively low voltage operation of these microprocessors. Consider an example from Intel who announced recently the world’s first 2-billion transistor

microprocessor code-named Tukwila. With the massive amount of transistors in the new processor,even higher output current supply will be in demand, and hence more challenging for VRMs. Another example is the current Intel Core i7-980x which has a thermal design power of 130W. However, according to its data sheet, the processor can

The classic one would be shooting up an

electrolytic capacitor to the ceiling...This definitely taught me a lesson to respect electricity more, and to be extra

careful dealing with polarized capacitors.

actually pull as much power as 180W at 1.263VDC. Again, this means the VRMs have to be able to supply high output current with relatively low voltage. There are other processors out on the market that demand the VRM to supply upwards of 400W. The bottom line is, when output power is this high while the output voltage is kept low, the task for designing an efficient

VRM for these microprocessors becomes very challenging. Hence, the use of conventional multiphase buck topology would no longer suffice and meet the efficiency requirement.

Our project was then aimed to prove that our proposed new topologies offer benefits in terms of improved efficiency and performance compared to the traditional multiphase buck at high power output and low output voltage. Two variations of the new topologies were designed, built, and tested here in the power electronics lab at Cal Poly. The new topologies are unique in that they employ passive storage components to achieve improvements in performance and efficiency rather than introducing more converter stages or more active switches. Consequently, the new topologies are much less complex to design compared to approaches using additional converter stage or additional active switches. Combined with the use of interleaving technique, we found that the proposed new topologies are able to maintain the high efficiency comparable to or better than those measured from VRMs currently available in the market. Other performances of the new topologies were also tested and evaluated exhibiting the very tight line and load regulations, very small output voltage ripple at full load, and fast dynamic response. These new topologies recently received a patent from the USPTO.

EEWeb | Electrical Engineering Community Visit www.eeweb.com 6

INTERVIEWFEA

TURED IN

TERVIEW

Although the project has been completed, we are currently planning to further test the capability of the new topologies with even much higher output currents (> 200A). In addition, we plan to develop the soft-switching version of these topologies for even higher overall VRM efficiency.

Do you have any note-worthy engineering experiences?The classic one would be shooting up an electrolytic capacitor to the ceiling. This happened in my first circuit lab back when I was in college. I accidentally placed the capacitor on my circuit with the wrong polarity. This definitely

taught me a lesson to respect electricity more, and to be extra careful dealing with polarized capacitors.

What are you currently working on?These days I’ve been involved in several projects, all in the area of power electronics. The main one is the design and development of DC House to help people get access to electricity. It is currently being studied and eventually developed at Cal Poly to provide electricity to those without it by taking advantage of renewable energy sources and other creative ways of generating power. The project is open access and is

still in its initial phase. I welcome anyone to participate and any ideas are greatly appreciated. The website for the project is http://www.calpoly.edu/~taufik/dchouse/

Other projects I’ve been working on are wind-energy harvesting for urban areas, isolated one-stage power factor correction, and improved inverter for Photovoltaic system.

Off campus, I have been an engineering consultant for Enerpro Inc. where I’ve mostly performed transformer designs. I am also assisting a university half-way around the world with getting its international accreditation.

From design to service, Microtips offers a variety of competitively priced Liquid Crystal Display modules which includes standard character and graphic monochrome, passive and active color displays with white LED as well as custom LCD modules and complete OEM services.

For your own design needs please contact Microtips Technology: www.microtipsusa.com1.888.499.8477mtusainfo@microtipsusa.com

7” High Bright

240 x 160 COG w/LED Backlight

QVGA Green w/LED Backlight

LCD for Any Application

Microtips Technology

Automotive, Medical, Telecom, POSLCD for Any Application

Microtips Technology

Automotive, Medical, Telecom, POS

MoonstoneTM Tri-color Power LED light source from Avago Technologies: ASMT-MT00

Avago’s MoonstoneTM Tri-color Power LED light sources are high performance energy efficient devices which can handle high thermal and high driving current. The exposed pad design has excellent heat transfer from the package to the mother board.

The advanced 3x1Watt RGB MoonstoneTM package delivers typical 108 lumens at 350mA.

The robust package design makes it an excellent choice for color mixing applications.

Applications

•ArchitecturalLighting

•Decorative&MoodLighting

•RetailLighting

•Gardenlighting

•ShowLighting

Avago Technologies

MoonstoneTM 3x1 Watt

RGB High Power LED

gives you a reliable,

energy efficient, long

life operation product

for ease of design

in any type of color

mixing application.

www.avagotech.com/led

Avago Technologies LED Lighting Solutions Technology

Any Color. One Device.

For more information or to request a sample please go to:

EEWeb | Electrical Engineering Community Visit www.eeweb.com 8

PROJECTFEA

TURED PRO

JECT

The DC House Project

By Dr. Taufik

Providing Access to Electricityfor the Less Fortunate

Background

There are an estimated 1.4 billion people in the world today who do not have access to electricity. This figure represents a significant issue in today’s world as electricity is essential for economic growth, because it provides basic needs such as lighting, refrigeration, and the operation of most household appliances. Without these essential services, schools go unlit, some medicines cannot be stored, and water must often be hand-carried for miles just to supply adequate hydration and sanitation.

Traditionally, transmission lines are necessary to transmit large amounts of power generated from large-scale power plants to regions of high population density that can use it for commercial and residential applications. A large portion of those without electricity live in remote areas with a more dispersed population density. It becomes a problem of economics—the high initial cost of the infrastructure is tough to justify for a small village of dispersed people. In essence, it is prohibitively expensive to bring the traditional electrical grid to remote areas of the world. Ironically, renewable energy sources are plentiful in many of these remote areas, but not yet exploited. This creates an opportunity for engineers to apply new technologies to fulfill these empty humanitarian gaps that still exist despite globalization and huge strides in the development of technology in the western world. The DC House project aims to bridge these gaps by operating the house directly off renewable energy sources which generally produce DC power. As the name suggests, the DC House will employ a low voltage DC distribution system to provide basic energy needs to a single family such as lighting, and hence offering the benefit, for example, of replacing the need for dangerous kerosene lamps that are still used in many remote villages.

The current primary energy sources for the world come from fossil fuels: petroleum, coal, and natural gas. One

problem that arises with the use of these resources for energy is sustainability because fossil fuels are finite resources. This inherently makes them a non-sustainable energy source because they will eventually be completely consumed. Hence, finding alternative and renewable energy sources, as well as effective and efficient systems to use them, is vital to achieving a sustainable future. In the U.S. for example, electricity production from renewable energy is still minute compared to that from fossil fuels; however, the number has been increasing over time. The picture globally follows the same pattern with 14 percent of total world energy supply projected to come from the renewable by 2030. The DC House project takes advantage of this momentum by using renewable energy sources to power a house locally.

Another benefit stemming from the DC House project is in terms of global warming, which is a phenomenon where greenhouse gases produced from burning fossil fuels such as petroleum and coal warms the earth. This creates many negative environmental effects which affect both human and non-human life on earth. The DC House project will utilize renewable energy sources which do not emit greenhouse gases, and can help stop this problem from getting worse.

The DC House

As previously mentioned, a DC house is a house that operates solely on DC power from renewable and sustainable energy sources. The DC system is selected to provide optimum matching to renewable energy sources which mostly produce DC power. This in turn eliminates the intermediate conversion process which will otherwise be required in traditional AC-powered homes. Figure 1 illustrates the block diagram of the DC House system. Unfortunately, because the reliability of many renewable energy sources is subject to season, weather, or time of day, it will be necessary to incorporate a battery system to provide stability.

EEWeb | Electrical Engineering Community Visit www.eeweb.com 9

PROJECTFEA

TURED PRO

JECT

A DC-powered electrical system is not a new or uncommon concept. For example, the electronics in a car or recreational vehicle (RV) are powered on a 12 VDC system with one or more batteries. The car’s motor drives an alternator which produces AC voltage. The AC power is rectified to DC and the voltage level is regulated via a voltage regulator. The regulator feeds into the car battery. The regulator controls the power flow to the battery so that the battery is never overcharged. This system is used to power the on-board electronics and lighting in a car. The reason that the car uses DC is for several reasons. DC power is required for many onboard electronics such as the car stereo. DC also permits the use of a battery which gives the car’s power system some flexibility. This way, the car’s motor doesn’t have to be on to power the lights, radio, and electronics. This basic power system is very similar in motivation and function to a power system that incorporates renewable energy sources. It provides a voltage bus that supplies DC-powered loads, and via battery provides power to those loads when the energy source is inactive (cloudy weather for photovoltaic generation).

The DC house is meant to serve as a replacement to the traditional AC-powered home. Therefore it must fulfill the needs that a typical home provides. The home should at least provide indoor and outdoor lighting, food storage capabilities and food preparation options, and other services. In its initial phase, the DC house will be designed to have power capacity from 100W to 500W

with DC lighting being the major load.

The complete DC House project has several design themes and goals to be accomplished in each phase of operation. The over-arching theme of this project is to apply engineering principles from several disciplines to address problems associated with the DC house. In its initial phase, several initial studies have been conducted to investigate issues such as the most optimum DC bus level, types of DC loads, DC wall outlet, and DC-DC converters providing the DC bus and interfacing the renewable energy sources. In the following phases, a small-scale model of the DC house will be designed and built before a full-scale model can be constructed. Additionally, the DC House project is intended to be an open-source project where anyone around the world is welcome to participate. Currently, several partner universities from different countries around the world (e.g., Indonesia, Philippines) have agreed to join this effort and to assist in the final field testing of the DC house.

Finally, besides providing electricity to remote areas, it is also our hope that the DC house someday will be useful in emergency-preparedness application such as to provide temporary homes for people living in areas hit by natural disasters. This will further emphasize the true meaning of “The DC House Project: Providing Access to Electricity for the Unfortunates.”

For further info, please visit the DC House Project website: http://www.calpoly.edu/~taufik/dchouse.

Figure 1: Block Diagram of the DC House System

EEWeb | Electrical Engineering Community Visit www.eeweb.com 10

HD, 3DService Aggregation DrivesBandwith in Professional Video

Juan GarzaVideo Product Marketing Manager

When professional studio mixers and switchers were limited to the aggregation

of SD and composite video signals, hardware needs were significant, but not always cutting edge. The slow but steady arrival of 3G HDTV, 3D HDTV, 4K2K, and Super Hi-Vision (Ultra HD) has put multi-gigabit switching performance and associated routing infrastructure on the front burner.

Meanwhile, the effort to move first-pass mixing tasks from centralized studios to remote digital TV vans has placed demands for low power and high integration to a level that meets and exceeds the needs of signal quality to maintain uninterrupted broadcasts to the viewing audience. Changes in site-based video switching have followed two related trends favoring denser switches. When possible, broadcasters

would benefit with capture and transmit of uncompressed HD video at remote sites using IP gateways that would simplify the underlying hardware. Utilizing alternative technologies would simplify transmission systems and dispense with the use of bulky, HD-ready remote studio trailers that are often the size of semi trucks. Instead, mini video switching platforms could lead to reduced sizes, lower power and simplified architectures in remote transmission.

An emerging trend is the packetization of high-bandwidth traffic, a familiar trend that has played out in telecom and cable TV environments. In fact, if there is a partial bright side to the architectural demands of new video switching architectures, it comes in the packet-centric methodologies permeating digital video editing. The video industry

has evolved from analog input and composite traffic over RF cable, to emerging architectures featuring sophisticated control, scalability and embedded audio capabilities. While video switches still push performance and scalability on a larger scale than multiport Gigabit Ethernet switches, the chip-level design shares more in common with packet switches, particularly in integrated low latency routing and Quality of Service packet prioritization methods.

The trend to packet traffic can be seen in the standards developed by the Society of Motion Picture and Television Engineers. SMPTE’s series of favored Serial Digital Interface, or SDI standards, only recently began striving for interoperability with telecom and CATV packet traffic. The 3G-SDI interface, specifying a 2.97-

EEWeb | Electrical Engineering Community Visit www.eeweb.com 11

TECHN

ICA

L ARTIC

LETECHNICAL ARTICLE

Gbit/sec link, has been promoted as a replacement for dual-link HDTV SGI. Initial development work is being carried out on 10G-SGI and 12G-SGI, with a deliberate intent of mapping the higher-end standards into 10G, 40G, and 100G Ethernet.

Meanwhile, SMPTE also worked on a standard for Video Over IP, which has been realized in the new 2022 standard for Forward Error Correction. When a professional video studio elects to move to packet transport, it must either insure minimal packet loss by adopting effective end-to-end QoS strategies, or it must retain the ability to reconstruct dropped packets at the receiving end, through the use of FEC techniques such as those specified in SMPTE2022. In any event, these packet trends favor the use of semiconductor switches and physical-layer devices from vendors familiar with both QoS and FEC techniques as well as traditional SMPTE SDI implementations.

A video router that looks more like a standardized, high-bandwidth Ethernet switch than routers and mixers of the past can offer the type of scaling one might see in terabit packet routers from the telecom world. What also has not been common in past crosspoint architectures for the video studio is the

high bandwidth per port, with 3 Gbits/sec assumed on many applications— the high number of ports required in many system architectures— and the increased need to control jitter and return loss. The latter concerns are driving chip-level architectural decisions such as standardized input signal equalization and on-chip diagnostics.

From the perspective of a control engineer at the console of a modern video switcher system, many real-time aggregation decisions are automated, but the number of channels and the different types of video signals place demands on watching for degradation or loss of signal, as well as more significant network failures. In effect, the console engineer in a video studio often must monitor signal quality regimes as multifaceted and complex as the network managers in telecom networks responsible for overseeing Service Level Agreements.

In many respects, the growing ubiquity of multiple types of SD, HD, Quad HD services can be considered the proverbial best and worst of times for the manager of a professional digital video studio. The move to packet transport and standard multi-gigabit interfaces means that broadcast video

can now enter the brave new world where telecom and CATV standard already have blazed a trail with existing standards that can be leveraged in the studio. But the need to monitor and control the aggregation of such traffic means that all video switching topologies must become QoS-aware.

Many emerging semiconductor architectures in switch and physical-layer domains offer “baked-in” support for device diagnostics, system diagnostics, network timing, and QoS prioritization. Choosing intelligent components in video switch architecture can simplify the task of moving to packet transport. But system-level design engineers at video OEMs, as well as mixing editors in the studios themselves, must share a responsibility of becoming more network-aware, both in terms of understanding how the multi-gigabit HD traffic of the future is moving to universal packet transport, and of understanding how this packet traffic is monitored and controlled to insure lossless delivery of the many emerging HD traffic types.

About the Author

Juan Garza, video product marketing & applications manager for Vitesse, has more than 17 years of experience in the communications and semiconductor industries. Juan has held various business and marketing positions at Texas Instruments, Agere Systems, and Level One/Intel. His experience in networking and communications includes a variety of technology areas including digital signal processors, network processors, modem chipsets, and DSL transceivers. Juan holds a Bachelor of Science degree in Electrical Engineering from the University of Texas at Austin. He has also served on the Board of Directors of the Network Processing Forum and participated in DSL standards work at the International Telecommunications Union.

Figure 1: Studio Mixers and Switchers

Wideband, Low-Power, Ultra-High Dynamic Range Differential AmplifierISL55210The ISL55210 is a very wide band, Fully Differential Amplifier (FDA) intended for high dynamic range ADC input interface applications. This voltage feedback FDA design includes an independent output common mode voltage control.

Intended for very high dynamic range ADC interface applications, at the lowest quiescent power (115mW), the ISL55210 offers a 4.0GHz Gain Bandwidth Product with a very low input noise of 0.85nV/√(Hz). In a balanced differential I/O configuration, with 2VP-P output into a 200Ω load configured for a gain of 15dB, the IM3 terms are <-100dBc through 110MHz. With a minimum operating gain of 2V/V (6dB), the ISL55210 supports a wide range of higher gains with minimal BW or SFDR degradation. Its ultra high differential slew rate of 5,600V/µs ensures clean large signal SFDR performance or a fast settling step response.

The ISL55210 requires only a single 3.3V (max 4.2V) power supply with 35mA typical quiescent current. This industry leading low current solution can be further reduced when needed using the optional power shutdown to <0.4mA supply current. External feedback and gain setting resistors give maximum flexibility and accuracy. A companion device, the ISL55211, includes on-chip feedback and 3 possible gain setting connections where an internally fixed gain solution is preferred. The ISL55210 is available in a leadless, 16 Ld TQFN package and is specified for operation over the -40ºC to +85ºC ambient temperature range.

Features• Gain Bandwidth Product . . . . . . . . . . . . . . . . . . . . . . . . 4.0GHz

• Input Voltage Noise . . . . . . . . . . . . . . . . . . . . . . . 0.85nV/√(Hz)

• Differential Slew Rate . . . . . . . . . . . . . . . . . . . . . . . 5,600V/µs

• 2VP-P, 2-tone IM3 (200Ω) 100MHz . . . . . . . . . . . . . . -109dBc

• Supply Voltage Range . . . . . . . . . . . . . . . . . . . . . . 3.0V to 4.2V

• Quiescent Power (3.3V Supply) . . . . . . . . . . . . . . . . . .115mW

Applications• Low Power, High Dynamic Range ADC Interface

• Differential Mixer Output Amplifier

• SAW Filter Pre/Post Driver

• Differential Comms-DAC Output Driver

Related Products• ISL55211 - Fixed Gain Version of the ISL55210

• ISLA112P50 - 12-bit, 500MSPS ADC (<500mW)

• ISLA214P50 - 14-bit, 500MSPS ADC (<850mW)

SNRFS = 64.9dBFSHD2 = -83dBcHD3 = -84dBcENOBFS = 10.5 Bits

FIGURE 1. TYPICAL APPLICATION CIRCUIT

0.1µF

1:2

ISL55210

+3.3V

+

-

Vcm

20pF

20pF

33nH

33nH

V+

V-

ISLA112P50

ADT4-1WT

0.1µF

0.1µF

Vb

CLK500MSPS

105MHz SINGLE TONE180mVpp for -1dBFS

35mA (115mW)

Vi

12 Bit<500mW

500kHz

Vdiff

Vi

Vdiff= 17.3dB gain

180MHz SPAN

20log ( )

PD

100

50

100

495

495

210

210

40.2

10k

40.2

March 2, 2011FN7811.0

Get the Datasheet and Order Samples

http://www.intersil.com

Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2011All Rights Reserved. All other trademarks mentioned are the property of their respective owners.

EEWeb | Electrical Engineering Community Visit www.eeweb.com 13

The Taylor Expansion forRF Mixers:

Christopher MarkiDirector of Research

Pretty, and Pretty Useless

“I have never let my schooling interfere with my education.” -Mark Twain

In my blogging past, I have always written to a very RF savvy audience. Now that we are in a more generalized electrical engineering forum, I believe it would be most appropriate to talk about something that Marki Microwave is most well known for: RF/Microwave mixers.

For those unfamiliar with Marki Microwave, we offer the world’s largest selection of “hybrid” mixers (more on hybrid technology some other time). With a career dating back four decades, my father started Marki Microwave in 1991 with the intention of offering the broadest selection of high-performance mixers in the industry. In time, I will educate my readers about the nuances and history of mixer technology, and how Marki has fit into this grand framework. Before we can get into the details, however, I need to insult some professors.

Most electrical engineers do not really know what a mixer is. In short, a mixer is a 3-port electrical device whose output signal frequency is equal to the sum (or the difference) of the 2 input signals’ frequencies (see Fig. 1). In other words,

We include the absolute value here because we do not have negative frequencies.

In my experience, few electrical engineers actually know the above equation. More typically, people think of the mixer as a “multiplier” or two signals. This is understandable; the mixer symbol literally looks like a “times” symbol (see Fig. 1), and technically, the mixer does behave with a “multiplication-like” effect. The multiplicative notion of the mixer is further reinforced in RF courses. Often, when the

| |frequency frequency frequencyout IN IN1 2!=

EEWeb | Electrical Engineering Community Visit www.eeweb.com 14

TECHN

ICA

L ARTIC

LETECHNICAL ARTICLE

mixer is introduced, the professors describe mixer operation based on the concept of the Taylor series expansion of two or more signals on a nonlinear device. It looks something like this for a single diode mixer:

the I-V characteristics of the device (usually a diode). In practice, a mixer will work quite well, even when the large signal and small signal are within 3 dB! Certainly, the requisite small signal assumption is not a necessity to create excellent mixers in the real world.

Next, due to the tedium of the algebra, the professor will often truncate the expansion to the 3rd order and represent the higher order terms with the catchall symbol for laziness: “…” I am not suggesting that a reasonable derivation would include higher order terms (that is, after all, usually saved for some horrifyingly malicious homework problem), I am simply saying that by stopping at the 3rd order, the student is mislead into believing that 4th order and higher terms are not important. In practice, we find that higher order terms can wreak havoc on a system if not properly controlled. The Taylor expansion understanding of mixers trivializes this concept.

Lastly, and most sinfully, the Taylor expansion derivation concludes that the sum and difference frequencies are proportional to the large signal voltage. This would imply that by turning up the large signal (i.e., the LO voltage), one could increase the output level of the mixed signal. Let me put this in

DOWNCONVERSION

Frequency

Radio Frequency(fRF)

Local Oscillator(fLO)

Intermediate Frequency(fIF)

DC

R IL

Powe

r

UPCONVERSIONfIF = |fLO - fRF| fRF1 = fLO - fIF fRF2 = fLO + fIF

RF

LO

IF

Frequency

Radio Frequency(fRF)

Local Oscillator(fLO)

Intermediate Frequency(fIF)

DC

IRL

Powe

r

RF1

LO

IFRF2

( ) ' ( ) "( ) "' ( ) ...I V I v I V v I V v I VDC Dc DC DC2 3$ $ $= + + + +

After some smoke and mirrors (i.e., algebra and trigonometry), the college professor usually arrives at the conclusion that the second order expansion includes two important terms:

The critical function of frequency translation of signals, therefore, is distilled into a few crude mathematical brush strokes. Digging deeper, we can show that this approach to explaining and understanding mixers is terribly flawed and leads to many erroneous and misleading conclusions.

First, the Taylor expansion necessarily assumes that one of the signals is a “large signal” and one of the signals is a “small signal.” Basically, the math only works well if the small signal only slightly perturbs

( )cosSum Frequency V V tRF LO RF LO\ $ $ ~ ~+

( )cosDifference Frequency V V tRF LO RF LO\ $ $ ~ ~+

Figure 1: Figure explaining up and down conversion. Taken from the Marki Mixer Tutorial..

EEWeb | Electrical Engineering Community Visit www.eeweb.com 15

TECHN

ICA

L ARTIC

LETECHNICAL ARTICLE

simple terms: Passive mixers do not provide gain, EVER! The notion that I can simply turn up the voltage swing on my large signal, and subsequently increase the power level of my converted signal, is a horrible misrepresentation of the actual physics. Yes, active mixers do exist, but the signal gain is attributed to some kind of DC bias on the nonlinear devices. The concept of taking energy from a strong AC signal, and imparting some of that energy onto a weak AC signal is extremely important and interesting, but the classic RF mixer does not do this (Incidentally, there is a class of amplifiers called Parametric Amplifiers, that do perform this kind of mixing/amplifying. The physics is extremely interesting. I even once dabbled in such research while at UCSD). As a mixer guy, I wish mixers behaved like parametric processers, but they do not. Alas, passive mixers always have loss—such is Mother Nature.

To conclude, it is important to recognize the Taylor expansion approach for what it is: a convenient mathematical technique to introduce students to the idea that “nonlinear” devices spread energy in the frequency domain. Most undergraduate electrical engineering curriculums barely touch upon the concepts of the nonlinear interaction of signals in semiconductor devices, so it is not surprising that the mixer is so often poorly explained. It is my hope that I can reprogram some of these concepts and offer a more physically intuitive understanding of

what makes a good RF mixer. For more information about RF/microwave mixers, you can read our tutorial.

For what it’s worth, there is one professor who does in fact teach mixers in a way that actually makes physical sense; he is Professor Lee at Stanford. I highly recommend his text, it gives an excellent introduction to RF mixers, even if Marki-style mixers are totally ignored.

About the Author

Christopher F. Marki received his B.S.E.E. from Duke University in 2002 and his M.S.E.E. and Ph.D. from University of California, San Diego in 2004 and 2007, respectively. While in graduate school, Christopher studied high speed fiber optics and consulted for San Diego start-up Ziva Corporation. Following graduate school, Christopher decided to forego a life in Photonics and opted, instead, to work with his father at Marki Microwave and learn the “family business” of microwave mixers. While at Marki Microwave, Christopher has served as Director of Research and has been responsible for the design and commercialization of many of Marki’s fastest growing product lines including filters, couplers and power dividers. Dr. Marki has authored and co-authored numerous journal and conference publications and frequently serves as an IEEE reviewer for Photonics Technology Letters and Journal of Lightwave Technology.

EEWebElectrical Engineering Community

Join Todaywww.eeweb.com/register

EEWeb | Electrical Engineering Community Visit www.eeweb.com 16

RETURN TO

ZERORETURN TO ZERO

EEWeb | Electrical Engineering Community Visit www.eeweb.com 17

RETURN TO

ZERORETURN TO ZERO

Contact Us For Advertising Opportunities

1.800.574.2791advertising@eeweb.com

www.eeweb.com/advertising

Electrical Engineering CommunityEEWeb