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22 www.rfdesign.com October 2005

Semiconductor Technology

Silicon TV tuners poised to replace cansWhile the evolution of TV receivers has accelerated on many fronts in the lastdecade, fully integrated silicon tuner design has lagged behind this evolutionarywave. The silicon TV tuner is now perfected and will rapidly replace traditionalcan tuners, just as transistors replaced vacuum tubes during the mid-1960s.

By Alvin Wong and Jordan Du Val

The past decade delivered an unprecedentedand multifront evolution of TV broad-

casts and receivers. These advances includestereo audio, HDTV, flat-screen technologyusing LCD and plasma displays, and TVreceivers integrated into personal computers.

The ultimate goal for TV receivers is a fullyintegrated solid-state TV with a flat-screenLCD or plasma display.

While significant progress has been madetoward this goal, tuners have fallen behindin the evolutionary development. This lag,however, is in the process of rapidly chang-ing. Demand for smaller and lower-powertelevisions, flat-screen miniaturization, andeven government standards are driving thedevelopment of silicon tuners to the razorsedge. In fact, the Federal CommunicationsCommission (FCC) has set standards requir-ing all new televisions to incorporate digital

tuners within the next two years.

Tuner historyThe traditional tuner design for decades

has been the can tuner, appropriately namedbecause they are housed in metal enclosuresto minimize RF interference and cross-talk.Despite the long history of use, can tunershave some major deficiencies.

First, the requisite use of tunable and fixedcoils has virtually dictated discrete transistordesigns for the tuner. This results in poortemperature characteristics and a physi-cally large, power-hungry modulesome as

large as two inches by four inches. Perhapsthe primary deficit with can tuners thoughis that each must be tuned individuallyas part of the manufacturing process. Notonly is this a time-consuming step, thetolerance of the passive components resultsin a relatively broad acceptance standard forcan tuner quality control.

As the disadvantages of the can tunerbecome more evident in todays moderndevices, the silicon tuner is poised to unseatthe can tuner in virtually all applications, inthe same vein as transistors replaced vacuumtubes. Silicon tuners have the potential tooffer a number of advantages and capabilitiesthat the can tuner lacks.

Highly integrated silicon tuners are mucheasier to manufacture, and no tuning isrequired, reducing the overall cost of thetuner. The tuner can also be made extremelysmall compared to the can tuner because ofthe high level of integration.

Another notable advantage of silicon tunersis that a single tuner can receive TV signals us-

ing any of the several worldwide transmissionstandards. This means that an internationalmanufacturer need only stock a single, meets-all-standards tuner, instead of one or multiplecan tuners for each disparate standard.

Other advantages of silicon tuners include: integrated analog and digital tuners; multiple tuners in the same package for

picture-in-picture and other applications; greater reliability; superior thermal stability; tighter quality control standards; and quicker channel lock: ~5 ms vs.

~150 ms.These advantages, coupled with recent

IC design rules and techniques have enabled

practical silicon tuners. New IC techniquesbeing used include enhanced BiCMOS pro-cesses, silicon-germanium (SiGe) transistors,and 0.18 m design rules. This design evolu-tion, when added with government dictates,will result in a rapid and universal transitionto silicon tuners.

Overcoming physical andintegration problemsThe fact that development of silicon

tuners has lagged behind virtually all otherTV developments clearly identifies thatsilicon tuner technology had difficult chal-lenges to overcome in order to realize aproducible tuner. And indeed, a number ofdifficult hurdles had to be crossed before apractical, manufacturable silicon tuner couldbe produced at a reasonable cost.

An obvious question at this pointmight be why are tuners even necessary?Why not do it all digitally? Ideally, such atuner would be produced with a simple (inconceptextremely complex in design)

Figure 1. Narrowband vs. broadband tuning.

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analog-to-digital converter (ADC), wherebyanalog TV signals would be directly convertedto a digital datastream without tuned circuits,including input and output filtering.

Even a cursory look at TV bandwidthsreveals the magnitude of the ADC problem to

be overcome. The Nyquist theorem requiresnearly two billion samples per second us-ing an ADC converter to sample the analoginput signal across the entire 860 MHz TVbandwidth, and with enough bits of resolu-tion to reproduce an HDTV-quality picture.

ADC converters with that kind of samplingrate and resolution currently are expensive.

This extreme sampling speed and resolutionis necessary because of the very large band-width associated with broadcast television.However, if a tuner is used, this broadband

input can be tuned to a single, basebandsignal that is significantly easier to processwith ADCs. Because the tuner simply pushesthe difficulty of handling this very large band-width from an ADC converter to the tuner,problems dealing with the large bandwidth

still had to be solved.Most receiver de-

signs cover a relativelysmall frequency range.A couple of examplesinclude 802.11b wire-

less LANs and cellu-lar phones. The tunerin a cellular phonetunes about 500 kHzof bandwidth. A TVreceiver, by compari-son, must tune about860 MHzthree or-ders of magnitudemore bandwidth. Theextreme differencein bandwidths resultsin many proven nar-rowband design tech-

niques not transfer-ring to TVs widebandrequirements. Figure 1illustrates the magni-tude difference in thetwo receiver applica-tions. New techniqueshave replaced tradi-

tional analog designs to facilitate broadbandcapability with new silicon tuners.

An even bigger obstacle in the realizationof silicon tuners was designing highly inte-grated circuitry to accommodate the enormousdynamic range required for broadcast TV sig-

nals. Signals reaching the receiver are affectedby the variable and arbitrary distance fromthe transmitter. Its not unusual to have signalstrength variations of several-thousand-fold.

Cable signals are of relatively uniformsignal strength and integrity, which al-

Figure 3. Block diagram of XC3028 analog and digital silicon tuner.

Figure 2. Broadcast signals vs. cable signals.

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lowed some early silicon tuner designs towork in that environment. However, onlyrecently have silicon tuners achieved thedynamic range required to reliably reproducea quality TV picture and audio (Figure 2).Silicon tuners, such as Xceives XC2028 and

XC3028 have a dynamic range of 80 dB,more than enough to handle the challengeof broadcast signal quality.

The large dynamic range also demands thatthe receiver be extremely sensitive to receivevery weak signalsyet not prone to front-end overload caused by very strong signals.

New active filter designs have produced thesensitivity required, while remaining im-mune to overload induced by strong, localsignals. This results in a superior sensitivity of

83 dBm or better.

Silicon tuner solutionsSeveral manufacturers have full or partial

silicon tuner solutions. We have produced aone-design-fits-all-TV-standards analog tunerIC. While XC2028 is a complete analog RF-to-baseband tuner, the XC3028 is a completeanalog and digital RF-to-baseband tuner.

Both these chips are based on a systematic,iterative design approach to optimize highlyintegrated functions in traditional and non-traditional ways. The basic block diagram ofthe silicon tuner is shown in Figure 3. Thisdesign is significantly more sophisticated

than a can tuner, incorporating substantialdigital processing circuitry in addition to theRF signal conditioning and tuning front end.For instance, the XC3028 integrates on-chipwideband tunable filters, image rejection filter,programmable channel filter, and widebandvoltage-controlled oscillator (VCO).

Not only are silicon tuners a significant im-provement over can tuners in the areas outlinedabove, they have a much tighter QC accep-tance tolerance due to eliminating high-toler-ance passive components. Figure 4 shows thefrequency response of two individual XceiveEVK4 silicon tuners vs. two high-quality can

tuners. Note how little variation exists in thesilicon tuners compared to can tuners.

To further illustrate this point, several cantuners were tested separately. It was observedthat 1 dB to 2 dB of variation across thefrequency range is normal. In addition, eachtuner has a slightly different transfer character-istic, resulting in slight variations in the picturequality of the completed TV receiver.

In addition, the designers have extensivelyanalyzed the sources of non-linear signaldegradation to further enhance dynamic rangeover the full TV bandwidth. Each non-lineardegradation was cancelled with an inverse-

acting non-linear source. Another advance-ment is that no external low noise amplifier(LNA) is required with Xceive's silicon tuners.Other solutions may require external LNAs toachieve the -83 dBm sensitivity of the Xceivedesign (ATSC signal).

A final factor in physically being able tointegrate the full tuner function was the fab-rication of the IC itself. The fabrication tookadvantage of improvements in the BiCMOSprocess, as well as benefiting from small,0.18 m architecture. Both factors contributeto speed and low power consumption.

Perhaps even more important in the fabri-

cation process is the use of SiGe transistors.These active devices are faster, more powerefficient, and more important, have improvednoise characteristics compared to traditionalsilicon transistors. Incorporation of thisleading-edge technology also significantlyimpacts the ability to incorporate the silicontuner in a package smaller than a dime.

ApplicationsThere are many obvious applications for

silicon tunersthey will replace can tuners invirtually every consumer TV set within just afew years. Beyond that, however, the reductionin size and power requirements opens a newand diverse universe of applications.

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Tuners for PCs: The demand forTV receivers integrated with PCs alreadyexists. New silicon tuners will make themsignificantly more practical. For example,Compro has designed a USB 2.0 compatibleTV receiver based on the XC3028. This tinydevice (VideoMate U880) is about the samesize as a USB flash drive. Flat panel TVs: Another market that

will get a boost from silicon tuners is pic-ture-in-picture. Because of the low-powerdesign and adjacent-channel interferencerejection, multiple silicon tuners can beincorporated into a single design, allowinginstant access to several broadcasts.Cellular phone/PDA: The size of silicon

tuners, with their stingy use of battery power,allow for TV reception in a cell phone or PDA.

The TV broadcast industry has been in themidst of sweeping changes over the last 10 to15 years. One of the last components to experi-ence this sweeping evolution is the tuner.

Only recently have tuner designs caughtthe innovation wave. Newly designed silicon

tuner chips, integrating the full tuner functionhave performance, packaging and power ad-vantages over traditional can tuners.RFD

ABOUT THE AUTHORS

Alvin K. Wong is vice president of mar-keting for Xceive Corp. He joined Xceivein December 2004, bringing 16 years ofmanagement experience in the semicon-ductor industry. Most recently at InfineonTechnologies, Wong was the vice presidentof marketing, responsible for buildingstrategies and running operations in North

America for the wireless division.

Jordan Du Val is vice president of sales forXceive Corp. He joined Xceive in January2002. He was formerly president and CEOof SpotNet. He holds a Bachelor degreein commerce, with Honors from CarletonUniversity, Canada and holds four patents ininteractive TV architecture and systems.

Figure 4. Superior tolerance of silicon vs. can tuners.

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