The fact that development of silicon tuners has lagged behind virtually all other TV developments clearly identifies that silicon tuner technology had difficult challenges to overcome in order to realize a producible tuner. And indeed, a number of difficult hurdles had to be crossed before a practical, manufacturable silicon tuner could be produced at a reasonable cost.

An obvious question at this point might be ‘why are tuners even necessary? Why not do it all digitally?’ Ideally, such a tuner would be produced with a simple (in concept…extremely complex in design) analog-to-digital converter (ADC), whereby analog TV signals would be directly converted to a digital datastream without tuned circuits, including input and output filtering.

Even a cursory look at TV bandwidths reveals the magnitude of the ADC problem to be overcome. The Nyquist theorem requires nearly two billion samples per second using an ADC converter to sample the analog input signal across the entire 860 MHz TV bandwidth, and with enough bits of resolution to reproduce an HDTV-quality picture. ADC converters with that kind of sampling rate and resolution currently are expensive.

This extreme sampling speed and resolution is necessary because of the very large bandwidth associated with broadcast television. However, if a tuner is used, this broadband input can be tuned to a single, baseband signal that is significantly easier to process with ADCs. Because the tuner simply pushes the difficulty of handling this very large bandwidth from an ADC converter to the tuner, problems dealing with the large bandwidth still had to be solved.

Most receiver designs cover a relatively small frequency range. A couple of examples include 802.11b wireless LANs and cellular phones. The tuner in a cellular phone tunes about 500 kHz of bandwidth. A TV receiver, by comparison, must tune about 860 MHz — three orders of magnitude more bandwidth. The extreme difference in bandwidths results in many proven narrowband design techniques not transferring to TV's wideband requirements. Figure 1 illustrates the magnitude difference in the two receiver applications. New techniques have replaced traditional analog designs to facilitate broadband capability with new silicon tuners.

An even bigger obstacle in the realization of silicon tuners was designing highly integrated circuitry to accommodate the enormous dynamic range required for broadcast TV signals. Signals reaching the receiver are affected by the variable and arbitrary distance from the transmitter. It's not unusual to have signal strength variations of several-thousand-fold.

Cable signals are of relatively uniform signal strength and integrity, which allowed some early silicon tuner designs to work in that environment. However, only recently have silicon tuners achieved the dynamic range required to reliably reproduce a quality TV picture and audio (Figure 2). Silicon tuners, such as Xceive's XC2028 and XC3028 have a dynamic range of 80 dB, more than enough to handle the challenge of broadcast signal quality.

The large dynamic range also demands that the receiver be extremely sensitive to receive very weak signals — yet not prone to front-end overload caused by very strong signals. New active filter designs have produced the sensitivity required, while remaining immune to overload induced by strong, local signals. This results in a superior sensitivity of -83 dBm or better.

Several manufacturers have full or partial silicon tuner solutions. We have produced a one-design-fits-all-TV-standards analog tuner IC. While XC2028 is a complete analog RF-to-baseband tuner, the XC3028 is a complete analog and digital RF-to-baseband tuner. Both these chips are based on a systematic, iterative design approach to optimize highly integrated functions in traditional and non-traditional ways. The basic block diagram of the silicon tuner is shown in Figure 3. This design is significantly more sophisticated than a can tuner, incorporating substantial digital processing circuitry in addition to the RF signal conditioning and tuning front end. For instance, the XC3028 integrates on-chip wideband tunable filters, image rejection filter, programmable channel filter, and wideband voltage-controlled oscillator (VCO).

Not only are silicon tuners a significant improvement over can tuners in the areas outlined above, they have a much tighter QC acceptance tolerance due to eliminating high-tolerance passive components. Figure 4 shows the frequency response of two individual Xceive EVK4 silicon tuners vs. two high-quality can tuners. Note how little variation exists in the silicon tuners compared to can tuners.

To further illustrate this point, several can tuners were tested separately. It was observed that 1 dB to 2 dB of variation across the frequency range is normal. In addition, each tuner has a slightly different transfer characteristic, resulting in slight variations in the picture quality of the completed TV receiver.

In addition, the designers have extensively analyzed the sources of non-linear signal degradation to further enhance dynamic range over the full TV bandwidth. Each non-linear degradation was cancelled with an inverse-acting non-linear source. Another advancement is that no external low noise amplifier (LNA) is required with Xceive's silicon tuners. Other solutions may require external LNAs to achieve the -83 dBm sensitivity of the Xceive design (ATSC signal).

A final factor in physically being able to integrate the full tuner function was the fabrication of the IC itself. The fabrication took advantage of improvements in the BiCMOS process, as well as benefiting from small, 0.18 µm architecture. Both factors contribute to speed and low power consumption.

Perhaps even more important in the fabrication process is the use of SiGe transistors. These active devices are faster, more power efficient, and more important, have improved noise characteristics compared to traditional silicon transistors. Incorporation of this leading-edge technology also significantly impacts the ability to incorporate the silicon tuner in a package smaller than a dime.

There are many obvious applications for silicon tuners — they will replace can tuners in virtually every consumer TV set within just a few years. Beyond that, however, the reduction in size and power requirements opens a new and diverse universe of applications.

• Tuners for PCs: The demand for TV receivers integrated with PCs already exists. New silicon tuners will make them significantly more practical. For example, Compro has designed a USB 2.0 compatible TV receiver based on the XC3028. This tiny device (VideoMate U880) is about the same size as a USB flash drive.

• Flat panel TVs: Another market that will get a boost from silicon tuners is picture-in-picture. Because of the low-power design and adjacent-channel interference rejection, multiple silicon tuners can be incorporated into a single design, allowing instant 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 the midst of sweeping changes over the last 10 to 15 years. One of the last components to experience this sweeping evolution is the tuner.

Only recently have tuner designs caught the innovation wave. Newly designed silicon tuner chips, integrating the full tuner function have performance, packaging and power advantages over traditional can tuners.

Alvin K. Wong is vice president of marketing for Xceive Corp. He joined Xceive in December 2004, bringing 16 years of management experience in the semiconductor industry. Most recently at Infineon Technologies, Wong was the vice president of marketing, responsible for building strategies and running operations in North America for the wireless division.

Jordan Du Val is vice president of sales for Xceive Corp. He joined Xceive in January 2002. He was formerly president and CEO of SpotNet. He holds a Bachelor degree in commerce, with Honors from Carleton University, Canada and holds four patents in interactive TV architecture and systems.

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Silicon tuner aids transition to digital TV
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