Although the TV market continues to mature, the underlying architectures inside the television continue to evolve to drive down prices. "Cost-down" are the two most spoken words in consumer electronics. Increasing cost pressure drove architectural shifts that led to rapid consolidation in the system-on-chip (SOC) market and accelerated adoption of silicon tuners in the television. The ability to achieve the lowest cost system solution without compromising performance requires disruptive technology. This article will look at key TV market trends and their effect on next-generation TV front-end solutions.
Changing TV landscape Every year more than 250 million TVs ship into analog only and hybrid (analog plus digital) markets worldwide. By the end of 2011, a select few SOC companies accounted for the vast majority of all TVs shipped. The most popular SOCs have integrated functions that are implemented most cost-effectively in the digital domain. At the same time, many silicon tuners have retained this functionality using expensive RF/analog processes, which adds unnecessary system cost and complexity.
Traditionally, many CAN tuners were MOPLL-based (Mixer Oscillator Phase-Locked Loop). As the cost/performance tradeoff improves, silicon tuners are rapidly replacing MOPLLs and are projected to approach nearly 100 percent market penetration in television within the next 18 months. Designing silicon tuners directly on the main TV printed circuit board (PCB) and in the CAN are both common – the implementation depends on the relative RF expertise of the TV maker.
Evolution of architecture The key to cost reduction is achieved by migrating functions from the analog/RF to digital domain. Fundamentally, the TV front-end is comprised of analog / RF circuits that tune and process off-air or cable television signals into a suitable format. These signals are then sampled by an ADC (analog-to-digital converter) which resides within the digital SOC. The economics and performance of the ADC determines which functions can be integrated into the digital SOC as the ADC is the demarcation point between the analog/RF and digital domains.
Over the last decade, the IF (intermediate frequency) AGC amplifier, multiple SAW (surface acoustic wave) filters, and the analog demodulator have been integrated into the most popular SOCs in order to meet the cost requirements of the television market.
Figure 1 illustrates the typical front-end architecture in 2004. The tuner function was comprised of an MOPLL chip plus hundreds of discrete components that required hand tuning. Several discrete SAW filters output a filtered IF signal that fed into an external downstream analog demodulator. The outputs of the demodulator were digitized by the ADC inside the SOC. These large SAW filters limited how thin the TV panel could be. Thin-profile SAW filters were very expensive but necessary with the growing demand for ultra-thin flat panel televisions. At the same time, different SAW filters (6/7/8Mz bandwidth support) were required depending on the end TV market, thereby forcing region-specific TV SKUs that increased the operational and manufacturing costs.
Figure 1: SOC Architecture in 2004 with a discrete IF AGC Amplifier, SAW filters, and analog demodulator
Starting in 2009, ADC performance improvements at a viable cost point became widely available. The introduction of this disruptive technology enabled the tuner output signal to be sampled directly, eliminating the need for expensive, discrete SAW filters and an external analog demodulator. The availability of advanced ADCs enabled a significant architectural transition to integrate these functions into the SOC as shown in Figure 2. The transition is gradual and as such, there is still duplication of functionality in the analog and digital domains. This redundancy can be further optimized by eliminating the duplicated functions in the tuner.
Figure 2: Latest SOC architecture with integrated IF AGC amplifier, SAW filters, analog and digital demodulators
Design principles for achieving lower system costs in TV The cost advantages offered by the latest generation of TVs SOCs can be attributed to technology advancements in the ADC. Until recently, ADCs with the necessary dynamic range had a large die size and high power consumption making it difficult to effectively integrate the SAW filter function into the SOC. ADC dynamic range refers to the range of signals that can be digitized by the ADC. The relative level between the undesired (U) and desired (D) channels (U/D ratio), CNR (carrier-to-noise ratio determined by modulation method), and required margin determines the dynamic range of the ADC as shown in Figure 3.
Figure 3: ADC dynamic range
To meet system dynamic range requirements, previous generation TV systems had to use multiple external SAW filters. SAW filter characteristics depend on the U/D ratio as specified by the field condition or performance standard as shown in Figure 4. The stronger the undesired channel, the more complex a filter profile required. This filtering function adds significant cost to the overall TV BOM (bill-of-materials) especially as a filter that is integrated into most silicon tuner chips.
Figure 4: Filtering characteristics
ADCs with a much smaller die area, low power consumption and wide dynamic range are now widely available. As discussed earlier, these advanced ADCs have enabled SOC manufacturers to integrate the IF AGC amplification, digital and analog demodulation, and SAW filtering.
At the same time, many silicon tuners have retained full SAW filtering, and some chips still include analog demodulation. The duplication of these functions adds unnecessary system cost and complexity as shown in Figure 5. These functions are implemented most cost-effectively in digital in the SOC rather than in more expensive RF processes used by many silicon tuners today.
Figure 5: Many existing silicon tuners duplicate SAW filtering already in today’s SOCs