Selecting a silicon TV tuner for next-gen iDTV designs

Selecting a silicon TV tuner for next-gen iDTV designs

There are many challenges and architectural complexities when choosing this part

BY BILL SIMCOE
Product Manager, Broadcast Video
Products, Silicon Labs
www.silabs.com

Today’s iDTV and set-top box (STB) makers are adopting silicon TV tuners over legacy mixer oscillator phase-locked loop (MOPLL) CAN tuners to reduce system cost and size and improve performance. Silicon tuner adoption began before 2007 and gained significant traction during 2010 when flat-panel TVs and STBs experienced a jump in sales. Designing silicon TV tuners that matched MOPLL performance levels was the main hurdle for adoption, but semiconductor suppliers have met this performance standard, clearing the road for market acceptance of TV tuner products. Navigating the competing options can be a complex process given the wide range of issues surrounding TV tuner IC selection.

In recent years, TV makers have begun replacing MOPLL-based CAN tuners with silicon tuners to reduce cost and complexity, harmonize across regional standards and shrink form factors. A CAN tuner consists of an MOPLL IC surrounded by more than 150 discrete components housed in a metal can. See Fig. 1 for a close-up view of a CAN tuner PCB.

Fig 1: Example of MOPLL CAN tuner, which requires 150+ components.

Advanced silicon tuners, which integrate the MOPLL, demodulator ICs, and most of the discrete components into a single-chip IC, now match and often exceed the performance of MOPLL CAN solutions, enabling TV makers to deliver improved picture quality and better reception for analog and digital broadcasts. As TVs grow slimmer and adopt dual tuner and multimedia reception while requiring BOM cost reductions, MOPLL CAN tuners cannot fit the TV industry’s form factor and price point needs. In addition, MOPLL CAN tuners require considerable design and manufacturing resources as each can must be tuned manually.

Today’s silicon tuners enable a more economical, streamlined manufacturing process, support dual tuner designs, and allow TV makers to reduce the size and cost of their front-end solutions. Silicon tuners can be implemented directly on the TV motherboard or inside a CAN module. Some TV makers may choose a two-step approach, first using a silicon tuner inside a CAN module and later directly on-board for the ultimate cost savings. Although MOPLL-based CAN tuners will be around for a few more years in legacy designs, silicon tuner adoption rates are rising exponentially.

Many TVs must support both analog and digital transmission standards to meet consumer demands. Examples of analog transmission standards include NTSC and PAL/SECAM. In this case, “analog” describes the transmission modulation format and not the specific processing technology used to decode it. Many countries are in various stages of executing analog switch-over plans that will terminate terrestrial analog broadcasts in favor of higher quality digital broadcasts.

Even in countries that have theoretically switched over to digital, the analog transmissions remain active, and consumers continue to demand support for these transmissions. Japan is an exception, having converted to all digital, but TVs sold in virtually every other region are forced to support analog reception to deal with low-power analog broadcasts, slow-to-upgrade cable networks, and legacy consumer electronics devices. Tuner support for analog transmissions will be required by all major TV brands outside of Japan for several more years and possibly for up to 10 more years.

Top-tier TV brands are accelerating their adoption of silicon tuners to save cost, improve reliability, reduce component count and support thinner TV form factors. These advantages are driving significant opportunities in second- and third-tier TV brands where the adoption of silicon TV tuners is just starting. Because today’s silicon tuner ICs must support all worldwide terrestrial and cable broadcast standards, these smaller TV brands benefit from the intensive work already accomplished by the top brands.

Connected TVs expand program sources beyond the antenna and cable and are gaining traction as “apps” make their way to large-screen TVs. New TV communication interfaces such as Wi-Fi, Ethernet, and LTE are delivering rich content beyond traditional broadcast sources. These interfaces present technical challenges for over-the-air broadcast tuners. New RF enhancements in next-generation TV tuners, such as Silicon Labs’ Si21x8 tuner family, provide high tolerance to Wi-Fi and LTE interference without requiring external filtering components. In addition, the reduced noise floor enabled by these next-generation tuners delivers exceptional video signal-to-noise ratio (VSNR) for analog TV reception. The combination of these enhancements results in a clearer, less grainy picture with more channels received.

Silicon TV tuner selection challenges

TV tuners must cleanly receive a single low-power transmission in a crowded spectrum, which puts considerable pressure on a tuner’s RF front-end. The complexities present at the geographic boundaries of two differing transmission standards create additional challenges. Add to this the architectural complexities of popular DTV and STB SoCs, and it becomes apparent that a single silicon TV tuner IC cannot meet the needs of the entire market. Fortunately numerous tuner ICs are available that address these varying platform needs. The challenge is to select the right device for your TV application.

Channel reception: The keys to achieving clear TV broadcast reception are sensitivity and selectivity. These characteristics are based on low noise figure (NF), high RF front-end linearity and high-quality RF front-end filtering. Low NF means that the RF front-end contributes little unwanted noise to the incoming signal, while high sensitivity means that there is ample VSNR even with weak input signals. TV tuners often must receive a single broadcast in the presence of many other signals. The tuner IC’s selectivity — the ability to block or exclude content on nearby “blocker” channels — is essential for clean reception. To achieve high selectivity in a cost-effective solution, a TV tuner needs both high linearity and high quality filtering in the RF front-end. As a result, silicon TV tuner ICs with high sensitivity and excellent selectivity performance, as shown in Fig. 2 , result in more channels received under real-world conditions.

Fig. 2: Advanced TV tuners [red trace] offer exceptional blocking performance compared to alternative products [blue trace].

Field testing: Unusual broadcast conditions occur more frequently than you might realize. This is especially true at the geographic boundaries between broadcasting standards where issues become very complex. For example, in Europe a single TV can receive numerous analog and digital standards across international borders. To address these non-standard reception conditions, the TV tuner and demodulator must detect and compensate for non-standard transmissions. These conditions are corrected on a case-by-case basis, requiring extensive field testing. Without the TV tuner’s extensive control and configuration capabilities, these increasingly challenging requirements could not be addressed. TV manufacturers put TV tuners through rigorous field testing, highlighting both standard performance as well as performance under anomalous broadcasts. TVs destined for cost-sensitive regional markets may choose a lower cost TV tuner, but TVs destined for broader export markets will require robust worldwide performance.

High integration: TV manufacturers continually look for ways to minimize BOM cost through reduced component count. One way to reduce the system BOM is to select a TV tuner solution, such as the Si21x8 family, that requires no balun on the RF input, thereby reducing component count and system cost. The Si21x8 tuners also include an integrated power-on reset monitor and the ability to operate with a single 3.3 V power supply, further reducing system design cost and complexity. In addition, enhanced electrostatic discharge (ESD) protection reduces BOM cost for TV modules that require higher ESD immunity. Furthermore, the highly integrated Si21x8 TV tuners do not require wirewound inductors, loop filter capacitors, tracking filter inductors or crystal load capacitors.

Flexible Architectures: Greater choice in TV tuner architectures has been a positive development for iDTV and STB suppliers. Several silicon tuner IC variations are now available to meet the specific architecture needs of iDTV and STB platforms. Modern TV and STB platforms have three main circuit functions: the silicon TV tuner, the demodulators, and the audio/video processing and graphics SoC. The output of the tuner drives the input of the demodulator, and the output of the demodulator drives the input of the audio/video processing and graphics SoC.

TV and STB platforms have varying needs for analog and digital tuners. For example, a simple narrowband cable access box may need a single digital-only tuner. In contrast, a high-volume iDTV will likely support analog and digital terrestrial broadcast as well as cable input sources. For larger TV brands, these tuners must support all analog and digital transmission standards worldwide. TV tuner ICs are now available to support numerous architectural configurations such as digital only, multichannel digital only, analog and digital tuners, analog and digital tuners with analog TV demodulator, and various receiver configurations with a tight linking of tuner and demodulator ICs. ■