Electronic Design

Single-Chip TV Tuner Kicks the Can

The fully integrated Si2170 TV tuner from Silicon Laboratories is a real milestone in mixedsignal design (Fig. 1). It not only decreases the size of the TV front end, it also greatly improves on the performance specifications of even the best discrete component “can” tuners. Eventually, it will have a huge impact on consumer electronics.

One of the most visible features inside a TV set is the metal can enclosure that contains the tuner. Of course, the tuner is the front end that includes the RF filters and low-noise amplifier (LNA) fed by the antenna or cable connection, the mixer, the local oscillator (LO) for channel selection, and some initial interface (IF) amplification and filtering, usually with a surface acoustic wave (SAW) filter.

The early tuners were large because they used tubes and a big multilayer switch for channel selection. They were expensive and difficult to tune and adjust. Transistors and then ICs made these devices progressively smaller over the years. However, they have never been able to eliminate a good number of discrete components or the metal shield that keeps the high-frequency local-oscillator signals from disturbing everything around them.

More recently, numerous brave semiconductor companies have attempted to make a single-chip TV tuner that reduces the number of discrete components to a minimum and eliminates the shield. A half dozen or so devices came close to this ultimate goal but never met the requirements of minimum size, parts count, and exceptional performance all at the same time.

Then along comes Silicon Laboratories with its extensive mixed-signal design expertise and a flare for innovating unique ICs. After a two-year effort, its end result is the Si2170, which is an outgrowth of the company’s remarkable success with its single-chip analog FM radio tuner line.

Several years ago, Silicon Labs set out to put a standard FM radio on a chip with minimal external parts. The result was the Si47xx line of integrated FM radios, which includes versions with a single FM receiver (Rx), FM Rx and transmitter (Tx), and both AM and FM radios. Virtually all parts are on chip, including filters and even the popular RDS feature. Millions of these chips are inside cell phones, laptops, clock radios, and consumer stereo receivers.

Silicon Labs also had built a line of single-chip GSM/GPRS/EDGE cell-phone ICs, which it sold to NXP a number of years ago. Working from that success, a mixed-signal team was formed to tackle the ultimate mixed-signal RF challenge, the TV tuner (Fig. 2).

REWARDS AND CHALLENGES
With several hundred million units sold every year, the TV set is a prime target for IC manufacturers because of the huge volume and profit potential, said Tyson Tuttle, VP of the Silicon Labs Broadcast Division. Capturing a high percentage of the market for TV sets, including those with two tuners for picture-in-picture, cable set-top boxes, and PCs and laptops with internal TV, would provide a big growth spurt. A small tuner additionally would make it easier to build TV into other products.

Tuttle also said that the challenge in making a single-IC TV tuner required a strong background in standard CMOS RF design as well as the invention of some unique circuits that met the tough testing standards of TV manufacturers. The greatest challenge, Tuttle added, was overcoming the blocking and harmonic generation problems. Blocking occurs when a strong out-of-band and unwanted signal interferes with the desired signal. The result is usually a reduction of the receiver sensitivity by 3 dB or more.

As for the harmonics problem, the phase-locked loop (PLL) synthesizer generates harmonics of the LO signal that fall into the 43- to 1002-MHz input frequency range of the tuner. The harmonics can further produce intermodulation distortion under the right conditions.

Silicon Labs minimized both of these problems by making the mixers as linear as possible. In addition, the company created a unique and patented tunable high-Q tracking filter for the front end that essentially eliminates the blocking problem.

FEATURES AND SPECIFICATIONS
The Si2170 is a worldwide hybrid TV tuner that can be used in TV sets, cable set-top boxes, DVD players, personal video recorders, and TV cards and dongles for PCs. It’s compatible with the ATSC/QAM, DVB-T/C, and ISDB-T/C digital TV standards. Digital demodulation is external with the Silicon Labs Si2165 digital demodulator chip.

Also, the Si2170 handles the NTSC, PAL, and SECAM analog TV standards, and the demodulator is on-chip. While the U.S. and much of Europe and Asia have converted to digital TV, analog TV is alive and thriving across the world. There is still a large demand for standard analog TV sets.

Only a few external components are used, including a crystal, an input balun, and a couple of bypass capacitors (Fig. 3). No SAW filters are needed, as in most other tuner implementations. The basic design is a low-IF superheterodyne. The IF can be set to a frequency in the 3- to 5-MHz range.

The highly linear front end provides superior blocking performance, resulting in higher sensitivity in crowded and both near and far reception conditions with strong undesired channels and interference. The I/Q filters are on-chip. A complete frequency synthesizer selects the desired channel in the 43- to 1002-MHz range.

The noise figure with maximum gain is 4 dB. Third-order intercept (IIP3) performance with maximum gain is +23 dBm wideband and –2 dBm inband. The analog receiver sensitivity is –68 dBm for NTSC and –67.5 dBm for PAL/SECAM. Adjacent channel attenuation in the digital TV (DTV) modes is 80 dB. LO phase noise at 860 MHz in the DTV modes is –96/–95/–104 dBc/ Hz for 1-/10-/100-kHz offset, respectively.

The Si2170 comes in three forms. The Si2170 covers all analog and digital TV standards. The Si2171 covers only the PAL/ SECAM and DVB-T/C standards used in Europe. The Si2172 covers only the NTSC, ATSC/QAM, and ISDB-TC standards. All three are made with a standard 110-µm CMOS process and housed in a 7- by 7-mm, 48-pin quad flat no-lead (QFN) package. They operate from 1.8- and 3.3-V supplies and have a maximum power consumption of 1 W. Pricing begins at $3.95 in quantities of 10,000.

A DEEPER LOOK
The Si2170 is the industry’s first silicon TV tuner to exceed the performance of traditional discrete TV tuners. This will enable TV makers to deliver improved picture quality and better reception for both analog and digital broadcasts. The high level of integration eliminates more than 100 discrete components, enabling simpler design, lower manufacturing costs, higher production yields, and improved reliability for integrated digital televisions (iDTVs), set-top boxes, and PC TV applications.

For years, the industry has attempted to replace the traditional discrete tuner with an integrated silicon tuner to enable cost reductions, reduce complexity, harmonize across standards, and improve consumer device form factors. To date, silicon tuners have not been able to achieve these goals. Today, iDTVs still use traditional discrete tuners to achieve the best performance in real-world reception conditions. Simultaneously, the system complexity and cost of these solutions have increased to support the reception of hybrid analog and digital broadcasts as well as regional broadcast standards and system requirements.

To exceed the performance of traditional discrete TV tuner implementations, the Si2170 integrates a highly linear RF frontend design incorporating a unique, merged low-noise amplifier (LNA) and high-Q tracking filter to provide gain only around the desired channel frequency. This enables superior sensitivity and rejection of strong undesired channels and interference in severe broadcast conditions. That translates into the reception of more channels and weak signals as well as improved picture clarity.

Silicon Labs’ patented and proven digital low-IF architecture enables the Si2170 to truly achieve a high level of performance and integration while addressing the challenges created by hybrid analog and digital reception and multiple regional standards. The architecture allows many functions typically relying on analog and discrete fixed components to be implemented with cost-effective and programmable digital signal processing. This permits TV manufacturers to optimize system parameters and comply with all worldwide cable and terrestrial broadcast standards.

Eliminating more than 100 discrete components, including the tracking filter function, eliminates costly manual inductor tuning and other alignment procedures and results in significantly lower manufacturing costs. The Si2170 not only enables a simpler design, reduced bill of materials, and lower manufacturing costs, its high level of integration improves reliability and printed-circuit board (PCB) production yields. It even reduces field returns. Finally, as TV makers continue to design thinner form factors, the PCB footprint of the Si2170 helps to enable the next generation of ultra-slim flat-panel TVs.

TAGS: NXP
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