Background information: SGS-THOMSON and the Set-top Box

From its introduction just two years ago to an installed base of several million units in 1996, the digital set-top box (STB) has proved to be one of the most successful introductions of a new consumer electronics product. Sales in its first year outstripped those of CD players and vcrs during their own first year. Moreover, STB sales are expected to increase tenfold within the next few years, reaching an estimated 75 million units by the end of the decade. Semiconductor sales for STB applications are expected to grow from around $1.5 billion in 1996 to $4.3 billion in 2000, according to industry analyst Dataquest.

The success of the STB is due in large part to a digital technology: the power of MPEG digital video compression. This technology greatly increases the number of TV channels that can be transmitted using the existing bandwidths of today's satellite transponders and CATV networks. For example, the world's first commercial system, a partnership between DirecTV, USSB, and RCA, the Direct Satellite System (DSS), offers viewers up to 150 channels, thanks to SGS-THOMSONÆs MPEG-2 decoder chips. This increases viewer choice, generates greater revenues for operators from the same infrastructure, and paves the way for advanced concepts such as video-on-demand. SGS-THOMSON's ability to deliver silicon solutions that meet the most demading price/performance constraints has fueled a rapid growth in the STB market.

MPEG is an international data compression standard based on the fact that a typical video image frame incorporates considerably more data than is actually required, either because it contains information that the human eye does not notice, or because much of the content is the same as the data in the previous frame.

Compression removes this redundancy using a two-step process. First, pixels from a video frame the eye does not notice are removed. Sequential frames are then compared to eliminate repetitive information (such as a constant blue sky background), and only the information defining the difference in the frames is transmitted. In this way, an MPEG-encoded movie, TV program or audio track can be transmitted using a fraction of the bandwidth that the uncompressed version would require. Hundreds of compressed programs can be broadcast using the same bandwidth a single uncompressed program would require.

What Does the STB Do?

Instead of broadcasting a single uncompressed TV program, a digital satellite transponder broadcasts a signal that includes a large number of different programs, some scrambled so only authorized subscribers can view them.

The role of the STB is to receive the broadcast signal, extract the digital bitstream, perform the descrambling, demultiplexing and decompression functions, and finally produce a composite video output signal for existing TV sets. The STB architecture is essentially the same for both cable and satellite systems. The difference is in the ôfront endö circuitry that demodulates the signal. For example, cable systems use Quadrature Amplitude Modulation (QAM), but satellite systems use the Quadrature Phase Shift Keying (QPSK) technique.

Designed for the satellite set-top market, SGS-THOMSON's STV0196 digital satellite receiver front end is a multi-standard solution. The chip integrates all the functions needed to demodulate incoming digital satellite TV signals from the tuner: Nyquist filters, Quadrature Phase Shift Keying (QPSK) demodulator, signal power estimator, automatic gain control, Biterbi decoder, de-interleaver, Reed-Solomon decoder and energy dispersal descrambler. It is fully compliant with most of the DBS digital standards in use today in the USA, Europe, Asia, and Japan.

The DVB Standard

In the Digital Video Broadcast (DVB) standard, the output of the front-end block is a stream of bits, known as the Transport Stream, whose structure is defined by the MPEG-2 protocol. Typically, a transport stream has a data rate of 30-40 Mbit/s and contains data for a number of different TV channels or programs. The Transport Stream is structured as 188-byte data packets, and for each program there are substreams of audio and video data also organized into data packets (PES packets, or Packetised Elementary Streams).

In addition to the audio and video information for the different programs, the Transport Stream carries data packets for system management and control. For example, some data packets relate to the control of the conditional access subsystem that authorizes the descrambling of premium or pay channels.

What Does the STB Need?

Like other emerging ôhigh techö consumer products such as the multimedia PC and the video-CD, the STB requires very high performance semiconductor technology at prices compatible with the traditional constraints of the consumer market. That would be a demanding enough requirement alone, but the STB needs more. STB manufacturers have no control over the basic functions performed by the system because these are defined by the international standard, yet the need remains for competitors to differentiate their products.

It follows that the STB industry needs the most advanced system solution possible, with an optimized system level architecture and a chip set produced using world-class manufacturing expertise. SGS-THOMSON was the first supplier to produce a five-chip solution for STB manufacturers in volume. The company will reduce the number of ICs needed ultimately to two devices - one for the front end using existing QPSK demodulation, and one for the back-end, which incorporates the ST20 microprocessor and the MPEG-2 decoder.

As the latest MPEG-2 market data confirms, SGS-THOMSON stands head and shoulders above the rest of the world-wide industry in meeting these requirements. In fact, according to Dataquest, SGS-THOMSON had a 71.4% share of the $119 million market for MPEG-2 silicon in 1995.

SGS-THOMSONÆs leadership position is a reflection of its vast experience in this technology, its early entry into the market, and its ability to deliver the highest quality product at competitive prices. The company began working in this area in the late 1980s and has achieved numerous 'firsts'. According to Guy Lauvergeon, general manager of SGS-THOMSON's Image Processing Business Unit, MPEG-2 is one of the fundamental technologies for digital entertainment and will be prevalent throughout multimedia PCs, DVD players, and possibly other products such as STB-based Internet terminals and camcorders.

This expertise will also be available to customers via SGS-THOMSONÆs Superintegration program, allowing ST customers to achieve true system-level integration and the most competitive solutions, both now and in the future.

November 1996

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