Set-Top Silicon Moves Add Flexibility

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At the heart of new generations of set-top boxes are increasingly sophisticated chip sets that enable a new class of services.

The oft-quoted Moore's Law-which stipulates that the capacity in a given area of silicon doubles every 18 months-has held steady for the past 10 years and remains a reliable benchmark, according to Rich Nelson, Broadcom Corp.'s director of product marketing for cable.

In general, the trend for set-top-box chip sets has been to take what were previously multiple-chip configurations and squeeze them into single pieces of silicon.

More and more integration of functions-such as cable-modem tasks, hard-drive support and home-networking capability-is resulting in highly sophisticated reference designs.

Broadcom's latest set-top reference design, "BCM 93725," demonstrated last week at the National Show in New Orleans, integrates a host of features.

They include a second Data Over Cable Service Interface Specification Internet-protocol channel with its own tuner; support for enhanced 2-D and 3-D graphics; MPEG high-definition video decoding; Home Phoneline Networking Alliance (HomePNA) 2.0 support, enabling data rates of 10 megabits per second; and IDE (integrated drive electronics) hard-drive interface support.

The BCM 93725 is available with either a 250 or 350 RISC (reduced-instruction-set computer) microprocessor.

The laundry list of features of the new reference design is intended to support several advanced interactive-TV features.

In addition to a separate channel and tuner for MPEG-2 video, the second IP channel and tuner is designed to support the DOCSIS 1.1 specification and to enable a separate IP-data stream for interactive-TV applications. This allows video-content viewers to simultaneously access Web sites, call up different camera angles and make IP phone calls.

The IP channel includes a quadrature-amplitude-modulation demodulator and media-access controller that acts as a "traffic cop" for IP data. Eventually, the second channel will handle video-over-IP applications, Nelson said.

The reference design's 3-D capabilities are intended to support both electronic-commerce and online-gaming applications. Adding 3-D could help to spur e-commerce and make it more appealing. The boosted 2-D support will enable better-quality graphics and crisp text to enhance Internet content, Nelson added.

Support for the HomePNA 2.0 spec is a step toward allowing higher throughput rates, with 32 mbps the next target and 100 mbps the longer-term goal, according to Nelson. Wireless-network connectivity "is the solution long-term," he added.

Set-top disk-drive support has been added to allow for real-time storage and retrieval of Internet files-especially MP3-formatted music clips-and video programming for personal-video-recording functionality. Drive-interface silicon supports compression and decompression of MPEG-2 video streams.

Conexant Systems Inc. will soon introduce a new set of video decoders for set-tops. Building upon the "CN8600AVD/ CN8610AVD" line, the new decoders feature advanced RISC machine "490" processors running at 175 MIPS (million instructions per second) at 100 megahertz or 200 MIPS at 180 MHz.

Employing a unified memory architecture, the new products, "CX22490/CX224910," are designed to support "every existing standard-definition and digital-TV application," director of consumer broadband David Jones said.

The chip set's transport-stream demultiplexer supports MPEG-2 and DVB (Digital Video Broadcasting) standards, as well as proprietary transmissions systems, he added.

The CX22490/CX224910's video/graphics display compositing engine with graphics processor and display coprocessor supports Web content displayed on a TV. Jones said Conexant is working toward adding cable-modem functions to its silicon product.

Both Conexant and Broadcom attended Cable Television Laboratories Inc.'s certification dry run in January, but neither has won certification yet.

In late March, consumer-electronics giant Royal Philips Electronics created set-top silicon-maker TriMedia Technologies Inc., formed from a unit within Philips Semiconductors.

With Philips and Sony Corp. as investors, the company is poised to create a digital-video platform. The platform will build upon TriMedia's VLIW (very long instruction word) core processor technology. Philips uses TriMedia technology for its digital TVs and set-tops, and hopes to attract new customers to TriMedia by spinning it off.

Dave Barringer, director of marketing for the set-top-box segment of Philips Semiconductors' digital-media-business line, said TriMedia's processor is a MIPS processor that can run real-time operating systems such as PSOS, Linux, VRTX and Windows CE, and it is part of Philips' "Nexperia" digital-video platform.

Supported middleware includes "Microsoft TV," Liberate 'Technologies' software, OpenTV Inc. and Mediahighway.

The VLIW chip can launch five instructions per clock cycle, and it performs audio and video digital-signal processing while supporting PVR and videoconferencing functions. The MPEG decoding engine can decode standard-definition, high-definition and 3-D graphics, Berringer said. The chip can also implement the "Java Virtual Machine."

Reflecting the huge market potential for digital set-top components, semiconductor heavyweight IBM Microelectronics made a splash into the cable set-top sector in March when it announced new chips, based on its "PowerPC" architecture, targeted to the set-top market.

The chips include "PowerPC 405" and "401" processors, and they integrate an MPEG-2 audio/video decoder, a memory-interface subsystem and peripheral interfaces, including an IDE hard-drive interface. The "STB032xx" and "STB034xx" PowerPC-based chips run at 108 MHz or 162 MHz with a 16-kilobyte instruction and 8-KB data cache.

The chips have 2-D on-screen-display graphics functionality, but not high-definition capability. Although DOCSIS support is not included, IBM Microelectronics marketing manager for digital-video products Amand Cochet said the PowerPC chips "can interface with that functionality at the system level."

According to Cochet, the company is flexible about what operating systems are ported on its chips. "We will do whatever software enablement drives the most business for our chips," he added, although there is no formal plan to support Microsoft Corp.'s Microsoft TV client.

While the PowerPC chip architecture has yet to make much of a dent in the cable set-top sector, Cochet said, "The architecture of choice for the future in the set-top market is not decided."

Addressing the tuning portion of set-top silicon, Microtune Inc. showed its "MM8838 MicroModule" at the National Show. It includes the "MicroTuner 2030" chip, a diplexer to separate digital/analog video from data signals and an out-of-band tuner.

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