Electronic Design

Single-Chip Tuner Rids Cable Modems Of Bulky Tin-Can Boxes

The cost, power consumption, and size of cable modems have dropped steadily as integration and manufacturing processes have improved. However, the familiar, bulky, metal-can tuner that houses the sensitive, RF mixed-signal components has stubbornly refused to fall in line—until now.

In an announcement that leapfrogs the competition, Conexant Systems, Newport Beach, Calif., has introduced the first single-chip, all-silicon, cable-modem tuner. Designated the Info-Surge CN2811, the device accepts RF signals ranging from 44 to 870 MHz, and converts them to IF signals at 36 or 44 MHz. All that's required for a complete tuner solution is the addition of a pre-amp, automatic gain control, filters, and external tank circuits.

The CN2811 supports all popular cable-modem industry standards, including Cable Television Laboratories Inc. (CableLabs), the Data Over Cable Service Interface Specification (DOCSIS) 1.0/1.1, and others established by the EuroDOCSIS, Digital Video Broadcast (DVB), and Digital Audio Visual Council (DAVIC) organizations. The chip uses mainstream bipolar processes; incorporates a component-efficient, double-conversion architecture; and weighs in with a power consumption of under 1.5 W.

Conexant is a key player in the digital modem and set-top-box arena. Its announcement simply emphasizes the fact that the 2811 wasn't developed in a vacuum. The device is designed to interface directly to the analog-to-digital-converter input of the company's previously announced CN9414 single-chip cable modem. Together, the duo forms a comprehensive system solution for subscriber cable-modem products that manufacturers can software-upgrade to support all popular worldwide standards.

In support of this effort, the company also has released a cable-modem reference design, the CN9420CM. It includes all necessary silicon and software to create a complete subscriber modem that can support all popular worldwide standards. A vital component of the design, based on the CN9414 modem, is the inclusion of application software above the TCP/IP stack. This allows for registration, authentication, software downloading, and other functions.

Discussing the CN9414, Scott Keller of Conexant says, "Other companies did just the MAC and PHY layers and called it a single-chip cable modem. We did that, but included host processing (a 200-MIPS ARM processor) and a complete Ethernet transceiver—all on one chip."

Though Conexant is the first to make an official announcement, its main competitor, Broadcom Corp., Irvine, Calif., is likely to speed up its announcement of a single-chip tuner. Details were vague at press time (the next issue will have the full story), but the all-CMOS chip will use a triple-conversion architecture, with the tank circuits on board.

The CN2811 comes in a 48-pin, thermally enhanced, TQFP (ETQFP). Pricing, which includes the CN9414 cable modem, is $40 each per 10,000. Samples are available now, with production due by the second quarter of this year. The CN9420CM reference-design kit is priced at $50,000.

Conexant Systems Inc., 4311 Jamboree Rd., Newport Beach, CA 92660; (800) 854-8099; Internet: www.conexant.com.

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