Cable-modem ICs meet MCNS

standard for interoperability

A number of chip vendors have demonstrated support for the Multimedia
Cable Network System (MCNS) standard through recent introductions of cable-modem
ICs. The MCNS standard–one of several intended to promote interoperability
among cable modems–was created by a consortium of multiple-system operators
and issued at this year's National Cable Television Trade Show.

Stanford Telecom (Sunnyvale, CA), for example, a manufacturer of digital
communications products, has announced the STEL-2176, a device that integrates
all of the modulator/demodulator functions required for subscriber modems
in hybrid fiber/coaxial (HFC) cable networks. The IC complies with MCNS
standards as well as IEEE 802.14 and DAVIC/DVB specifications, providing
5 to 7-Mbaud operation in the U.S.or Europe. In addition, the chip is
compatible with any head-end receiver.

According to the manufacturer, the STEL-2176 features simple and cost-effective
interfaces, and integrates upstream and downstream clock plans. For downstream
communications, the demodulator can be programmed to receive 16-, 64-,
or 256-QAM signals with high acquisition speed.

Demodulator features include A/D conversion, analog and fast digital
AGC functions, and digital carrier tracking. An analog carrier tracking
loop is not required. Output complies with the MPEG-2 format.

For upstream communications, the modulator is programmable for either
QPSK or 16-QAM PSK-modulated signals with optimal spectral shaping and
fine tuning resolution across a 5 to 65-MHz output. Features include a
D/A converter and an optional Reed-Solomon encoder.

The STEL-2176 will be packaged in a 208-pin SQFP and priced at under
$30 in production quantities, which are expected in the first quarter of
1998. Engineering samples will be available in October.

Analog Devices (Norwood, MA) has announced an agreement with Libit Signal
Processing (Los Altos, CA) to develop MCNS-compliant ICs for both the head
end and subscriber end of HFC networks. The first offering will be a programmable
chip for two-way data transfer at the subscriber end.

The IC will combine Libit's core modem technology with Analog Device's
mixed-signal expertise and integrate a downstream QAM demodulator, an upstream
QPSK/16-QAM modulator, and A/D and D/A converters. The modem will interface
with a standard TV RF tuner and cable driver to deliver full-duplex operation
at 50 Mbits/s downstream and 10 Mbits/s upstream. Engineering samples will
be available in November with production quantities to follow in January.

Anadigics (Warren, NJ) has also expressed support for the MCNS specification,
through an existing RF-tuner chipset. The ACU50750 50 to 860-MHz upconverter
and ACD0900 900 to 1,200-MHz downconverter are low-cost GaAs MMICs intended
for use in dual-conversion tuners.

Each device integrates a low-noise amplifier, a high-linearity double-balanced
mixer, a phase splitter, and an oscillator in a 16-pin SOP. Chipset pricing
is $5.20 each in quantities of 100,000.

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