A single-chip universal cable set-top box/modem transceiver

摘要

A mixed-signal digital cable-TV transceiver IC containing two distinctly separate quadrature amplitude modulation (QAM) receivers and a single QAM modulator has been designed. An integrated 10-b analog-to-digital converter (AID) interfaces the first receiver directly to an analog signal. This receiver demodulates 4/16/32/64/128/256-QAM signals carrying the television programs or cable modem data with a variable symbol rate from 1 to 7 MBaud. A 6-b A/D is integrated to interface the second receiver to an analog signal. This receiver, used by cable operators for access control, demodulates quadrature phase shift keying (QPSK) signals with a variable symbol rate from 0.75 to 1.6 MBaud. The upstream modulator provides two-way communication required for interactive television or cable modem services. Capable of QPSK/16-QAM modulation with a variable transmission rate up to 25 Mb/s, the modulator also includes an integrated 10-b digital-to-analog converter to provide radio-frequency analog output from 0 to 65 MHz. Both receivers and the transmitter incorporate on-chip forward error correction compliant with multiple worldwide standards allowing global deployment. The carrier, phase, and timing recovery for each receiver is achieved with on-chip tracking loops. Adaptive decision feedback equalizers are incorporated to eliminate intersymbol interference. The transmitter incorporates preamble prepending and preequalization to facilitate reception. The device further integrates access control message separation, set-top box control circuitry, and a parallel microprocessor bus interface to boost system performance. The design employs a combination of semicustom and custom circuit design techniques for speed, mixed-signal performance, and layout density. Fabricated in a single poly, four-layer metal, 0.35-/spl mu/m standard CMOS process, the chip area is 64 mm/sup 2/. The device is packaged in a 256 tape ball grid array (TBGA), and dissipates 3 W at 3.3 V.