CODEC for echo-canceling, full-rate ADSL modems

A CODEC, fabricated in 3.3-V CMOS, provides the low-voltage transmitter and receiver interfaces between the modem digital signal-processing engine and the high-voltage hybrid circuitry for either the central office or the remote terminal ends of the subscriber loop, configurable by metal mask option. Extensive use of digital interpolation filters in the transmitter, decimation filters in the receiver, and oversampled data converters minimize the complexity of analog filters. On-chip filtering and 14-bit data converters support echo-canceling modems without requiring external filters. With additional external filters, frequency-division duplexing is also supported. The die area is 67.5 mm(2). The-power dissipation in the central office and remote terminal are 600 and 760 mW, respectively.