A CMOS HDSL2 analog front-end

Abstract

HDSL2 is the second generation of High-bit-rate Digital Subscriber Line service. ANSI HDSL2 standard requires full duplex transmission with a symmetric payload of 1.544 Mb/s over the full Carrier Serving Area (9 kft, with noise) on a single twisted pair, i.e., same level of service and performance that the traditional HDSL provides over two twisted pairs. There is also tremendous interest in the industry to provide variable rate service over longer cable lengths. HDSL2 transmission spectrums provide robust performance in a mixed crosstalk environment and are spectrally compatible with other services like ADSL, HDSL, T1, etc. The Upstream (US) and Downstream (DS) spectrums overlap and deliver over 16.5 dBm transmit power to the line. This requires the HDSL2 Analog Front-End (AFE) to process a large echo signal along with a weak receive signal.