DSL Advances

3.5. The Analog Front End (AFE)

ADSL transmission systems benefit greatly from well-designed analog interface to the telephone line. Transmit filter designs are covered in [1] in detail. This section instead discusses precision requirements and sampling methods for both transmit DAC and receiver ADC on an ADSL line. Basically the requirements are stringent. Fortunately, although perceived as difficult at the time of standardization of first ADSLs, today, analog front ends (or AFEs) for ADSL abound in low-cost high-performance packages.

3.5.1. Linearity and Noise Requirements

ADSL at time of conception, and still today, is one of the more challenging analog designs known to engineers. The basic problem can almost seem insurmountable in that a ...