Audio Processor Integrated Circuit for Cellular Radios

A CMOS integrated circuit performing all the necessary analogue signal processing for TACS and NMT cellular telephones is described. Voiceband filtering for transmit and receive signal paths, receive and transmit data filtering, microphone and loudspeaker amplifiers, and expander and compressor functions are all provided on one 7mm × 7mm integrated circuit. The triode transconductor technique used to implement the continuous time filters and non-linear circuits is discussed, and measured results taken from prototype devices are presented.