A digital signal-processing codec filter for PCM applications

A programmable signal-processing codec filter (SICOFI) which performs its main filter functions by means of digital signal processing (DSP) is described. Besides PCM coding and band limitation, the circuit provides programmable adjustment of level control, impedance matching, hybrid balancing, and frequency response correction. Circuit performance, chip area, and power consumption have been optimized and a set of consistent CAD tools were developed for complete verification. Progress in circuit-design simulation techniques and an advanced CMOS technology allowed the economic integration of the analog and digital parts consisting of 36000 transistors on a 37.5-mm/SUP 2/ die.