A single-chip CMOS PCM codec

Describes a single-chip full duplex per channel PCM codec implemented in a metal gate CMOS process. An 8-bit companding DAC, a novel autozeroed analog subsystem, and a 3.5-MHz frame interface control logic comprise the 175/spl times/195-mil integrated circuit. The DAC is implemented with matched n channel devices and utilizes redundancy and feedback to achieve the required accuracy. The analog subsystem contains two sample and hold circuits, autozeroing circuitry, CMOS amplifiers, and a fast CMOS comparator.