A Single-Chip CMOS PCM Codec

A single-chip full duplex per channel PCM codec implemented in a metal gate CMOS process is presented. An 8-bit companding DAC, a novel autozeroed analog subsystem, and a 3.5-MHz frame interface control logic comprise the 175 × 195-mil integrated circuit. The DAC is implemented with matched -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 compatator. The circuit operates from a single supply, consumes 90 mW (typ) and features a powerdown capability to less than 1 mW (max). Individual component performance and the resulting system performance are quantified within the text.