A monolithic voltage-comparator array for A/D converters

A monolithic circuit consisting of an array of 8 voltage comparators, a resistive voltage divider, and associated logic circuits has been fabricated. Intended as an encoding component for high-speed parallel analog-to-digital (A/D) converters, this '3-bit quantizer' uses regeneration for voltage gain and signal storage. A Gray-code output minimizes the problem of comparator indecision. The principal error sources are an asymmetry-induced comparator offset with 2-mV standard deviation and a thermally induced offset of as much as plus or minus 2.5 mV, dependent on signal history. The quantizer has been incorporated in an experimental 6-bit 200 megasample/sec A/D converter.