Patent Number: 6,295,012

Title: CMOS DAC with high impedance differential current drivers

Abstract: High-performance, digital-to-analog conversion (DAC) suitable for use insystems implemented with low-voltage, low-power integrated circuitfabrication processes is disclosed. Encoder circuitry receives a binarynumber for which an analog representation is sought. Segments of thebinary number are thermometer encoded and complemented to provide signalsto drive analog conversion circuitry. The analog conversion circuitryincludes sets of current cells, with each cell in a set contributing anequal amount to one or the other of the complementary legs of the analogoutput of the converter. Each current cell is a fully differential currentswitch with charge canceling, fed by a regulated cascode current source.The regulated cascode current source offers uncharacteristically highimpedance that contributes to good circuit performance even inlow-voltage, low-power implementations. Other design factors of thecurrent cell contribute significantly to overall performance. Hierarchicalgradient symmetry cancellation techniques are also employed to reduceintegral non-linearity attributable to process-related surface gradients.

Inventors: Greig; David Vetea (Pasadena, CA)


International Classification:

Expiration Date: 09/25/2013