Algorithmic ADC for use in ASIC design

Abstract

An algorithmic analog to digital converter is described which combines a fast conversion time of less than 300 ns with a small circuit area of 0.8 mm/sup 2/. The circuit operates from a+5 V power supply and is ideally suited for use as a general purpose cell in analogue and mixed signal ASIC design. The ADC operates in current mode and an accurate current sensing technique allows the comparators to operate very quickly even in the presence of small signal differences. The current mode approach has the advantage of small signal voltage swings, low node capacitance and therefore fast operation. The resolution of the converter is 8-bits as this will satisfy the requirements of many applications including digital mobile radio and disk drive servo control chips. Results are presented for a prototype chip fabricated on a 2- mu m BiCMOS process.<>