Analysis of high-performance counter-type A/D converters using RSFQ logic/memory elements

A new family of counter-type Josephson-junction A/D converters using ultrafast rapid single-flux quantum (RSFQ) logic/memory elements is proposed. The converters are built in two main blocks: a low-bit differential-code A/D converter running with subterahertz clock speed and a RSFQ-logic-based digital processing unit providing digital low-pass filtering and sample rate reduction. It is shown that such converters can be treated as digital SQUIDs possessing an extremely high slew rate (up to 10/sup 11/ phi /sub 0//s) combined with flux resolution close to that of analog DC SQUIDs (up to 10/sup -6/ phi /sub 0/Hz/sup -1/2/). Several ways of implementing both main blocks to make it possible to tradeoff these parameters against converter complexity are presented and discussed.