A/D converter in superconductor-semiconductor hybrid technology
Erland Wikborg
Abstract:
Josephson junctions can act as fundamentally accurate voltage-to-frequency converters, and niobium-based superconductor A/D converters (ADCs) have therefore been show-cases for superconductor electronics. But the need for cooling to liquid helium temperature (of 4K) has so far precluded any commercial applications. In the European project SUPER-ADC (IST 2001- 33468) an alternative "high-temperature" superconductor approach is being pursued: a hybrid ADC, in which a high-Tc superconductor delta- sigma modulator is interfaced with a CMOS decimation filter. This approach takes advantage of the very high over-sampling rate and fundamental exactness of a high-Tc super-conductor delta-sigma modulator, and the outstanding capability of CMOS technology for complex filtering. The "penalty" is an interface, which has to bridge a (mV-to-V) voltage and a (20 GHz-to-1 GHz) speed mismatch, besides a 30K to room-temperature difference. This presentation describes, briefly, the underlying surprisingly simple superconductor "rapid single flux quantum" (RSFQ) technology, and some of the details of the hybrid ADC realization.
