A flash Josephson A/D converter constructed with one-junction SQUIDs

A novel approach to the construction of a flash-type Josephson A/D (analog/digital) converter is presented. Simulations show that one-junction SQUID (superconducting quantum interference device) comparators can have a greater than fivefold advantage in bandwidth over the two- or three-junction SQUIDs in an A/D circuit. Assuming a Nb junction technology, the simulations show that a 6-bit A/D converter using one-junction SQUID comparators could have a sampling rate of approximately 20 GHz with approximately 5 bits of resolution for a 5-GHz input signal. Detailed analysis and simulations of an A/D converter constructed with one-junction SQUIDs are presented. Further improvement can be made by using a coding algorithm which requires 2N-1 comparators, instead of N, for an N-bit A/D converter.>