Speed-limiting factors in flash-type Josephson A/D converters

The authors discuss the causes of speed limitations in various A/D (analog/digital) converter designs. The upper limit on bandwidth is extracted with the help of Josephson SPICE simulations. In the Josephson A/D converter circuits discussed, the dynamic properties of the SQUIDs (superconducting quantum interference devices) determine the aperture time and dictate the bandwidth. Designs for 4-bit A/D converters that show potential for bandwidths on the order of 10 GHz are described. Particular attention is given to the bit-parallel A/D converter with self-gating AND comparator and bit-parallel A/D converters with CLAM (current latching analog microcomparator) and variable-pulse peak comparators.<
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