Design and low speed testing of a four-bit RSFQ multiplier-accumulator

We have designed and RSFQ multiplier-accumulator, the central component of our decimation digital filter. The circuit consists of 38 synchronous RSFQ cells of six types arranged into a rectangular systolic array fed by one parallel input and one serial input. Timing is based on counter-flow clock distribution scheme with simulated maximum clock frequency of 11 GHz. The circuit, fabricated at Hypres, Inc., contains 1100 Josephson junctions, has power consumption less than 0.2 mW, and area less than 2.5 mm/sup 2/. The multiplier-accumulator has been tested at low frequency demonstrating full functionality and stable operation over a 24 hour testing period. This four-bit multiplier accumulator is one of the largest reported RSFQ circuits verified experimentally to date.