A SUBNANOSECOND CLOCK JOSEPHSON 4-BIT PROCESSOR

A Josephson 4-b processor with a 4-b slice microprocessor, a 4-b multiplier, a 12-b accumulator, an 8-kb ROM, and a sequencer is described. The chip was fabricated with 1.5-μm all-niobium technology, and contains 24,000 Nb/AlOx/Nb Josephson junctions. The processor was designed using a bit slice structure and a simple ripple-carry method, and it has a data sequence based on a three-stage pipeline. Experiments confirmed that the processor functions operated correctly. The critical path measurements for each stage show that the ROM has a 100-ps access time, the microprocessor can be clocked at 1.1 GHz, and the multiplier has a 200-ps multiplication time. The power dissipation of the chip was 6.1 mW.