Access time measurements of Josephson–CMOS hybrid memory using single-flux-quantum circuits

Abstract

We have measured the access time of a 16-kbit Josephson-CMOS hybrid memory by using a single-flux-quantum (SFQ) delay measurement system. The delay measurement system is composed of a Josephson latching driver for generating input signals for the memory, an SFQ clock generator and counter for measuring the time interval, and a current-sense circuit for detecting the current output from the memory. The time resolution of the system corresponds to a clock period of the clock generator, which is 50 ps in our design. In these preliminary measurements, we have observed a memory access time of about 4 ns, where the parasitic capacitance of the bonding pad of the Josephson chip limits the access time at present. This is the first demonstration of the access time measurement of a complete Josephson-CMOS hybrid memory.