Current Recycling Technique Using Capacitive Grounding

Current recycling is an essential technique for realizing large-scale integrated single-flux-quantum circuits, since it can reduce bias current supply from several amperes to hundreds of milliamperes. Recently, there have been two reports proposing current recycling techniques. However, the fluctuation of global bias current, due to the switching of Josephson junctions, was not considered in these reports. Moreover, junctions cannot be grounded at the same point due to the use of isolated ground planes. In this paper, we propose a modified version of the current recycling technique using capacitive grounding, which will solve all these issues. We present an optimized driver and receiver for this technique. We have verified its workability and evaluated its characteristics by using several simulated tests, including evaluating bias set-up time, evaluating the relation of ground capacitance and signal capacitance to global bias margin, verifying its workability in a more complicated circuit, and performing high-speed test at frequencies up to 80 Gbps.