Energy Reduction in Shunt-resistor-free Low-voltage Rapid Single-flux-quantum Circuits

Abstract

We report energy reduction in low-voltage rapid single-flux-quantum (LV-RSFQ) circuits using shunt-resistor-free Josephson junctions. The LV-RSFQ logic is one of energy-efficient derivatives of rapid single-flux-quantum (RSFQ) logic, which operates in a constant voltage mode. By lowering bias voltages, we can reduce power consumption at bias resistors which account for more than 90% of total power consumption, and also reduce the energy dynamically consumed during switching events because of slower transition of superconductor phase. Voltage drops across Josephson junctions cause a complicated trade-off between operation speed and power consumption. In this paper, we evaluated shunt-resistor-free LV-RSFQ shift-registers in terms of operation speed, power consumption, and energy-efficiency. Numerical simulation revealed their faster operation by up to 50% and accordingly higher energy-efficiency. Experimental results showed that a 0.5mV shift-register had superiority in operation speed and energy-efficiency.