Adiabatic Quantum-Flux-Parametron Constant Cells using Asymmetrical Structures

Abstract

We have been developing adiabatic quantum-flux-parametron (AQFP) circuits as an ultra-low-power superconductor logic for energy-efficient computing. In AQFP logic, logic circuits are designed by arraying the four types of building block cells, that include buffer, NOT, constant, and branch. The constant cell is a gate which always switches to a specific logic state when excited and is used in AND and OR gates. In this paper, we discuss the design method of the constant cell. Since the constant cell works thanks to the asymmetry in inductances or excitation fluxes, we analyzed the relationship between operation margins and asymmetry in inductances or excitation fluxes. The simulation results show that the asymmetry in excitation fluxes can easily increase the operation margins, compared to that in inductances. Taking into account the simulation results, we redesigned a constant cell, to which excitation fluxes are applied asymmetrically. We designed and fabricated AND and XOR gates using the constant cell. The measurement results show that the logic circuits designed using the constant cell work with wide operation margins.