Self-Resetting Interface Between Rapid Single-Flux-Quantum and Adiabatic Quantum-Flux-Parametron Circuits

Various superconductor logic families have been proposed to build energy-efficient digital systems. Each logic family has its respective advantages and disadvantages, so in some systems, it is crucial to combine different superconductor logic families. We previously developed adiabatic quantum-flux-parametron (AQFP)/rapid single-flux-quantum (RSFQ) hybrid systems, such as a readout circuit for superconducting photon detectors and a flux-bias circuit for superconducting quantum bits. To facilitate the design of AQFP/RSFQ hybrid systems, here we propose a self-resetting RSFQ-to-AQFP (SR-R2A) interface as a compact signal converter from RSFQ logic into AQFP logic. The SR-R2A interface comprises an RSFQ latch and an AQFP comparator, where the AQFP comparator detects the flux state of the RSFQ latch. A previously proposed RSFQ-to-AQFP (R2A) interface requires single-flux-quantum clock signals to reset the flux state of the RSFQ part in the R2A interface, whereas the SR-R2A interface does not require such signals because the excitation current for the AQFP part also resets the flux state of the RSFQ latch. This feature allows the SR-R2A to be incorporated into AQFP/RSFQ hybrid systems without hardware overhead. We demonstrate an SR-R2A interface chip, fabricated with the AIST 10-kA/cm
²
Nb high-speed standard process, at 4.2 K in liquid helium. The experimental results indicate reasonably wide operating margins for the excitation currents and bias voltage for the SR-R2A interface.