1000-Fold Double-Flux-Quantum Voltage Multiplier Employing Directional Propagation of Flux Quanta Through Asymmetrically Damped Junction Branches

Abstract

Precise voltage generation is a unique feature of single-flux-quantum (SFQ) circuits, in addition to their high-speed digital signal processing with low power consumption. We investigated SFQ pulse-frequency modulation D/A converters for metrological applications. In our SFQ-based D/A converters, the maximum output voltage is determined by the maximum SFQ pulse-frequency at the pulse number multiplier, and by the voltage multiplication factor at the voltage multiplier. In this study, we present our new design for a double-flux-quantum amplifier (DFQA) that works as a quantum voltage multiplier. In the new parameter set, we tuned the damping parameters of the Josephson junctions to realize proper propagation of SFQ pulses. A 1000-fold DFQA designed with the new parameter set was fabricated using a 25- ${\boldsymbol \mu} $ A/ ${\boldsymbol \mu} $ m $^2$ Nb/AlO $_x$ /Nb integration technology. A 1000-fold voltage multiplication was confirmed for the input voltage up to 43 ${\boldsymbol \mu} $ V, with a corresponding SFQ repetition frequency of 21 GHz. That is, the output voltage reached 43 mV.