Journal of Physics Conference Series

Experimental Validation of Key Elemental Circuits for RSFQ All-Digital Phase Locked Loop

Yoshinao Mizugaki, Daiki Fukuyo

Published Jul 1, 2026• 0 citations

Abstract

Abstract An all-digital phase-locked loop (ADPLL) is a critical component for generating a precise clock sequence synchronized to a reference signal. For applications in superconducting qubit control, RSFQ ADPLL technology is promising due to its high-speed operation, low power consumption, and cryogenic compatibility. In this paper, we present the experimental validation of key elemental circuits for an improved RSFQ ADPLL: a digitally controlled oscillator (DCO), a time-to-digital converter (TDC), a buffer circuit in the proportional-differential (PD) controller, and a DCO controller. These test circuits were fabricated using a 10 kA/cm 2 Nb/AlO x /Nb process and characterized in a liquid helium bath. The experimental results demonstrated the successful operation of each circuit. Specifically, the DCO exhibited linear frequency control, and the TDC correctly generated digital signals according to the input time slots. The functional integrity of the PD controller’s buffer and the DCO controller was also confirmed. These results provide a foundation for the full integration of the RSFQ ADPLL.

DOI: 10.1088/1742-6596/3278/1/012022

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