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The Japan Society of Applied Physics

Improvement of spatial resolution of superconducting imaging systems using single-flux-quantum double-oscillator time-to-digital converters

Yuma Tomitsuka, Yutaka Abe, Nobuyuki Zen, Yuki Yamanashi, Nobuyuki Yoshikawa

Published Feb 8, 2018• 0 citations
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We have been developing superconducting time-of-flight mass spectrometry systems that utilize superconducting strip particle detectors and single-flux-quantum (SFQ) time-to-digital converters (TDCs). We previously demonstrated a 24-bit SFQ TDC with a 3 × 24-bit first-in first-out (FIFO) buffer using the AIST Nb standard process (STP2) with a time resolution of 100 ps. In this study, we improved the SFQ TDC by using a current recycling technique. The technique enables us to increase the FIFO buffer capacity without increasing the total supply current, and the result is an improvement of ion count rates. We designed and demonstrated the SFQ TDC with a 12 × 24-bit FIFO buffer, whose total supply current was reduced by 71% with the current recycling technique.
Direct measurements of propagation delay of single-flux-quantum (SFQ) circuits were performed using SFQ double-oscillator time-to-digital converters. The propagation delay of several SFQ logic gates in our cell library named CONNECT were measured in picosecond resolution. Small discrepancy in the propagation delay of picosecond level was observed between measurement and circuit simulation results. The discrepancy is well explained assuming the parasitic inductance around shunt resistors of Josephson junctions.