Operation of Josephson comparator under Josephson noise from SQUID

Operation of a Josephson comparator for analog-to-digital conversion of signal from a SQUID is studied. In the study, a test circuit consisting of the SQUID and the comparator is used. The measured result shows that the comparator responds to AC noise due to the AC Josephson effect. Numerical simulation shows amplitude, which is determined from the response of the comparator, is smaller than the original AC noise amplitude. The difference comes from low-pass characteristics of the Josephson junction in the comparator due to the turn-on delay. The delay is effective in reducing the AC noise, and provides a means for the accurate conversion. >