100GHz operation of a 4-bit single-flux-quantum pulse-frequency modulator designed for bipolar D/A conversion

[摘要] We designed and operated a 4-bit single-flux-quantum pulse-frequency modulator for bipolar D/A conversion. It was based on our previously-proposed “sum of selected bit sequence” configuration. Two functions, a synchronization scheme with a reference signal source and a complement number system for realization of bipolar output voltage, were implemented. A test circuit excluding the output analog stage (dual double-flux-quantum amplifier) was fabricated using a 10kA/cm2 Nb/AlOx/Nb integration process. The synchronization function was evaluated in terms of the average voltages, which agreed well with the expected values. The bipolar D/A conversion was successfully emulated by using the positive and negative output signals. The maximum over-biased input voltage was determined to be 230µV, of which the corresponding SFQ repetition frequency was 111GHz.

[学科分类] 电子、光学、磁材料

[关键词] Josephson effects;quantum voltage;niobium;superconducting integrated circuits;cryogenic electronics