Measurements of an RSFQ digital SQUID system

Farshad Foroughi, Ali Bozbey, Mehdi Fardmanesh

Komei Higuchi, Hiroshi Shimada, Yoshinao Mizugaki

Masaaki Maezawa, Fuminori Hirayama, Motohiro Suzuki

We propose a simple method of measuring bit error rates (BERs) for rapid single flux quantum (RSFQ) circuits operating at high frequencies. An error detector based on a SQUID current comparator, which operates without a timing clock, is employed to simplify the test system and measurements. We successfully investigated high-frequency operation of RSFQ cells that were utilized to implement our RSFQ digital-to-analogue converter for metrology applications. Sufficiently low BERs were demonstrated in the circuit operation at several tens of gigahertz.

Pasquale Carelli, Maria Gabriella Castellano

Pascal Febvre, Siham Badi, Torsten Reich +2 more

Superconductive microwave rapid single-flux-quantum (RSFQ) digital circuits offer the possibility to digitally process signals in the frequency range of tens of GHz. An example of application to bring the advantages of this technology deals with digital SQUIDs, used for sensitive magnetometry with a broadband dynamics connected to a slew-rate in the GHz range. First recently obtained results of digital SQUID operation, based on Nb/Al-Al2O3/Nb shunted Josephson junctions, are presented in this article. In order to obtain the best performance of RSFQ circuits, and especially to push their speed at its limits, a precise diagnostic of such circuits is needed. We are developing a time-resolved diagnostic system based on sensitive photoconductive switches to sample the weak signals coming out of RSFQ circuits at cryogenic temperature. This system includes two different sorts of opto-RSFQ interfaces, based on superconducting and semiconducting materials, respectively. Some simulation results in the microwave range, along with measurements giving the potentialities of different photoswitches are presented.

Friedrich Uhlmann, St Lange, M. Khabipov +1 more