We investigated the gray zone width of Josephson comparators by means of circuit simulations and experiments, looking at the dependences on different circuit parameters and topologies. Eight different comparator circuits were simulated and designed for a 1 kA cm −2 niobium device. With our sophisticated measurement set-up, the lowest reported gray zone width of 3.2 μA at 4.2 K was measurable. Moreover, the results obtained allow us to derive a set of design rules for further reduction of the gray zone width, which was the original goal of our investigations.
This paper investigates the robustness of different ground plane configurations of superconducting circuits against magnetic flux trapping. The robustness of the circuit is determined by the change of the error rate at a specific operating point under the influence of an external magnetic field. A large number of thermocycles are used to determine the statistic properties of the error rate. The proposed measurement setup allows a fast scan of a two-dimensional operating area.
We present a new kind of rapid-single-flux-quantum (RSFQ) output driver together with a pseudomorphic high electron mobility transistor (p-HEMT) amplifier both operating at liquid helium temperature. The passive interconnect including the interchip connection between the RSFQ output driver and the first transistor stage of the semiconductor amplifier is the key element for signal matching and was optimized for minimizing the reflections to the RSFQ circuit. The RSFQ output driver is based on a single-flux-quantum to dc converter and a voltage doubler. The circuit is realized in the Niobium based 1 kA/cm 2 process of FLUXONICS Foundry and provides up to 438-V output voltage. We demonstrate high-speed experiments of the output driver in combination with two different semiconductor amplifier circuits at liquid helium temperature. The output voltage of a 2-Gb/s data stream was measured to be about 3.5 mV.Index Terms-Cryogenic amplifiers, high-speed interface, single-flux quantum (SFQ), superconductive electronics.
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