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Review of Scientific Instruments

Multiple channel superconducting quantum interference device controller using a digital signal processor

Berkeley N. Limketkai, J. Granger, Mark A. Weilert, Inseob Hahn

Published Oct 31, 2002• 1 citation
Publisher

Abstract

We report on the design, performance, and limitations of an improved multiple superconducting quantum interference device (SQUID) controller based upon a digital signal processor. The flux noise level of the dc SQUID controller system is comparable with the commercial analog system, ∼4 μΦ0/Hz1/2 at 100 Hz. The measured maximum slew rate of the system is approximately 800 Φ0/s. The current system could control up to five SQUID channels.

DOI
10.1063/1.1511805

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We report on the design, performance, and limitations of an improved multiple superconducting quantum interference device (SQUID) controller based upon a digital signal processor. The flux noise level of the dc SQUID controller system is comparable with the commercial analog system, ∼4 μΦ0/Hz1/2 at 100 Hz. The measured maximum slew rate of the system is approximately 800 Φ0/s. The current system could control up to five SQUID channels.
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We have studied flux quanta counting in an open loop as a way to implement superconducting quantum interference device (SQUID) amplifiers with a large dynamic range and small power dissipation simultaneously. Good signal-to-noise ratio at all flux values is provided by using two SQUIDs, one yielding sin(ϕ) and the other cos(ϕ) proportional signals. In principle, the lack of feedback lifts the slew rate limitation due to the loop causality present in previously implemented flux quanta counters. Experimental results are shown for up to 180 Φ0 peak-to-peak flux ranges with a 1.5 μΦ0 Hz−1/2 noise floor, dominated by the digitizer noise. The SQUID and low-noise amplifier would allow a 0.07 μΦ0 Hz−1/2 noise floor with a more silent digitizer. Operation up to a 13 Φ0 μs−1 slew rate was demonstrated, but this is not a fundamental limitation. In our experiment, the mismatch between the sin(ϕ) and cos(ϕ) channels limited the practically achievable slew rate.
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