Flux-bias stabilization scheme for a radio-frequency amplifier based on a superconducting quantum interference device

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Abstract
A magnetic flux stabilization scheme involving a low-frequency flux-locked loop has been developed to regulate the gain of a radio-frequency amplifier based on a superconducting quantum inteference device (SQUID). The flux-locked loop largely eliminates drifts in the gain arising from drifts in the flux bias. Tests on a microstrip SQUIDamplifier operating at 777 MHz inside a superconducting shield show that the peak-to-peak drift in the gain is no more than 0.3 dB/day.