High slew rate ´channel equalized´ DC SQUID flux-locked loop: concept and simulation

The concept of improving conventional DC superconducting quantum interference device (SQUID) flux-locked loop (FLL) performance by applying a channel equalization circuit after the pre-amp, but prior to the demodulation process in order to compensate for bandwidth limitations imposed by conventional DC SQUID impedance matching networks is discussed. The equalization circuit is a bandlimited inverse filter which corrects for the phase and amplitude distortion caused primarily by the DC SQUID impedance matching network. Improvements in the FLL performance were verified with analog circuit simulations in both the time and frequency domains. Using an analog circuit simulator the various subcircuits of the FLL were modeled, and a comparison between a conventional FLL and an equalized one was performed. Computer simulations for the open and closed loop cases were used to quantify the increase in slew rate for the equalized FLL system.<>