A dual SQUID linearization concept using a phase modulation scheme

A critical control system evaluation is presented of basic flux-locked loop systems. The development of a new superconducting quantum interference device (SQUID) linearization method is then described, where no magnetic flux feedback is necessary to cancel the applied flux. It is shown that a dual SQUID configuration will be able to produce a true phase modulation system that is easily demodulated with a phase-locked loop. The theoretical performance of the proposed configuration is verified by simulations, and the performance and limitations are discussed in detail. It is shown that small dc correction voltages at the output of the SQUID´s significantly decrease output noise, as is the case with an increase in SQUID dc bias currents. An optional feedback system is also described for optimal performance of the dual SQUID configuration.