Superconducting analog-to-digital converter and digital magnetometer and related method for its use

摘要

A device for use as an analog-to-digital converter or a digital magnetometer using a double-junction superconducting quantum interference device (SQUID) and having an extremely fine sensitivity, but a large dynamic range and the ability to handle rapid signal slew rates. The SQUID receives a composite signal, including the analog signal, a correction signal, and a high-frequency dither signal, the latter being selected to produce two output pulses from the SQUID when operated at a quiescent operating point. Departure from the operating point is detected by monitoring the SQUID output pulses and controlling a feedback register to record the degree of movement from the operating point. The feedback register provides the less significant bits of digital output from the converter. The value stored in the feedback register is also converted to analog form and fed back to the SQUID as the correction signal, thereby locking the device onto the desired operating point. Rapid or slow movement equivalent to more than one flux quantum is also detected in the device, and is recorded in an integer register, which provides the more significant bits of the digital output.