High slew rate, ultrastable direct-coupled readout for dc superconducting quantum interference devices

A very fast and thermostable readout electronics for dc superconducting quantum interference devices (SQUIDs) is presented. The authors have applied a concept which gives them the opportunity to combine several, at first sight contradictory, important parameters for the SQUID system user. With their flux-locked-loop electronics they could reach more than 16MΦ0∕s slew rate while using a 1.3m cable between the electronics and a conventional low transition temperature SQUID (with a maximum peak-peak voltage of the flux-to-voltage transfer function of ⩾63μV). By making use of thermocurrent compensation in the first stage of the amplifier they have achieved a thermal drift of about 5nV∕K for a temperature range between 0 and 65°C. The system demonstrated a white noise voltage level of ∼0.32nV∕Hz1∕2, with a flicker noise corner frequency of about 0.1Hz.