Improved direct-coupled dc SQUID read-out electronics with automatic bias voltage tuning

摘要: A low-noise wideband read-out electronics for dc superconducting quantum interference devices (SQUIDs) is presented. The preamplifier which directly connected to the SQUID has white voltage and current noise levels of 0.4 nV//spl radic/Hz 6.2 pA//spl with 1/f corners at 0.2 Hz 13 Hz, respectively. can be operated both bias ac up 250 kHz. In latter case, a special circuit synchronously detects component output automatically removes it by tuning voltage. An in-system programmable microcontroller used control all functions system via serial RS-485 interface. It also generates clock sets working point D/A converters. been operate magnetometers. Noise down 35 fT//spl 0.9 about 2 have achieved thin-film magnetometers 77 K 4.2 K, With static high bandwidth 6 MHz was without affecting level. 100 kHz reversal rms increased 3% when increasing from 1.4 MHz. slew rate /spl Phi//sub 0///spl mu/s 2.3 mu/s. short integrator reset time <1 allows one increase dynamic range utilizing periodicity vs. flux characteristic.