DC-SQUID ELECTRONICS BASED ON THE NOISE CANCELLATION SCHEME

We have constructed a compact de SQUID electronics unit, in which the noise of the room-temperature amplifier is measured by the SQUID and c ancelled out. This makes it unnecessary to use a transformer and a mod ulation scheme to achieve noise matching between the SQUID and the amp lifier. The electronics unit contains a PI3/2-controller and it has de monstrated a bandwidth of 100 kHz, a 1.2 mu Phi(0)/Hz white noise leve l and a 1/f noise corner of 0.3 HE in a flux-locked loop mode. The des ign criteria for the noise-cancelled electronics are discussed, includ ing the problem of exess noise.