Low-noise integrated SQUID electronics operating in liquid nitrogen

Directly coupled electronics for a de SQUID was developed as a fully integrated circuit designed for operation at liquid nitrogen temperature. It was fabricated on the base of BiCMOS technology. The parameters of the model used for the design were extracted from the measurements of resistors, capacitors, and all types of transistors (npn, pMOS and nMOS) possible in this technology at 77 K, The npn transistors are favorable for the input stage as they have lower noise level. Up to 1280 transistor cells were connected in parallel to decrease the noise. Such a macro transistor has a white noise level of 160 pV/Hz(1/2) and power dissipation of 7 mW. The entire flux locked loop electronics containing a preamplifier built of two macro transistors and operational amplifier as an integrator has been tested with a high T(c) SQUID. The flux locked loop operated stable. The white noise level corresponds to the expected value. It is determined mainly by the intrinsic noise of the SQUID itself.