Cryogenic direct current superconducting quantum interference device readout circuit

We have designed and tested a superconducting quantum interference device (SQUID) readout circuit, which can be operated at liquid helium temperatures. Although room-temperature SQUID electronics perform well, it is sometimes desirable to keep the wires between SQUID, readout electronics, and feedback coil as short as possible to minimize phase shifts and time delays. Cooling the readout circuit to low temperatures can also decrease its thermal noise. Our readout circuit uses conventional ac-flux modulation, which significantly reduces low frequency excess noise and drift in the preamplifier. In this case, simple complementary metal–oxide–semiconductor circuits with low power dissipation can be used as amplifier, phase-sensitive detector and integrator. The power dissipation of the complete readout is less than 15mW at 5V supply voltage.