Integrated two stage dc SQUID-based amplifier with double transformer coupling scheme

The integrated version of a two stage dc SQUID-based low frequency amplifier has been designed, fabricated and tested. The value of the gain of the applied flux d Phi(SQ2)/d Phi(SQ1) in the range 30-70 and an overall flux-to-voltage transfer factor dV(SQ2)/d Phi(SQ1) as high as 3 mV/Phi(0) have been obtained. An effective input inductance L-IN equal to 1.8 mu H, a current sensitivity 1.33 mu A/Phi(0), and an effective coupling coefficient k(IN)(2) close to 0.1 have been found in the accordance with the design.