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/spl Phi//sub SQ2//d/spl Phi//sub SQ1/ in the range 30-70 and an overall flux-to-voltage transfer factor d/spl Phi//sub SQ2//d/spl Phi//sub SQ1/ as high as 3 mV//spl Phi//sub 0/ have been obtained. An effective input inductance L/sub IN/ equal to 1.8 /spl mu/H, a current sensitivity 1.33 /spl mu/A//spl Phi//sub 0/, and an effective coupling coefficient k/sup 2//sub IN/ close to 0.1 have been found in the accordance with the design.