A newly developed current injection logic circuit is described. Input signal currents are directly injected into the inductor of a Josephson interferometer instead of being magnetically coupled to it. This circuit realizes excellent isolation characteristics between input and output signals. The additional offset-bias circuit increases the drivability and extends the operating margin. Experimental circuits forming cascade chains of 100 gates were fabricated using 10 µm-square lead-alloy Josephson junctions. The measured switching delay time was about 30 ps at a power dissipation of 15 µW.

A DC-powered complementary circuit employing interferometers in investigated using simulation. It is shown that an output inductor and two kinds of damping resistors are necessary to suppress circuit oscillations. Switching speed is expected to be less than 25 ps at a current density of 5000 A/cm2 for lead-alloy devices.