JPH0644033B

PURPOSE:To improve measuring accuracy by removing influence to be exerted upon the 1st DC magnetic flux parametron (DCFP) circuit by the operating current of a magnetic flux coupling element in a circuit consisting of the 2nd superconductive circuit including the magnetic flux coupling element connected to the 1st DCFP circuit and a signal line. CONSTITUTION:A transformer 10i and a control line 6 for a current detecting circuit 10 are connected to an output line 108 of a DCFP circuit having Josephson junctions 101, 102 and exciting windings 103, 104 as loads. A current IS is supplied from a pulse current source 200 to a magnetic flux coupling quantum interference element in a circuit 10 and monitored by a voltmeter 201 and a reference current Ir is supplied from a scanning current source 300. When an offset current Ig, is supplied in the reverse direction against the currents Ig, Ir through the wiring 110 of the transformer 109, magnetic flux based upon the currents Ig, Ir is prevented from being superposed to the control line 6 and the current IS to be measured can be found out from the reference current Ir on the basis of the thereshold characteristics of the circuit 10 by fizing the current Ig. Since the signal IS of the DCFP circuit can be extracted by removing the influence of the detecting circuit, the measuring accuracy can be improved.