PURPOSE: To eliminate turbulence in transmission waveform and to obtain a small-sized transmitter/receiver circuit by forming each winding of a pulse transformer of a spiral superconductor while enclosing the pulse transformer integrally in the same plane with an interface unit(IFU), and obtaining a desired magnitude of self-inductance while keeping the internal resistance value of the pulse transformer at zero.

CONSTITUTION: A pulse transformer 30 connected between an IFU 1 and a transmission path 2 has a primary winding 31 and a secondary widing 32 both formed spirally on a chip board 33. These windings are formed of a thin film of a superconductor and laid one over another with an insulating material interposed therebetween, so that a sufficiently large number of windings can be obtained with a cross-sectional area sufficiently decreased. Accordingly, self-inductance can be set at a magnitude as required while the internal resistance value is kept zero, so that the turbulence in transmission waveform is eliminated. Further, since the IFU 1 and the pulse transformer 30 are enclosed integrally in the same board 40, the size of a transmitter/receiver circuit can be decreased substantially.