Patent ID: 7304509

Claim:
An impedance circuit connected to an external circuit, comprising: a first current inverter circuit having an input terminal connected to outside; a passive circuit having an input terminal connected to an output terminal of the first current inverter circuit; and a second current inverter circuit having an input terminal connected to an output terminal of the passive circuit and an output terminal connected to outside, wherein the first and second current inverter circuits work in cooperation with each other, to make the magnitude of impedance of the impedance circuit proportional to the impedance of the passive circuit, and to invert a polarity of the impedance of the impedance circuit, and the first and second current inverter circuits each have one operational amplifier, two diodes connected in inverse-parallel to each other between an output terminal of the operational amplifier and a non-inverted input terminal thereof, and two diodes connected in inverse-parallel to each other between the output terminal of the operational amplifier and an inverted input terminal thereof.