Electronic impedance circuit including a compensation arrangement for d.c. offset

摘要

An electronic impedance circuit is constructed of a voltage-current converter and a variable gain current amplifier. The voltage-current converter includes first and second transistors of the PNP-type differentially connected. The variable gain current amplifier includes third and fourth transistors of the NPN-type differentially connected, and fifth and sixth transistors of the PNP-type as load means. The bases of the third and fourth transistors are respectively driven by collector signals of the first and second transistors, and a collector signal of the third transistor is fed back to the base of the second transistor. In order to reduce a d.c. offset attributed to a current flowing between the base of the second transistor and the collector of the third transistor, a compensation circuit is connected to the variable gain amplifier. This compensation circuit can provide compensation by producing a compensation current for cancelling the current between the base of the second transistor and the collector of the third transistor.