Reactance control circuit with a DC amplifier for minimizing a variation of a reference reactance value

摘要

A reactance control circuit comprising a variable reactance circuit whose reactance is determined by the currents flowing to first and second differential transistor circuits, a differential amplifier for producing first and second currents in accordance with an input voltage, and a DC amplifier circuit for amplifying the first and second currents and supplying the amplified currents to the variable reactance circuit in order to control the currents flowing to the first and second differential transistor circuits. The DC amplifier circuit includes first and second transistors for supplying output currents to the variable reactance circuit, and a base potential control circuit for, when the first and second currents are equal to each other, supplying a predetermined low potential to the bases of the first and second transistors so that the currents flowing to the first and second transistors are both reduced.