An electrically variable impedance circuit in which a voltage-current converter circuit (3) is provided to produce a current (I') having a megnitude corresponding to an instantaneous input signal potential (v) applied to an input terminal (1) and a current variation of the vottage-current converter circuit is fed back to the input terminal (1), the current variation being controlled by a control signal (Vc) to vary the circuit impedance seen from the Input terminal (1). In order to expand the range of linesrity in impedance, the voltage-current converter is so arranged that the varying component of its output current is linsariy proportional to the inatan- taneous input signal potendial (v). and a current converter circuit (4) is provided which linearly converts the output current of the voltage-current converter circuit and whose output is coupled to the input terminal (1). The current converter circuit (4) is comprised of a PN junction (51) which develops a voltage which is the logarithm of the output current of the voltage-current converter (3) and a transistor (81) between the base and emitter of which is spplied the voltage developed by the PN junction (5 1 ) to produce a current which is the exponential of the voltage developed by the PN junction. (Fig. 1)