Abstract: A circuit having an effective output capacitance the value of which can be varied over a predetermined range of values includes first and second differential amplifiers. The differential inputs of the second differential amplifier are connected to the differential outputs of the first differential amplifier, the latter of which receives a variable control signal. The second differential amplifier includes a pair of transistors the emitters of which are AC coupled to ground. A capacitor is coupled between the base and collector of one of the pair of transistors, the collector of which is coupled to the output of the circuit. A diode is AC coupled between the base and ground of the one transistor whereby the impedance thereof is varied in direct relationship to the conduction of the one transistor in response to the control signal thereby causing the value of the output capacitance of the circuit to be varied.