Abstract: A tuning signal having a duty cycle representing a transmission frequency to be received is converted by a D/A converter to a tuning voltage which in turn is applied to a voltage variable tuning capacitance in the receiver input stage. To avoid the effects of ripple on the tuning voltage, the instantaneous d.c. level of the tuning voltage is stored on a capacitor during the tuning operation. On completion of tuning, the tuning voltage is disconnected and the stored capacitor voltage is applied to the tuning capacitance, thereby eliminating the unwanted ripple voltage. The tuning voltage produced by the D/A converter as well as that stored by the storage capacitor, are connected to the input of a voltage follower amplifier whose output is connected to the tuning capacitance. The amplifier design is such that when its input and output voltages are equal, its quiescent current is small whereas when its input and output voltages differ a current source is switched to provide a large output current.