Abstract: A charge coupled device for sampling an analog signal voltage. If charge is inputted to a charge coupled device by the so-called phase-referred input method, a minority charge carrier source region (10) in a semiconductor body (1) is clocked in phase with a charge transfer gate (6) so that a metering potential well formed under a metering electrode (4) is alternately filled via a d.c. gate (5) with carriers to a predetermined level and then surplus carriers are drained back via the d.c. gate and the remainder exit via the transfer gate. This mechanism tends to degrade at high frequencies and, in order to improve the high frequency performance, a very short further gate (20) is provided between the d.c. gate and the metering well. This further gate is clocked in antiphase to the source region (10) and the transfer gate (6) so that it creates a rising potential barrier when the surplus carriers are being drained back, thereby isolating the metering well from the source (10) and the d.c.