5.1 Introduction – Pulse and Digital Circuits


When a signal is transmitted through a capacitive coupled network, the dc component associated with the input is lost in the output since the capacitor blocks the dc. If the dc component needs to be restored, a clamping circuit is used. Thus, clamping circuits reintroduce the dc component lost during transmission through a capacitive coupled network and hence, are called either dc restorers or dc re-inserters. The output reaches the steady-state value in a few cycles after the application of the input to the clamping circuit (transient period). Circuits that clamp the positive peak of the signal to the zero level are called negative clampers and those that clamp the negative peak of the signal to the zero level are called positive clampers. In general, the output can be referenced to any arbitrarily chosen reference voltage. Circuits that clamp the output to zero or to any dc level are considered here. The necessary relations that enable us to plot the steady-state responses are then derived. The effect of the internal resistance of the source on the output and the influence of diode characteristics on the clamping voltage are also examined. In some applications, clamping is needed only for a finite duration and the time interval for which this is to be accomplished is determined by an external signal called the control signal. The circuit that performs this operation, called synchronized clamping circuit, is also discussed.