A clamper circuit or dc restorer is used to clamp a peak of a waveform to a specific DC level compared with a capacitive coupled signal which swings about its average DC level (normally 0 V). If the diode is removed from the clamper, it defaults to a simple coupling capacitor – that is, no clamping. Therefore, we can simply define clamping as the process of introducing a dc level into an ac signal.
Let’s consider a signal illustrated in Figure 1.1 below. It is a sine wave with equal positive and negative swings of ± 5 V about 0 V. Therefore, its average value over one cycle is zero (it has no dc level).
The signal waveform in Figure 1.2 below has been lifted up so as to just touch the horizontal axis. It is said to have acquired a dc level of 5 V. This output wave-form is said to be positively clamped at 0 V.
Applications of Clamper/DC restorer Circuits
Clamping circuits are typically utilized in TV receivers as dc restorers. The incoming composite video signal is usually processed through capacitive-coupled amplifiers which eliminate the dc component thereby losing the black and white reference levels and the blanking level. These reference levels have to be restored before applying the video signal to the picture tube.
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