A clamping circuit
is an electronic circuit with which AC voltagesare fixed to a reference potential, the clamping voltage.With capacitive coupling
, AC voltages change their average value depending on the positive and negative signal components. This is the case, for example, with asymmetrical pulse trains - many zeros, few ones - or with the television picture, whose mean value shifts to brighter or darker values depending on the brightness component.These shifts are avoided by clamping circuits in which a signal component intended for this purpose is clamped to the clamping voltage. The analogue television signal can be taken as an example. So that the brightness level is not affected by the mean brightness value of the picture, the black shoulder
has been selected as the reference value and is used as the black level reference. During the black shoulder, the coupling capacitance, which has been charged by the changing average value, is briefly charged to the reference potential via a clamping pulse. For pulse trains, the clamping potential can be the pulse ground. The clamping circuit itself is a simple circuit of diodes, clamping diodes, or Zener diodes that clamps the voltage to the clamping voltage when a predetermined reference level is exceeded.