Clamper (electronics)
A clamping circuit is used to add a DC voltage to AC voltage behind a coupling capacitor.
Purpose
A pulsating voltage is applied to a coupling capacitor, so only the AC component is transferred to a lower limit frequency ( Ua1 see in the picture). Lower frequencies or DC components are lost. These will be either restored or replaced by a predetermined voltage. This occurs frequently in the news media on (for example, clamp level picture tubes in television receivers or monitors ).
Operation
A distinction is mainly between the passive and the active Spitzenklemmung Tastklemmung.
Is a prerequisite for the functioning of a clamping that the target signal has periodically known DC voltage values and that the period is significantly smaller than the time constant of the high pass of the transmission path.
Spitzenklemmung
Is, for example, as in the image, an input voltage which periodically includes a fixed reference level, it is possible by means of a clamp diode, which acts as a switch which can be clamped to the reference potential, since the coupling capacitor recharges again. The time constant of Ra and C. should be as large as possible, so that the capacitor discharges very little during the breaks. Conversely, the time constant of R and C be as small as possible, so that the coupling capacitor can charge quickly. By reversing the polarity of the diode or a series circuit of voltage (terminal voltage) of the DC component of the same polarity and the clamp can be selected. A disadvantage of the Spitzenklemmung that the diode has a forward voltage and the circuit is also responsive to noise spikes.
Tastklemmung
With this the disadvantages of Spitzenklemmung be largely avoided. Through a mostly realized as a semiconductor device switch (pictured S) of the desired signal portion is scanned and then forced the lock. A disadvantage of a higher circuit complexity arises because a synchronous controller for controlling the sampling is needed. The dimensioning is carried out as in the Spitzenklemmung.