A clamper is circuit that places a input signal to a different DC level. A clamping circuit consists of a diode, resistor and capacitor. Three types of clampers are positive, negative and biased clampers. The time constant RC should be high to avoid capacitor's discharge while diode is non conducting.So care should be taken while choosing the value of capacitor(C) and resistor(R).
A negative clamper circuit is considered. It shifts original input signal in a downward direction.While positive input is applied, diode is forward biased. The output voltage is Vo which is equal barrier potential of the diode. The capacitor is charged to V-Vo.
When negative input cycle, diode does not conduct because it is reverse biased and the capacitor can not discharge very much because time constant (RC) choosen is high. Now output is sum of input voltage and capacitor voltage and it is equal to -(2V – Vo). Now peak to peak output voltage is difference of output voltages when positive and negative half cycles and it is equal to V-(-(2V – Vo)) or 2V.
In negative clamper, input signal is pushed downward and positive peak of the output signal coincides with zero level.
In positive clamper circuit, unlike in negative clamper circuit, diode is connected reversely.There is no change in connection of capacitor. But resistor is connected after diode. Positive clamping circuit shifts a input signal in upward direction. The output of this circuit shows that negative peak of signal coincides with zero level.