 The magnitude of R and C must be chosen such that the time constant RC is large enough to ensure that the voltage across the capacitor does not discharge significantly during the interval the diode is nonconducting.Clamp circuits are categorised by their operation; negative or positive, and biased or unbiased.A positive clamp circuit (negative peak clamper) outputs a purely positive waveform from an input signal; it offsets the input signal so that all of the waveform is greater than 0 V. A negative clamp is the opposite of this—this clamp outputs a purely negative waveform from an input signal.