Design clamper for given waveforms

A clamper circuit is a circuit that shifts the dc level of an input waveform up or down without changing its shape or peak-to-peak value. It uses a capacitor, a diode, a resistor and, if needed, a dc battery.

Design for the given waveforms

• Input: square wave from −20 V to +20 V (peak-to-peak 40 V).
• Output: square wave from −10 V to +30 V (peak-to-peak 40 V, the same shape).
• So the waveform is shifted up by 10 V: Vout = Vin + 10 V. A positive clamper is needed whose negative peak is clamped at −10 V.

Design (ideal diode)

• The diode must turn ON when Vout goes below −10 V, so the diode anode is connected to a −10 V point (a 10 V battery with its negative end to the anode and its positive end to ground) and the cathode to the output.
• Capacitor voltage: when Vin = −20 V, Vout = −10 V, so Vc = Vin − Vout = −20 − (−10) = −10 V. The capacitor is charged to 10 V.
• Then Vout = Vin + 10: at Vin = +20 V, Vout = +30 V.

              C
 Vin o-------| |-------+--------+---o Vout
                       |        |
                     -----      |
                      / \   D   R
                     /___\      |
                       |        |
                     - |        |
                      ---       |
                     -----  10 V|
                     + |        |
 GND o-----------------+--------+---o

• The anode of D joins the negative terminal of the 10 V battery; its positive terminal is at ground. The cathode of D is at the output.
• R is large (RC much greater than the period of the square wave), for example R = 100 kΩ, C = 1 µF.

For a real silicon diode, use a 9.3 V battery so that the clamp level stays at −10 V.