Build A Voltage-Controlled Dual Clipper

In the clipper circuit shown, V_IN is the input signal, V1 and V2 are the dc reference voltages (clipping levels), and V_O2 is the output signal (Fig. 1). The Q1/Q2 npn transistor pair acts as a “High Level Signal” pass circuit.

For V_IN > V1, transistor Q1 is in its active region, transistor Q2 is off, and V_O1 = V_IN. For V_IN < V1, V_O1 = V1. (VO1 will have a −0.6 V level shift due to the V_BE of the Q1/Q2 transistor pair). Similarly, the Q3/Q4 pnp transistor pair produces an output signal at V_O2, which is the lowest voltage level of the V_O1 and V_2A input signals.

Transistor Q5 acts as a level shifter to compensate for a V_BE drop of Q4. V_IN and V1 don’t experience any dc shift due to cancellation of V_BE drops. If a 6-V p-p sine wave is applied at the V_IN input, V1 = −2 V, and V2 = +2 V, the resulting output waveform is as shown in Figure 2.

Other reference polarities could be used. The circuit has reasonably highfrequency response and accuracy. The input and reference voltages should be such that base-emitter breakdown voltages are not exceeded.