Wave shaping circuits are designed to alter the form of an input signal, typically by attenuating specific parts of it or by shifting its overall DC level. These circuits are fundamental in applications ranging from signal protection to waveform modification. This section analyzes the two primary types of wave shaping circuits built with operational amplifiers: clippers and clampers.

5.1 Clippers

A clipper circuit, sometimes called a limiter, removes or “clips” a portion of an input signal that is either above or below a specified reference level. Clippers are particularly useful for eliminating noise spikes or protecting subsequent circuit stages from over-voltage conditions.

Positive Clipper

A positive clipper circuit clips the part of the input signal that exceeds a positive reference voltage (V_{ref}).

• When : The op-amp’s output is positive relative to its inverting input, forward-biasing the feedback diode. This closes the feedback loop, and the circuit behaves as a voltage follower, resulting in V_0 = V_i.
• When : The op-amp’s output attempts to swing positive to follow the input. This reverse-biases the diode, effectively opening the feedback loop. This configuration leverages the op-amp’s open-loop behavior to clamp the output precisely at V_{ref}, so V_0 = V_{ref}.

The result is a waveform where the positive peaks are cleanly clipped off at the V_{ref} level.

Negative Clipper

A negative clipper performs the opposite function, clipping the portion of the input signal that falls below a reference voltage (V_{ref}). The circuit is similar to the positive clipper, but the diode is reversed.

• When : The diode conducts, the feedback loop is closed, and the circuit acts as a voltage follower, with V_0 = V_i.
• When : The op-amp output attempts to swing negative, reverse-biasing the diode and opening the feedback loop. The output voltage is clamped to the reference level, so V_0 = V_{ref}.

This configuration effectively removes the negative-going portions of the waveform below the specified reference voltage.

5.2 Clampers

A clamper circuit, also known as a DC restorer, shifts the entire input signal vertically (up or down) by a specific DC value. Unlike a clipper, a clamper does not change the peak-to-peak amplitude or the shape of the input waveform; it only alters its DC offset.

Positive Clamper

A positive clamper produces an output where the input waveform is shifted vertically upward by a reference voltage, V_{ref}. The core mechanism involves a capacitor and a diode. During the initial negative excursions of the input signal, the diode becomes forward-biased, allowing the capacitor to charge to a DC level determined by the input peak and the reference voltage. When the input signal swings positive, the diode reverse-biases, trapping this DC charge on the capacitor. This trapped voltage acts as a new DC reference, effectively shifting the entire AC waveform upwards.

Negative Clamper

A negative clamper produces an output where the input waveform is shifted vertically downward by a reference voltage, V_{ref}. The operation is analogous to the positive clamper but with the diode reversed. During the initial positive excursions of the input signal, the capacitor charges to a specific DC level. When the input goes negative, the diode reverse-biases, and this trapped DC charge effectively shifts the entire AC waveform downwards.

Beyond shaping existing signals, operational amplifiers can also be used to create new ones from scratch. The following sections will detail how op-amps are used in oscillators and waveform generators to produce periodic signals.