Which circuit has a diode in series with the output signal?

A limiter circuit specifically employs a diode in series with the output signal to control the voltage level and prevent it from exceeding specified limits. The diode allows current to flow in one direction, which helps to "limit" the voltage seen at the output to a certain threshold. When the input signal rises above this threshold, the diode becomes forward-biased and clamps the output, thereby reducing the amplitude of the signal to protect downstream components from excessive voltage.

In contrast, capacitor circuits typically focus on energy storage and filtering but do not necessarily use diodes to control output signal levels. Transformer circuits are utilized for impedance matching and voltage transformation, and while they may involve diodes in rectification processes, a diode is not inherently part of the output signal configuration. Filter circuits primarily serve to allow or block certain frequencies but do not inherently use diodes for output control. Thus, the presence of a diode in series with the output signal is a defining characteristic of limiter circuits.