Parasitic oscillation

Parasitic oscillation is an unintended self-sustaining oscillation in an electronic circuit, typically caused by unintentional feedback combined with sufficient gain and phase shift in an amplifying device. It occurs most commonly in RF and audio amplifiers, but can arise in many types of analog electronic circuits. It is one of the fundamental issues addressed by control theory.

Parasitic oscillation is undesirable for several reasons. The oscillations may be coupled into other circuits or radiate as radio waves, causing electromagnetic interference (EMI) to other devices. In audio systems, parasitic oscillations can sometimes be heard as annoying sounds in the speakers or earphones. The oscillations waste power and may cause undesirable heating. For example, an audio power amplifier that goes into parasitic oscillation may generate enough power to damage connected speakers. A circuit that is oscillating will not amplify linearly, so desired signals passing through the stage will be distorted. In digital circuits, parasitic oscillations may only occur on particular logic transitions and may result in erratic operation of subsequent stages; for example, a counter stage may see many spurious pulses and count erratically.