The problem occurs notably in RF,[1] audio, and other electronic amplifiers[2] as well as in digital signal processing.
The oscillations may be coupled into other circuits or radiate as radio waves, causing electromagnetic interference (EMI) to other devices.
Parasitic oscillation in an amplifier stage occurs when part of the output energy is coupled into the input, with the correct phase and amplitude to provide positive feedback at some frequency.
In some solid-state or vacuum electron devices there is sufficient internal capacitance to provide a feedback path.
Using Bode plots, a design engineer checks whether there is a frequency where both conditions for oscillations are met: the phase is zero (positive feedback) and the loop gain is 1 or greater.
When parasitic oscillations occur, the designer can use the various tools of control loop engineering to correct the situation – to reduce the gain or to change the phase at problematic frequencies.
Amplifier circuits are laid out so that input and output wiring are not adjacent, preventing capacitive or inductive coupling.