Squegging

Squegging, also known as self-quenching (or sometimes self-blocking), is oscillation that builds up and dies down (possibly to quiescence, or merely to a significantly reduced amplitude) with a much longer time constant than the fundamental frequency of oscillation, and differs from normal amplitude modulation in that the mechanism that causes the oscillation also causes the amplitude to fluctuate (possibly irregularly) not from a supplied modulating signal applied to a separate stage after a steady-amplitude oscillator. It is therefore a circuit that oscillates at two or more frequencies at the same time.

Usually this is unwanted, and caused by feedback in electronic circuits where the build up of oscillations causes some side effect (such as reduction in power supply voltage) that then reduces (quenches) the oscillations. There are situations where such self-quenching (or "self-blocking"^[1]) action is needed, for example:

• some forms of blocking oscillators are designed to squegg as oscillations build up a negative grid bias,^[2] although most blocking oscillators do not burst into oscillation when unblocked and so produce only a single frequency plus its harmonics.
• the Regenerative circuit#super-regenerative receiver is essentially a squegging oscillator.

Unwanted Squegging

Squegging can sometimes be heard as a motorboating sound from amplifiers where unwanted positive feedback occurs (for example: through power supply rails due to inadequate decoupling capacitors or poor Power supply rejection ratios).

References