Basic Electronic Oscillators

Abstract

The possibility of instabilities in amplifiers has been introduced earlier. Because of internal feedback in the active devices, external feedback paths, or connections in the amplifier, a feedback signal proportional to the output is produced. If this feedback signal is in phase with the input, a regenerative situation exists, and if the magnitude of the feedback is large enough, an unstable circuit is obtained. That is, if any input, including noise, is applied to or is present in a circuit which is initially at rest, growing transients occur. After a period of time, these growing transients are sufficiently large to produce a nonlinear response of the circuit elements, and these nonlinearities finally stop the growth of the signals. Eventually, then, steady-state oscillations can occur, and the circuit becomes an (unwanted) oscillator.