Sine Wave Oscillator

This note describes the operational amplifier (op-amp) sine-wave oscillator, together with the criteria for oscillation to occur using RC components. It delineates the roles of phase shift and gain in the circuit and then discusses considerations of the op amp. A brief analysis of a Wien-Bridge oscillator circuit is provided. Several examples of sine-wave oscillators are given, although it is recognized that there exist many additional types of oscillator to which the principles of this application note also apply.

Oscillators are circuits that produce specific, periodic waveforms such as square, triangular,sawtooth, and sinusoidal. They generally use some form of active device, lamp, or crystal,surrounded by passive devices such as resistors, capacitors, and inductors, to generate theoutput.

There are two main classes of oscillator: relaxation and sinusoidal. Relaxation oscillators generate the triangular, sawtooth and other nonsinuoidal waveforms and are not discussed in this note. Sinusoidal oscillators consist of amplifiers with external components used to generate oscillation, or crystals that internally generate the oscillation. The focus here is on sine wave oscillators, created using operational amplifiers op amps. Sine wave oscillators are used as references or test waveforms by many circuits. A pure sine wave has only a single or fundamental frequency—ideally no harmonics are present. Thus, a sine wave may be the input to a device or circuit, with the output harmonics measured to determine the amount of distortion. The waveforms in relaxation oscillators are generated from sine waves that are summed to provide a specified shape.