RC phase shift and wein bridge oscillators

A phase shift oscillator usually uses an amplifier that has 180° of phase shift. The reactive components bump a specific frequency by a set amount of degrees, the classic phase shift oscillator is 3 RC circuits, each handling around 60° (give or take). The total phase shift for only one frequency is 180°, the rest is more or less due to the reactance. Therefore only one frequency is selected. Another rather unique phase shift design is the "Bubba Oscillator", found in Sine Wave Oscillators, a PDF abstract by TI.

http://en.wikipedia.org/wiki/Phase_shift_oscillator



A Wien Bridge uses two RC circuits, one as a high pass filter, one as a low pass filter. The end result is a band pass filter made up of RC components.

http://en.wikipedia.org/wiki/Wein_bridge_oscillator

 

Bill Hewlett (of HP) made HP by making the first really stable, really pure sine wave generator, whose design you see a simplification of above. The light bulb used as a automatic gain control was a major breakthrough.