Wien bridge oscillator

A Wien bridge oscillator is a type of electronic oscillator that generates sine waves. It can generate a large range of frequencies. The oscillator is based on a bridge circuit originally developed by Max Wien in 1891 for the measurement of impedances. The bridge comprises four resistors and two capacitors. The oscillator can also be viewed as a positive gain amplifier combined with a bandpass filter that provides positive feedback. Automatic gain control, intentional non-linearity and incidental non-linearity limit the output amplitude in various implementations of the oscillator.

The circuit shown to the right depicts a once-common implementation of the oscillator, with automatic gain control using an incandescent lamp. Under the condition that R₁=R₂=R and C₁=C₂=C, the frequency of oscillation is given by:

${\displaystyle f={\frac {1}{2\pi RC}}}$

and the condition of stable oscillation is given by

${\displaystyle R_{b}={\frac {R_{f}}{2}}}$

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