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:

f

h

z

=

1

2

π

R

C

{\displaystyle f_{hz}={\frac {1}{2\pi RC}}}

and the condition of stable oscillation is given by

R

b

=

R

f

2

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

Background

There were several efforts to improve oscillators in the 1930s. Linearity was recognized as important. The "resistance-stabilized oscillator" had an adjustable feedback resistor; that resistor would be set so the oscillator just started (thus setting the loop gain to just over unity).