# Wien Bridge Sine Wave Oscillator / Generator

### The Op amp Wien Bridge sine wave oscillator or generator is an excellent circuit for generating a sine wave signal at audio frequencies and above.

One of the popular methods of generating a sine wave with an operational amplifier is to use the Wien bridge configuration.

As the name implies, the op amp Wien bridge oscillator or generator is based around the Wien bridge. This is a form of bridge circuit that was developed by Max Wien in 1891 and it comprises four resistors and two capacitors.

## What is a Wien bridge

The basic Wien Bridge circuit is shown below and as it can be seen from this.

The basic bridge circuit was used in many applications including measuring the value of capacitors where variable resistors and a known capacitor could be used to determine the value of a capacitor, typically C1.

The Wien bridge is particularly flexible and does not require equal values of R or C. At some frequency, the reactance of the series R2–C2 arm will be an exact multiple of the R1–C1 arm. If the two R3 and R4 arms are adjusted to the same ratio, then the bridge will balance.

In terms of determining the balance frequency some simple equations can be used.

The equations simplify if one chooses R1 = R2 and C1 = C1; the result is R4 = 2 R3.

In practice, the values of R1 / R2 and C1 / C2 will never be exactly equal, but the equations above show that for fixed values in these arms, the bridge will balance at some ω and some ratio of R4/R3.

## Op amp Wien bridge oscillator

This fact can be used within an oscillator circuit, as the bridge can be used within the feedback loop and the circuit is able to oscillate at the balance point. Also the very high input impedance levels and very low output impedance levels of the operational amplifier mean that there is minimal loading on the bridge elements.

The basic Wien bridge oscillator or generator circuit is shown below and contains the elements of the bridge circuit wrapped around the operational amplifier itself. The oscillator can also be viewed as a positive gain amplifier combined with a band-pass filter that provides positive feedback.