Wien Bridge Oscillator

The Wien bridge oscillator is shown in the schematic below.

The circuit will oscillate when the ratio R_f / R_s is slightly greater than two. Let R_f  be 22 KΩ. Making R_s a series combination of a 8 kΩ fixed resistor and a 10 kΩ variable resistor (potentiometer) allows the ratio to be adjusted easily.

The frequency of oscillation is given by

For example, we used the following resistance and capacitance, from which we calculated τ = RC and the frequency f.

R (kΩ)	C (µF)	τ (ms)	f    (Hz)
1.492	0.1	0.1492	1066.7

In our test of this circuit, we used a power supply value of ±9 V.

The following oscilloscope images were captured when this oscillator was tested.
The measured frequency corresponds to a capacitance value of 0.101 µF.

	frequency 1058 Hz amplitude 14.5 V
	The feedback ratio was set by adjusting the potentiometer until output just oscillates. We measured the ratio Rf / Rs to be 2.06.
	frequency 966 Hz amplitude 15 V
	THe feedback ratio adjusted for full saturation.

A Multisim simulation of the oscillator is shown below (download schematic from wien.zip).

Maintained by John Loomis, last updated 23 Nov 2010