# AN-111: Single-Supply Wien Bridge Oscillator

Wien bridge oscillators have the advantage of requiring only one op amp, and this advantage is particularly important for battery-oriented applications. The oscillator circuit operates from a single 9V battery.

The conditions for Wien bridge oscillation are:

where *β* is the ratio of output voltage feedback to the inverting input. If R_{1} = R_{2} and C_{1} = C_{2}, then *ω*_{O} is 1/RC and *β* is 1/3.

This oscillator should be set to just diverse in amplitude. Diodes are used to obtain a nonlinear feedback characteristic which will limit the divergence without causing too much distortion. The condition for oscillation is:

As a design example, consider:

C_{1} = C_{2} = 0.01*μ*F

R_{1} = 15.8kΩ

2R_{2} = 31.8

R_{3} = 50kΩ

R_{4} = 10kΩ

R_{5} = 40kΩ nominally

Diodes = 1N914 or 1N4148

R_{S} = 1MΩ

Using these component values, f_{O} will be 1004Hz. Resistor R_{5} must be adjusted for best amplitude stability. If R_{5} is too low, the oscillation might converge; if too large, then the oscillation will diverge until the output clips. An oscillation output of 6V peak-to-peak when operating from a 9V battery is recommended. Resistor R_{5} needs to be a nominal 40kΩ with a ±2.5kΩ adjustment range.

The OP-22 is operated with a 1MΩset resistor for a set current of 7.8*μ*A which corresponds to a supply current of approximately 100*μ*A. Gain-bandwidth product and slew-rate vary directly with the set current, so R_{S} should be optimized for the specific oscillation frequency. Supply drain can be reduced for lower frequencies. The OP-22 works well for frequencies in the range of 100Hz to 1kHz; the OP-27 is recommended for higher frequencies.