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 R₁ = R₂ and C₁ = C₂, 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:

C₁ = C₂ = 0.01μF
R₁ = 15.8kΩ
2R₂ = 31.8
R₃ = 50kΩ
R₄ = 10kΩ
R₅ = 40kΩ nominally
Diodes = 1N914 or 1N4148
R_S = 1MΩ

Using these component values, f_O will be 1004Hz. Resistor R₅ must be adjusted for best amplitude stability. If R₅ 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 R₅ 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 7.8μA which corresponds to a supply current of approximately 100μA. 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.

Author

James Wong

Mr. Wong is a RF Product Marketing Manager at Analog Devices. He served in senior marketing and sales roles for more than 25 years. Additionally, he has been designing RF, analog circuits and systems for more than 25 years.