Opamp Wien-bridge oscillator

Oscillators

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1 Introduction
2 Basic principles of the sinusoidal oscillators
3 Basic structure of the sinusoidal oscillators
4 Non linear amplitude control of a sinusoidal oscilator

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5 Wien Bridge Oscillator
6 Phase-shift oscillator
7 LC Oscillator
8 Crystal Oscillator
9 Crystal oscillators. Series and parallel resonance

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This article is part of the following tutorial >>

Oscillator circuits with operational amplifiers and a RC network

This section discusses some practical oscillators that use operational amplifiers and RC networks.

The Wien bridge oscillator

The Wien-bridge oscillator, as shown in the basic outline of the picture, consists of an Operational Amplifier (OA) in a non-inverting configuration with gain 1 + R2/R1 and a RC feedback network with transfer function:

Where

Combining the first and the second equation we get:

The loop gain (BA) is:

The Barkhausen criterion defines the conditions for oscillation at frequency ƒo:

To ensure the conditions of oscillation, R2/R1 must be chosen slightly higher than 2 to correct small variations in the circuit. Furthermore, the amplitude of oscillation can be determined and stabilized using a nonlinear circuit as shown in picture above. The diodes D1 and D2 and resistors R2 and R3 act as limiting the output amplitude.