Sep 182014
 

Wien-bridge Oscillator using Op-Amp

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

Wien_bridge_oscillator_transfer_function

Where:

Parallel Impedance Wien Bridge Oscillator

Combining the first and the second equation we get:

Wien_bridge_oscillator_transfer_function_1

The loop gain (BA) is:

open_loop_gain_BA

Wien-Bridge Oscillator basic design and amplitude control

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

Barkhausen_criterion_1

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.

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