WIEN BRIDGE OSCILLATOR

The WIEN BRIDGE OSCILLATOR (figure shown below) largely relies on a pair of LR resonant networks for shifting the output signal by exactly 180 degree and one particular frequency. Then this phase-shifted signal is fed back to the non-inverting (1) input of the op amp. It is amplified and add force to the output signal. A strong sinusoidal waveform is generated. In Wien network, the two capacitors and both od the resistors are equal in value. The signal frequency is f = 1/2πRC.

The benfit of using the amplifier is that it is easily made tunable by making use of a dual ganged variable resistor for the 2 resistors in the Wien network.

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Phase shift oscillator

First thing to know is that all three oscillators depend on +ve feedback to keep them oscillating. Some part of the output produced by the op amp is required to be fed back to its non-inverting input to keep itself in the oscillations.

The voltage level at the +ve terminal of the op amp is kept constant at half the supply, and stabilized by making use of capacitor.

A rising voltage at the output is fed back to the inverting inputs (2) that as a result cause a fall of output. This is +ve feedback and the op amp would have as table output. Also there is +ve feedback across the phase shift network.

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