Wien Bridge Oscillator

Wien Bridge Oscillator 

Wien Bridge Oscillator Circuit: In most of the cases this oscillator is used in the audios. The oscillators are designed simply, size is compressed and it has stable in frequency output. Hence the maximum output frequency of the Wien bridge oscillator is 1MHz

Definition: One of the simplest sine wave oscillators which use a RC network in place of the conventional LC tuned tank circuit to produce a sinusoidal output waveform is called a Wien Bridge Oscillator.

                     A Wien bridge oscillator is a type of electronic oscillator that generates sine waves. It can generate a large range of frequencies. The oscillator is based on a bridge circuit originally developed by Max Wien in 1891 for the measurement of impedances. The bridge comprises four resistors and two capacitors. The oscillator can also be viewed as a positive gain amplifier combined with a band pass filter that provides positive feedback. Automatic gain control, intentional non-linearity and incidental non-linearity limit the output amplitude in various implementations of the oscillator.

 A practical oscillator circuit uses an op-amp and RC bridge circuit, with the oscillator frequency set by the R and C components. Following figure shows a basic version of a Wien bridge oscillator circuit. Note the basic bridge connection. Resistors R₁ and R₂ and capacitors C₁ and C₂ form the frequency-adjustment elements, and resistors R₃ and R₄ form part of the feedback path. The op-amp output is connected as the bridge input at points a and c. The bridge circuit output at point’s b and d is the input to the op-amp.

Neglecting loading effects of the op-amp input and output impedances, the analysis of the bridge circuit results in

Circuit Diagram

if, in particular, the values are R₁ = R₂ = R and C₁ = C₂ = C, the resulting oscillator frequency is

and                                                               

Thus a ratio of R₃ to R₄ greater than 2 will provide sufficient loop gain for the circuit to oscillate at the frequency calculated using equation 2

Applications of Wien Bridge Oscillators

·         It is used to measure the audio frequency.

·         Wien bridge oscillator designs the long range of frequencies

·         It produces sine wave.

Advantages

·         Distortion testing of power amplifier.

·         It supplies the signals for testing filters.

·         Excitation for AC Bridge.

·         To fabricate pure tune.

·         Long distance can be spanned by the resting beams.

Disadvantages

·         The Wheatstone bridge is not used for the high resistance.

·         The circuit needs the high no. of other components.

·         The limited output frequency is obtained because the amplitude and the phase shift characters of the amplifier.

Problem solving

a.        Calculate the resonant frequency of the Wien bridge oscillator of following figure.

Solution: 

Let us take required equation: 

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