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Wien-Bridge Oscillator Circuits

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Why Look At the Wien-Bridge? It generates an oscillatory output signal without having any input source

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Basics About the Wien-Bridge Uses two RC networks connected to the positive terminal to form a frequency selective feedback network Causes Oscillations to Occur

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Basics About the Wien-Bridge Amplifies the signal with the two negative feedback resistors

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Modification to Circuit

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Analysis The loop gain can be found by doing a voltage division

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Analysis The two RC Networks must have equal resistors and capacitors

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Analysis Need to find the Gain over the whole Circuit: Vo/Vs Solve G equation for V1 and substitute in for above equ.

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Analysis We now have an equation for the overall circuit gain Simplifying and substituting jw for s

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Analysis If G = 3, oscillations occur If G < 3, oscillations attenuate If G > 3, oscillation amplify

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G = 3 G = 2.9 G = 3.05

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Ideal vs. Non-Ideal Op-Amp Red is the ideal op-amp. Green is the 741 op-amp.

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Making the Oscillations Steady Add a diode network to keep circuit around G = 3 If G = 3, diodes are off

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Making the Oscillations Steady When output voltage is positive, D1 turns on and R9 is switched in parallel causing G to drop

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Making the Oscillations Steady When output voltage is negative, D2 turns on and R9 is switched in parallel causing G to drop

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Results of Diode Network With the use of diodes, the non- ideal op-amp can produce steady oscillations.

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Frequency Analysis By changing the resistor and capacitor values in the positive feedback network, the output frequency can be changed.

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Frequency Analysis Fast Fourier Transform of Simulation

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Frequency Analysis Due to limitations of the op-amp, frequencies above 1MHz are unachievable.

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Conclusions No Input Signal yet Produces Output Oscillations Can Output a Large Range of Frequencies With Proper Configuration, Oscillations can go on indefinitely

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