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Wien-Bridge Oscillator Circuits
Why Look At the Wien-Bridge? It generates an oscillatory output signal without having any input source
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
Basics About the Wien-Bridge Amplifies the signal with the two negative feedback resistors
Modification to Circuit
Analysis The loop gain can be found by doing a voltage division
Analysis The two RC Networks must have equal resistors and capacitors
Analysis Need to find the Gain over the whole Circuit: Vo/Vs Solve G equation for V1 and substitute in for above equ.
Analysis We now have an equation for the overall circuit gain Simplifying and substituting jw for s
Analysis If G = 3, oscillations occur If G < 3, oscillations attenuate If G > 3, oscillation amplify
G = 3 G = 2.9 G = 3.05
Ideal vs. Non-Ideal Op-Amp Red is the ideal op-amp. Green is the 741 op-amp.
Making the Oscillations Steady Add a diode network to keep circuit around G = 3 If G = 3, diodes are off
Making the Oscillations Steady When output voltage is positive, D1 turns on and R9 is switched in parallel causing G to drop
Making the Oscillations Steady When output voltage is negative, D2 turns on and R9 is switched in parallel causing G to drop
Results of Diode Network With the use of diodes, the non- ideal op-amp can produce steady oscillations.
Frequency Analysis By changing the resistor and capacitor values in the positive feedback network, the output frequency can be changed.
Frequency Analysis Fast Fourier Transform of Simulation
Frequency Analysis Due to limitations of the op-amp, frequencies above 1MHz are unachievable.
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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