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Wien-Bridge Oscillator Circuits

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

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Wien-Bridge Oscillator Circuits

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  1. Wien-Bridge Oscillator Circuits

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

  3. 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

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

  5. Z1 Z2 Modification to Circuit

  6. Z1 Z2 Analysis • The loop gain can be found by doing a voltage division

  7. Z1 Z2 Analysis • The two RC Networks must have equal resistors and capacitors

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

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

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

  11. G = 3 G = 2.9 G = 3.05

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

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

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

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

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

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

  18. Frequency Analysis Fast Fourier Transform of Simulation

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

  20. 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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