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Wien-Bridge Oscillator Circuits. By Darren De Ronde May 15, 2002. Why Look At the Wien-Bridge?. It generates an oscillatory output signal without having any input source. Basics About the Wien-Bridge.

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wien bridge oscillator circuits

Wien-Bridge Oscillator Circuits

By Darren De Ronde

May 15, 2002

why look at the wien bridge
Why Look At the Wien-Bridge?
  • It generates an oscillatory output signal without having any input source
basics about the wien bridge
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 bridge4
Basics About the Wien-Bridge
  • Amplifies the signal with the two negative feedback resistors
analysis

Z1

Z2

Analysis
  • The loop gain can be found by doing a voltage division
analysis7

Z1

Z2

Analysis
  • The two RC Networks must have equal resistors and capacitors
analysis8
Analysis

Need to find the Gain over the whole Circuit: Vo/Vs

Solve G equation for V1 and substitute in for above equ.

analysis9
Analysis

We now have an equation for the overall circuit gain

Simplifying and substituting jw for s

analysis10
Analysis

If G = 3, oscillations occur

If G < 3, oscillations attenuate

If G > 3, oscillation amplify

slide11

G = 3

G = 2.9

G = 3.05

ideal vs non ideal op amp
Ideal vs. Non-Ideal Op-Amp
  • Red is the ideal op-amp.
  • Green is the 741 op-amp.
making the oscillations steady
Making the Oscillations Steady
  • Add a diode network to keep circuit around G = 3
  • If G = 3, diodes are off
making the oscillations steady14
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 steady15
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
Results of Diode Network
  • With the use of diodes, the non-ideal op-amp can produce steady oscillations.
frequency analysis
Frequency Analysis
  • By changing the resistor and capacitor values in the positive feedback network, the output frequency can be changed.
frequency analysis18
Frequency Analysis

Fast Fourier Transform of Simulation

frequency analysis19
Frequency Analysis
  • Due to limitations of the op-amp, frequencies above 1MHz are unachievable.
conclusions
Conclusions
  • No Input Signal yet Produces Output Oscillations
  • Can Output a Large Range of Frequencies
  • With Proper Configuration, Oscillations can go on indefinitely