Wien-Bridge Oscillator Circuits

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# Wien-Bridge Oscillator Circuits - PowerPoint PPT Presentation

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

By Darren De Ronde

May 15, 2002

Why Look At the Wien-Bridge?
• It generates an oscillatory output signal without having any input source
• Uses two RC networks connected to the positive terminal to form a frequency selective feedback network
• Causes Oscillations to Occur
• Amplifies the signal with the two negative feedback resistors

Z1

Z2

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

Z1

Z2

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.
• Add a diode network to keep circuit around G = 3
• If G = 3, diodes are off
• When output voltage is positive, D1 turns on and R9 is switched in parallel causing G to drop
• 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