wein bridge oscillators {by viresh g. roll no.10}
TRANSCRIPT
Wien-Bridge Oscillator
By Mr. Viresh Vilas GawadeBhavans college
T.Y.BscRoll no.10
Saturday, December 12th 2011
Outline Basics about the wein bridge Modification to the circuits Analysis Making the oscillations Frequency analysis Conclusions Reference
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
Vo s( ) V1 s( )Z 2 s( )
Z 1 s( ) Z 2 s( )
Analysis The two RC
Networks must have equal resistors and capacitors
Z1 s( ) R1
s C
Z2 s( )
R1
s C
R1
s C
Analysis
Operational amplifier gain
GV1 s( )
Vs s( )1
R2
R1
Vo s( ) V1 s( )Z 2 s( )
Z 1 s( ) Z 2 s( )
Need to find the Gain over the whole Circuit: Vo/Vs
Vo s( ) G V s s( )s R C
s2R2 C
2 3 s R C 1
Solve G equation for V1 and substitute in for above equ.
Analysis
T s( )Vo s( )
V s s( )
s R C G
s2R2 C
2 3 s R C 1
We now have an equation for the overall circuit gain
T j j R C G
1 2R2 C
2 3 j R C
Simplifying and substituting jw for s
Analysis
In order to have a phase shift of zero,
1 2R2 C
2 0
This happens at RC When RC, T(j) simplifies to:
T j G
3
If G = 3, oscillations occur
If G < 3, oscillations attenuate
If G > 3, oscillation amplify
Time
0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0msV(R5:2)
-4.0V
0V
4.0V
G = 3
Time
0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0msV(R5:2)
-4.0V
0V
4.0V
G = 2.9
Time
0s 100us 200us 300us 400us 500us 600usV(R5:2)
-20V
0V
20V
G = 3.05
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
Time
0s 0.2ms 0.4ms 0.6ms 0.8ms 1.0msV(D2:2)
-4.0V
0V
4.0V
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.
R 10k C 1nF
1
R C 1 10
5rad
sec
f
2 f 15.915kHz
Frequency Analysis
Frequency
0Hz 10KHz 20KHz 30KHz 40KHzV(D2:2)
0V
2.0V
4.0V(15.000K,2.0539)
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
Reference www.circuitstoday.com www.ecircuitcenter.com/circuits/op
wien www.jensign.com/wien www.sciencelabequipments.net/
wein-bridge-oscillator
Thank You.