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OSCILLATOR
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AGENDA
What is oscillation
Frequency = 1 / total time
Analog oscillation
Variationa
WIEN bridge oscillator
Summary
High pass and
low pass combined
Relaxatin oscillator
RC circuit 15k and 10 nF
Voltage diviver 15k and 15k
Comparator
Signals and output
Charge
Discharge
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What is oscillation
Circuit powered by Vcc and Vee
No input signal, only output signal
Wienbridge Oscillator; output signal is sine wave
(used for making radio frequencies)
Relaxation Oscillatoer; output signal is a “digital” block signal
(used for clock or count circuits)
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What is analog oscillation
WIEN bridge oscillator
Barkhausen criterium:
Loopgain = 1
Total phase = 0 or 360
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WIEN bridge oscillator
Oscillator for
High frequency
Sine signals
It uses 2 filters;
High pass and low pass
For one frequency the
phase = 0 degrees !!!!
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High Pass and Low Pass combinated
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WIEN bridge oscillator
Barkhausen criterium:
Loopgain = 1
Total phase = 0 or 360
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WIEN bridge oscillator
Uout

Uin R 
1
After “short” mathematics;
R2
1
jwC1
1
 R2
jwC2
1
jwC1
wR2C2
Uout

Uin w  R1C2  R2C1  R2C2   j w2 R1R2C1C2  1

w2 R1 R2C1C2  1  0
f oscillation
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
2 RC

for R1  R2  R and C1  C2  C
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WIEN bridge oscillator
Uout

Uin
1
R2
jwC1
1
R2 
jwC1
1
R2
jwC1
1
R1 

jwC2 R  1
2
jwC1
1
R2
jwC1


1 
1 
1
 R1 
 R2 
  R2
jwC2 
jwC1 
jwC1

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WIEN bridge oscillator
1
R2
jwC1
Uout

Uin R R  R1  R2  1  R2
1 2
jwC1 jwC2 w2C1C2 jwC1
R2
Uout

C1
1
Uin
jwR1 R2C1  R1  R2
j
 R2
C2
wC2
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WIEN bridge oscillator
R2
Uout

C1
1
Uin
jwR1 R2C1  R1  R2
j
 R2
C2
wC2
wR2C2
Uout

Uin w  R1C2  R2C1  R2C2   j w2 R1R2C1C2  1


For phase = o degrees; imaginair part = 0
w2 R1 R2C1C2  1  0
f oscillation
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for R1  R2  R and C1  C2  C
1

2 RC
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WIEN bridge oscillator
wR2C2
Uout

Uin w  R1C2  R2C1  R2C2   j w2 R1R2C1C2  1


For R1 = R2 = R
And C1 = C2 = C
At oscillation
IM = 0
Au = 1/3
so amplificaton should be +3
Rf = 2 Rs
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WIEN bridge oscillator
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What is “digital” oscillation
Relaxation oscillator
RC-circuit 15k and 10nF;
charge / discharge
Voltage divider 15k and 15k;
high treshold / low treshold
Comparator
Output:
block Vcc / Vee
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RC-circuit 15k and 10nF
Vin = Vcc = +12 for charge
And = Vee = -12 for discharge
Vc  V final  V final  Vinitial  e
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
t
RC
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Voltage divider 15k and 15k
Vin = +12 volt = opamp output high or
Vin = - 12 volt = opamp output low
V treshold up = +6 V for +12 opamp output
V treshold low = -6 V for – 12 opamp output
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Comparator
Inverting input;
Uc, capacitor voltage
Non inverting input;
Treshold voltage, high (+6 Volt)
or low (-6 volt)
Output:
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

Vout  A0 V  V


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Signals
and
output
Blue = output signal (+12 Volt or – 12 Volt)
Green = treshold signal (+6 Volt of – 6 Volt)
Red = capacitor signal
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Vc  V final  V final  Vinitial  e

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t
RC
Charge
Calculate
2nd charge track! Why?
Vc  V final  V final  Vinitial  e

Vinitial   6 V
switch at Vc   6 Volt
6  12  12   6 e
tch arg e  0,165 ms
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
t
15 k .10 n
t
RC
R = 15 k
C = 10 nF
Vfinal = +12 V
Vinitial = -6 V
Switch at Vc = +619 Volt
Discharge
Vc  V final  V final  Vinitial  e

t
RC
Vinitial   6 V
switch at Vc   6 Volt
6   12   12   6 e
tdisch arg e  0,165 us

t
15 k .10 n
R = 15 k
C = 10 nF
Vfinal = -12 V
Vinitial = +6 V
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Switch at Vc = -620Volt
Frequency = 1 / (total time)
tch arg e  0,165 ms

tdisch arg e  0,165 ms
ttotal  0,33 ms
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f oscillator  3, 0321kHz
Variations 1
By using diodes;
Charge time
and
Discharge time
are different !!
Treshold remains the same
So … duty cylce is controlable; up time ≠ down time
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Variations 2
Frequency
control by
changing
the voltage
divider
Vtreshold up
Vtreshold low
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Summary 1
Analyse
yourself
..
..
..
Conclusion?
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Summary 2
Analyse
yourself
..
..
..
Conclusion?
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