analog circuits and systems...function generator and vco (contd.,) vco is an important building...
TRANSCRIPT
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Analog Circuits and Systems Prof. K Radhakrishna Rao
Lecture 35: Non-Sinusoidal Oscillators
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Review
� Regenerative Comparator Schmitt Trigger � Pulse Width Modulation � Duty Cycle Generator � Inverting and Non-inverting Schmitt Trigger � Hysteresis � FM and FSK Generation
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Astable multi-vibrator/Function Generator
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( ) ( )( )Given
T 2RCs sV 1 1 e 2 V
1 1T 2RCln ;f1 T
−+ β − = β
+ β= =− β
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Simulation 1
� R1=R2=R=1k�; C=1�F;T=2RCln3=2.2msec; f=454Hz
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Simulation 2
� Single Supply based Astable Multivibrator � R1=R2=R=1k�; C=1�F;T=2RCln3=2.2msec; f=454Hz
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On-Off Temperature Controller
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Monostable multivibrator
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( )
( )
LM 555 Timer; Cost = $0.48
T2RC
r s s r
r s
V V 1 e V V
1 V VT RCln
1
−⎛ ⎞⎜ ⎟⎝ ⎠
⎛ ⎞⎜ ⎟+ − = β +⎜ ⎟⎝ ⎠
+=
− β
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Simulation- Timer Circuit
� R1=R2=R=1k�; C=1�F;T=0.693msec; f=100Hz; Square Wave; 7V
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Function Generator
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Waveforms
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s 1s
2
1
2
2
1
V 2RT VRC 2 R
RT 4RCRR1f
T 4RCR
=
=
= =
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Simulation
� R=R1=1k �; R2=2.2k�; C=1�F; T=1.82msec; f0=550Hz
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Saw-tooth Waveform Generator
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Saw-tooth Waveform Generator (contd.,)
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s a 11 s
2
s11
2 s a
s12
2 s a
1 2
2s1
2 22 s a
V V 2RT VRC R
VRT 2RCR V V
VRT 2RCR V V
T T T
VR4RCR V V
−⎛ ⎞ =⎜ ⎟⎝ ⎠
=−
=+
= +
⎛ ⎞= ⎜ ⎟−⎝ ⎠
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Simulation- Function generator with asymmetry
� R=R1=1k �; R2=2.2k�; C=1�F; Va=5V
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Simulation- Function generator with asymmetry (contd.,)
� R=R1=1k �; R2=2.2k�; C=1�F; Va=-5V
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Function generator with offset
� R=R1=1k �; R2=2.2k�; C=1�F; Voff=1V
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Function Generator and VCO
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Sensitivity of the VCO:
c 2
1
2vco
c 1 c
V Rf40RC R
Rf fK Hz / VV 40RCR V
=
∂= = =∂
• FM (Frequency Modulation) generator • FSK (Frequency Shift Keying) generators
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Function Generator and VCO (contd.,)
� VCO is an important building block in a Phase Locked Loop. � A function generator is an oscillator which produces square wave,
triangular wave, rectangular wave with specific duty cycle and saw tooth.
� It can also output sine wave by converting the triangular wave to sine wave using diode function generator.
� It is the VCO circuit that was discussed earlier XR2206, function generator IC manufactured by EXAR that is popularly used in all test oscillators in laboratories today.
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Simulation – FSK Generation
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Simulation –FM Generation
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XR2206 – Features
� Low-Sine Wave Distortion, 0.5%, Typical � Excellent Temperature Stability, 20ppm/°C, Typ. � Wide Sweep Range, 2000:1, Typical � Low-Supply Sensitivity, 0.01%V, Typ. � Linear Amplitude Modulation � TTL Compatible FSK Controls � Wide Supply Range, 10V to 26V � Adjustable Duty Cycle, 1% to 99%
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XR2206 – Datasheet
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Min. Typ. Max. Units
Max. Operating Frequency
Lowest Practical Frequency
Frequency Accuracy
Temperature Stability
Frequency Sine Wave
Amplitude Stability2 Supply
Sensitivity Sweep Range
0.5
1000:1
1
0.01
+1
+10
4800
0.01
2000:1
+4
+50
0.1
MHz
Hz
%
ppm/
�C
ppm/
�C
%/V
fH=fL
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LM 566 - Features
� Wide supply voltage range: 10V to 24V � Very linear modulation characteristics � High temperature stability � Excellent supply voltage rejection � 10 to 1 frequency range with fixed capacitor � Frequency programmable by means of current, voltage, resistor or
capacitor
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LM566- Data Sheet
Min. Typical Max. Units Maximum Operating Frequency 0.5 1 MHz VCO Free running Frequency -30 0 30 % VCO Sensitivity 6.0 6.6 7.2 kHz/V
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Conclusion
� Limitations due to comparator characteristics ◦ Rise time ◦ Fall time
� Limitations due to opamp characteristics ◦ Maximum frequency of oscillation
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Conclusion
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