Analog Circuits and Systems...Function Generator and VCO (contd.,) VCO is an important building...
Transcript of Analog Circuits and Systems...Function Generator and VCO (contd.,) VCO is an important building...
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
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
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
=
=
= =
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
−⎛ ⎞ =⎜ ⎟⎝ ⎠
=−
=+
= +
⎛ ⎞= ⎜ ⎟−⎝ ⎠
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
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
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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