PPT: Oscillator | Analog and Digital Electronics - Electrical Engineering (EE) PDF Download

 Page 1


CHAPTER 2:
OSCILLATOR 
Page 2


CHAPTER 2:
OSCILLATOR 
INTRODUCTION
?
convert dc energy to ac energy at a very high frequency.  
?
If the feedback signal is large enough and has correct phase, 
there will be an output signal even though there is no external 
input signal.
?
The criterion is that the signal fed back to the input of the 
amplifier must be in phase. In-phase feedback is also called 
positive feedback, or regenerative feedback.
?
It is an unstable amplifier.
Page 3


CHAPTER 2:
OSCILLATOR 
INTRODUCTION
?
convert dc energy to ac energy at a very high frequency.  
?
If the feedback signal is large enough and has correct phase, 
there will be an output signal even though there is no external 
input signal.
?
The criterion is that the signal fed back to the input of the 
amplifier must be in phase. In-phase feedback is also called 
positive feedback, or regenerative feedback.
?
It is an unstable amplifier.
?
 Electronic oscillators are divided into:
?
 Sinusoidal (or harmonic) oscillators-which produce 
an output having sine waveform
?
Non-sinusoidal (or relaxation) oscillator-the output is 
square, rectangular or saw-tooth or pulse shape.
?
Oscillators are widely applied in many digital devices, 
Signal generator, Touch-tone telephone, musical 
instrument and radio/television transmitter and etc.
Page 4


CHAPTER 2:
OSCILLATOR 
INTRODUCTION
?
convert dc energy to ac energy at a very high frequency.  
?
If the feedback signal is large enough and has correct phase, 
there will be an output signal even though there is no external 
input signal.
?
The criterion is that the signal fed back to the input of the 
amplifier must be in phase. In-phase feedback is also called 
positive feedback, or regenerative feedback.
?
It is an unstable amplifier.
?
 Electronic oscillators are divided into:
?
 Sinusoidal (or harmonic) oscillators-which produce 
an output having sine waveform
?
Non-sinusoidal (or relaxation) oscillator-the output is 
square, rectangular or saw-tooth or pulse shape.
?
Oscillators are widely applied in many digital devices, 
Signal generator, Touch-tone telephone, musical 
instrument and radio/television transmitter and etc.
BLOCK DIAGRAM
Closed loop transfer function with positive feedback:
If,   ßA= 1 + j0 or   ßA = 1?0
o
Page 5


CHAPTER 2:
OSCILLATOR 
INTRODUCTION
?
convert dc energy to ac energy at a very high frequency.  
?
If the feedback signal is large enough and has correct phase, 
there will be an output signal even though there is no external 
input signal.
?
The criterion is that the signal fed back to the input of the 
amplifier must be in phase. In-phase feedback is also called 
positive feedback, or regenerative feedback.
?
It is an unstable amplifier.
?
 Electronic oscillators are divided into:
?
 Sinusoidal (or harmonic) oscillators-which produce 
an output having sine waveform
?
Non-sinusoidal (or relaxation) oscillator-the output is 
square, rectangular or saw-tooth or pulse shape.
?
Oscillators are widely applied in many digital devices, 
Signal generator, Touch-tone telephone, musical 
instrument and radio/television transmitter and etc.
BLOCK DIAGRAM
Closed loop transfer function with positive feedback:
If,   ßA= 1 + j0 or   ßA = 1?0
o
?
Barkhausen  criterion :
?
The feedback factor or loop gain . The gain is 
infinite, this represent the condition for oscillation.
?
The net phase shift around the loop 0° (or an 
integral multiple of 360° ). In other word, feedback 
should be positive.
?
The amplifier gain must be greater than the loss in 
the feedback path.