Fundamentals of Oscillators

1. OSCILLATORS
Presented By,
Nagaveni G H

2. OSCILLATORS:
An Oscillator is an electronic circuit which
converts DC voltage to AC voltage of required
frequency.
It generates a periodic waveform on its output
without a external signal source.
The waveform can be sine wave, square wave,
triangular wave and saw tooth wave.

3. DIFFERENCE BETWEENAMPLIFIER AND
OSCILLATOR:

4. FEED BACK
The process of taking a part of the output
signal and feeding it back into the input
circuit or input signal.
Types of Feedback
Positive Feedback Negative Feedback
Feedback voltage is in phase
with the input signal
Feedback voltage is out of phase
with the input signal

5. TYPES OF NEGATIVE FEEDBACK
Voltage series Feedback
Input Impedance is increased
Voltage shunt Feedback
Input impedance is decreased.
Current series feedback
Both the input and output of the
amplifier is increased.
Current shunt Feedback
Output resistance of the amplifier is
increased while the input resistance
is decreased.

6. Types of Oscillators
Linear or Harmonic
Oscillators
Feedback Oscillator
Negative resistance
Oscillator
Non linear or
Relaxation Oscillators
RC Oscillator
LC Oscillator
Crystal
Oscillator
Wein Bridge Oscillator
Phase shift Oscillator
Colpitts Oscillator
Hartley Oscillator
Clapp Oscillator

7. BARKHAUSEN CRITERIA FOR OSCILLATION
For positive feedback, 𝑽𝒊𝒏 = 𝑽𝒊𝒏 + 𝜷𝑽 𝒐𝒖𝒕
∴ 𝑽𝒊𝒏 + 𝜷𝑽 𝒐𝒖𝒕 𝑨 = 𝑽 𝒐𝒖𝒕
∴ 𝑽𝒊𝒏 =
𝑽 𝒐𝒖𝒕 𝟏 − 𝜷𝑨
𝑨
• Where A is called Open loop gain and A β is called feedback factor or
loop gain.
• If βA = 1 and 𝑽𝒊𝒏 = 0, then amplifier acts as an oscillator

8. Two conditions for maintaining the
oscillations in the oscillatory circuit are-
The feedback must be positive and feedback
factor Aβ = 1.
The total phase shift around the loop is
integral multiple of 2π or 0˚.

9. IC – 741 PIN
CONFIGURATION

10. PHASE SHIFT OSCILLATOR

11. The RC network produces a Phase shift of 180˚
between its input and output voltages.
An additional Phase shift of 180˚ is produced by
Transistor.
Hence the total phase shift produced
by Phase shift oscillator is 0˚or 360˚.

12. The frequency of oscillation is given by
If 𝑹 𝟏 = 𝑹 𝟐 = 𝑹 𝟑 = 𝑹 and 𝑪 𝟏 = 𝑪 𝟐 = 𝑪 𝟑 = 𝑪
𝒇 =
𝟏
𝟐𝝅𝑪 𝟒𝑹𝑹 𝒄 + 𝟔𝑹 𝟐

13. ADVANTAGES OF PHASE SHIFT OSCILLATOR:
This circuit is very simple and cheap as it
comprises of resistors and capacitors (not bulky
and expensive high value inductors.
It provides good frequency stability.
The output of this circuit is sinusoidal that is quite
distortion free.
The phase shift oscillator is simpler than wein
bridge oscillator circuit because it does not need
negative feedback and stabilization arrangements.
They have wide range of frequency (from few Hz
to several hundreds of kHz)
They are particularly apt for low frequencies, say
of the order of 1 Hz, so these frequencies can be
easily gained by using R and C of large values.

14. DISADVANTAGES OF PHASE SHIFT
OSCILLATOR:
The output is small and it is due to smaller
feedback.
The frequency stability is not as good as
that of the wein bridge oscillator.
It is difficult for the circuit to start
oscillations as the feedback is usually small.
It needs high voltage battery (12 V) so as
to develop a sufficiently large feedback
voltage.

15. APPLICATIONS OF PHASE
SHIFT OSCILLATOR:
FET phase shift oscillators is used for
generating signals over a wide range
of frequencies.
RC phase shift oscillators are used in
musical instruments, voice synthesis
and in GPS units since they work at
all audio frequencies.

16. WEIN BRIDGE OSCILLATOR

17. • It employs two transistors, each producing
the phase shift of 180˚.
Hence the total phase shift produced
by Phase shift oscillator is 0˚or 360˚.

18. The frequency of oscillation is given by
If 𝑹 𝟏 = 𝑹 𝟐 = 𝑹 and 𝑪 𝟏 = 𝑪 𝟐 = 𝑪
𝒇 =
𝟏
𝟐𝝅 𝑹 𝟏 𝑪 𝟏 𝑹 𝟐 𝑪 𝟐
𝒇 =
𝟏
𝟐𝝅 𝑹𝑪

21. MULTIVIBRATORS
Multivibrators are sequential logic circuits that
operate continuously between two distinct states
of HIGH and LOW.
Clock pulses are generally continuous square or
Rectangular shaped waveform that is produced by a
single pulse generator circuit such as a Multivibrator.

22. TYPES OF MULTIVIBRATORS:
• Free-running multivibrator that has NO
stable states but switches continuously
between two states
• This action produces a train of square wave
pulses at a fixed frequency.
Astable
multivibrators
• One-shot multivibrator that has only ONE
stable state and is triggered externally with it
returning back to its first stable state.
Monostable
multivibrators
• A flip-flop that has TWO stable states that
produces a single pulse either positive or
negative in value.
Bistable
multivibrators

23. INPUT AND OUTPUT WAVEFORMS OF
DIFFERENT TYPES OF MULTIVIBRATORS:

24. ASTABLE
MULTIVIBRATOR
USING IC-555

25. IC 555 PIN CONFIGURATION

26. ASTABLE MULTIVIBRATOR

27. OUTPUT WAVEFORM:

28. Astable multivibrators period time,
Frequency of Oscillation,

29. ADVANTAGES OF ASTABLE
MULTIVIBRATOR:

30. DISADVANTAGES OF
ASTABLE MULTIVIBRATOR:

31. APPLICATIONS OF ASTABLE
MULTIVIBRATOR: