wave form generator

1. Unit V
Waveform Generators &
special Function ICs

2. Types of Waveforms
⊳ Sine wave
⊳ Square wave
⊳ Triangular wave
⊳ Sawtooth Wave
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3. Oscillator
⊳ A oscillator is a circuit which basically acts as a
generator.
⊳ It generates an output signal which oscillates
with constant amplitude and constant desired
frequency.
⊳ It does not require any input signal.
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4. Barkhausen Criterion
⊳ Total phase shift around a loop is 0 or 360 ie integral
multiplier of 2π radians
⊳ The magnitude of the product of the open loop gain of
the amplifier and feedback factor is unity.
⊳ For sustained oscillation Aβ = 1
⊳ Magnitude condition is IAβI = 1 phase condition 0 or
360
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5. Based on circuit Components
⊳ RC Oscillators
⊳ LC Oscillators
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7. Phase Shift Oscillator using op-amp
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12. Wein Bridge Oscillator
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13. 13

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19. Multivibrators using Op-Amp
⊳ Multivibrator is an important group of regenerative
circuit used in timing application
o Monostable Multivibrator
o Astable Multivibrator
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20. Monostable Multivibrator
⊳ One shot Multivibrator
⊳ The circuit produces single output pulse of adjustable
time duration in response to trigger signal
⊳ Hence only one stable state exist
⊳ The Width of output pulse depends only one external
components connected to opamp.
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21. Contd…
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22. Contd…
⊳ When External trigger is applied, output changes state.
The new state is quasi-stable state
⊳ Circuit remains in this state for fixed interval of time
and then comes back to original state
⊳ The internal trigger produced by charging and
discharging of capacitor drives the circuit to original
stable state
⊳ Monostable multivibrator is a circuit which produces
single output pulse of adjustable time duration in 22

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28. Contd…
⊳ The monostable multivibrator is also referred as time
delay circuit as it generates fast transition at
predetermined time after application of input trigger.
⊳ It is also called gating circuit, as it generates
rectangular waveform at definite time.
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29. Astable Multivibrator
⊳ It is called as free running oscillator
⊳ Principle of generation of square wave output is to force
opamp to operate in saturation region.
⊳ It has two quasi-stable states. No external no stable
state
⊳ Signal is required to produce the change in state
component values used decide the time for which
circuit remains in each state 29

30. Contd…
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35. 35

36. Triangular Wave generator
⊳ It is obtained by integrating a square wave
⊳ Frequency of triangular and square wave is same but the
amplitude of triangular wave decreases as frequency increases.
This is due to reactance of capacitance C2 decreases at high
frequency.
⊳ R4 is connected to avoid saturation problem at low frequency
⊳ Triangular wave generator with less number of components is 2
level comparator and Integrator
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37. 37

38. Contd…
⊳ Output of A1 is +Vsat then output A2 is negative going
Ramp.
⊳ At t = t1, when negative going ramp = -Vramp
⊳ Votage at P< o V. Switches occurs from +Vsat to –Vsat
⊳ When output is – Vsat
Output of A2 increases in positive direction. At t = t2
value of voltage at P> 0V. Output switches from –Vsat to
+Vsat. This cycle repeats and generates triangular 38

39. 39

40. Contd…
⊳ Frequency of triangular wave is effective voltage at
point ‘P’ during the time when output of A1 is at +Vsat
level is given by
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43. 43

44. Sawtooth Waveform Generator
⊳ The difference between the triangular waveform and
sawtooth waveform is that the rise time of a triangular
wave is always equal to its fall time.
⊳ In triangular wave generator, the same amount of time
is taken by the triangular wave to swing from –Vramp to
+Vramp as from +Vramp to –Vramp.
⊳ Sawtooth waveform has unequal rise and fall times.
⊳ It may rise many times faster than it falls negatively or
vice versa. 44

45. Contd..
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46. Contd…
⊳ The triangular wave generator can be converted into a
sawtooth wave generator by applying a variable dc
voltage into the non inverting terminal of the integrator
A2.
⊳ Using potentiometer and connecting it to the +Vcc and
+VEE
⊳ Depending on the R4 setting a certain DC level is
inserted in the output of A2
⊳ Suppose that the output of A1 is a square wave and the 46

47. 47

48. Contd…
⊳ The output of A2 will be triangular wave, rising on some
dc level that is a function of the R4 setting.
⊳ The duty cycle of the square wave will be determined by
the polarity and amplitude of this dc level.
⊳ A duty cycle less than 50% will then cause the output of
A2 to be a sawtooth.
⊳ With the wiper at the center of R4 , the output of A2 is a
triangular wave.
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49. Contd…
⊳ For any other position of R4 wiper, the output is a
sawtooth waveform.
⊳ Specifically as the R4 wiper is moved toward –VEE , the
rise time of the sawtooth wave becomes longer than the
fall time.
⊳ On the other hand, as wiper is moved towards +VCC, the
fall time becomes longer than the rise time. Also, the
frequency of the sawtooth decreases as R4 is adjusted
towards +VCC or -VEE 49