Unit v waveform generators

wave form generator

1. Unit V Waveform Generators & special Function ICs

2. Types of Waveforms Sine wave Square wave Triangular wave Sawtooth Wave 2

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. 3

4. Barkhausen Criterion Total phase shift around a loop is 0 or 360 ie integral multiplier of 2 π radians The magnitude of the product of the open loop gain of the amplifier and feedback factor is unity. For sustained oscillation A β = 1 Magnitude condition is IA β I = 1 phase condition 0 or 360 4

5. Based on circuit Components RC Oscillators LC Oscillators 5

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7. Phase Shift Oscillator using op-amp 7

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12. Wein Bridge Oscillator 12

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19. Multivibrators using Op-Amp Multivibrator is an important group of regenerative circuit used in timing application Monostable Multivibrator Astable Multivibrator 19

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 . 20

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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 response to a triggering signal 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. 28

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

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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 C 2 decreases at high frequency . R 4 is connected to avoid saturation problem at low frequency Triangular wave generator with less number of components is 2 level comparator and Integrator 36

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38. Contd … Output of A 1 is + V sat then output A 2 is negative going Ramp. At t = t 1 , when negative going ramp = - V ramp Votage at P< o V. Switches occurs from + V sat to – V sat When output is – V sat Output of A 2 increases in positive direction. At t = t 2 value of voltage at P> 0V. Output switches from – V sat to + V sat . This cycle repeats and generates triangular waveform. 38

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40. Contd … Frequency of triangular wave is effective voltage at point ‘P’ during the time when output of A 1 is at + V sat level is given by 40

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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 – V ramp to + V ramp as from + V ramp to – V ramp . Sawtooth waveform has unequal rise and fall times. It may rise many times faster than it falls negatively or vice versa. 44

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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 A 2 . Using potentiometer and connecting it to the + V cc and +V EE Depending on the R 4 setting a certain DC level is inserted in the output of A 2 Suppose that the output of A 1 is a square wave and the potentiometer R is adjusted for a certain dc level. 46

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48. Contd … The output of A 2 will be triangular wave, rising on some dc level that is a function of the R 4 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 A 2 to be a sawtooth. With the wiper at the center of R 4 , the output of A 2 is a triangular wave. 48

49. Contd … For any other position of R 4 wiper, the output is a sawtooth waveform. Specifically as the R 4 wiper is moved toward –V EE , the rise time of the sawtooth wave becomes longer than the fall time. On the other hand, as wiper is moved towards +V CC , the fall time becomes longer than the rise time. Also, the frequency of the sawtooth decreases as R 4 is adjusted towards +V CC or -V EE The amplitude of the sawtooth wave is independent of the R 4 setting. 49