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Wave Generation and Shaping
Chapter 12 Wave Generation and Shaping Voltage Comparators Hysteresis and Schmitt Triggers Oscillators The Barkhausen Criterion The RC Phase-Shift Oscillator The Wien-Bridge Oscillator The Colpitts Oscillator The Hartley Oscillator The 8038 Integrated-Circuit Function Generator Clipping and Rectifying Circuits Clamping Circuits
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Wave Generation and Shaping
Chapter 12 Wave Generation and Shaping Voltage Comparators Hysteresis and Schmitt Triggers Oscillators The Barkhausen Criterion The RC Phase-Shift Oscillator The Wien-Bridge Oscillator The Colpitts Oscillator The Hartley Oscillator The 8038 Integrated-Circuit Function Generator Clipping and Rectifying Circuits Clamping Circuits
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FIGURE 12-1 The operational amplifier used as a voltage comparator
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE The comparator output switches to + Vmax when v+ - v- > 0 V, which corresponds to the time points where v+ rises through +6 V. The output remains high as long as v+ - v- > 0, or v+ > 6 V. Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-3 Operation of the voltage comparator as a zero-crossing detector
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-5 Response time and rise time of a voltage comparator
Lacking of switching speed due to slew rate makes op-amp voltage comparators unsuitable in applications requiring precision and high speed. Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-6 A voltage comparator with hysteresis (Schmitt trigger)
Hysteresis is a desirable characteristic because it prevents the comparator from switching back and forth in response to random noise fluctuations in the input Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Repeat (1) if VREF = 0V and the output switches between 0V and +6V.
Example 12-1 Find the upper and lower trigger levels and the hysteresis of the Schmitt trigger. Sketch the hysteresis loop. The output switches between ±15V. Repeat (1) if VREF = 0V. Repeat (1) if VREF = 0V and the output switches between 0V and +6V. FIGURE (Example 12-1) Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE (Example 12-1) Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-9 The noninverting Schmitt trigger
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-10 A possible final design for Example 12-2
Design a voltage-level detector with noise immunity that indicates when an input signal crosses the nominal threshold of -2.5V. The output is to switch from high to low when the signal crosses the threshold in the positive direction, and vice versa. Noise level expected is 0.2 V p-p, maximum. Assume the output levels are VH = 10 V and VL = 0V. FIGURE A possible final design for Example 12-2 Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Wave Generation and Shaping
Chapter 12 Wave Generation and Shaping Voltage Comparators Hysteresis and Schmitt Triggers Oscillators The Barkhausen Criterion The RC Phase-Shift Oscillator The Wien-Bridge Oscillator The Colpitts Oscillator The Hartley Oscillator The 8038 Integrated-Circuit Function Generator Clipping and Rectifying Circuits Clamping Circuits
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FIGURE 12-18 Block diagram on an oscillator
In order for the system shown below to oscillate, the loop gain Aβ must satisfy the Barkhausen criterion, namely A β = 1 Note: unity gain means not only a gain magnitude of 1 but also an in-phase signal reinforcement. FIGURE Block diagram on an oscillator Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Example 12-5 The gain of a certain amplifier as a function of frequency is A(jω) = -16 x 106/j ω. A feedback path connected around it has β(jω) = 103/(2 x j ω)2. Will the system oscillate? If so, at what frequency?
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FIGURE 12-19 An RC phase-shift oscillator
op-amp is used as an inverting amplifier and provides 180° phase shift. RC network is used in the feedback to provide additional 180° phase shift FIGURE An RC phase-shift oscillator Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Feedback Ratio Determination
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Design an RC phase-shift oscillator that will oscillate at 100 Hz.
Example 12-6 Design an RC phase-shift oscillator that will oscillate at 100 Hz. FIGURE (Example 12-6) Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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The Wien-Bridge Oscillator FIGURE 12-21 The Wien-bridge oscillator
The Wien-Bridge Oscillator FIGURE The Wien-bridge oscillator. Z1 and Z2 determine the feedback ratio to the noninverting input. Rf and Rg control the magnitude of the loop gain Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-22 The Wien-bridge oscillator showing the RC networks that form Z1 and Z2
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Example 12-7 Design a Wien-bridge oscillator that oscillates at 25 kHz.
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FIGURE 12-23 The Colpitts oscillator
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e FIGURE The Colpitts oscillator Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Example 12-8 Design a Colpitts oscillator that will oscillate at 100 KHz. Solution Let us choose R1 = Rf = 5 kΩ and C = µF. From equation L = 2 / [(2π)2fo2C] = 5(mH) Check on Q (2 to 10 is OK)
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FIGURE 12-24 The Hartley oscillator
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-25 The 8038 function generator
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Wave Generation and Shaping
Chapter 12 Wave Generation and Shaping Voltage Comparators Hysteresis and Schmitt Triggers Oscillators The Barkhausen Criterion The RC Phase-Shift Oscillator The Wien-Bridge Oscillator The Colpitts Oscillator The Hartley Oscillator The 8038 Integrated-Circuit Function Generator Clipping and Rectifying Circuits Clamping Circuits
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FIGURE 12-26 Waveforms and transfer characteristics of clipping circuits
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-27 Another form of clipping. Compare with Figure 12-26.
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE Examples of biased diodes and the signal voltages vi required to forward bias them. (Ideal diodes are assumed.) In each case, we solve for the value of vi that is necessary to make VD > 0 Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-29 Examples of parallel clipping circuits
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-30 An operational-amplifier limiting circuit
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-31 Operational-amplifier limiting circuits using zener diodes
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-32 Double-ended clipping, or limiting
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-33 A double-ended limiting circuit using zener diodes
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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A rectifier is a device that allows current to pass through it in one direction only.
FIGURE A precision rectifier. When vi is positive, the diode is forward biased, and the amplifier behaves like a voltage follower, maintaining v+ ≈ v- = vL Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE A precision rectifier circuit that amplifies and inverts the negative variations in the input voltage Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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Wave Generation and Shaping
Chapter 12 Wave Generation and Shaping Voltage Comparators Hysteresis and Schmitt Triggers Oscillators The Barkhausen Criterion The RC Phase-Shift Oscillator The Wien-Bridge Oscillator The Colpitts Oscillator The Hartley Oscillator The 8038 Integrated-Circuit Function Generator Clipping and Rectifying Circuits Clamping Circuits
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FIGURE A clamping circuit that shifts a waveform up by an amount equal to the negative peak value Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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FIGURE 12-37 A clamping circuit consisting of a diode and a capacitor
Bogart/Beasley/Rico Electronic Devices and Circuits, 6e Copyright ©2004 by Pearson Education, Inc. Upper Saddle River, New Jersey All rights reserved.
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