Comparators

"This book explores circuit designs that accomplish the conversion of an analog signal to a digital signal of a single bit. Starting with the simple comparator, many alternative circuit arrangements and enhancements are elaborated, including hysteresis, negative feedback and a variety of adaptive thresholds. Further, the non-ideal behavior of practical elements and circuits are covered, including input offsets, noise, delay, delay dispersion and oscillation, along with techniques for dealing with these aspects. The wide variety of available components is discussed in terms of performance and applicability. No stone is left unturned in addressing each and every issue that can affect the engineering tasks related to comparators, from the viewpoint of how their performance can affect the system in which they are a critical component. Covers all aspects of the specification, circuit design and functioning of a comparator effectively in one book; Includes new information dealing with non-ideal behaviors, including how to measure and compute their effects, as well as how to accommodate in designs; Discusses wide variety of available components, in terms of performance and applicability."--Cover page 4 Preface 5 About the Author 6 About This Book 7 List of Symbols 8 Contents 10 Chapter 1: Basic Concepts 13 1.1 Introduction 13 1.2 Synonyms 13 1.3 Basic Functions 13 1.3.1 Comparator Versus Operational Amplifier 15 1.3.2 Functional Details 17 1.4 Nonideal Parameters 20 1.4.1 Input Offset Voltage 20 1.4.2 Input Bias Current 20 1.4.3 Input Offset Current 21 1.4.4 Input Noise Voltage 21 1.4.5 Input Noise Current 21 1.4.6 Oscillatory Transitions 21 1.4.7 Propagation Delay 21 1.4.8 Propagation Delay Dispersion 22 References 22 Chapter 2: Major Applications 23 2.1 Major Applications of Comparators 23 2.1.1 Digitizing an Analog Signal 23 2.1.2 Finding the Center of the Eye 23 2.1.3 Timing Signals 24 2.1.4 FM Reception 24 2.1.5 Audio Amplification 24 2.1.6 Instrumentation 25 2.1.7 Time-Based Signal Processing 26 2.1.8 Human Interfaces 27 2.1.9 Software Implementation 27 References 27 Chapter 3: Enhancements 28 3.1 Enhancements 28 3.1.1 Offset Nulling 28 3.1.2 Hysteresis 28 Offset Effect of Hysteresis 30 Comparators with Built-In Hysteresis 31 How Much Hysteresis? 31 3.1.3 Decision-Level Setting: Adaptive Thresholds 31 Average Tracking 31 Peak Mean Tracking 36 3.1.4 Ground Differences 48 3.1.5 Negative Feedback 49 Combining Negative Feedback with Hysteresis 49 3.1.6 Oscillators 52 3.1.7 Switch De-Bouncers 57 3.1.8 Voltage-Controlled Phase Shifter 59 3.1.9 Timer IC 60 3.1.10 Voltage-to-Frequency Converters 63 3.1.11 Multiplexed Comparators 64 References 65 Chapter 4: Nonideal Behavior 66 4.1 Dispersion, AM-to-PM Conversion 66 4.1.1 Comparator Design for Low Dispersion 69 4.1.2 Limiting Amplifiers 70 4.1.3 Dispersion Angle versus Time 70 4.1.4 Dispersion Slopes, Overdrive Versus Slew Rate 71 4.2 Noise Measurement 73 4.2.1 Why Radians Rather Than Seconds? 76 4.2.2 Comparator Noise Measurement Example 77 4.2.3 Jitter Added by Noise 78 4.2.4 Hysteresis Can Increase Jitter 79 4.2.5 Noise Figure-of-Merit 79 4.2.6 Noise Spectra 81 4.2.7 Noise Examples 82 References 84 Chapter 5: Application Details 85 5.1 Op-Amp Enhanced Comparator 85 5.2 Detailed Circuit Example 88 5.3 Detailed System Example 89 5.4 Multiple-Comparator Circuits 92 5.4.1 Window Comparator 92 5.4.2 Voltage-Controlled Oscillator 95 5.4.3 Dot-Bar Display Drivers 96 5.4.4 Flash Analog-to-Digital Converter 99 5.5 Latched Comparators 100 References 101 Chapter 6: Logic Elements 102 6.1 Logic Elements as Comparators 102 6.2 Logic Elements as Oscillators 106 6.3 Logic Elements’ Thresholds and Hysteresis 108 References 109 Chapter 7: Comparator Design and Effects 110 7.1 Bipolar Integrated Comparator Design 110 7.2 MOS-Integrated Comparator Design 110 7.3 Choices of Semiconductor Technology 111 7.4 Hard Limiter Effects on Signal-to-Noise Ratio 112 7.4.1 Benefits for a Phase-Locked Loop 113 7.4.2 Zonal Bandpass Filter 114 7.4.3 FM Capture Ratio 114 References 115 Index 116