.THEORY. APPLICATIONS. CIRCUITS I~!)~ ~cL , FIRST EDITION (Sixth Printing) HANDBOOK OF OPERATIONAL AMPLIFIER APPLICATIONS This handboak has been compi led by the Applications Engineering Section of Burr-Brown Research Corporation . This section wi II welcome the opportunity of offering its technical assistance in the application of operational amplifiers. BURR-BROWN RESEARCH CORPORATION Copyright 1963 P. 0. BOX 11400 Printed in U. $. A. TUCSON. ARI ZONA. 85706 Copyright 1963 by Burr-Brown Research Corporation Circuit diagrams in this handbook are included to illustrate typical operational amplifier applications and are not intended as constructural information. Although reasonable care has been taken in preparing this handbook, no responsibil ity is assumed for inaccuracies or consequences of using information presented. Furthermore, such information does not convey to the purchaser of the amplifiers described any I icense under the patent rights of Burr-Brown Research Corporation or others. ii PREFACE The purpose of this handbook is to provide a single source of information covering the proper design of circuits employing the versatile modern operational amplifier. This manual will be helpful to the experienced user of operational amplifiers, as well as the new user, in extending the range of potential applica- tions in which these devices can be used to advantage. It is assumed that the reader will have a basic knowledge of electronics, but no particular knowlege of operational amplifiers is needed to use this handbook. The operational ampl ifier is treated as a circuit component inherently subject to certain rules of operation. The design of the operational amplifiers themselves is considered only when necessary to describe their less evident properties. Readers with a working knowlege of operational amplifiers will want to refer directly to the circuit collection. Those concerned with evaluation and inspection should refer to the section on testing. Readers whose job functions have not previously brought them in contact with operational amplifiers will want to pro- ceed directly through the handbook until the desired degree of familiarity is obtained. Refinements are continuously being made in the design and application of operational amplifiers, yet the basic principles of application remain the same. Please do not hesitate to contact Burr-Brown at any time with questions or comments arising from the use of this handbook. It is, after all, intended for you, the user. -~ ~ I? L". 9.- -- Thomas R. Brown, Jr., President iii TABLE OF CONTENTS Preface iii SECTION 1- Operational Amplifier Theory Introduction Computat ion-Contro I-I nstrumentat ion The Feedback Technique 1 Notation and Terminology 2 Input Terminals 2 Output Terminals 3 Chopper Stabilized Amplifier Notation 3 Power Connections 3 Summary of Notation 4 Electrical Circuit Models 4 Circuit Notation 5 The Ideal Operational Amplifier 5 Defining the Ideal Operational Amplifier 6 A Summing Point Restraint 6 Circuits and Analyses Using the Ideal Operational Amplifier 6 The Desirability of Feedback 7 Two Important Feedback Circuits 7 Voltage Follower 8 Non-lnverting Ampl ifier 10 Inverting Ampl ifier 12 Intuitive Analysis Techniques 12 Current Output 14 Reactive Elements 14 Integrator 15 Differentiator 15 Voltage Adder 15 Scaling Summer 17 Combining Circuit Functions 17 Differential Input Ampl ifier 17 Balanced Amplifier 19 Ideal-Real Comparison 21 iv ~ ~OV-O8v (v ~~) :XV'd S~te-OSt (t ..~) :eUO1ld v Page Characteristics of Practical Operational Ampl ifiers 23 Open Loop Characteristics 24 Open Loop Transfer Curve 24 Open Loop Operation 24 Output Limiting 25 Frequency Dependent Properties 26 Introduction 26 Open Loop Gain and the Bode Plot 26 Bode Plot Construction 26 Closed Loop Gain 27 Stabil ity 27 Compensation 28 Compensation Changes 29 Bandwidth 31 Loop Gain 32 The Significance of Loop Gain 33 How Much Loop Gain? 33 Bode Plots and Basic Practical Circuitry 33 Voltage Follower 33 Inverter 33 X1OOO Amplifier 33 Differentiator 36 Integrator 38 Other Important Properties of Operational Amplifiers 38 Summing Point Restraints 38 Closed Loop Impedance Levels 39 Output Impedance 40 Input Impedance 40 Increasing Input Impedance 41 Differential Inputs and Common Mode Rejection 42 The Common Mode Voltage Limit 42 Offset 42 Drift 43 Capacitive Loading 43 SECTION II -Circuit Collection 45 Voltoge Detectors and Comparators 45 Buffers and Isolation Amp! ifiers 47 Voltage and Current References 49 50 Integrators Differentiotors 53 DC Amplifiers 54 Differential Ampl ifiers 57 Summing and Averaging Amplifiers 59 AC Amplifiers 61 Current Output Devices 63 Oscillators and Mu!tivibrators 65 Phase Lead and Lag Networks 67 Additional Circuits 69 vi Page SECTION 111- How to Test Operotional Amplifiers 74 Standard Test Circuits 75 Test Procedures 77 SECTION IV- Selecting the Proper Operational Amplifier 80 Focus on Limiting Specifications 80 Avoid Closed Loop vs. Open Loop Confusion 81 Selection Check List 81 Assistance Avai lable from Burr-Brown 82 APPENDIX 83 Specifications 83 Mechanical Data 85 Reactance Chart 87 SECTION I OPERATIONAL AMPLIFIER THEORY I NTRODUCTION The operotional amplifier is an extremely efficient and versatile device. Its applications span the broad electronic industry filling requirements for signal conditioning, special transfer functions, analog instrumentation, analog compu- tation, and special systems design. Circuits utilizing operational amplifiers are characterized by the analog assets of simplicity and precision. Computation -Control -Instrumentation Originally, the term, "Operational Amplifier," was used in the comput- ing field to describe amplifiers that performed various mathematical operations. It was found that the application of negative feedback around a high gain DC amplifier would produce a circuit with a precise gain characteristic that depended only on the feedback used. By the proper selection of feedback components, operational amplifier circuits could be used to add, subtract, average, integrate, and differentiate. As practical operational ampl ifier techniques became more widely known, it was apparent that these feedback techniques could be useful in many control and instrumentation applications. Today, the general use of operational amplifiers has been extended to include such applications as DC Amplifiers, AC Amplifiers, Comparators, Servo Valve Drivers, Deflection Yoke Drivers, Low Distortion Oscillators, AC to DC Converters, Multivibrators, and a host of others. What the operational ampl ifier can do is I imited only by the imagination and ingenuity of the user. With a good working knowledge of their characteristics, the user will be able to exploit more fully the useful properties of operational ampl ifiers. The Feedback Technique The precision and flexibility of the operational amplifier is a direct resul of the use of negative feedback. Generally speaking, amplifiers employing 1 2 RJ Ro feedback will have superiar aperating characteristics at a sacrifice of gain. OEinpuTt- r--v '>-0 ~E With enough feedback, the closed loop output amplifier characteristics become a func- E t t R -=- tion of the feedback element~. In the ou pu O =- R typical feedback circuit, Fig. I, the E input I ' F 1 O . I I.f' feedback elements are two resistors. The Ig. .peratlona amp I ler with feedback. precisian of the "closed loop" gain is set by the ratio of the two resistors and is practically independent of the "open loop" amplifier. Thus, amplification to almost any degree of precision can be achieved wit~ ease. NOTATION AND TERMINOLOGY Various operational amplifier symbols are presently employed in industry. Since there is no real standardization, symbology must be agreed upon before cir- cuits may be discussed. The symbols employed by Burr-Brown Research Corporation (shown in Fig. 2) will be used here. Only input a) b) :c)&: and output terminals ~I A ~ A :4 A 4 are commonly shown. 2 2 5 In Fig. 2, there are d) e) f) either one or two input ? G> and output terminals I A A o~- t"-v '""' depending on the amplifier type. The Fig.2. Burr-Brown standard symbols: a) single ended, b) differential input, c) differential output, d) chopper stabil- number appearing at ized, e) symbol without terminals shown, f) special purpose each terminal is the amplifier. identification used on Burr-Brown's popular encapsulated units and is used here for convenience in specifying the significance of each terminal connection. Input Terminals In Fig. 2a, 2b, 2c, and 2d, pin (1) is the "inverting input" or "summing point," meaning a positive voltage at (I) produces a negative Fig. 3. Encapsulated Modules voltage at (4). When only one input or output