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Op Amps For Everyone Design Guide.pdf
Foreword
Contents
Figures
Tables
Examples
Ch 1-The Op Amp’s Place In The World
Ch 2-Review of Circuit Theory
Ch 3-Development of the Ideal Op Amp Equations
Ch 4-Single-Supply Op Amp Design Techniques
Ch 5-Feedback and Stability Theory
Ch 6-Development of the Non Ideal Op Amp Equations
Ch 7-Voltage-Feedback Op Amp Compensation
Ch 8-Current-Feedback Op Amp Analysis
Ch 9-Voltage- and Current-Feedback Op Amp Comparison
Ch 10-Op Amp Noise Theory and Applications
Ch 11-Understanding Op Amp Parameters
Ch 12-Instrumentation: Sensors to A/D Converters
Ch 13-Wireless Communication: Signal Conditioning for IF Sampling
Ch 14-Interfacing D/A Converters to Loads
Ch 15-Sine Wave Oscillators
Ch 16-Active Filter Design Techniques
Ch 17-Circuit Board Layout Techniques
Ch 18-Designing Low-Voltage Op Amp Circuits
App A-Single-Supply Circuit Collection
App B-Single-Supply Op Amp Selection Guide
Index
Op Amps For Everyone
Ron Mancini, Editor in Chief
Design
Reference
August 2002
Advanced Analog Products
SLOD006B
IMPORTANT NOTICE
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Forward
Everyone interested in analog electronics should find some value in this book, and an ef-
fort has been made to make the material understandable to the relative novice while not
too boring for the practicing engineer. Special effort has been taken to ensure that each
chapter can stand alone for the reader with the proper background. Of course, this causes
redundancy that some people might find boring, but it’s worth the price to enable the satis-
faction of a diversified audience.
Start at Chapter 1 if you are a novice, and read through until completion of Chapter 9. After
Chapter 9 is completed, the reader can jump to any chapter and be confident that they
are prepared for the material. More experienced people such as electronic technicians,
digital engineers, and non-electronic engineers can start at Chapter 3 and read through
Chapter 9. Senior electronic technicians, electronic engineers, and fledgling analog engi-
neers can start anywhere they feel comfortable and read through Chapter 9. Experienced
analog engineers should jump to the subject that interests them. Analog gurus should
send their additions, corrections, and complaints to me, and if they see something that
looks familiar, they should feel complimented that others appreciate their contributions.
Chapter 1 is a history and story chapter. It is not required reading for anyone, but it defines
the op amp’s place in the world of analog electronics. Chapter 2 reviews some basic phys-
ics and develops the fundamental circuit equations that are used throughout the book.
Similar equations have been developed in other books, but the presentation here empha-
sizes material required for speedy op amp design. The ideal op amp equations are devel-
oped in Chapter 3, and this chapter enables the reader to rapidly compute op amp transfer
equations including ac response. The emphasis on single power supply systems forces
the designer to bias circuits when the inputs are referenced to ground, and Chapter 4
gives a detailed procedure that quickly yields a working solution every time.
Op amps can’t exist without feedback, and feedback has inherent stability problems,
so feedback and stability are covered in Chapter 5. Chapters 6 and 7 develop the voltage
feedback op amp equations, and they teach the concept of relative stability and com-
pensation of potentially unstable op amps. Chapter 8 develops the current feedback op
amp equations and discusses current feedback stability. Chapter 9 compares current
feedback and voltage feedback op amps. The meat of this book is Chapters 12, 13, and
14 where the reader is shown how design the converter to transducer/actuator interface
with the aid of op amps.
The remaining chapters give support material for Chapters 12, 13, and 14. Chapter 18
was a late addition. Portable applications are expanding rapidly and they emphasize the
need for low-voltage/low-power design techniques. Chapter 18 defines some parameters
in a new way so they lend themselves to low voltage design, and it takes the reader
through several low voltage designs.
i
Thanks to editor James Karki for his contribution. We never gave him enough time to do
detailed editing, so if you find errors or typos, direct them to my attention. Thanks to Ted
Thomas, a marketing manager with courage enough to support a book, and big thanks
for Alun Roberts who paid for this effort. Thomas Kugelstadt, applications manager,
thanks for your support and help.
Also many thanks to the contributing authors, James Karki, Richard Palmer, Thomas Ku-
gelstadt, Perry Miller, Bruce Carter, and Richard Cesari who gave generously of their time.
Regards,
Ron Mancini
Chief Editor
ii
Contents
Contents
1
The Op Amp’s Place In The World
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1-1
2 Review of Circuit Theory
Introduction
Laws of Physics
Voltage Divider Rule
Current Divider Rule
Thevenin’s Theorem
Superposition
Calculation of a Saturated Transistor Circuit
Transistor Amplifier
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2-1
2-1
2-1
2-3
2-4
2-5
2-8
2-9
2-10
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
3 Development of the Ideal Op Amp Equations
Ideal Op Amp Assumptions
The Noninverting Op Amp
The Inverting Op Amp
The Adder
The Differential Amplifier
Complex Feedback Networks
Video Amplifiers
Capacitors
Summary
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3-1
3-1
3-3
3-4
3-5
3-6
3-7
3-9
3-9
3-11
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4.1
4.2
4.3
4.4
4 Single Supply Op Amp Design Techniques
Single Supply versus Dual Supply
Circuit Analysis
Simultaneous Equations
4.3.1 Case 1: VOUT = +mVIN+b
4.3.2 Case 2: VOUT = +mVIN – b
4.3.3 Case 3: VOUT = –mVIN + b
4.3.4 Case 4: VOUT = –mVIN – b
Summary
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4-1
4-1
4-3
4-8
4-9
4-13
4-16
4-19
4-22
5
Feedback and Stability Theory
5.1 Why Study Feedback Theory?
5.2
5.3
Block Diagram Math and Manipulations
Feedback Equation and Stability
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5-1
5-1
5-1
5-6
iii
Contents
5.4
5.5
5.6
5.7
Bode Analysis of Feedback Circuits
Loop Gain Plots are the Key to Understanding Stability
The Second Order Equation and Ringing/Overshoot Predictions
References
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5-7
5-12
5-15
5-16
6 Development of the Non Ideal Op Amp Equations
Introduction
Review of the Canonical Equations
Noninverting Op Amps
Inverting Op Amps
Differential Op Amps
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6-1
6-1
6-2
6-5
6-6
6-8
6.1
6.2
6.3
6.4
6.5
7 Voltage-Feedback Op Amp Compensation
Introduction
Internal Compensation
External Compensation, Stability, and Performance
Dominant-Pole Compensation
Gain Compensation
Lead Compensation
Compensated Attenuator Applied to Op Amp
Lead-Lag Compensation
Comparison of Compensation Schemes
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7.1
7.2
7.3
7.4
7.5
7.6
7.7
7.8
7.9
7.10 Conclusions
7-1
7-1
7-2
7-8
7-9
7-12
7-13
7-16
7-18
7-20
7-21
8 Current-Feedback Op Amp Analysis
Introduction
CFA Model
Development of the Stability Equation
The Noninverting CFA
The Inverting CFA
Stability Analysis
Selection of the Feedback Resistor
Stability and Input Capacitance
Stability and Feedback Capacitance
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
8.9
8.10 Compensation of CF and CG
8.11 Summary
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8-1
8-1
8-1
8-2
8-3
8-5
8-7
8-9
8-11
8-12
8-13
8-14
9 Voltage- and Current-Feedback Op Amp Comparison
Introduction
Precision
Bandwidth
Stability
Impedance
Equation Comparison
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9-1
9-1
9-2
9-3
9-6
9-7
9-8
9.1
9.2
9.3
9.4
9.5
9.6
iv
Contents
10.3 Types of Noise
10.4 Noise Colors
10.4.1 White Noise
10.4.2 Pink Noise
10.4.3 Red/Brown Noise
10.5 Op Amp Noise
10 Op Amp Noise Theory and Applications
10.1 Introduction
10.2 Characterization
10.3.1 Shot Noise
10.3.2 Thermal Noise
10.3.3 Flicker Noise
10.3.4 Burst Noise
10.3.5 Avalanche Noise
10.2.1 rms versus P-P Noise
10.2.2 Noise Floor
10.2.3 Signal-to-Noise Ratio
10.2.4 Multiple Noise Sources
10.2.5 Noise Units
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10-1
10-1
10-1
10-1
10-3
10-3
10-3
10-4
10-4
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10-10
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10-11
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10-12
10-12
10-13
10-14
10-16
10-17
10-18
10-18
10-19
10-23
10.5.1 The Noise Corner Frequency and Total Noise
10.5.2 The Corner Frequency
10.5.3 Op Amp Circuit Noise Model
10.5.4 Inverting Op Amp Circuit Noise
10.5.5 Noninverting Op Amp Circuit Noise
10.5.6 Differential Op Amp Circuit Noise
10.5.7 Summary
10.6 Putting It All Together
10.7 References
11 Understanding Op Amp Parameters
Introduction
11.1
11.2 Operational Amplifier Parameter Glossary
11.3 Additional Parameter Information
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11.3.1 Input Offset Voltage
11.3.2 Input Current
11.3.3 Input Common Mode Voltage Range
11.3.4 Differential Input Voltage Range
11.3.5 Maximum Output Voltage Swing
11.3.6 Large Signal Differential Voltage Amplification
11.3.7 Input Parasitic Elements
11.3.8 Output Impedance
11.3.9 Common-Mode Rejection Ratio
11.3.10 Supply Voltage Rejection Ratio
11.3.11 Supply Current
11-1
11-1
11-2
11-8
11-8
11-10
11-11
11-11
11-12
11-13
11-13
11-14
11-15
11-15
11-16
Contents
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Contents
11.3.12 Slew Rate at Unity Gain
11.3.13 Equivalent Input Noise
11.3.14 Total Harmonic Distortion Plus Noise
11.3.15 Unity Gain Bandwidth and Phase Margin
11.3.16 Settling Time
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11-16
11-17
11-18
11-19
11-22
12 Instrumentation: Sensors to A/D Converters
12.1 Introduction
12.2 Transducer Types
12.3 Design Procedure
12.4 Review of the System Specifications
12.5 Reference Voltage Characterization
12.6 Transducer Characterization
12.7 ADC Characterization
12.8 Op Amp Selection
12.9 Amplifier Circuit Design
12.10 Test
12.11 Summary
12.12 References
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12-1
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12-11
12-12
12-12
12-13
12-15
12-15
12-16
12-23
12-23
12-23
13 Wireless Communication: Signal Conditioning for IF Sampling
13.1 Introduction
13.2 Wireless Systems
13.3 Selection of ADCs/DACs
13.4 Factors Influencing the Choice of Op Amps
13.5 Anti-Aliasing Filters
13.6 Communication D/A Converter Reconstruction Filter
13.7 External Vref Circuits for ADCs/DACs
13.8 High-Speed Analog Input Drive Circuits
13.9 References
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14 Interfacing D/A Converters to Loads
14.1 Introduction
14.2 Load Characteristics
14.2.1 DC Loads
14.2.2 AC Loads
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14.3.1 Types of D/A Converters — Understanding the Tradeoffs
14.3.2 The Resistor Ladder D/A Converter
14.3.3 The Weighted Resistor D/A Converter
14.3.4 The R/2R D/A Converter
14.3.5 The Sigma Delta D/A Converter
14.4.1 Accuracy versus Resolution
14.4.2 DC Application Error Budget
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14-1
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14-2
14-2
14-2
14-2
14-3
14-4
14-5
14-6
14-7
14-7
14.3 Understanding the D/A Converter and its Specifications
14.4 D/A Converter Error Budget
vi
