2nd Edition

Designing Audio Power Amplifiers

By Bob Cordell Copyright 2019
    792 Pages
    by Routledge

    792 Pages
    by Routledge

    This comprehensive book on audio power amplifier design will appeal to members of the professional audio engineering community as well as the student and enthusiast. Designing Audio Power Amplifiers begins with power amplifier design basics that a novice can understand and moves all the way through to in-depth design techniques for very sophisticated audiophiles and professional audio power amplifiers. This book is the single best source of knowledge for anyone who wishes to design audio power amplifiers. It also provides a detailed introduction to nearly all aspects of analog circuit design, making it an effective educational text.

    Develop and hone your audio amplifier design skills with in-depth coverage of these and other topics:

    • Basic and advanced audio power amplifier design
    • Low-noise amplifier design
    • Static and dynamic crossover distortion demystified
    • Understanding negative feedback and the controversy surrounding it
    • Advanced NFB compensation techniques, including TPC and TMC
    • Sophisticated DC servo design
    • MOSFET power amplifiers and error correction
    • Audio measurements and instrumentation
    • Overlooked sources of distortion
    • SPICE simulation for audio amplifiers, including a tutorial on LTspice
    • SPICE transistor modeling, including the VDMOS model for power MOSFETs
    • Thermal design and the use of ThermalTrak™ transistors
    • Four chapters on class D amplifiers, including measurement techniques
    • Professional power amplifiers
    • Switch-mode power supplies (SMPS).

     Part 1: Audio Power Amplifier Basics

    1. Introduction

    1.1 Organization of the Book

    1.2 The Role of the Power Amplifier

    1.3 Basic Performance Specifications

    1.4 Additional Performance Specifications

    1.5 Output Voltage and Current

    1.6 Basic Amplifier Topology

    1.7 Summary

    2. Power Amplifier Basics

    2.1 BJT Transistors

    2.2 JFETs

    2.3 Power MOSFETs

    2.4 Basic Amplifier Stages

    2.5 Current Mirrors

    2.6 Current Sources and Voltage References

    2.7 Complementary Feedback Pair (CFP)

    2.8 Vbe Multiplier

    2.9 Operational Amplifiers

    2.10 Amplifier Design Analysis

    3. Power Amplifier Design Evolution

    3.1 About Simulation

    3.2 The Basic Power Amplifier

    3.3 Adding Input Stage Degeneration

    3.4 Adding a Darlington VAS

    3.5 Input Stage Current Mirror Load

    3.6 The Output Triple

    3.7 Cascoded VAS

    3.8 Paralleling Output Transistors

    3.9 Higher Power Amplifiers

    3.10 Crossover Distortion

    3.11 Performance Summary

    3.12 Completing an Amplifier

    3.13 Summary

    4. Building an Amplifier

    4.1 The Basic Design

    4.2 The Front-End: IPS, VAS and Pre-Drivers

    4.3 Output Stage: Drivers and Outputs

    4.4 Heat Sink and Thermal Management

    4.5 Protection Circuits

    4.6 Power Supply

    4.7 Grounding

    4.8 Building the Amplifier

    4.9 Testing the Amplifier

    4.10 Troubleshooting

    4.11 Performance

    4.12 Scaling

    4.13 Upgrades

    5. Noise

    5.1. Signal-to-Noise Ratio

    5.2. A-weighted Noise Specifications

    5.3 Noise Power and Noise Voltage

    5.4 Noise Bandwidth

    5.5 Noise Voltage Density and Spectrum

    5.6 Relating Input Noise Density to Signal-to-Noise Ratio

    5.7 Amplifier Noise Sources

    5.8 Thermal Noise

    5.9 Shot Noise

    5.10 Bipolar Transistor Noise

    5.11 JFET Noise

    5.12. Op Amp Noise

    5.13 Noise Simulation

    5.14 Amplifier Circuit Noise

    5.15 Excess Resistor Noise

    5.16 Zener and LED Noise

    6. Negative Feedback Compensation and Slew Rate

    6.1 How Negative Feedback Works

    6.2 Input-referred Feedback Analysis

    6.3 Feedback Compensation and Stability

    6.4 Feedback Compensation Principles

    6.5 Evaluating Loop Gain

    6.6 Evaluating Stability

    6.7 Compensation Loop Stability

    6.8 Slew Rate

    7. Amplifier Classes, Output Stages and Efficiency

    7.1 Class A, AB and B Operation

    7.2 The Complementary Emitter Follower Output Stage

    7.3 Output Stage Efficiency

    7.4 Complementary Feedback Pair Output Stages

    7.5 Stacked Output Stages

    7.6 Classes G and H

    7.7 Class D

    8. Summary of Amplifier Design Considerations

    8.1 Power and Loads

    8.2 Sizing the Power Supply

    8.3 Sizing the Output Stage

    8.4 Sizing the Heat Sink

    8.5 Protecting the Amplifier and Loudspeaker

    8.6 Power and Ground Distribution

    8.7 Other Considerations

     

    Part 2: Advanced Power Amplifier Design

    9. Input and VAS Circuits

    9.1 Single-Ended IPS-VAS

    9.2 JFET Input Stages

    9.3 Buffered Input Stages

    9.4 CFP Input Stages

    9.5 Complementary IPS and Push-Pull VAS

    9.6 Unipolar Input Stage and Push-Pull VAS

    9.7 Input Common Mode Distortion

    9.8 Early Effect

    9.9 Baker Clamps

    9.10 Current Feedback Amplifiers

    9.11 Example IPS/VAS

    10. DC Servos

    10.1 Origins and Consequences of DC Offset

    10.2 DC Servo Basics

    10.3 The Servo Is in the Signal Path

    10.4 DC Offset Detection and Protection

    10.5 DC Servo Example

    10.6 Eliminating the Input Coupling Capacitor

    10.7 DC Servo Design Issues and Nuances

    11. Advanced Forms of Feedback Compensation

    11.1 Understanding Stability Issues

    11.2 Miller Compensation

    11.3 Miller Input Compensation

    11.4 Two-Pole Compensation

    11.5 Transitional Miller Compensation

    11.6 A Vertical MOSFET TMC Amplifier Example

    11.7 Conclusion

    12. Output Stage Design and Crossover Distortion

    12.1 The Class AB Output Stage

    12.2 Static Crossover Distortion

    12.3 Optimum Bias and Bias Stability

    12.4 Output Stage Driver Circuits

    12.5 Output Transistor Matching Considerations

    12.6 Dynamic Crossover Distortion

    12.7 The Output Emitter Resistors

    12.8 Output Networks

    12.9 Output Stage Frequency Response and Stability

    12.10 Sizing the Output Stage

    12.11 Delivering High Current

    12.12 Driving Paralleled Output Stages

    12.13 Advanced Output Transistors

    13. Output Stages II

    13.1. VAS Output Impedance and Stability

    13.2. Complementary Feedback Pair

    13.3 Output Stages with Gain

    13.4 Bryston Output Stage

    13.5 ThermalTrak™ Output Stage

    13.6 Class A Output Stage

    13.7 Crossover Displacement (Class XD™)

    13.8 Double Cross™ Output Stage

    13.9 Sliding Bias and Non-switching Output Stages

    13.10 LT1166 Output Stage

    13.11 Measuring Output Stage Distortion

    13.12 Setting the Bias

    14. MOSFET Power Amplifiers

    14.1 MOSFET Types and Characteristics

    14.2 MOSFET Advantages and Disadvantages

    14.3 Lateral vs. Vertical Power MOSFETs

    14.4 Parasitic Oscillations

    14.5 Biasing Power MOSFETs

    14.6 Crossover Distortion

    14.7 Driving Power MOSFETs

    14.8 Paralleling and Matching MOSFETs

    14.9 Simulating MOSFET Power Amplifiers

    14.10 A Lateral MOSFET Power Amplifier Design

    14.11 A Vertical MOSFET Power Amplifier Design

    15. Error Correction

    15.1 Feedforward Error Correction

    15.2 Hawksford Error Correction

    15.3 Error Correction for MOSFET Output Stages

    15.4 Stability and Compensation

    15.5 Performance and Design Issues

    15.6 Circuit Refinements and Nuances

    15.7 A MOSFET Power Amplifier with Error Correction

    16. Other Sources of Distortion

    16.1 Distortion Mechanisms

    16.2 Early Effect Distortion

    16.3 Junction Capacitance Distortion

    16.4 Grounding Distortion

    16.5 Power Rail Distortion

    16.6 Input Common Mode Distortion

    16.7 Resistor Distortion

    16.8 Capacitor Distortion

    16.9 Inductor and Magnetic Distortions

    16.10 Magnetic Induction Distortion

    16.11 Fuse, Relay and Connector Distortion

    16.12 Load Induced Distortion

    16.13 EMI-Induced Distortion

    16.14 Thermally Induced Distortion (Memory Distortion)

     

    Part 3: Real World Design Considerations

    17. Output Stage Thermal Design and Stability

    17.1 Power Dissipation vs. Power and Load

    17.2 Thermal Design Concepts and Thermal Models

    17.3 Transistor Power Ratings

    17.4 Sizing the Heat Sink

    17.5 The Bias Spreader and Temperature Compensation

    17.6 Thermal Bias Stability

    17.7 Thermal Lag Distortion

    17.8 ThermalTrak™ Power Transistors

    17.9 A ThermalTrak™ Power Amplifier

    18. Safe Area and Short Circuit Protection

    18.1 Power Transistor Safe Operating Area

    18.2 Output Stage Safe Operating Area

    18.3 Short Circuit Protection

    18.4 Safe Area Limiting Circuits

    18.5 Testing Safe Area Limiting Circuits

    18.6 Protection Circuits for MOSFETs

    18.7 Protecting the Driver Transistors

    18.8 Loudspeaker Protection Circuits

    19. Power Supplies and Grounding

    19.1 The Design of the Power Supply

    19.2 Sizing the Transformer

    19.3 Sizing the Rectifier

    19.4 Sizing the Reservoir Capacitors

    19.5 Rectifier Speed

    19.6 Regulation and Active Smoothing of the Supply

    19.7 SPICE Simulation of Power Supplies

    19.8 Soft-Start Circuits

    19.9 Grounding Architectures

    19.10 Radiated Magnetic Fields

    19.11 Safety Circuits

    19.12 DC on the Mains

    19.13 Switching Power Supplies

    20. Switching Power Supplies

    20.1 Line DC Supply

    20.2 Isolated DC-DC Converter

    20.3 Buck Converters

    20.4 Synchronous Buck Converter

    20.5 Boost Converters

    20.6 Buck-Boost Converters

    20.7 Boost-Buck Converters

    20.8 Cuk Converters

    20.9 Forward Converters

    20.10 Flyback Converters

    20.11 Half-bridge Converters

    20.12 Full-bridge Converters

    20.13 Control ICs for PWM Converters

    20.14 Resonant Converters

    20.15 Quasi-Resonant Converters

    20.16 EMI Filtering and Suppression

    20.17 Power Factor Correction

    20.18 Auxiliary Supplies

    20.19 Switching Supplies for Power Amplifiers

    20.20 Switching Supplies for Class D Amplifiers

    21. Clipping Control and Civilized Amplifier Behavior

    21.1 The Incidence of Clipping

    21.2 Clipping and Sticking

    21.3 Negative Feedback and Clipping

    21.4 Baker Clamps

    21.5 Soft Clipping

    21.6 Current Limiting

    21.7 Parasitic Oscillation Bursts

    21.8 Selectable Output Impedance

    22. Interfacing the Real World

    22.1 The Amplifier-Loudspeaker Interface

    22.2 EMI Ingress – Antennas Everywhere

    22.3 Input Filtering

    22.4 Input Ground Loops

    22.5 Mains Filtering

    22.6 EMI Egress

    22.7 EMI Susceptibility Testing

     

    Part 4: Simulation and Measurement

    23. SPICE Simulation

    23.1 Linear Technologies LTspice®

    23.2 Schematic Capture

    23.3 DC, AC and Transient Simulation

    23.4 Distortion Analysis

    23.5 Noise Analysis

    23.6 Controlled Voltage and Current Sources

    23.7 Swept and Stepped Simulations

    23.8 Plotting Results

    23.9 Subcircuits

    23.10 SPICE Models

    23.11 Simulating a Power Amplifier

    23.12 Middlebrook and Tian Probes

    24. SPICE Models and Libraries

    24.1 Verifying SPICE Models

    24.2 Tweaking SPICE Models

    24.3 Creating a SPICE Model

    24.4 JFET Models

    24.5 Vertical Power MOSFET Models

    24.6 LTspice VDMOS Models

    24.7 The EKV Model

    24.8 Lateral Power MOSFETs

    24.9 Installing Models

    25. Audio Instrumentation

    25.1 Basic Audio Test Instruments

    25.2 Dummy Loads

    25.3 Simulated Loudspeaker Loads

    25.4 THD Analyzer

    25.5 PC-Based Instruments

    25.6 Purpose-Built Test Gear

    26. Distortion and its Measurement

    26.1 Nonlinearity and its Consequences

    26.2 Total Harmonic Distortion

    26.3 SMPTE IM

    26.4 CCIF IM

    26.5 Transient Intermodulation Distortion (TIM) and SID

    26.6 Phase Intermodulation Distortion (PIM)

    26.7 Interface Intermodulation Distortion (IIM)

    26.8 Multi-Tone Intermodulation Distortion (MIM)

    26.9 Highly Sensitive Distortion Measurement

    26.10 Input-Referred Distortion Analysis

    27. Other Amplifier Tests

    27.1 Measuring Damping Factor

    27.2 Sniffing Parasitic Oscillations

    27.3 EMI Ingress Susceptibility

    27.4 Burst Power and Peak Current

    27.5 PSRR Tests

    27.6 Low-frequency Tests

    27.7 Back-Feeding Tests

     

    Part 5: Topics in Amplifier Design

    28. The Negative Feedback Controversy

    28.1 How Negative Feedback Got its Bad Rap

    28.2 Negative Feedback and Open-loop Bandwidth

    28.3 Spectral Growth Distortion

    28.4 Global Versus Local Feedback

    28.5 Timeliness of Correction

    28.6 EMI from the Speaker Cable

    28.7 Stability and Burst Oscillations

    28.8 Clipping Behavior

    29. Amplifiers without Negative Feedback

    29.1 Design Tradeoffs and Challenges

    29.2 Additional Design Techniques

    29.3 An Example Design with No Feedback

    29.4 A Feedback Amplifier with Wide Open-loop Bandwidth

    30. Balanced and Bridged Amplifiers

    30.1 Balanced Input Amplifiers

    30.2 Bridged Amplifiers

    30.3 Balanced Amplifiers

    31. Integrated Circuit Power Amplifiers and Drivers

    31.1 IC Power Amplifiers

    31.2 The Gain Clones

    31.3 The Super Gain Clone

    31.4 Integrated Circuit Drivers

    31.5 Summary

    32. Professional Power Amplifiers

    32.1 Environment and Special Needs

    32.2 Output Stages and Output Power

    32.3 Power Supplies

    32.4 Cooling and Heat Removal

    32.5 Microcomputers

    32.6 Networked Control and Monitoring

    32.7 Digital Signal Processing

    32.8 DSP-Based Protection and Monitoring

    32.9 The DSP to Class D Interface

    32.10 Programming

    32.11 Audio Networking

     

    Part 6: Class D Audio Amplifiers

    33. Class D Audio Amplifiers

    33.1 How Class D Amplifiers Work

    33.2 Class D Output Stages

    33.3 Bridge Tied Load Designs

    33.4 Negative Feedback

    33.5 Noise Shaping in PWM Modulators with Feedback

    33.6 Summary

    34. Class D Design Issues

    34.1 The Output Filter and EMI

    34.2 Spread Spectrum Class D

    34.3 Filterless Class D Amplifiers

    34.4 Buck Converters and Class D Amplifiers

    34.5 Sources of Distortion

    34.6 Bus Pumping

    34.7 Power Supply Rejection

    34.8 Power Supplies for Class D Amplifiers

    34.9 Damping Factor and Load Invariance

    34.10 Summary

    35. Alternative Class D Modulators

    35.1 Self-Oscillating Loops

    35.2 Sigma-Delta Modulators

    35.3 Digital Modulators

    36. Class D Measurement, Efficiency and Designs

    36.1 Hybrid Class D

    36.2 Measuring Class D Amplifiers

    36.3 Achievable Performance

    36.4 Integrated Circuits for Class D Amplifiers

    36.5 Example Class D Amplifiers and Measurements

    Biography

    Bob Cordell is an electrical engineer who has been deeply involved in audio since his adventures with vacuum tube designs in his teen years. He is an equal-opportunity designer to this day, having built amplifiers with vacuum tubes, bipolar transistors and MOSFETs. Bob is also a prolific designer of audio test equipment, including a high-performance THD analyzer and many purpose-built pieces of audio gear. He has published numerous articles and papers on power amplifier design and distortion measurement in the popular press and in the Journal of the Audio Engineering Society. In 1983 he published a power amplifier design combining vertical power MOSFETs with error correction, achieving unprecedented distortion levels of less than 0.001% at 20 kHz. He also consults in the audio and semiconductor industries.

    Bob is also an avid DIY loudspeaker builder, and has combined this endeavor with his electronic interests in the design of powered audiophile loudspeaker systems. Bob and his colleagues have presented audiophile listening and measurement workshops at the Rocky Mountain Audio Fest and the Home Entertainment Show.

    As an Electrical Engineer, Bob has worked at Bell Laboratories and other related telecommunications companies, where his work has included design of integrated circuits and fiber optic communications systems. Bob maintains an audiophile website at www.cordellaudio.com where diverse material on audio electronics, loudspeakers and instrumentation can be found.

    "Essential reading for anyone fascinated by the superficially simple idea of how to make a small electrical signal powerful enough to drive a loudspeaker without degrading that signal in the process." - John Atkinson, Stereophile

     

    "A complete text ideal for newcomers to amplifier design engineering as well as a great reference for practicing audio design engineers already working in the industry. [...] Because of the tiered approach of the first three parts of the book, its usefulness will grow with you as you become more proficient at amplifier design. I’m happy to find a place for this book in my technical library, as should you." - Dennis Fink, Fink Analog Audio, Journal of the Audio Engineering Society