Designing Audio Power Amplifiers (2^nd Ed.)

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

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.