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 (TM) Output Stage 13.6 Class A Output Stage 13.7 Crossover Displacement (Class XD (TM)) 13.8 Double Cross (TM) 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 (TM) Power Transistors 17.9 A ThermalTrak (TM) 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 (R) 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.
"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