Designing audio power amplifiers

Contents......Page 8
Preface......Page 30
Acknowledgments......Page 32
Part 1 Audio Power Amplifier Basics......Page 34
1.1 Organization of the Book......Page 36
1.2 The Role of the Power Amplifier......Page 37
1.3 Basic Performance Specifications......Page 38
1.4 Additional Performance Specifications......Page 40
1.5 Output Voltage and Current......Page 43
1.6 Basic Amplifier Topology......Page 44
References......Page 47
2.1 About Transistors......Page 48
2.2 Circuit Building Blocks......Page 58
2.3 Amplifier Design Analysis......Page 74
References......Page 84
3.1 The Basic Power Amplifier......Page 86
3.2 Adding Input Stage Degeneration......Page 88
3.3 Adding a Darlington VAS......Page 92
3.4 Input Stage Current Mirror Load......Page 95
3.5 The Output Triple......Page 97
3.6 Cascoded VAS......Page 101
3.7 Paralleling Output Transistors......Page 102
3.8 Higher-Power Amplifiers......Page 105
3.9 Crossover Distortion......Page 106
3.11 Completing an Amplifier......Page 108
References......Page 110
4.1 How Negative Feedback Works......Page 112
4.2 Input-Referred Feedback Analysis......Page 113
4.3 Feedback Compensation and Stability......Page 114
4.4 Feedback Compensation Principles......Page 117
4.5 Evaluating Loop Gain......Page 120
4.6 Evaluating Stability......Page 122
4.7 Compensation Loop Stability......Page 125
4.8 Slew Rate......Page 126
References......Page 128
5.1 Class A, AB, and B Operation......Page 130
5.2 The Complementary Emitter Follower Output Stage......Page 131
5.3 Output Stage Efficiency......Page 136
5.4 Complementary Feedback Pair Output Stages......Page 138
5.5 Stacked Output Stages......Page 141
5.6 Classes G and H......Page 143
References......Page 148
6.1 Power and Loads......Page 150
6.2 Sizing the Power Supply......Page 151
6.3 Sizing the Output Stage......Page 152
6.4 Sizing the Heat Sink......Page 153
6.6 Power and Ground Distribution......Page 154
6.7 Other Considerations......Page 155
References......Page 156
Part 2 Advanced Power Amplifier Design Techniques......Page 158
7.1 Single-Ended IPS-VAS......Page 160
7.2 JFET Input Stages......Page 164
7.3 Complementary IPS and Push-Pull VAS......Page 169
7.4 Unipolar Input Stage and Push-Pull VAS......Page 175
7.5 Input Common Mode Distortion......Page 179
7.6 Early Effect......Page 180
7.8 Amplifier Noise......Page 181
References......Page 186
8 DC Servos......Page 188
8.1 Origins and Consequences of DC Offset......Page 189
8.2 DC Servo Basics......Page 193
8.3 The Servo Is in the Signal Path......Page 197
8.5 DC Servo Example......Page 200
8.7 DC Servo Design Issues and Nuances......Page 202
9 Advanced Forms of Feedback Compensation......Page 204
9.2 Miller Compensation......Page 205
9.3 Two-Pole Compensation......Page 210
9.4 Miller Input Compensation......Page 213
9.5 Transitional Miller Compensation......Page 215
References......Page 216
10.1 The Class AB Output Stage......Page 218
10.2 Static Crossover Distortion......Page 219
10.3 Optimum Bias and Bias Stability......Page 221
10.4 Output Stage Driver Circuits......Page 223
10.5 Output Transistor Matching Considerations......Page 226
10.6 Dynamic Crossover Distortion......Page 228
10.7 The Output Emitter Resistors......Page 233
10.8 Output Networks......Page 234
10.9 Output Stage Frequency Response and Stability......Page 238
10.10 Sizing the Output Stage......Page 242
10.11 Delivering High Current......Page 243
10.13 Advanced Output Transistors......Page 245
References......Page 246
11 MOSFET Power Amplifiers......Page 248
11.1 MOSFET Types and Characteristics......Page 249
11.2 MOSFET Advantages and Disadvantages......Page 251
11.3 Lateral versus Vertical Power MOSFETs......Page 257
11.4 Parasitic Oscillations......Page 258
11.5 Biasing Power MOSFETs......Page 260
11.6 Crossover Distortion......Page 264
11.7 Driving Power MOSFETs......Page 267
11.8 Paralleling and Matching MOSFETs......Page 273
11.9 Simulating MOSFET Power Amplifiers......Page 274
References......Page 276
12.1 Feed-Forward Error Correction......Page 278
12.2 Hawksford Error Correction......Page 279
12.3 Error Correction for MOSFET Output Stages......Page 281
12.4 Stability and Compensation......Page 283
12.5 Performance and Design Issues......Page 286
12.6 Circuit Refinements and Nuances......Page 290
References......Page 292
13.1 Distortion Mechanisms......Page 294
13.3 Junction Capacitance Distortion......Page 295
13.5 Power Rail Distortion......Page 296
13.7 Resistor Distortion......Page 297
13.8 Capacitor Distortion......Page 299
13.9 Inductor and Magnetic Distortions......Page 300
13.11 Fuse, Relay, and Connector Distortion......Page 301
13.14 Thermally Induced Distortion (Memory Distortion)......Page 306
References......Page 307
Part 3 Real-World Design Considerations......Page 308
14.1 Power Dissipation versus Power and Load......Page 310
14.2 Thermal Design Concepts and Thermal Models......Page 312
14.3 Transistor Power Ratings......Page 318
14.4 Sizing the Heat Sink......Page 319
14.5 The Bias Spreader and Temperature Compensation......Page 323
14.6 Thermal Bias Stability......Page 332
14.7 Thermal Lag Distortion......Page 336
14.8 ThermalTrak™ Power Transistors......Page 337
References......Page 346
15.1 Power Transistor Safe Operating Area......Page 348
15.2 Output Stage Safe Operating Area......Page 351
15.3 Short Circuit Protection......Page 356
15.4 Safe-Area-Limiting Circuits......Page 362
15.5 Testing Safe-Area-Limiting Circuits......Page 366
15.7 Protecting the Driver Transistors......Page 367
15.8 Loudspeaker Protection Circuits......Page 368
References......Page 374
16.1 The Design of the Power Supply......Page 376
16.2 Sizing the Transformer......Page 379
16.3 Sizing the Rectifier......Page 381
16.4 Sizing the Reservoir Capacitors......Page 382
16.5 Rectifier Speed......Page 384
16.6 Regulation and Active Smoothing of the Supply......Page 386
16.7 SPICE Simulation of Power Supplies......Page 387
16.8 Soft-Start Circuits......Page 388
16.9 Grounding Architectures......Page 390
16.11 Safety Circuits......Page 392
16.12 DC on the Mains......Page 393
16.13 Switching Power Supplies......Page 394
References......Page 395
17.1 The Incidence of Clipping......Page 396
17.3 Negative Feedback and Clipping......Page 397
17.4 Baker Clamps......Page 398
17.5 Soft Clipping......Page 401
17.6 Current Limiting......Page 402
17.7 Parasitic Oscillation Bursts......Page 403
References......Page 404
18.1 The Amplifier-Loudspeaker Interface......Page 406
18.2 EMI Ingress: Antennas Everywhere......Page 409
18.4 Input Ground Loops......Page 413
18.7 EMI Susceptibility Testing......Page 414
References......Page 415
Part 4 Simulation and Measurement......Page 416
19.1 LTspice......Page 418
19.2 Schematic Capture......Page 420
19.3 DC, AC, and Transient Simulation......Page 423
19.4 Distortion Analysis......Page 427
19.5 Noise Analysis......Page 429
19.6 Controlled Voltage and Current Sources......Page 430
19.7 Swept and Stepped Simulations......Page 431
19.8 Plotting Results......Page 433
19.9 Subcircuits......Page 436
19.10 SPICE Models......Page 439
19.11 Simulating a Power Amplifier......Page 441
References......Page 450
20 SPICE Models and Libraries......Page 452
20.1 Verifying SPICE Models......Page 453
20.2 Tweaking SPICE Models......Page 454
20.3 Creating a SPICE Model......Page 457
20.4 JFET Models......Page 473
20.5 Vertical Power MOSFET Models......Page 475
20.6 LTspice™ VDMOS Models......Page 480
20.7 The EKV Model......Page 483
20.8 Hybrid VDMOS-EKV Model......Page 487
20.9 Lateral Power MOSFETs......Page 488
References......Page 489
21.1 Basic Audio Test Instruments......Page 492
21.2 Dummy Loads......Page 493
21.3 Simulated Loudspeaker Loads......Page 494
21.4 THD Analyzer......Page 495
21.5 PC-Based Instruments......Page 497
21.6 Purpose-Built Test Gear......Page 498
References......Page 503
22.1 Nonlinearity and Its Consequences......Page 504
22.2 Total Harmonic Distortion......Page 505
22.3 SMPTE IM......Page 507
22.4 CCIF IM......Page 508
22.5 TIM and SID......Page 509
22.6 PIM......Page 511
22.7 IIM......Page 513
22.9 Highly Sensitive Distortion Measurement......Page 517
22.10 Input-Referred Distortion Analysis......Page 518
References......Page 519
23.1 Measuring Damping Factor......Page 522
23.2 Sniffing Parasitic Oscillations......Page 523
23.3 EMI Ingress Susceptibility......Page 524
23.4 Burst Power and Peak Current......Page 525
23.6 Low-Frequency Tests......Page 526
23.7 Back-Feeding Tests......Page 527
References......Page 528
Part 5 Topics in Amplifier Design......Page 530
24.1 How Negative Feedback Got Its Bad Rap......Page 532
24.2 Negative Feedback and Open-Loop Bandwidth......Page 533
24.3 Spectral Growth Distortion......Page 535
24.7 Stability and Burst Oscillations......Page 538
References......Page 539
25.1 Design Trade-Offs and Challenges......Page 542
25.2 Additional Design Techniques......Page 552
25.3 An Example Design with No Feedback......Page 555
25.4 A Feedback Amplifier with Wide Open-Loop Bandwidth......Page 557
References......Page 559
26.1 Balanced Input Amplifiers......Page 560
26.2 Bridged Amplifiers......Page 564
26.3 Balanced Amplifiers......Page 566
27.1 IC Power Amplifiers......Page 570
27.2 The Gain Clones......Page 571
27.3 The Super Gain Clone......Page 572
27.4 Integrated Circuit Drivers......Page 575
27.5 An Integrated Circuit Bias Controller......Page 577
References......Page 583
Part 6 Class D Amplifiers......Page 584
28 Class D Audio Amplifiers......Page 586
28.1 How Class D Amplifiers Work......Page 587
28.2 Buck Converters......Page 588
28.3 Class D Output Stages......Page 595
References......Page 597
29.1 The Output Filter and EMI......Page 598
29.2 Sources of Distortion......Page 602
29.3 Bus Pumping......Page 607
29.4 Power Supply Rejection......Page 608
29.5 Power Supplies for Class D Amplifiers......Page 609
29.6 Negative Feedback......Page 610
29.7 Damping Factor and Load Invariance......Page 613
References......Page 614
30.1 Self-Oscillating Loops......Page 616
30.2 Sigma-Delta Modulators......Page 620
30.3 Digital Modulators......Page 626
References......Page 627
31.1 Hybrid Class D......Page 628
31.2 Measuring Class D Amplifiers......Page 630
31.3 Achievable Performance......Page 632
References......Page 633
C......Page 634
D......Page 635
H......Page 636
M......Page 637
O......Page 638
R......Page 639
T......Page 640
Z......Page 641