Class D功率放大器的主要優點是高功率效率(典型值大於90%)，然而對於開迴路的Class D功率放大器而言，有兩個在設計上會遇到的問題，一個為總體諧波失真，另一個為輸出直流靜態電流造成功率效率下降的問題，總體諧波失真是由脈衝寬度調變電路(Pulse Width Modulation Circuit)中非理想的三角波取樣載子所引起，而輸出直流靜態電流主要是由於輸出級中電晶體的不匹配轉移特性所產生，對於電路設計者來說，這兩個問題會對設計上造成很大負擔，因此我們提出了含被動RC回授的Class D功率放大器來改善這兩個問題，根據模擬及實際的量測結果顯示，我們提出的電路在250Hz到4KHz的頻率之間，其功率效率都可以超過90%，除此之外，在4KHz時模擬及量測的THD值都小於0.24%。

The primary advantage of Class D amplifier is high power efficiency (typically >90%). However, there are two problems in open-loop Class D design: Total Harmonic Distortion (THD) and output dc static current (the power efficiency will be degraded). The THD is rising from non-ideal sample carrier in Pulse Width Modulation circuit, and output dc static current is due to the non-match transfer characteristic in output stage. For designer to have such problems will be a large load. To improve these two problems, we proposed a Class D power amplifier with passive feedback design. Simulation and Measurement results show that the power efficiency is higher than 90% at 250Hz ~ 4KHz. Furthermore, the THD is less than 0.24% at 4 KHz in both simulation and experimental results.

Abstract

Chapter 1 Introduction 1

Chapter 2 Previous Class D Power Amplifier 3
2.1 Class D Power Amplifiers 3
2.2 The Figure of Merit of Power Amplifiers 6
2.3 Killion’s Open-Loop Class D Amp [8] for Hearing Aids 7
2.4 Chaig’s Class D Power Amp with Active Feedback[6] 12
2.4.1 The Theory of Active Feedback Design 12
2.4.2 The Problem of This Feedback Design 14

Chapter 3 The Proposed Circuit 15
3.1 The Feedback Principle for Class D Amps 15
3.2 The Class D Amp with Passive RC Feedback 18
3.2.1 The Difference Amplifier 20
3.2.2 The Triangular Wave Generator 23
3.2.3 The β Network 25
3.2.4 The Analysis of PWM and Feedback Process 27
3.2.5 Output Stage and Low-Pass Filter 29
3.2.5.1 The Effect of Inverter on-Resistance 30
3.2.5.2 The Inherent Threshold Voltage of Inverter 32
3.2.5.3 The Second-Order Low-Pass Filter 34
3.2.6 The Transfer Function 36

Chapter 4 Simulations and Experimental Results 37
4.1 Hspice Simulation 39
4.2 Experimental Results 42

Chapter 5 Conclusion 46

Reference 47

[1] B. Putzeys, “Mini but mighty Class D amps are forging audio’s future,” IEEE Spectrum March 2003, Page(s):34-41.
[2] D. Dapkus, “Class-D Audio Power Amplifiers: An Overview,” Consumer Electronics, 2000. ICCE. 2000 Digest of Technical Papers. International Conference on 13-15 June 2000 Page(s):400 – 401.
[3] B. H. Gwee, J. S. Chang, V. Adrian, H. Amir, “A novel sampling process and pulse generator for a low distortion digital pulse-width modulator for digital class D amplifiers,”Circuits and Systems, 2003. ISCAS '03. Proceedings of the 2003 International Symposium on Volume 4, 25-28 May 2003 Page(s):IV-504 - IV-507 vol.4.
[4] J. S. Chang, M. T. Tan; Z. Cheng; Y. C. Tong, “Analysis and design of power efficient class D amplifier output stages,” IEEE Trans. Circuits and Systems I: Fundamental Theory and Applications on Volume 47, NO. 6, Page(3):897-920, 2000.
[5] O. Andersson, “Class D Hearing Aid Amplifier with Feedback,” United States Patent, no. 5815581, 1998.
[6] J. S. Chang, B. H. Gwee, Y. S. Lon; M. T. Tan, “A novel low-power low-voltage Class D amplifier with feedback for improving THD, power efficiency and gain linearity,” Circuits and Systems, 2001. ISCAS 2001. The 2001 IEEE International Symposium on Volume 1, 6-9 May 2001 Page(s):635 - 638 vol. 1.
[7] N. R. Malik, “Electronic circuits analysis, simulation, and design,” Perentice Hall International Edittions,Volume 10, Page(s):751-798, 1995.
[8] M.C. Killion and E.G. Village, “Class D Hearing Aid Amplifier,” United States Patent, no. 4,689,819,1987.
[9] M. T. Tan, J. S. Chang, Y. C. Tong, “A novel self-tuning pulse width modulator based on master-slave architecture for a Class D amplifier,”Circuits and Systems,1999. ISCAS '99. Proceedings of the 1999 IEEE International Symposium on Volume 2, 30 May-2 June 1999 Page(s):164 - 167 vol.2.
[10] A. S. Sedra, K. C. Smith, “Microelectronic Circuits,” Oxford University Press, Page(s):1049-1058, 1998.