用於音訊處理的高效能低失真D類放大器

A Class D Amplifier with High Efficiency and Low Distortion for Audio Application

洪邦楨(Pang-Chan Hung)

指導教授 ： 黃柏鈞

國立清華大學/電機資訊學院/電機工程學系/碩士(2007年)

摘要

中文摘要
隨著可攜式聲音輸出裝置的普及，低耗能的聲音處理系統已逐漸的被研究以及發
展。過往聲音輸出採用線性AB類放大器。線性AB類放大器的優點在於線性的訊號操
作能使音質輸出良好，但AB類放大器由於在電源供應與地之間有著導通電路，因此
會造成大量的功率流失。相較於過往線性的AB類放大器而言，D類放大器藉由開關式
的操作，能夠使得大部分的電流由電源供應輸出至負載。如此功率消耗能夠達到降
至最低的程度。因此於此次的研究中，我們將針對D類放大器做研究。
然而D類放大器在操作上會增加許多非線性的現象，導致在音質的輸出表現降低。在
這次的研究報告中，為了補償數位輸入形式的D類放大器輸出失真的效應，我們設計
了一個新的補償調變系統，稱作脈寬積差調變(Pulse Width Delta Modulation)系
統。此系統將利用撞擊控制系統的磁滯概念將失真錯誤加以補償。而雙迴路的脈寬
積差調變系統能夠增加補償系統的效率而使得失真更為降低。於此次的研究中，亦
會比較與其他補償系統間的優劣，以顯現脈寬積差調變系統的前瞻性。
為了驗證脈寬積差調變系統的可使用性，此次研究中使用CMOS標準製程實現一脈寬
積差調變電路。在回授電路上採用積分功能之電路以做錯誤的累加。而在磁滯電路
上設計了一磁滯比較器以補償錯誤失真。在輸出級上採用標準D類放大器輸出級以及
二階巴特伍茲低通濾波器已達到解調的功能。而在實做後量測的結果，相較於開路
的D類放大器系統，脈寬積差調變系統將失真度下降了18dB，而電源供應產生的雜訊
也藉由脈寬積差調變系統下降了10dB。而輸出的電壓值更因此能夠達到更為精準的
輸出值。

關鍵字

D類放大器 ； 脈寬積差調變 ； 音頻應用

並列摘要

Abstract
Instead of traditional class-AB amplifier, class-D amplifier is gradually used in audio application.
Class-D amplifier itself is high efficient but non-linear structure. Many feedback solutions
to reduce analog-input class-D amplifier non-linearity are revealed in recent years. However, the
feedback system is hard to be used at digital-input class-D amplifier. In this thesis a modified
class-D amplifier topology is proposed to solve the total harmonic distortion problem of digitalinput
class-D amplifier.
The basic operation of class-D amplifier is introduced in the first part. Several modulation methods
are discussed and compared. The theoretic and practical views, especially on non-linear effects are
discussed in the following. Based on these analysis, a hybrid modulation scheme is proposed. It
uses the hysteresis concept to solve the pulse timing and amplitude error.
To verify the availability of the proposed structure. a digital PWM inputted output stage is prototyped
using TSMC 0.35 2P4M (Mixed-Signal) process. Simulation results show the nonlinearity
can be improved by pulse width delta modulation. Measured data indicates that the improvement
in nonlinearity issue.
Although there are some non-ideality like blanking delay error to be solved, the experiment result
has demonstrated that the proposed pulse width delta modulation analytical and technique can efficiently
reduce the non-linearity of output loading and timing error. The total harmonic distortion
can be improved from 35dB to 55dB. The full system can work on a 8ohm 2watt general speaker.

並列關鍵字

class-D amplifier ； PWDM ； audio application

參考文獻

[1] A. Oliva and S. Ang, “A multi-loop voltage feedback filterless class-d switching audio amplifier

using unipolar pulse-width-modulation.,” IEEE Trans. Consumer Electron., vol. 59,

pp. 312–319, 2004.

principle for power digital-analog conversion,” 102nd Audio Engineering Society Convention,

[4] J. Chang and B. H. Gwee, “A novel sampling process and pulse generator for a low distortion