Amplificador clase d

Class D Audio Amplifier
The design of a live audio Class D audio amplifier with greater than 90% efficiency and less than 1% distortion.
A Major Qualifying Project Submitted to the Faculty of the WORCESTER POLYTECHNIC INSTITUTE in partial fulfillment of the requirements for the Degree of Bachelor of Science in Electrical Engineering by

Briana Morey

Ravi Vasudevan

Ian Woloschin May 2008APPROVED:

Professor John McNeill, Advisor

Professor Andrew Klein, Advisor

Abstract The purpose of this project was to design and produce a 90% efficient, 80W Class D audio amplifier, with less than 1% Total Harmonic Distortion (THD) for the NECAMSID Lab. The amplifier consisted of a second order, three-level ∆Σ modulator, an H-bridge power stage, and a second order, passive Butterworth filter.Testing confirmed that the efficiency, THD, and power specifications were met in the final revision of the design.

ACKNOWLEDGEMENTS We would like to thank Professor McNeill and Professor Klein for advising this project. We would also like to thank the NECAMSID lab for sponsoring this project.

Contents
1 Introduction 1.1 Project Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 1.2 Report Organization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Background 2.1 Class D Amplification . . . . . . . . . . . . . . . . . . . . . . 2.1.1 Operation of Class D Audio Amplifiers . . . . . . . . . 2.1.2 Advantages and Disadvantages of Class D . . . . . . . 2.1.3 Applying Class D to Audio Design . . . . . . . . . . . 2.2 The Modulation Stage . . . . . . . .. . . . . . . . . . . . . . 2.2.1 Pulse Width Modulation (PWM) . . . . . . . . . . . . 2.2.2 Delta Sigma Modulation (∆Σ) . . . . . . . . . . . . . . 2.3 The Power Stage . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Half-Bridge Amplifiers . . . . . . . . . . . . . . . . . . 2.3.2 H-Bridge Amplifiers . . . . . . . . . . . . . . . . . . . 2.3.3 A Critical Evaluation of Half- and H-BridgeAmplifiers 2.3.4 MOSFET Drivers . . . . . . . . . . . . . . . . . . . . . 2.4 Noise and the Filtering Stage . . . . . . . . . . . . . . . . . . 2.4.1 Types of Noise . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Passive Filters vs. Active Filters . . . . . . . . . . . . . 2.4.3 Single Ended Filters vs. Balanced Filters . . . . . . . . 3 Preliminary Design 3.1 The Modulation Stage . . . . . . . . .. . . . . . . . . 3.1.1 The First Order Delta Sigma Modulator Design 3.2 The Power Stage . . . . . . . . . . . . . . . . . . . . . 3.2.1 Amplifier Configuration . . . . . . . . . . . . . 3.2.2 MOSFET Selection . . . . . . . . . . . . . . . . 3.2.3 MOSFET Drivers . . . . . . . . . . . . . . . . . 3.3 Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Filter Components . . . . . . .. . . . . . . . . 3.4 System Implementation . . . . . . . . . . . . . . . . . . 3.4.1 First Order Modulator . . . . . . . . . . . . . . 3.4.2 PCB Layout for Power Stage and Filter . . . . . 3.4.3 Full System Assembly . . . . . . . . . . . . . . ii . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 2 2 33 4 6 7 8 9 10 12 12 13 14 15 15 16 19 20 22 22 23 26 26 26 30 31 32 34 34 35 36

4 Preliminary Results 4.1 Functionality Testing . . . . . . . . . . . . . . . 4.1.1 Modulator Functionality . . . . . . . . . 4.1.2 Power Stage Functionality . . . . . . . . 4.1.3 Filter Functionality . . . . . . . . . . . . 4.1.4 System Functionality . . . . . . . . . . . 4.2 Efficiency Testing . . . . . . . . ....