採用Σ－Δ調變之全橋功率放大器

Abstract

本論文以Σ－Δ為調變基礎設計並實現一數位功率放大器，以切換式訊號為輸入之數位功率放大器相較於類比A/B類，擁有體積小、功率效益較高的優點，而其重點在於可將任意訊號調變為單位元表示之前級訊號調變器，相較於常見的PWM調變法，Σ－Δ調變器沒有倍頻雜訊，其較低的切換次數使系統減少切換損失。本論文將證明與分析高階Σ－Δ系統於單位元與1.5位元運算之穩定特性，由結果可以知道1.5位元運算於雜訊抑制的能力，以及切換次數之減低皆優於單位元運算。數位Σ－Δ調變器將實現於FPGA，並配合後級之全橋功率放大器，作雙聲道之音頻訊號的放大與撥放。

This thesis proposes a design of full-digital class-D amplifier using sigma-delta modulation. The class-D amplifier operating the MOSFET (or IGBT) in saturation mode has the advantages of smaller size and higher power efficiency over traditional class-A/B ones. The underlying principle of generating the switching command is to convert the input signal into an oversampled binary signal. Compared with PWM modulation, sigma-delta modulation produces less distortion, noise and number of switching. The design and stability analysis of digital sigma-delta modulation are studied in this thesis using both 1- and 1.5-bit quantization schemes. The results show that the 1.5-bit scheme further improves the noise shaping performance and switching number reduction. The digital sigma-delta modulator is implemented on an FPGA and a full-bridge power stage is constructed to verify the design method. The resulting experimental platform is able to achieve a stereo amplifier with 22.05KHZ audio bandwidth.