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姓名 林煒翔(Wei-Hsiang Lin)  查詢紙本館藏   畢業系所 通訊工程學系
論文名稱 可調式切換頻率低功耗D類放大器於語音播放系統之應用
(A Power Saving Variable Switching Frequency Class-D Amplifier for Voice Playback System)
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摘要(中) 結合D類放大器之數位式音訊放大器在近年來被廣泛的研究,如何達到高傳真(High fidelity)為其重點,而為了達到高傳真之效果,D類放大器的切換頻率需固定在一高切換頻率,使音訊放大器的輸出失真能儘量降至最低。傳統上,與全數位式音訊放大器相關的系統架構均採固定切換頻率方式。但在語音通訊的應用上,有許多情況如靜音、高背景雜訊時,是不需要如此高的切換頻率。由於功耗消耗與切換頻率成正比,在這些情況下,高切換頻率造成了不必要的功率消耗。為了減少功率消耗,延長可攜式通訊裝置電池的使用時間,本論文提出一種切換頻率調變機制,根據輸入語音訊號的頻率成份及音框分類結果,動態調整D類放大器的切換頻率,以達到降低功率消耗之效果,同時提供高品質之語音播放。經由模擬實驗結果證實,與固定切換頻率於256kHz時相比較,本系統輸出之語音訊號品質與其相近,同時平均而言可降低23%的功率消耗,證明本系統之輸出可維持在一定的品質之上,而同時達到節省功率消耗的目的。
摘要(英) Digital class-D amplifiers have been widely used in both Hi-Fi and portable audio playback systems because of its high power efficiency. How to reach the high fidelity while maintaining low power dissipation is a major concern in designing a class-D amplifier. The switching frequency plays a key factor in the tradeoff between the fidelity and the power efficiency. Conventionally, all digital amplifiers are operated at a fixed switching frequency for convenience. In order to achieve the high fidelity performance, this switching frequency must be designed to be high enough so that a simple analog low-pass filter in the output stage can be used. In speech communication applications, a high switching frequency is not required in many operating situations such as in silence or with background noise. This thesis proposes a switching frequency modulation scheme, in which the switching frequency is adaptive modulated in accordance with the speech spectrum and the frame classification. The power dissipation is thus reduced while the high speech quality is maintained. The simulation results show that the speech quality of the proposed digital amplifier with a variable switching frequency achieves similar speech quality compared with the system with a fixed switching frequency operating at 256 kHz while the power dissipation is reduced by 23%.
關鍵字(中) ★ 數位音訊放大器
★ D類放大器
★ 雜訊塑型器
★ 語音播放系統
★ 可調式切換頻率
關鍵字(英) ★ class-D amplifier
★ voice playback system
★ variable switching frequency
★ noise shaper
★ digital audio amplifier
論文目次 目錄
中文摘要 I
Abstract II
目錄 IIi
圖目 V
表目 VII
第一章 緒論 1
1.1 前言 1
1.2 研究動機 2
1.3 論文架構 3
第二章 全數位式音訊放大器的工作原理 5
2.1 量化雜訊分析 8
2.2 擴展取樣 ( Up-sampling ) 對量化雜訊的影響 10
2.3 雜訊塑型 ( Noise Shaping ) 12
2.4 PWM訊號之切換頻率與低通濾波器之關係 16
第三章 G.729語音編碼標準 21
3.1 語音的特性 22
3.2 G.729編碼標準介紹 24
3.3 語音品質評估方法 41
3.3.1 主觀的語音評估方法 42
3.3.2 客觀的語音評估方法 42
第四章 全數位式音訊放大器之切換頻率調變機制 44
4.1 PWM訊號的頻譜分析 45
4.2 切換頻率調變機制 47
4.2.1 頻譜計算 47
4.2.2 有聲音框之音頻內失真預測 48
4.2.3 無聲音框及靜音音框處理方式 52
4.2.4 類比LC低通濾波器之模擬 56
4.3 擴展取樣率參數嵌入於G.729已壓縮之語音資料 59
第五章 實驗結果與討論 61
5.1 模擬環境及語音資料 61
5.2 客觀語音品質評估 61
5.3 主觀語音品質評估 67
5.4 省電效率評估 .68
第六章 結論與未來展望 72
6.1 結論 72
6.2 未來展望 72
參考文獻 73
圖目
圖2.1 傳統使用D類放大器的訊號處理流程 5
圖2.2 全橋式D類放大器與LC低通濾波器電路圖 6
圖2.3 全數位式音訊放大器訊號處理流程 7
圖2.4 量化器之加雜訊模型 8
圖2.5 的機率密度函數 9
圖2.6 量化誤差的功率頻譜密度 10
圖2.7 結合擴展取樣器之加雜訊模型 11
圖2.8 擴展取樣後量化誤差之功率頻譜密度變化 11
圖2.9 雜訊塑型器(a)時域方塊圖(b) z-domain分析 14
圖2.10 雜訊塑型之頻譜示意圖 15
圖2.11 D類放大器中電晶體之電流電壓 18
圖2.12 諧振頻率與切換頻率之關係 18
圖3.1 Source-Filter Model 22
圖3.2 語音片段(a)時域波形、(b)頻域波形 23
圖3.3 G.729編碼架構 25
圖4.1 切換頻率調變機制系統架構圖 44
圖4.2 4kHz弦波在切換頻率為256kHz時之PWM頻譜 45
圖4.3 不同輸入頻率及不同切換頻率之ANSR 50
圖4.4 MPEG Psychoacoustic Model II之絕對聽力臨界值ATH 53
圖4.5(a) 未考慮背景雜訊重建之時域波形圖 55
圖4.5(b) 考慮背景雜訊重建之時域波形圖 55
圖4.6 LC低通濾波器電路圖 56
圖4.7 低通濾波器之頻譜 58
圖4.8 G.729中各參數的錯誤敏感度 59
圖4.9 擴展取樣率參數於G.729編碼端之嵌入方式 60
圖4.10 擴展取樣率參數於G.729解碼端之擷取方式 60
圖5.1(a) 切換頻率為64k時產生之雜訊能量頻譜分佈 63
圖5.1(b) 切換頻率為128k時產生之雜訊能量頻譜分佈 63
圖5.1(c) 切換頻率為256k時產生之雜訊能量頻譜分佈 63
圖5.1(d) 切換頻率為512k時產生之雜訊能量頻譜分佈 63
表目
表3.1 G.729的位元配置表 25
表3.2 固定性碼簿脈衝結構 37
表4.1 不同輸入頻率及不同切換頻率之ANSR 50
表4.2 音頻內頻譜權重失真預測 52
表5.1 切換頻率調變機制結合(a)有聲/無聲音框分類與(b)有聲/無聲/靜音音框分類之SSNR與切換頻率比較 64
表5.2 固定切換頻率之SSNR比較 65
表5.3 切換頻率調變機制之主觀聽覺測試結果 67
表5.4 固定切換頻率的總功率消耗 69
表5.5 使用切換頻率調變機制時各語音訊號的平均總功率消耗 70
參考文獻 參考文獻
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指導教授 張寶基(Pao-Chi Chang) 審核日期 2005-7-8
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