pcm通信系統(tǒng)設(shè)計

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1、課程設(shè)計任務(wù)書學(xué)生姓名：駱準(zhǔn)專業(yè)班級：電信0601班指導(dǎo)教師：陳永泰作單位：信息工程學(xué)院題目：PCM通信系統(tǒng)設(shè)計初始條件：具備通信課程的理論知識；具備模擬與數(shù)字電路基本電路的設(shè)計能力；掌握通信電路的設(shè)計知識，掌握通信電路的基本調(diào)試方法；自選相關(guān)電子器件；可以使用實驗室儀器調(diào)試。要求完成的主要任務(wù)：（包括課程設(shè)計工作量及其技術(shù)要求，以及說明書撰寫等具體要求）1、PCM碼速率128KB，兩路時分復(fù)用，通信雙方有線連接，語音信號無明顯失真，采用A律壓縮13折線芯片；2、系統(tǒng)時鐘信號頻率2.048MHZ，時隙同步信號頻率

2、為8KHZ；3、選用相應(yīng)合適的芯片，設(shè)計確定電路形式，對單元電路和整體系統(tǒng)進(jìn)行計算、仿真驗證。4、進(jìn)行系統(tǒng)仿真，調(diào)試并完成符合要求的課程設(shè)計書。時間安排：二十二周一周，其中3天硬件設(shè)計，2天硬件調(diào)試指導(dǎo)教師簽名：年月日系主任（或責(zé)任教師）簽名：年月日目錄摘要·····························································I1PCM原理·······················································11.1PCM

3、系統(tǒng)組成················································11.2抽樣·······················································21.3量化·······················································21.4編碼·······················································32時分復(fù)用原理················

4、···································43實驗電路圖·····················································73.1編譯碼芯片介紹··············································73.2引腳圖·····················································73.3PCM編譯碼電路···································

5、··········84仿真圖························································115心得體會······················································13參考文獻(xiàn)························································14致謝····························································1

6、51PCM原理1.1PCM系統(tǒng)組成干擾音頻信號編碼量化信道譯碼低通濾波音頻信號抽樣圖1.1PCM通信系統(tǒng)方框圖1.2抽樣低通抽樣定理指出，一個頻帶受限信號m(t)，如果它的最高頻率為fh，則可以唯一地由頻率等于或大于2fh的樣值序列所決定。在滿足抽樣定理的條件下，抽樣信號保留了原信號的全部信息。并且，從抽樣信號中可以無失真地恢復(fù)出原始信號。音頻信號頻譜如圖1.2。因為對時域信號進(jìn)行采樣相當(dāng)于將時域信號按抽樣抽樣頻率為周期進(jìn)行周期延擴(kuò)，因此需要在抽樣后得到的信號后一級加上一個低通濾波器，將音頻信號濾出。抽樣后信號頻

7、譜如圖1.3。1.2音頻信號的頻譜1.3抽樣后的頻譜由于語音信號的頻率范圍為300～3400HZ,通常將語音信號通過一個3400Hz低通濾波器（或通過一個300～3400Hz的帶通濾波器），限制語音信號的最高頻率為3400Hz，這樣可以用頻率大于或等于6800Hz的樣值序列來表示。抽樣分為自然抽樣和平頂抽樣。自然抽樣是在抽樣脈沖持續(xù)期間，樣值幅度隨輸入信號變化而變化。平頂抽樣是抽樣值的幅度為抽樣時刻信號的瞬時值，在抽樣脈沖持續(xù)期間樣值幅度。1.3量化量化是把經(jīng)過抽樣得到的瞬時值將其幅度離散，即用一組規(guī)定的電平，把

8、瞬時抽樣值用最接近的電平值來表示。一個模擬信號經(jīng)過抽樣量化后，得到已量化的脈沖幅度調(diào)制信號，它僅為有限個數(shù)值。因此量化后信號是離散的。量化分為均勻量化和非均勻量化。均勻量化是把輸入信號的量化范圍按等間隔分割的量化。均勻量化中，每個量化區(qū)間的量化電平均取在各區(qū)間的中點。均勻量化的信號的動態(tài)范圍受到較大的限制，小信號的信噪比小，由于門限效應(yīng)，編碼時的位數(shù)相對較多，設(shè)備較復(fù)雜。