多媒體課件(西電科大趙建勛)

1、射頻電路基礎(chǔ)多媒體教學(xué)課件射頻電路基礎(chǔ)多媒體教學(xué)課件西安電子科技大學(xué)西安電子科技大學(xué)電子工程學(xué)院電子工程學(xué)院趙建勛趙建勛Multimedia Courseware of Fundamental Radio-Frequency Electronic Circuits Zhao JianxunSchool of Electronic EngineeringXidian University開開 始始 Start西安電子科技大學(xué)西安電子科技大學(xué) Xidian University本課件講授大學(xué)本科本課件講授大學(xué)本科射頻電路基礎(chǔ)射頻電路基礎(chǔ)課程的代表內(nèi)容課程的代表內(nèi)容非線性器件非線性器件振幅調(diào)制，失真

2、和平衡對(duì)消。振幅調(diào)制，失真和平衡對(duì)消。課件主要配合教師課堂教學(xué)使用，講授過程中始終以教師講述為主，課課件主要配合教師課堂教學(xué)使用，講授過程中始終以教師講述為主，課件只提供必要的文字和圖像信息。件只提供必要的文字和圖像信息。學(xué)生本人使用該課件預(yù)習(xí)和復(fù)習(xí)功課時(shí)，可以選擇向?qū)У膸椭?。向?qū)Ъ皩W(xué)生本人使用該課件預(yù)習(xí)和復(fù)習(xí)功課時(shí)，可以選擇向?qū)У膸椭?。向?qū)Ъ皶r(shí)提供豐富的文字講解，起到了教師指導(dǎo)的作用。因?yàn)榧闪讼驅(qū)Чδ?，本時(shí)提供豐富的文字講解，起到了教師指導(dǎo)的作用。因?yàn)榧闪讼驅(qū)Чδ?，本課件也可以作為網(wǎng)絡(luò)課件使用。課件也可以作為網(wǎng)絡(luò)課件使用。 The courseware is materialized o

3、n nonlinear-device amplitude modulation, distortion, and balanced cancellation, which are representative contents of Fundamental Radio-Frequency Electronic Circuits, a course for undergraduate students. With the major purpose to assist the classroom lecturing, the courseware provides necessary liter

4、al and image information to help the teacher, who plays the main role in the lecturing. The courseware itself is also a net-based one. The integrated guide timely provides detailed literal explanations for students in preparing and reviewing the course. The guidance serves as the instructions from t

5、eachers. 簡(jiǎn)介簡(jiǎn)介 Introduction西安電子科技大學(xué)西安電子科技大學(xué) Xidian University結(jié)束結(jié)束 End封面封面 Cover目錄目錄 Content課課 件件 簡(jiǎn)簡(jiǎn) 介介A brief introduction of the courseware翻到封面翻到封面 To the cover幫幫 助助 Help西安電子科技大學(xué)西安電子科技大學(xué) Xidian University返回返回 Return封面封面 Cover目錄目錄 Content簡(jiǎn)簡(jiǎn) 要要 幫幫 助助A concise help返回返回 Return封面封面 Cover幫助幫助 Help沒有向?qū)У慕缑鏇]

6、有向?qū)У慕缑?The interface without the guide有向?qū)У慕缑嬗邢驅(qū)У慕缑?The interface with the guide目錄目錄 Content結(jié)束結(jié)束 End翻到幫助頁面翻到幫助頁面 To the help page翻到目錄翻到目錄 To the content返回上一頁返回上一頁 To the last page結(jié)束放映結(jié)束放映 End the screening第五章振幅調(diào)制與解調(diào)第五章振幅調(diào)制與解調(diào)結(jié)束結(jié)束 End向向 導(dǎo)導(dǎo) Guide封面封面 Cover幫助幫助 HelpChapter 5 Amplitude modulation and dem

7、odulation振幅調(diào)制方法的分類振幅調(diào)制方法的分類 Types of amplitude modulation approaches西安電子科技大學(xué)西安電子科技大學(xué) Xidian University您好，歡迎使用射頻電路基礎(chǔ)多媒體教學(xué)課件，請(qǐng)選擇是否需要向?qū)?。您好，歡迎使用射頻電路基礎(chǔ)多媒體教學(xué)課件，請(qǐng)選擇是否需要向?qū)?。Hello, welcome to Teaching Courseware of Fundamental Radio-Frequency Electronic Circuits. Please choose if you will need a guide. 使用向?qū)Вū?/p>

8、于瀏覽課件，課程預(yù)習(xí)和復(fù)習(xí)）使用向?qū)Вū阌跒g覽課件，課程預(yù)習(xí)和復(fù)習(xí)）Use the guide (For courseware browsing, course preparation and reviewing)不使用向?qū)Вū阌诮M織課堂教學(xué)）不使用向?qū)Вū阌诮M織課堂教學(xué)）No guide (For classroom lecturing organization)第五章振幅調(diào)制與解調(diào)第五章振幅調(diào)制與解調(diào)目目 錄錄 ContentChapter 5 Amplitude modulation and demodulation振幅調(diào)制方法振幅調(diào)制方法 Amplitude modulation ap

9、proaches 非線性器件調(diào)幅非線性器件調(diào)幅 Amplitude modulation with nonlinear devices線性時(shí)變電路調(diào)幅線性時(shí)變電路調(diào)幅 AM with linear time-varying circuits步驟步驟1 Step one步驟步驟2 Step two步驟步驟3 Step three非線性器件調(diào)幅失真非線性器件調(diào)幅失真 Distortions of nonlinear-device AM振幅調(diào)制的關(guān)鍵問題振幅調(diào)制的關(guān)鍵問題 Key problem of amplitude modulation失真來源失真來源 Source of distortion

10、s減小失真的方法減小失真的方法 Methods to reduce distortions平衡對(duì)消平衡對(duì)消 Balanced cancellation非線性器件調(diào)幅分析非線性器件調(diào)幅分析 Analysis of nonlinear-device AM振幅調(diào)制與解調(diào)振幅調(diào)制與解調(diào) Amplitude modulation (AM) and demodulation 振幅調(diào)制方法的分類振幅調(diào)制方法的分類 Types of amplitude modulation approaches振幅調(diào)制信號(hào)振幅調(diào)制信號(hào) Amplitude modulated signals西安電子科技大學(xué)西安電子科技大學(xué) X

11、idian University結(jié)束結(jié)束 End封面封面 Cover幫助幫助 Help結(jié)束結(jié)束 End目錄目錄 Content幫助幫助 Help第五章振幅調(diào)制與解調(diào)第五章振幅調(diào)制與解調(diào)目目 錄錄 ContentChapter 5 Amplitude modulation and demodulation振幅調(diào)制方法振幅調(diào)制方法 Amplitude modulation approaches 非線性器件調(diào)幅非線性器件調(diào)幅 Amplitude modulation with nonlinear devices線性時(shí)變電路調(diào)幅線性時(shí)變電路調(diào)幅 AM with linear time-varying

12、circuits步驟步驟1 Step one步驟步驟2 Step two步驟步驟3 Step three非線性器件調(diào)幅失真非線性器件調(diào)幅失真 Distortions of nonlinear-device AM振幅調(diào)制的關(guān)鍵問題振幅調(diào)制的關(guān)鍵問題 Key problem of amplitude modulation失真來源失真來源 Source of distortions減小失真的方法減小失真的方法 Methods to reduce distortions平衡對(duì)消平衡對(duì)消 Balanced cancellation非線性器件調(diào)幅分析非線性器件調(diào)幅分析 Analysis of nonlin

13、ear-device AM振幅調(diào)制與解調(diào)振幅調(diào)制與解調(diào) Amplitude modulation (AM) and demodulation 振幅調(diào)制方法的分類振幅調(diào)制方法的分類 Types of amplitude modulation approaches振幅調(diào)制信號(hào)振幅調(diào)制信號(hào) Amplitude modulated signals西安電子科技大學(xué)西安電子科技大學(xué) Xidian University繼續(xù)繼續(xù) Continue一種比較重要和常見的減小失真的方法是平衡對(duì)一種比較重要和常見的減小失真的方法是平衡對(duì)消技術(shù)，這是本次課程最后要學(xué)習(xí)的內(nèi)容。消技術(shù)，這是本次課程最后要學(xué)習(xí)的內(nèi)容。Bal

14、anced cancellation is an important and usual method for distortion reduction, which will be studied at the end of this lesson. 我們從本次課程開始學(xué)習(xí)振幅調(diào)制方法，這是第五章，振幅調(diào)制與解調(diào)的一個(gè)我們從本次課程開始學(xué)習(xí)振幅調(diào)制方法，這是第五章，振幅調(diào)制與解調(diào)的一個(gè)重要部分。重要部分。In this lesson, we begin to learn approaches of amplitude modulation, which is an important por

15、tion of Chapter 5, Amplitude modulation and demodulation. 為了解決失真問題，我們接下來尋找失為了解決失真問題，我們接下來尋找失真的來源，并由此提出減小失真的方法。真的來源，并由此提出減小失真的方法。To tackle the distortion problem, well search for the distortion source, and then bring forward methods for distortion reduction. 非線性器件調(diào)幅通過三個(gè)步驟非線性器件調(diào)幅通過三個(gè)步驟來實(shí)現(xiàn)。來實(shí)現(xiàn)。The nonl

16、inear-device amplitude modulation is performed in three steps. 首先，我們簡(jiǎn)要復(fù)習(xí)三種振幅調(diào)制信號(hào)，即首先，我們簡(jiǎn)要復(fù)習(xí)三種振幅調(diào)制信號(hào)，即普通調(diào)幅信號(hào)，雙邊帶調(diào)制信號(hào)和單邊帶調(diào)普通調(diào)幅信號(hào)，雙邊帶調(diào)制信號(hào)和單邊帶調(diào)制信號(hào)。制信號(hào)。First, well briefly review the three signals out of amplitude modulation, namely, the amplitude modulated signal, the double-sideband modulated signal, a

17、nd the single-sideband modulated signal. 為了生成這些信號(hào)，我們進(jìn)行振幅調(diào)制時(shí)需要解決一個(gè)關(guān)鍵問題，即調(diào)制信號(hào)與載波的為了生成這些信號(hào)，我們進(jìn)行振幅調(diào)制時(shí)需要解決一個(gè)關(guān)鍵問題，即調(diào)制信號(hào)與載波的相乘。相乘。We need to solve a key problem in the amplitude modulation to generate these signals, that is, the multiplication of the modulating signal and the carrier wave. 感謝使用向?qū)?。首先，我們?jiǎn)略瀏覽

18、本次課程的內(nèi)容和結(jié)構(gòu)。感謝使用向?qū)?。首先，我們?jiǎn)略瀏覽本次課程的內(nèi)容和結(jié)構(gòu)。 Thank you for using the guide. At first, lets briefly browse the content and structure of this lesson. 從分類上看，有兩種基本方法可以解決該問題，即非線性器件調(diào)幅和線性時(shí)從分類上看，有兩種基本方法可以解決該問題，即非線性器件調(diào)幅和線性時(shí)變電路調(diào)幅。本次課程學(xué)習(xí)非線性器件調(diào)幅。變電路調(diào)幅。本次課程學(xué)習(xí)非線性器件調(diào)幅。For solution, there are two basic types of amplitude

19、 modulation approach, namely, the amplitude modulation with nonlinear devices，and the amplitude modulation with linear time-varying circuits. The former is to be studied in this lesson. 非線性器件的應(yīng)用解決了前面提到的振非線性器件的應(yīng)用解決了前面提到的振幅調(diào)制的關(guān)鍵問題，但又產(chǎn)生了新的失幅調(diào)制的關(guān)鍵問題，但又產(chǎn)生了新的失真問題。真問題。The above-mentioned key problem of amp

20、litude modulation is solved by using nonlinear devices. However, the distortion occurs as a new problem. 結(jié)束結(jié)束 End目錄目錄 Content幫助幫助 Help第五章振幅調(diào)制與解調(diào)第五章振幅調(diào)制與解調(diào)第第 1 頁頁 Page 1Chapter 5 Amplitude modulation and demodulation西安電子科技大學(xué)西安電子科技大學(xué) Xidian University普通調(diào)幅信號(hào)普通調(diào)幅信號(hào) Amplitude modulated signal雙邊帶調(diào)制信號(hào)雙邊帶調(diào)制

21、信號(hào) Double-sideband modulated signal單邊帶調(diào)制信號(hào)單邊帶調(diào)制信號(hào) Single-sideband modulated signal調(diào)制信號(hào)調(diào)制信號(hào) Modulating signal u( t ) = U mcos t 載波載波 carrier waveuC ( t ) = U Cmcos Ct C C+ C CUmUCm繼續(xù)繼續(xù) Continue經(jīng)過調(diào)制，得到的振幅調(diào)制信號(hào)可能包含三個(gè)頻率分量。角頻率為經(jīng)過調(diào)制，得到的振幅調(diào)制信號(hào)可能包含三個(gè)頻率分量。角頻率為 C， C + 和和 C - 的頻率分量可以分別叫做載頻分量，上邊頻分量和下邊頻分量。的頻率分量可以

22、分別叫做載頻分量，上邊頻分量和下邊頻分量。After the modulation, the obtained amplitude modulated signal may contain three frequency components. Those with the angular frequencies of C , C + and C - are termed as the carrier component, the upper side-frequency component and the lower side-frequency component respectively

23、. 現(xiàn)在，我們開始學(xué)習(xí)本次課程的內(nèi)容。進(jìn)行振幅調(diào)制的目的是把低頻現(xiàn)在，我們開始學(xué)習(xí)本次課程的內(nèi)容。進(jìn)行振幅調(diào)制的目的是把低頻的語音、圖象等調(diào)制信號(hào)寄載到高頻載波上，從而實(shí)現(xiàn)信息的遠(yuǎn)程無的語音、圖象等調(diào)制信號(hào)寄載到高頻載波上，從而實(shí)現(xiàn)信息的遠(yuǎn)程無線傳輸。線傳輸。 Now, lets start the lesson. The amplitude modulation is aimed at mounting the low-frequency audio or visual modulating signal onto a high-frequency carrier wave, so that

24、 the information can be transmitted wirelessly at a long distance. 為簡(jiǎn)單起見，我們認(rèn)為調(diào)制信號(hào)和載波都是單頻為簡(jiǎn)單起見，我們認(rèn)為調(diào)制信號(hào)和載波都是單頻信號(hào)。這里給出了它們的時(shí)域表達(dá)式。信號(hào)。這里給出了它們的時(shí)域表達(dá)式。For simplicity, the modulating signal and the carrier wave are supposed to be single-frequency signals. These are their time-domain expressions. 在頻域上，調(diào)制信號(hào)和載波

25、都可以在頻域上，調(diào)制信號(hào)和載波都可以用其角頻率和振幅表示。用其角頻率和振幅表示。The modulating signal and the carrier wave are expressed in the frequency domain by using their angular frequencies and amplitudes. 包含所有三個(gè)頻率分量的信號(hào)稱為普通調(diào)幅信號(hào)，包含所有三個(gè)頻率分量的信號(hào)稱為普通調(diào)幅信號(hào)，只包含上邊頻分量和下邊頻分量的信號(hào)稱為雙邊只包含上邊頻分量和下邊頻分量的信號(hào)稱為雙邊帶調(diào)制信號(hào)，而單邊帶調(diào)制信號(hào)則只有上邊頻分帶調(diào)制信號(hào)，而單邊帶調(diào)制信號(hào)則只有上邊頻分

26、量或下邊頻分量中的一個(gè)。量或下邊頻分量中的一個(gè)。The signal with all three frequency components is called an amplitude modulated signal. That only with the upper and the lower side-frequency components is called a double-sideband modulated signal. The single-sideband modulated signal has only one of the side-frequency compo

27、nents. 結(jié)束結(jié)束 End目錄目錄 Content幫助幫助 Help第五章振幅調(diào)制與解調(diào)第五章振幅調(diào)制與解調(diào)第第 2 頁頁 Page 2Chapter 5 Amplitude modulation and demodulation振幅調(diào)制方法振幅調(diào)制方法 Amplitude modulation approaches非線性器件調(diào)幅非線性器件調(diào)幅 Amplitude modulation with nonlinear devices線性時(shí)變電路調(diào)幅線性時(shí)變電路調(diào)幅 Amplitude modulation with linear time-varying circuits頻域：頻域： C +

28、 ， C - Frequency domain: C + ， C - 振幅調(diào)制的關(guān)鍵問題振幅調(diào)制的關(guān)鍵問題 Key problem of amplitude modulation時(shí)域：時(shí)域：uC uTime domain: uC u西安電子科技大學(xué)西安電子科技大學(xué) Xidian University繼續(xù)繼續(xù) Continue為了生成前面的三種振幅調(diào)制信號(hào)，進(jìn)行振幅調(diào)制時(shí)，在時(shí)域上為了生成前面的三種振幅調(diào)制信號(hào)，進(jìn)行振幅調(diào)制時(shí)，在時(shí)域上要將調(diào)制信號(hào)和載波相乘，在頻域上看，這樣的相乘會(huì)生成上邊要將調(diào)制信號(hào)和載波相乘，在頻域上看，這樣的相乘會(huì)生成上邊頻分量和下邊頻分量，這個(gè)關(guān)鍵問題的解決需要用到非線

29、性電路。頻分量和下邊頻分量，這個(gè)關(guān)鍵問題的解決需要用到非線性電路。In order to generate the above three amplitude modulated signals, during the amplitude modulation, the modulating signal will be multiplied by the carrier wave in the time domain, which will produce the upper and the lower side-frequency components in the frequency d

30、omain. Nonlinear circuits are to be used to solve this key problem. 用非線性電路進(jìn)行振幅調(diào)制的方法有兩種，一種是利有源器件，如晶體管或場(chǎng)效應(yīng)管的用非線性電路進(jìn)行振幅調(diào)制的方法有兩種，一種是利有源器件，如晶體管或場(chǎng)效應(yīng)管的非線性實(shí)現(xiàn)調(diào)幅，另一種是基于線性時(shí)變電路實(shí)現(xiàn)調(diào)幅。非線性實(shí)現(xiàn)調(diào)幅，另一種是基于線性時(shí)變電路實(shí)現(xiàn)調(diào)幅。There are two types of amplitude modulation approach with the use of nonlinear circuits. One approach is t

31、o make use the nonlinear property of active devices, such as the transistor and the FET. The other approach is based on linear time-varying circuits.結(jié)束結(jié)束 End目錄目錄 Content幫助幫助 Help第五章振幅調(diào)制與解調(diào)第五章振幅調(diào)制與解調(diào)第第 3 頁頁 Page 3Chapter 5 Amplitude modulation and demodulation)(tu)(Ctu)(AMtu+CE+BE+)(Cti)(BEtu+)(betu西

32、安電子科技大學(xué)西安電子科技大學(xué) Xidian University繼續(xù)繼續(xù) Continueube (t) 經(jīng)過經(jīng)過 EB 的偏置，產(chǎn)生晶體管的輸入電壓的偏置，產(chǎn)生晶體管的輸入電壓 uBE(t)。With the biasing of EB upon ube (t), we get uBE(t), the input voltage on the transistor. 接下來，在接下來，在 uBE(t) 的作用下，晶體管產(chǎn)生輸出的作用下，晶體管產(chǎn)生輸出電流電流 iC(t)。In the following, the transistor generates the output curren

33、t iC(t) in response to uBE(t).該圖實(shí)際上給出了一個(gè)放大器電路。首先，載該圖實(shí)際上給出了一個(gè)放大器電路。首先，載波波 uC (t)和調(diào)制信號(hào)和調(diào)制信號(hào) u (t) 疊加產(chǎn)生交流輸入電疊加產(chǎn)生交流輸入電壓壓 ube (t)。The diagram is actually an amplifier circuit, where the carrier wave uC (t) and the modulating signal u (t) are added up first to produce the alternating input voltage ube (t)

34、. 最后，最后，iC(t) 經(jīng)由經(jīng)由 LC 并聯(lián)諧振回路選頻，產(chǎn)生并聯(lián)諧振回路選頻，產(chǎn)生普通調(diào)幅信號(hào)普通調(diào)幅信號(hào) uAM (t)。Finally, iC (t) flows through the frequency-selecting LC parallel resonant circuit, and produces an amplitude modulated signal uAM (t). 現(xiàn)在我們學(xué)習(xí)第一種振幅調(diào)制方法，即非線性器件調(diào)幅方法。該方法現(xiàn)在我們學(xué)習(xí)第一種振幅調(diào)制方法，即非線性器件調(diào)幅方法。該方法的原理電路如圖所示。的原理電路如圖所示。Now we come to lear

35、n the first amplitude modulation approach, i.e., the nonlinear-device amplitude modulation. Here is the basic circuit diagram of this approach. 結(jié)束結(jié)束 End目錄目錄 Content幫助幫助 Help第五章振幅調(diào)制與解調(diào)第五章振幅調(diào)制與解調(diào)第第 4 頁頁 Page 4Chapter 5 Amplitude modulation and demodulationtuC(t)0tu(t)0tube(t)0步驟步驟1 載波和調(diào)制信號(hào)載波和調(diào)制信號(hào)相加產(chǎn)生輸

36、入電壓相加產(chǎn)生輸入電壓 Adding up the carrier wave and the modulating signal to produce the input voltage)(tu)(Ctu+BE+)(BEtu+)(betu西安電子科技大學(xué)西安電子科技大學(xué) Xidian University繼續(xù)繼續(xù) Continue前面簡(jiǎn)要描述了非線性器件調(diào)幅的過程，在此基礎(chǔ)前面簡(jiǎn)要描述了非線性器件調(diào)幅的過程，在此基礎(chǔ)上，我們接下來觀察并研究該過程中一些值得注意上，我們接下來觀察并研究該過程中一些值得注意的細(xì)節(jié)。非線性器件調(diào)幅的原理電路可以分解為輸?shù)募?xì)節(jié)。非線性器件調(diào)幅的原理電路可以分解為輸入級(jí)

37、回路，晶體管和輸出級(jí)回路三部分，每部分各入級(jí)回路，晶體管和輸出級(jí)回路三部分，每部分各自完成振幅調(diào)制過程的一個(gè)步驟。自完成振幅調(diào)制過程的一個(gè)步驟。The process of the nonlinear-device amplitude modulation has been briefly described, based on which, we now come to observe and study some details in the process. The basic circuit can be decomposed into three parts, namely, the

38、 input loop, the transistor, and the output loop. Each part of the circuit performs one step of the amplitude modulation. 現(xiàn)在我們實(shí)時(shí)觀察現(xiàn)在我們實(shí)時(shí)觀察 uC (t)，u (t) 和和 ube (t) 的波形。注意載波的頻率遠(yuǎn)大于調(diào)的波形。注意載波的頻率遠(yuǎn)大于調(diào)制信號(hào)的頻率，而其振幅也大于調(diào)制制信號(hào)的頻率，而其振幅也大于調(diào)制信號(hào)的振幅。二者疊加產(chǎn)生的交流輸信號(hào)的振幅。二者疊加產(chǎn)生的交流輸入電壓入電壓 ube (t) 的高頻振蕩與載波一致，的高頻振蕩與載波一致，其起伏與調(diào)制

39、信號(hào)同步。其起伏與調(diào)制信號(hào)同步。Now, lets make a real-time observation of the waveforms of uC (t), u (t) and ube (t). It should be noticed that the carrier wave frequency is much higher than the modulating signal frequency. The same can be said of their amplitudes. The alternating input voltage ube (t) out of the a

40、ddition oscillates according to the carrier wave, whereas it rises and falls in accordance with the modulating signal. 首先，我們看第一個(gè)步驟。這是在輸入級(jí)回路首先，我們看第一個(gè)步驟。這是在輸入級(jí)回路中完成的，載波中完成的，載波 uC (t) 和調(diào)制信號(hào)和調(diào)制信號(hào) u (t) 在這里在這里相疊加產(chǎn)生交流輸入電壓相疊加產(chǎn)生交流輸入電壓 ube (t)。First, lets focus on step one, which is accomplished in the input

41、 loop, where the carrier wave uC (t) and the modulating signal u (t) are added up to produce the alternating input voltage ube (t). 結(jié)束結(jié)束 End目錄目錄 Content幫助幫助 HelptuC(t)0tu(t)0tube(t)0iC0uBEtuBE0EBiC0QICQEBICQt第五章振幅調(diào)制與解調(diào)第五章振幅調(diào)制與解調(diào)第第 5 頁頁 Page 5Chapter 5 Amplitude modulation and demodulation步驟步驟2 非線性器件

42、產(chǎn)生非線性器件產(chǎn)生輸出電流輸出電流 The nonlinear device generates the output currentCEBE)(BEtu+Ci西安電子科技大學(xué)西安電子科技大學(xué) Xidian University繼續(xù)繼續(xù) Continue我們現(xiàn)在把第一我們現(xiàn)在把第一個(gè)點(diǎn)垂直投影到個(gè)點(diǎn)垂直投影到轉(zhuǎn)移特性曲線上。轉(zhuǎn)移特性曲線上。Now, we vertically project the first point onto the transfer characteristic curve. 對(duì)對(duì) uBE(t) 中的每個(gè)點(diǎn)都中的每個(gè)點(diǎn)都進(jìn)行這樣的投影，我們進(jìn)行這樣的投影，我們就最終可

43、以得到就最終可以得到 iC (t) 的的波形。波形。Well finally get the iC (t) waveform after each uBE(t) point is thus projected. 在該投影過程中，我們可以發(fā)在該投影過程中，我們可以發(fā)現(xiàn)，晶體管的非線性，更確切現(xiàn)，晶體管的非線性，更確切地說，其轉(zhuǎn)移特性的非線性，地說，其轉(zhuǎn)移特性的非線性，引起了引起了 iC (t) 波形的變化。波形的變化。In the projecting process, we discover that, the nonlinearity of the transistor, or more a

44、ccurately, the nonlinearity of the transistors transfer characteristic, should be responsible for the alteration in the iC (t) waveform. 下面我們研究這樣的波形變化是如下面我們研究這樣的波形變化是如何產(chǎn)生的。我們首先在何產(chǎn)生的。我們首先在 uBE (t) 的波的波形上選取若干個(gè)點(diǎn)，接下來觀察這形上選取若干個(gè)點(diǎn)，接下來觀察這些點(diǎn)是怎樣投影確定些點(diǎn)是怎樣投影確定 iC (t) 的波形的。的波形的。 Next, lets find out how the wavef

45、orm alteration occurs. First, we select a couple of points on the uBE (t) waveform, then well observe in what way iC (t) is determined by the projection of these points. 接下來把該點(diǎn)水接下來把該點(diǎn)水平投影到平投影到 iC (t) 圖圖中該點(diǎn)對(duì)應(yīng)的時(shí)中該點(diǎn)對(duì)應(yīng)的時(shí)刻?？?。Next, we poject the point horizontally onto its corresponding instant in the iC

46、(t) diagram. 借助于該特性曲線，我借助于該特性曲線，我們可以通過投影方式從們可以通過投影方式從 uBE (t) 的波形畫出的波形畫出 iC (t) 的波形。的波形。With the characteristic curve, we can draw the waveform of iC (t) from uBE (t) by way of projection. 這里給出了晶體管的轉(zhuǎn)移特性這里給出了晶體管的轉(zhuǎn)移特性曲線，它描述了晶體管的輸入曲線，它描述了晶體管的輸入電壓電壓 uBE 和輸出電流和輸出電流 iC 的關(guān)系。的關(guān)系。Here is the transfer charact

47、eristic curve of the transistor, which describes the relation between the input voltage uBE and the output current iC. 這樣我們得到了這樣我們得到了 iC (t) 波形上的一個(gè)點(diǎn)。波形上的一個(gè)點(diǎn)。Therefore, one point on the iC (t) waveform is obtained. 如果將波形放大，我們會(huì)注意到如果將波形放大，我們會(huì)注意到 iC (t) 的波形和的波形和 uBE (t) 的波形并不一樣。的波形并不一樣。 與與 uBE (t) 比較而言，

48、比較而言，iC (t) 的上半周的上半周變得較為尖銳，而下半周則變得較為平緩。變得較為尖銳，而下半周則變得較為平緩。 If the waveforms are magnified, it will come to our attention that the waveforms of iC (t) and uBE (t) are not identical. Compared to uBE (t), the upper part of iC (t) becomes sharper, whereas its lower part becomes smoother. 接下來，我們看第二個(gè)步驟。這是

49、在晶體管中完接下來，我們看第二個(gè)步驟。這是在晶體管中完成的，交流輸入電壓成的，交流輸入電壓 ube (t) 經(jīng)過經(jīng)過 EB 的偏置后，的偏置后，成為晶體管的輸入電壓成為晶體管的輸入電壓 uBE (t)，在其作用下，晶，在其作用下，晶體管產(chǎn)生輸出電流體管產(chǎn)生輸出電流 iC(t)。Next, lets focus on the second step, which is accomplished in the transistor, where the alternating input voltage ube (t) is biased by EB and the input voltage u

50、BE (t) is produced, activated by which, the transistor generates the output current iC(t). 結(jié)束結(jié)束 End目錄目錄 Content幫助幫助 Help0beCnnnuai2be2be10uauaaiC0uBEtuBE0EBiC0QICQEBICQt第五章振幅調(diào)制與解調(diào)第五章振幅調(diào)制與解調(diào)第第 5 頁頁 Page 5Chapter 5 Amplitude modulation and demodulation)(BECufi 0beB)(C)(!1nnnuEfnibeBBEuEu)(!1B)(Efnannt

51、UutUuuuucoscosmCCmCCbe)(tu)(Ctu+BE+)(BEtu+)(betu西安電子科技大學(xué)西安電子科技大學(xué) Xidian University繼續(xù)繼續(xù) Continue為了對(duì)為了對(duì) iC 進(jìn)行分析，我們將其近似表示成前三項(xiàng)級(jí)進(jìn)行分析，我們將其近似表示成前三項(xiàng)級(jí)數(shù)和。利用已知的數(shù)和。利用已知的 ube，uC 和和 u 的表達(dá)式，我們可的表達(dá)式，我們可以得到以得到 iC 的一個(gè)具體結(jié)果。的一個(gè)具體結(jié)果。In order to analyze iC , we use the first three series to approximate it. A detailed res

52、ult of iC is derived by using the available expressions of ube, uC and u . 我們寫出晶體管轉(zhuǎn)移特性曲線的表達(dá)式，當(dāng)然這里的函數(shù)我們寫出晶體管轉(zhuǎn)移特性曲線的表達(dá)式，當(dāng)然這里的函數(shù) f 是非線性函數(shù)。是非線性函數(shù)。We write down the expression of the transistors transfer characteristic curve, where the function f is of course a nonlinear one. 這種非線性過程導(dǎo)致的波形變化暗示了這種非線性過程導(dǎo)致的波

53、形變化暗示了 iC (t) 中含有中含有 uBE (t) 中中沒有的新的頻率分量，下面我們通過解析方法確定沒有的新的頻率分量，下面我們通過解析方法確定 iC (t) 中有中有哪些頻率分量。哪些頻率分量。The waveform alteration caused by the nonlinear process indicates iC (t) contains some new frequency components besides those of uBE (t). In the following, well determine the iC (t) components. 參考原理電

54、路中的輸入級(jí)回路，我參考原理電路中的輸入級(jí)回路，我們還可以寫出晶體管輸入電壓們還可以寫出晶體管輸入電壓 uBE(t)。We can also write down uBE(t), the input voltage of the transistor, referring to the input loop of the basic circuit diagram. 這里，我們把這里，我們把 iC 展開成泰勒級(jí)數(shù)，展開的展開成泰勒級(jí)數(shù)，展開的中心位置選在中心位置選在 EB ，這樣就把晶體管輸出電，這樣就把晶體管輸出電流流 iC 表示成了交流輸入電壓表示成了交流輸入電壓 ube 的級(jí)數(shù)和的的級(jí)數(shù)

55、和的形式。形式。Next, we expand iC into a Taylor series. The expansion is centered at EB , therefore the output current of the transistor, iC, is expressed as the summation of the series about ube, the alternating input voltage. 結(jié)束結(jié)束 End目錄目錄 Content幫助幫助 Help第五章振幅調(diào)制與解調(diào)第五章振幅調(diào)制與解調(diào)第第 6 頁頁 Page 6Chapter 5 Amplit

56、ude modulation and demodulation步驟步驟3 濾波產(chǎn)生已調(diào)波濾波產(chǎn)生已調(diào)波 Produce the modulated wave by filtering)(AMtu+CE+)(Ctim1Ua2m22Ua22Cm22UaC2tUatUUatUUatUatUatUaUUaaiC2Cm2CCmm2CCmm2CCm12m2m12Cm2m20C2cos2)cos()cos(cos2cos2cos)(2IC()0 Cmm2UUaCCmm2UUaCCm1UaC)(22Cm2m20UUaa西安電子科技大學(xué)西安電子科技大學(xué) Xidian University中間三項(xiàng)分別是載頻分量，

57、下邊頻分量和上邊頻分量。中間三項(xiàng)分別是載頻分量，下邊頻分量和上邊頻分量。The three items in the middle are respectively the carrier, the upper side-frequency, and the lower side-frequency components. 我們根據(jù)其角頻率和振幅在頻域我們根據(jù)其角頻率和振幅在頻域上畫出該頻率分量。上畫出該頻率分量。We draw this component in the frequency domain according to its angular frequency and ampli

58、tude. 現(xiàn)在畫出該頻率分量?，F(xiàn)在畫出該頻率分量。Now, we draw this component. 最后一項(xiàng)的角頻率為最后一項(xiàng)的角頻率為 2 C。 The last item has an angular frequency of 2 C. 我們也畫出該頻率分量。我們也畫出該頻率分量。We draw this component too. 這三個(gè)頻率分量對(duì)我們是有用的。這三個(gè)頻率分量對(duì)我們是有用的。These three components are useful for us. 這樣我們就可以方便地畫出這樣我們就可以方便地畫出 iC 的頻譜，從而由前面的時(shí)域分析的頻譜，從而由前面的

59、時(shí)域分析過渡到后面的頻域分析。過渡到后面的頻域分析。So we can easily plot the spectrum of iC, and advance from the previous time-domain analysis to the following frequency-domain analysis. 現(xiàn)在，我們來到非線性器件調(diào)幅的第三步。前面得現(xiàn)在，我們來到非線性器件調(diào)幅的第三步。前面得到的到的 iC 的具體結(jié)果經(jīng)過整理，可以寫成其各個(gè)頻率的具體結(jié)果經(jīng)過整理，可以寫成其各個(gè)頻率分量疊加的形式。分量疊加的形式。We now come to the third step o

60、f the nonlinear-device amplitude modulation. The previously derived iC is reorganized and written down here in the addition form of its various frequency components. 現(xiàn)在畫出該分量。現(xiàn)在畫出該分量。Now, lets draw this component. 表達(dá)式的第一項(xiàng)是直流分量。表達(dá)式的第一項(xiàng)是直流分量。 The first item in the expression is a direct component. 第二項(xiàng)是