第六章,School of Communication and Information Engineering,第六章 角度的調(diào)制與解調(diào),School of Communication and Information Engineering,6.1 調(diào)角波的性質(zhì),調(diào)頻：FM 高頻振蕩的頻率受調(diào)制信號(hào)的控制,調(diào)相：PM 高頻振蕩的相位受調(diào)制信號(hào)的控制,等幅波：v(t)=Vmcos (t)= Vmcos(t)+0,初始相位,School of Communication and Information Engineering,調(diào)頻波、調(diào)相波：,1.調(diào)頻波,(t) = C + Kfv(t),若設(shè)調(diào)制信號(hào) v(t) = Vmcost,(t) = C + KfVm cost,m,(最大角頻率偏移與Vm成正比，與無關(guān)),School of Communication and Information Engineering,最大相位偏移，與成反比 調(diào)頻指數(shù),表達(dá)式：v(t) = Vmcos(Ct + mf sint),圖,School of Communication and Information Engineering,2. 調(diào)相波,(t) = Ct + KPV(t),設(shè)調(diào)制信號(hào)：v(t) = Vmcost,(t) = Ct + KPVmcost,mP,最大相位偏移，與Vm成正比、與無關(guān) 調(diào)相指數(shù),(t) = C mP sint,m,與成正比,v(t) = Vmcos( Ct + mPcost ),圖,School of Communication and Information Engineering,v(t) = Vmcos( Ct + mPcost ) PM,v(t) = Vmcos( Ct + mfsint ) FM,設(shè)調(diào)制信號(hào) v(t) = Vmcost 情況下：,當(dāng) 恒定時(shí)，調(diào)頻波,當(dāng) 恒定時(shí)，調(diào)相波,School of Communication and Information Engineering,設(shè)有一組正弦調(diào)制信號(hào)，信號(hào)頻率最低為 最高為 。調(diào)制信號(hào)為等幅振蕩。調(diào)頻時(shí)，最 大頻偏 ；調(diào)相時(shí)，最大相偏 試求調(diào)頻時(shí)調(diào)制指數(shù) 的變化范圍及調(diào)相時(shí)最大頻偏 的范圍。,例1.,School of Communication and Information Engineering,1. 調(diào)頻時(shí):,School of Communication and Information Engineering,2. 調(diào)相時(shí):,School of Communication and Information Engineering,調(diào)制信號(hào)v(t) 為周期重復(fù)的三角波。 畫出調(diào)頻波和調(diào)相波.,例2.,調(diào)頻9-1圖,調(diào)9-2相圖,School of Communication and Information Engineering,二. 調(diào)角信號(hào)的頻譜,FM、PM波的數(shù)學(xué)表示式是相似的，統(tǒng)一寫成調(diào)角波表示式,利用角函數(shù)展開：,在貝塞爾函數(shù)理論中，已經(jīng)證明存在下列關(guān)系：,School of Communication and Information Engineering,式中 是以m為宗數(shù)的n階第一 類貝塞爾函數(shù)。代入上式，整理得：,School of Communication and Information Engineering,調(diào)角的頻譜為：,無限多對(duì)上、下邊頻分量 當(dāng)n為偶數(shù)時(shí)，上、下邊頻分量相加 當(dāng)n為奇數(shù)時(shí)，上、下邊頻分量相減,School of Communication and Information Engineering,當(dāng)調(diào)制指數(shù) m 增大時(shí)，則具有較大 振幅的邊頻分量也增加。,當(dāng)m為某些特定值時(shí)，如m=2.405、 5.520、8.653、載波分量成 分 。用來測(cè)量頻偏 和調(diào)制指數(shù) 。,School of Communication and Information Engineering,第一類貝塞爾函數(shù),School of Communication and Information Engineering,三、調(diào)角信號(hào)的頻譜寬度,m1,窄帶調(diào)制,m很小，近似：,調(diào)角信號(hào)的頻譜與AM波頻譜相似。由 構(gòu)成。差別就是下邊頻的相位相反。頻譜寬度為 rad/s. 它廣泛運(yùn)用于移動(dòng)通信中。,School of Communication and Information Engineering,2) 寬帶調(diào)制 m1,頻譜是無限寬的，認(rèn)為當(dāng)邊頻幅度小于載頻的10%時(shí)，即忽略這些邊頻。因此，實(shí)際調(diào)角信號(hào)所占的有效頻譜寬度是有限的。當(dāng)m1時(shí)，m+1 以上各階頻譜的幅度均小于載波幅度10%。因而可以忽略。,School of Communication and Information Engineering,有效頻譜寬度為：,以上討論的是單音調(diào)制情況。,實(shí)際上，調(diào)制信號(hào)中包括很多頻率分量，設(shè)最高頻率 Fmax,School of Communication and Information Engineering,四. 各種調(diào)制方式的比較：,1. 抗干擾能力：,調(diào)角波的幅度不帶有調(diào)制信號(hào)的信息, 抗干擾能力強(qiáng).,2.信號(hào)頻譜及帶寬：,設(shè)調(diào)制信號(hào)的頻率F：（m1）,School of Communication and Information Engineering,FM與PM的比較：,但當(dāng)增加時(shí), 調(diào)頻:,調(diào)相:,School of Communication and Information Engineering,3. 設(shè)備的利用率,AM:,FM、PM：,調(diào)角波振幅不變，工作在最大工作 狀態(tài).,功率：,School of Communication and Information Engineering,根據(jù)第一類貝塞爾函數(shù)特性：,上式表明，當(dāng) 一定時(shí)，不論 為何值，調(diào)頻波的平均功率恒為定值，并且等于未調(diào)制的載波頻率。換句話說， 改變僅會(huì)引起載波分量和各邊帶分量之間功率的重新分配，但不會(huì)引起總功率的改變。,School of Communication and Information Engineering,例3.,已知,求(1)此時(shí)FM波和PM波的帶寬? (2)若 不變,F 增大一倍兩種調(diào)制信號(hào)的 帶寬如何? (3)若F 不變, 增大一倍兩種調(diào)制信號(hào)的 帶寬如何? (4)若 、F都增大一倍兩種調(diào)制信號(hào)的帶 寬如何?,School of Communication and Information Engineering,School of Communication and Information Engineering,School of Communication and Information Engineering,6.2 調(diào)頻的方法,間接調(diào)頻： 對(duì)調(diào)制信號(hào)先積分后調(diào)相 ( fC 較穩(wěn)定，但是頻偏小 ),直接調(diào)頻： 對(duì)振蕩器直接進(jìn)行頻率調(diào)制 ( 可獲大頻偏，但 fC 不穩(wěn)定 ),School of Communication and Information Engineering,1. 調(diào)制特性,要線性,調(diào)頻電路輸出電壓的頻率偏移與調(diào)制電壓的關(guān)系（ fV ）,一. 調(diào)頻電路的指標(biāo)：,School of Communication and Information Engineering,4. 1% 大頻偏 1% 小頻偏,單位調(diào)制電壓變化所產(chǎn)生的頻率偏移,3. 中心頻率 ( 載波頻率 ),要穩(wěn)定,2. 調(diào)制靈敏度：,School of Communication and Information Engineering,利用它的結(jié)電容受反向外加電壓控制而變化來實(shí)現(xiàn)調(diào)頻。,1. 變?nèi)荻O管,Cj0 反向電壓v = 0 時(shí)的結(jié)電容 VD PN結(jié)內(nèi)建電位差( 很小) 電容的變化指數(shù),二. 變?nèi)荻O管直接調(diào)頻電路：,School of Communication and Information Engineering,CjQ,當(dāng)調(diào)制信號(hào)為：,=,School of Communication and Information Engineering,School of Communication and Information Engineering,靜態(tài)時(shí)的結(jié)電容：,結(jié)電容的調(diào)制度,School of Communication and Information Engineering,2. 變?nèi)莨茏髡袷幓芈返目傠娙?,C1 隔直作用 C2 高頻濾波電容 ( 對(duì)高頻短路，對(duì)開路 ) L1 高頻扼流圈,大頻偏直接調(diào)制電路,應(yīng)滿足： | VQ | Vm,圖,School of Communication and Information Engineering,瞬時(shí)振蕩角頻率為:,School of Communication and Information Engineering,線性調(diào)制,最大角頻偏,中心頻率偏移,基波分量,兩次諧波分量,調(diào)制特性分析:,這時(shí)，調(diào)頻波獲得最大角頻偏為,School of Communication and Information Engineering,最大角頻偏,School of Communication and Information Engineering,例 調(diào)頻振蕩回路有電感L和變?nèi)荻O管組成。L=2mH,變?nèi)荻O管的參數(shù)為：,(1)載波fc,(2)由調(diào)制信號(hào)引起的載波漂移fc,(3)最大頻偏fm,(4)調(diào)頻系數(shù)kf,(5)二階失真系數(shù),School of Communication and Information Engineering,School of Communication and Information Engineering,School of Communication and Information Engineering,School of Communication and Information Engineering,140MHz的變?nèi)莨苤苯诱{(diào)頻電路,150pF,VQ,p型濾波,School of Communication and Information Engineering,L1與變?nèi)莨蹸j構(gòu)成振蕩回路并與晶體管Q1接成電感三點(diǎn)式 振蕩電路。,變?nèi)莨艿闹绷麟妷浩脧恼娫捶€(wěn)壓電路中通過兩個(gè)470W 電位器取出一部分提供，作為VQ。,調(diào)制信號(hào)通過1.7mH的高頻扼流圈L2和兩個(gè)150pF電容 C1、C2接成的p型濾波網(wǎng)絡(luò)加到變?nèi)莨苌稀?School of Communication and Information Engineering,C3為高頻濾波電容,小頻偏的直接調(diào)頻電路,3. 變?nèi)莨懿糠纸尤胝袷幓芈?,圖,School of Communication and Information Engineering,展開成冪級(jí)數(shù)，只考慮二次方項(xiàng)：,School of Communication and Information Engineering,C1、C2 的引入，使Cj 對(duì)回路總電容的影響減小， 從而c 的穩(wěn)定性提高,P ,m ,討論： C2 P1 C1 P2,School of Communication and Information Engineering,試指出各元器件的作用；畫出高頻等效電路；計(jì)算最大頻偏fm=？,School of Communication and Information Engineering,等效電路圖,克拉潑振蕩器,各元器件的作用略。,School of Communication and Information Engineering,最大頻偏：,School of Communication and Information Engineering,例：對(duì)題圖所示的變?nèi)莨苤苯诱{(diào)頻電路。 （1）說明電路中各元件的作用； （2）畫出該調(diào)頻振蕩器的高頻通路、變?nèi)莨艿闹绷魍泛鸵纛l通 路。 （3）若已知 ，變?nèi)莨芙Y(jié)電容 , 調(diào)頻指數(shù)mf =5，當(dāng)vW=0時(shí)的振蕩頻率為 fc=90MHz，試求變 容管所需的直流偏置電壓VQ，最大頻偏fm以及調(diào)制信號(hào)的 振幅VWm 。,School of Communication and Information Engineering,(1)R1、R2、R3、R4為晶體管提供直流偏置和直流通路，R4、R5、R6、R7為 變?nèi)莨芴峁┲绷鞣雌煤椭绷魍罚?000pF，0.001mF、0.002mF均為高頻 旁路電容，即高頻交流通路；47mH為高頻扼流圖，對(duì)高頻近似開路，對(duì)直 流、低頻近似短路；47 mF為隔直電容，對(duì)低頻近似短路；C1、C2、C3、 C4、C5、Cj和電感L1與晶體管Q1構(gòu)成電容三點(diǎn)式振蕩器； L1、L2互感 耦合輸出vFM。,School of Communication and Information Engineering,(2)高頻通路,School of Communication and Information Engineering,(3),School of Communication and Information Engineering,School of Communication and Information Engineering,School of Communication and Information Engineering,一. 間接調(diào)頻的原理：用調(diào)相電路得到調(diào)頻波,滿足：RC 1,6.3 間接調(diào)頻電路,先將調(diào)制信號(hào)積分, (例如RC積分電路),再 進(jìn)行調(diào)相, 所得結(jié)果就 是調(diào)頻波. 這里, 采用 高穩(wěn)定的晶振作為主 振級(jí), 調(diào)相是在后級(jí)進(jìn) 行, 對(duì)晶振頻率無影響.,School of Communication and Information Engineering,用 進(jìn)行調(diào)相,產(chǎn)生的相位偏移為,相當(dāng)于調(diào)頻時(shí):,調(diào)相電路可以間接取得調(diào)頻波。,School of Communication and Information Engineering,二. 調(diào)相電路,School of Communication and Information Engineering,1. 變?nèi)莨苷{(diào)相器,School of Communication and Information Engineering,若加在變?nèi)荻O管的電壓：,則有：,School of Communication and Information Engineering,圖,School of Communication and Information Engineering,調(diào)相電路便轉(zhuǎn)為間接調(diào)頻電路。,根據(jù)上述原理構(gòu)成的電路:,圖,School of Communication and Information Engineering,見書P168(b)三級(jí)單回路,上式表明最大頻偏m 與c 無關(guān)。,School of Communication and Information Engineering,2. 可變時(shí)延法調(diào)相電路,School of Communication and Information Engineering,圖,m為最大時(shí)延差，n為諧波次數(shù),理論上m=0.5Tc，而實(shí)際上限制m 0.4Tc 。,可見，脈沖調(diào)相電路有線性相移較大的優(yōu)點(diǎn)，用于調(diào)頻廣播發(fā)射機(jī)。,School of Communication and Information Engineering,三、間接調(diào)頻與直接調(diào)頻電路在性能上的差別,1、直接調(diào)頻,P = 1,P = (1+P1)(1+P2+P1P2),在直接調(diào)頻電路中，最大頻偏 m與c 成正比， 而在間接調(diào)頻電路中，最大頻偏 m與c 無關(guān)。,School of Communication and Information Engineering,2、間接調(diào)頻,如果調(diào)制信號(hào)中包含min、max眾多頻率分量，則當(dāng)m一定時(shí)（Vm一定時(shí)）,越小,mf就越大。,School of Communication and Information Engineering,在間接調(diào)頻電路中，最大頻偏 必發(fā)生在最低調(diào)制信號(hào)頻率上，m=mf min,例如 F : 1003400Hz, 這時(shí)Fmin=100Hz,當(dāng)采用變?nèi)荻O管調(diào)相時(shí)，,當(dāng)采用三級(jí)變?nèi)莨苷{(diào)相時(shí)，,當(dāng)采用脈沖調(diào)相時(shí)，,School of Communication and Information Engineering,四、擴(kuò)展線性頻偏的方法,方法1: 倍頻,方法2：混頻 + 倍頻,圖,圖,School of Communication and Information Engineering,調(diào)角波在產(chǎn)生過程中或多或少附帶寄生調(diào)幅，當(dāng)傳輸?shù)浇邮斩藭r(shí)，也會(huì)在調(diào)頻波上出現(xiàn)寄生調(diào)幅。通常用限幅器來消除調(diào)頻波的寄生調(diào)幅。,限幅器的組成：,非線性元件 + 諧振回路,常用限幅器：,晶體二極管限幅器 晶體三極管限幅器 差分對(duì)限幅器,6.4 限幅器,School of Communication and Information Engineering,鑒頻方法：,1、斜率鑒頻器，相位鑒頻器，比例鑒頻器,2、移相正交鑒頻器,3、脈沖計(jì)數(shù)式鑒頻器,6.5 鑒頻器,圖,School of Communication and Information Engineering,3. 非線性失真,1. 靈敏度 SD ,fc處的鑒頻特性曲線的斜率,(要求大),2. 線性范圍： BPP 2fm,(要求大),(要求小),一. 主要指標(biāo),鑒頻特性曲線：,School of Communication and Information Engineering,(變換器) FM FM、AM,1. 單失諧的斜率鑒頻器,實(shí)現(xiàn)框圖：,二. 斜率鑒頻器,School of Communication and Information Engineering,vR(t)變?yōu)榉确从乘矔r(shí)頻率變化的調(diào)頻波，稱其為調(diào)頻-調(diào)幅 (FM-AM)波。而后通過包絡(luò)檢波器完成鑒頻功能。,School of Communication and Information Engineering,School of Communication and Information Engineering,其中,School of Communication and Information Engineering,在 處，,取得最大值，即,可得最大鑒頻靈敏度,School of Communication and Information Engineering,取較小的對(duì)稱區(qū)域作為頻偏，取,School of Communication and Information Engineering,L1,2. 平衡斜率鑒頻器,實(shí)際上，單調(diào)諧回路的諧振曲線，其傾斜部分的線性范圍 是很小的，為了擴(kuò)展鑒頻特性的線性范圍，實(shí)用的斜率鑒 頻器都是采用兩個(gè)單失諧回路構(gòu)成的平衡電路。,School of Communication and Information Engineering,成對(duì)稱失諧：f01 fC = fC f02,設(shè)包絡(luò)檢波效率均為kd則:,f 不能過大，也不能過小，,則鑒頻特性的線性范圍達(dá)到最大,School of Communication and Information Engineering,平衡斜率鑒頻器 主要工作波形圖,School of Communication and Information Engineering,三. 相位鑒頻器,相位鑒頻器是利用耦合諧振回路次級(jí)和初級(jí)間的 相移隨頻率變化的特性來實(shí)現(xiàn)鑒頻的。,下面介紹利用互感耦合相位鑒頻器的原理。,School of Communication and Information Engineering,2.平衡型疊加鑒相器,圖,School of Communication and Information Engineering,(b)相位鑒頻器檢波回路等效電路,(b)圖中，加在二級(jí)管D1和D2兩端的高頻電壓為：,School of Communication and Information Engineering,1. 頻相轉(zhuǎn)換網(wǎng)絡(luò),(a)初、次級(jí)回路,（b）次級(jí)回路,假設(shè)，圖(a)中，初次級(jí)回路參數(shù)完全相同，即 ，則得初、,次級(jí)回路的阻抗為：,School of Communication and Information Engineering,初級(jí)回路 通過互感在次級(jí)產(chǎn)生的感應(yīng)電勢(shì)為：,School of Communication and Information Engineering,School of Communication and Information Engineering,2. 矢量圖：,f =fC,VO = 0,f fC,VO 0,VO 0,f fC,School of Communication and Information Engineering,(fc),綜上所述，當(dāng)調(diào)頻信號(hào)的瞬時(shí)頻率以 為中心而按調(diào)制信號(hào)的規(guī)律變化時(shí)，以及 和 間的相位差， 和 的幅值等，都隨之化，從而形成了調(diào)幅調(diào)頻波。經(jīng)過檢波后的輸出電壓即為調(diào)制電壓。,School of Communication and Information Engineering,對(duì)V0作精確推導(dǎo)：,圖,School of Communication and Information Engineering,特點(diǎn)： （1）f ( , )是 的奇函數(shù)；,(2)每條曲線在= 時(shí)取得最大值，而=- 出現(xiàn)最小值， 所以正負(fù)峰值之間距離為2，,(3)一般取 =1.5 3.,School of Communication and Information Engineering,School of Communication and Information Engineering,2、,School of Communication and Inf