矿大通信原理课件CH 53 角度调制

1、CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1 1 0cos ttmtScmh(t)m(t)cosctSm(t)频域表达式频域表达式 HMMSccm 21CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2 2波形CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin3 3特点CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin4 4因为频率或相位的变化都可以看成是载波角度的因为频

2、率或相位的变化都可以看成是载波角度的变化，故调频和调相又统称为变化，故调频和调相又统称为。 。鉴于FM用得较多，本节将主要讨论频率调制。CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin5 5 ttAtAtsc cos)(cos)()()(tmKtP ，tSPM tftfdmKdttmKdttdt ，tSFM瞬时相位瞬时相位偏移偏移瞬时频率瞬时频率偏移偏移参数CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin6 6pKfK频谱 5 . 06 dmKtf当当FM信号的最大瞬时相位偏移满足信

3、号的最大瞬时相位偏移满足CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin7 7频谱 dmKtAdmKtAfcfcsinsincoscos dmKtAtsfcNBFMcos)( tdmAKtAcfc sincos CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin8 8宽带调频 ccNBFMAS ccccfMMAK 2 ccAMAS ccMM 21CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin9 9频谱 dmKAtAtsfmcWB

4、FMcos)(tAtmmm cos)( tmtAmfc sincos mmmmffffAKm CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1010带宽 nmcnWBFMtnmJAts cos)( nmcmcfnFMnnmJAS tmtAtsmfcWBFM sincos CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin11 11 maxmmfFMfffmB 2212调制实现CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin121

5、2d()dtm(t)gFMsPM(t)(b)PMsPM(t)m(t)(a)调制原理.与调制之间的关系与调制之间的关系CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1313 ()d tm(t)gPMsFM(t)(b)FMsFM(t)m(t)(a)调制器原理CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1414晶振PDLFVCO调制信号F(t)FM或PM信号VCO tm tsFM tmKf 0it .与调制器实现与调制器实现倍频实现FMCommunicationCommunicati

6、onCUMT LIShiyinCUMT LIShiyin1515.倍频法实现调制倍频法实现调制(阿姆斯特朗法阿姆斯特朗法) tm tsWBFM tc Acos tsNBFM2倍频CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1616 tt2ioass tso tsi ttcostci As t2t2cos121tc2o aAs t2t2cos21c2 aA阿姆斯特朗法CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1717阿姆斯特朗法阿姆斯特朗法解调原理 tsWBFM tm tf1

7、2cos tf22cos 111fmff 111111fmnfnfn 1111211fmnfnffn 212112211.nnn1fmn.fn.ffn tsWBFM 212112211.nnn1ffcmnm.fnf.ffnfCommunicationCommunicationCUMT LIShiyinCUMT LIShiyin1818 tFMcFMdmKtttAtS )(cos)(，) t (Sd ttsintmKA)t (Scfcd tmKK)t (mfpo tu 鉴频鉴频特性特性pK性能分析CommunicationCommunicationCUMT LIShiyinCUMT LIShiy

8、in1919 tFMcFMdmKtttAtS )(cos)(，)(cos)()(tttVtnci FMFMiiBnABnANS020222 )(tniCommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2020 ，ttAtScFM cos)()(cos)()(tttVtnci FMiiBnANS022 )(cos)()(cos)()(tttVttAtntSScciFMit )(costttVc CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2121)()(cos)()()(sin)(a

9、rctan)()(tttVAtttVtt )()(sin)()()(ttAtVtt ，所以所以 )(tVA 0)()(sin)()()(cos)()()(sin)( AtttVtttVAtttV AtttVAtttV)()(sin)()()(sin)(arctan 微分器输出CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2222 )t ()t (sin)t (V)t (dn tn)t ()t ()t (sinA)t (V)t ()t (d tfdmKt 噪声功率 tsintsin)t (Vtcostcos)t (V)t (tsin)t

10、(V)t (cccin )t (sin)t (V)t (sn CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2323 )()(sin)()(tttVtdn )(sin)()()(sin)()(ttVttttVtscinn FMisdBntntntn0222 2B,20FMidfnfPfP 双双输出信号和噪声由于，由于，nd(t)、ns(t)为低通信号，而为低通信号，而ni(t)带通信号，因带通信号，因此此,前者的带宽是后者的一半，即前者的带宽是后者的一半，即BFM/2。所以有。所以有CommunicationCommunicationC

11、UMT LIShiyinCUMT LIShiyin2424dttdnAdttddttdtVdo)(1)()()( tV0dttd)(21 鉴频鉴频特性特性 )()(sin)()(1,)(0tttVtAddndttdntn 其中其中 tmKSfo22 tmKtmf 0)()(sin)()()(ttAtVtt 微分器输出：微分器输出： tfdmKt 噪声功率CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2525噪声功率谱变化噪声功率谱变化 2,2022221FMBfAnffPHfdAdP 双双 22224fHjH )()(sin)(ttAt

12、Vtnd dttdntndA)(10 CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2626iN0n2B2B fP fPd mf mf0Nf mmmffAfndffPN23020038 双双输出信噪比 fPd)(fPd fPd)(0fPCommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2727 3022220083mffntmKANS ttmiffnAmmmf cos223022 mBiifffmfFMNSmm12132 13200 ffiiFMmmNSNSG tmKSfo22 22

13、02038AfnNm mmmFfffKm CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2828 。13200ffiiFMmmNSNSG小信噪比CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin2929 CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin30306050403020100051015202010743FM2( )FM / dBSiNi( )FM / dBSiNi由图可见：（1） mf不同，门限值不同，mf越大，门限

14、点越高。（2）(Si/Ni)F M门限值时，(So/No)FM与(Si/Ni)FM呈线性关系，mf越大，输出信噪比改善越明显。 （3）(Si/Ni)F M门限值时，(So/No)FM随(Si/Ni)FM的下降而急剧下降。mf越大，(So/No)FM下降越快，甚至比DSB或SSB更差。 这表明，FM以带宽换取输出信噪比改善并不是无止境的。采用比鉴频器更优越的一些解调方法可以达到改善门限效应的要求，目前用的较多的有、和等。 加重fmCommunicationCommunicationCUMT LIShiyinCUMT LIShiyin3131 fP0f输出端抛物线形的噪声输出端抛物线形的噪声功率谱

15、，导致输出的高频功率谱，导致输出的高频信号部分的信噪比恶化。信号部分的信噪比恶化。接收端输出时，采用去加重技术，抑制高频段的噪声，接收端输出时，采用去加重技术，抑制高频段的噪声，提高输出高频信号部分的信噪比。提高输出高频信号部分的信噪比。同时在接收端采用预加重技术，消除去加重对信号导致同时在接收端采用预加重技术，消除去加重对信号导致的失真。的失真。 tm t0m ffdpH1H 电路原理CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin32325.5 各种模拟调制系统的比较 预预加加重重去去加加重重CommunicationCommunic

16、ationCUMT LIShiyinCUMT LIShiyin3333 1210max2tmtmtm 20nP 双双BnNi0 CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin3434 moiiiAMoofnSNSNS3132moiiiDSBoofnSNSNS 2moiiiSSBoofnSNSNS moifiiffFMoofnSmNSmmNS222313200005 . 4)/()/(fAMFMmNSNS调频系统与调幅系统的抗噪声性能：CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin

17、3535200005 . 4)/()/(fAMFMmNSNSCommunicationCommunicationCUMT LIShiyinCUMT LIShiyin3636 220000)(5 . 45 . 4)/()/(AMFMfAMFMBBmNSNS例题CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin3737各种模拟调制系统的性能曲线 moiAMoofnSNS313223 moifFMoofnSmNS320010510101031383 338321057105101010523 .CommunicationCommunication

18、CUMT LIShiyinCUMT LIShiyin3838200005 . 45 .11232007500)/()/(fAMFMmNSNS 各种模拟调制系统的性能曲线CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin39397060504030201001020304050FM:m m=6 6 m=3DSB/SSBAM 00NS mifnS0dBdB综合性能比较CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin4040FDMCommunicationCommunicationCUMT LIShiyinCUMT LIShiyin4141CommunicationCommunicationCUMT LIShiyinCUMT LIShiyin4242530KHz1