第4章傅里叶方法在信号与系统分析中的应用ppt课件

1、图图41 延续信号的取样模型延续信号的取样模型 f t( )f t( )sft( )p t取样脉冲取样信号连续信号 sft sftf t p t p t sFjFTf t p t12Fjp j sskF jp kk sskp kFjk p t43 p t ssnf nTtnT1sksFjkT p ts 221sTjktTssp kP t edtT221sTjktTsEedtT2sskESaT sft2ssskskEFjSaFjT 时限信号时限信号以以为周期等幅度的反复。为周期等幅度的反复。 11ssftFTFjFT 1sTsf tt1snsf tnTF js f tsT图44 频域冲击取样过程

2、与所对应的时域信号波形112T2ssT1TsT1TsT112T2ssT f t,hh f tshTsf nT f t sfthsT1122shhhTTf f tHjsFjsFjFjFj f tsFjHjFj0sccTHjcs 11sf tFTH jFTFj112ccj tsFTHjT edccSat 1sssnf tFTFjf nTtnT h t sincssnctf tf nTtnTtsincssncstnTf nTtnTt f t,hht tFj12shftssF nfn图图 46 频域取样与恢复原理方框频域取样与恢复原理方框图图sinhsnhhtnnFjFjttn12hstfHj00Mk

3、kdefkNkkkbjYjHjFjajYjHjF jYjHjF j线性非时变系统( )f t( )fyt()Fj()Hj()Yj*= =22( )( )( )43 ( )2 ( )d y tdy tdf ty tf tdtdtdt2( )e( )tf tu t2j2(j )(j )4(j )3Hj2(j1)(j3)21(j )e( )j2tFFTu tj2(j)(j)(j)(j1)(j2)(j3)YHF)()()()(3211tueejFFTtyttf图图01( )g t2( )g t3( )g t2NT2NTNTNTt1minNTTT1minNTTNIntTT 0y tkftt djj tH

4、jKeHje HjK dt ddtd f t 0h tKtt 1122sinsinf tEtEt12112 常 数1121212nn图图414 理想低通滤波器的特性理想低通滤波器的特性n428 jHjHje 0dj tce其它 0dct 其它10cHj其它n图图415 理想低通滤波器的脉冲理想低通滤波器的脉冲呼应呼应 1h tFTHjccdSatt( )h t0dtdctdctctc 1lim2cdccjt tdttedlimcccdSatt f tFj h tHj y tYjYjFjHj0ccFj012ccjt tFjed 12j ty tFjHjed g t h t g tu thdsin

5、tcdccdtdt 1sincxxg tdxx001sin1sincxxdxdxxx 0sinyixSydxx iSysin xx00sinsin2xxdxdxxx 011sin2cxxg tdxx112icdStt gth t2ccBfrt2112rccctfB y tg tg t1icdicdSttStt t()f t10dt2dtdtt()yt1212c h t 0h t 0t 2Hjd 22ln1Hjd sgn t 0sgnehth tt 0sgneh thtt11IRHjHj 1RHjd 11RIHjHj 1IHd22RIHjHjHj 1IRHjtgHj 0012X jG j ( )

6、f t( )x t( )g t0012G jG j n x t f t 011cos 222f tf tt 00cosftx tt 0cosx tAf tt 0Af t f t x t1( )g t1cost2( )g t2cost.( )NgtcosNt.( )f t至信道传输.t012345nn 0f t 0t f tf t u t 11IRId 11RIRdn457 1Hftf tt 1Hf tftt sgnHFjF jj00jFjjFj f t Hft 2sgnjHje2200jjejej sgnHF jFjjHFjHj 2sgnjHje2200jjejej f t Hft 0Hf t ft dt f t Hft H Hftf t 1212HH