第4章傅里葉方法在信號與系統(tǒng)分析中的應用ppt課件

1、圖圖41 延續(xù)信號的取樣模型延續(xù)信號的取樣模型 f t( )f t( )sft( )p t取樣脈沖取樣信號連續(xù)信號 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 時限信號時限信號以以為周期等幅度的反復。為周期等幅度的反復。 11ssftFTFjFT 1sTsf tt1snsf tnTF js f tsT圖44 頻域沖擊取樣過程

2、與所對應的時域信號波形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圖圖 46 頻域取樣與恢復原理方框頻域取樣與恢復原理方框圖圖sinhsnhhtnnFjFjttn12hstfHj00Mk

3、kdefkNkkkbjYjHjFjajYjHjF jYjHjF j線性非時變系統(tǒng)( )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圖圖01( )g t2( )g t3( )g t2NT2NTNTNTt1minNTTT1minNTTNIntTT 0y tkftt djj tH

4、jKeHje HjK dt ddtd f t 0h tKtt 1122sinsinf tEtEt12112 常 數(shù)1121212nn圖圖414 理想低通濾波器的特性理想低通濾波器的特性n428 jHjHje 0dj tce其它 0dct 其它10cHj其它n圖圖415 理想低通濾波器的脈沖理想低通濾波器的脈沖呼應呼應 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至信道傳輸.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