FUNDAMENTALS OF MODERN现代基础

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1、FUNDAMENTALSOFMODERNSPECTRALANALYSISMatthewT.Hunter,Ph.D.AGENDA•Introduction•SpectrumAnalyzerArchitecture•DynamicRange•InstantaneousBandwidth•TheImportanceofImageRejectionandAnti-Aliasing•ConclusionTheSpectrumAnalyzer•FundamentalTask–Measuresignalpowervs.frequency•Tra

2、ditionallyaccomplishedwithSweptSpectralAnalysis(SSA)•AdvancesindigitaltechnologyhaveledtotheprevalenceofFFT-basedanalysisTheDigitalRevolution•MajorityofSpectrumAnalyzer(SA)functionscannowbedonedigitally–RBWfiltering–Videodetection–Logarithmicprocessing•AllDigitalIFpro

3、cessingmeansmoreflexibility–TheSAcanbeaVSA,measuringreceiver,etc…DynamicRange•TheratioindB,ofthelargesttothesmallestsignalssimultaneouslypresentattheinputoftheSAthatallowsmeasurementofthesmallersignaltoagivendegreeofuncertainty[10].•Ithasbeenassertedthatdigitallyimple

4、mentedSSAsprovidebetterdynamicrangeperformancethanFFTSAs[11]SSADynamicRange•TheArgument–AnSSAcanhaveaverynarrowIFbandwidth–Thus,AGCcanbeusedtoadjustthesignallevelintotheADCsuchthatthesignalisquantizedwiththemaxnumberofbits–LeveladjustmentisalsodoneinFFTSAs,butBWistypi

5、callywider•Likelihoodofastrongsignalbeingpresentwithaweaksignalisgreatlyincreased.NotEnoughResolution•ADCresolutionsetsflooronachievabledynamicrange•Inthiscase,thestrongsignalblocksormaskstheweaksignalwhichmaygetquantizedwithonlyafewbitsandendupinthenoiseSolvingthePro

6、blem•Afewdifferentapproachescanbetaken–UseSSAandnarrowbandIFwithAGC•OnemayalsousethistechniquewithanFFTSA•However,itisnotnecessaryandinfactaddstothecomplexityofthesystem–Alternatively,ifthe“ultimate”indynamicrangeisdesired,theIFpathcanbesplit•Narrowbandpathconnectedto

7、ahighresolutionADC•WidebandpathconnectedtoahighspeedADC•Complicatesthesystembyaddinganextrasignalpath•Shouldonlybeusedinthemostdemandingapplications.SolvingtheProblem•ADCtechnologyhasimproveddramaticallyinthelastdecade,allowingdigitizationofbandwidthsontheorderof150MH

8、zwith14-bitsofprecision[9]•Thus,asinglepathcanprovidebothbandwidthanddynamicrange.•Iftheprevioustwosignalsareagaincompared,t