FMDetection：FM检测

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1、FMGenerationandDetectionAnalogandDigitalCommunicationsAutumn2005-2006Oct11,20051CS477:AnalogandDigitalCommunicationsFMBandwidthfallsoffquicklyforConsidercomponentsonlyforObservationforisinsignificantforConsidercomponentsonlyforObservationforConsiderToneModulationSignificantfreque

2、ncycomponentsliewithinSignificantfrequencycomponentsliewithinOct11,20052CS477:AnalogandDigitalCommunicationsFMBandwidth:SingleToneForworstcase,use:dependsupontheallowabledistortionlevelUsuallyapproximatedbyWhatisthecorrespondingvalueofIsthisthemaximumvalue?NO!Asmallermayresultinlar

3、gerOct11,20053CS477:AnalogandDigitalCommunicationsFMBandwidth:GenericSignalEstimateBWusingworstcasetonemodulation!DefineDeviationratio:Carson’srule:Carson’sruleisappliedforextremevaluesofdeviationratio.ItunderestimatestheBWforpracticalsystems.Use(DoExample5.2-1andExercise5.2-1intex

4、t)Approximations:Forpracticalsystems:Oct11,20054CS477:AnalogandDigitalCommunicationsTransmissionBW:SummaryCondition(s)SingleToneGenericSignalCarson’sRuleextremePracticaldesignsOct11,20055CS477:AnalogandDigitalCommunicationsGeneratingNBFMSignalsDirectmethodUseavoltage-controlledosci

5、llatorOutputfrequencyisproportionaltoinputvoltageUseinformationsignalastheinputvoltageRestrictedtolowpowerapplicationsMostcircuitsunstableatcarrierfrequencyNotsuitableforcommercialFMbroadcastRequiresophisticatedfeedbackcontrolOct11,20056CS477:AnalogandDigitalCommunicationsGeneratin

6、gNBFMSignalsIndirectmethod:(NBPM/NBFM)NBPMModulatorNBFMOutputInput900(NBPM)Oct11,20057CS477:AnalogandDigitalCommunicationsGeneratingWBFMSignalsDirectMethodUseaVCO(asincaseofNBFM)IndirectMethodGenerateNBFMfirstNBFMModulatorNon-linearDeviceBandpassFilterFrequencyMultiplierFrequency

7、ConverterFrequencyconvertermightbeneededifthemultiplierproducesacarrieratafrequencydifferentfromthedesiredcarrierfrequency!Oct11,20058CS477:AnalogandDigitalCommunicationsFMDetectionFourprimarymethodsDifferentiatorwithenvelopedetectorFMtoAMconversionPhase-shiftdiscriminatorApproxima

8、testhedifferentiatorZero-c