外文翻译相位锁相环

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1、外文翻译■THEPHASE-LOCKEDLOOP(PLL)ThePLLasanFMDemodulatorAsyouhaveseen,theVCOcontrolvoltageinaPLLdependsonthedeviationoftheincomingfrequency.ThePLLwillproduceavoltageproportionaltothefrequencyoftheincomingsignalwhich,inthecaseofFM,istheoriginalmodulatingsignal.Figure13-54s

2、howsatypicalconnectionfortheLM565asanFMdemodulator.IftheIFinputisfrequencymodulatedbyasinusoidalsignal,yougetasinusoidalsignalontheoutputasindicated.Sincethemaximumoperatingfrequencyis500kHz,thisdevicemustbeusedindouble-conversionFMreceiverisoneinwhichessentiallytwomi

3、xersareusedtofirstconverttheRFtoa10.7MHzIFandthenconvertthistoa455kHzIF.Thefree-runningfrequencyoftheVCOisadjustedtoapproximately455kHz,whichisthecenterofthemodulatedIFrange,C₁canbeanyvalue,butR₁shouldbeintherangefrom2kΩto20kΩ,Theinputvanbedirectlycoupledaslongasthere

4、isnodcvoltagedifferencebetweenpins2and3.TheVCOisconnectedtothephasedetectorbyanexternalwirebetweenpins4and5.DeterminethevaluesforR₁,C₁andC₂fortheLM565inFigure13-54forafree-runningfrequencyof455kHzandacapturerangeof±10kHz.Thedcsupplyvoltagesare±6V.SolutionUseEquation(1

5、3-5)tocalculateC₁.ChooseR₁=4.7kΩ.■COMMUNICATIONSCIRCUITSThelockrangeandcapturerangemustbedeterminedbeforeC₂canbecalculated.ThelockrangeisUseEquation(13-7)tocalculateC₂.Therefore,PracticeExerciseWhatcanyoudotoincreasethecapturerangefrom±10kHzto±15kHz?13-8REVIEWQUESTION

6、S1.Listthethreebasiccomponentsinaphase-lockedloop.2.WhatisanothercircuitusedinsomePLLsotherthanthethreelistedinQuestion1?3.WhatisthebasicfunctionofaPLL?4.WhatisthedifferencebetweenthelockrangeandthecapturerangelfaPLL?5.Basically,howdoesaPLLtracktheincomingfrequency?■A

7、SYSTEMAPPLICATIONTheDCE(datacommunicationsequipment)systemintroducedattheopeningofthischapterincludesanFSK(frequencyshiftkeying)modem(modulator/demodulator).FSKisonemethodformodulatingdigitaldatafortransmissionovervoicephonelinesandisbasicallyaformoffrequencymodulatio

8、n.Inthissystemapplication,thefocusisonthelow-speedmodulator/demodulator(modem)board,whichisimplementedwithaVCOfortransmittin