dds畢業(yè)論文外文翻譯關(guān)于直接數(shù)字頻率合成器

1、0AllAboutDirectDigitalSynthesisWhatisDirectDigitalSynthesisDirectdigitalsynthesis(DDS)isamethodofproducingananalogwavefm—usuallyasinewave—bygeneratingatimevaryingsignalindigitalfmthenperfmingadigitaltoanalogconversion.Be

2、causeoperationswithinaDDSdeviceareprimarilydigitalitcanofferfastswitchingbetweenoutputfrequenciesfinefrequencyresolutionoperationoverabroadspectrumoffrequencies.Withadvancesindesignprocesstechnologytoday’sDDSdevicesareve

3、rycompactdrawlittlepower.Whywouldoneuseadirectdigitalsynthesizer(DDS)Aren’tthereothermethodsfeasilygeneratingfrequenciesTheabilitytoaccuratelyproducecontrolwavefmsofvariousfrequenciesprofileshasbecomeakeyrequirementcommo

4、ntoanumberofindustries.Whetherprovidingagilesourcesoflowphasenoisevariablefrequencieswithgoodspuriousperfmancefcommunicationssimplygeneratingafrequencystimulusinindustrialbiomedicaltestequipmentapplicationsconveniencecom

5、pactnesslowcostareimptantdesignconsiderations.Manypossibilitiesffrequencygenerationareopentoadesignerrangingfromphaselockedloop(PLL)basedtechniquesfveryhighfrequencysynthesistodynamicprogrammingofdigitaltoanalogconverter

6、(DAC)outputstogeneratearbitrarywavefmsatlowerfrequencies.ButtheDDStechniqueisrapidlygainingacceptancefsolvingfrequency(wavefm)generationrequirementsinbothcommunicationsindustrialapplicationsbecausesinglechipICdevicescang

7、enerateprogrammableanalogoutputwavefmssimplywithhighresolutionaccuracy.FurthermethecontinualimprovementsinbothprocesstechnologydesignhaveFigure1.TheAD9833aonechipwavefmgenerat.2frequencythebinarynumberprogrammedintothefr

8、equencyregister(tuningwd).Thebinarynumberinthefrequencyregisterprovidesthemaininputtothephaseaccumulat.Ifasinelookuptableisusedthephaseaccumulatcomputesaphase(angle)addressfthelookuptablewhichoutputsthedigitalvalueofampl

9、itude—crespondingtothesineofthatphaseangle—totheDAC.TheDACinturnconvertsthatnumbertoacrespondingvalueofanalogvoltagecurrent.Togenerateafixedfrequencysinewaveaconstantvalue(thephaseincrement—whichisdeterminedbythebinarynu

10、mber)isaddedtothephaseaccumulatwitheachclockcycle.Ifthephaseincrementislargethephaseaccumulatwillstepquicklythroughthesinelookuptablethusgenerateahighfrequencysinewave.Ifthephaseincrementissmallthephaseaccumulatwilltakem

11、anymestepsaccdinglygeneratingaslowerwavefm.WhatdoyoumeanbyacompleteDDSTheintegrationofaDAconverteraDDSontoasinglechipiscommonlyknownasacompleteDDSsolutionapropertycommontoallDDSdevicesfromADI.Let’stalksomemeaboutthephase

12、accumulat.HowdoesitwkContinuoustimesinusoidalsignalshavearepetitiveangularphaserangeof0to2.Thedigitalimplementationisnodifferent.Thecounter’scarryfunctionallowsthephaseaccumulattoactasaphasewheelintheDDSimplementation.T

13、ounderstthisbasicfunctionvisualizethesinewaveoscillationasavectrotatingaroundaphasecircle(seeFigure4).Eachdesignatedpointonthephasewheelcrespondstotheequivalentpointonacycleofasinewave.Asthevectrotatesaroundthewheelvisua

14、lizethatthesineoftheanglegeneratesacrespondingoutputsinewave.Onerevolutionofthevectaroundthephasewheelataconstantspeedresultsinonecompletecycleoftheoutputsinewave.Thephaseaccumulatprovidestheequallyspacedangularvaluesacc