DDS正弦信号发生器设计外文文献.docx

DDS正弦信号发生器设计外文文献.docx

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DDSdevicestoproducehigh-qualitywaveform:

asimple,efficientandflexible

Abstract:

Directdigitalfrequencysynthesis（DDS）technologyforthegenerationandregulationofhigh-qualitywaveforms,widelyusedinmedical,industrial,instrumentation,communications,defenseandmanyotherareas.Thisarticlewillbrieflydescribethetechnology,onitsstrengthsandweaknesses,examinesomeapplicationexamples,andalsointroducedsomenewproductsthatcontributetothepromotion

1.Introduction

Akeyrequirementinmanyindustriesisanexactproduction,easyoperationandquickchangeofdifferentfrequencies,differenttypesofwaveforms.Whetheritisbroadbandtransceiverrequireslowphasenoiseandexcellentspurious-freedynamicperformanceofagilefrequencysource,orforindustrialmeasurementandcontrolsystemneedsastablefrequencyexcitation,fast,easyandeconomicaltoproduceadjustablewaveformwhilemaintainingphasecontinuitycapabilitiesarecriticaltoadesignstandard,whichiswhattheadvantagesofdirectdigitalfrequencysynthesis.

2.Frequencysynthesistask

Thegrowingcongestionofthespectrum,coupledwithlowerpowerconsumption,qualityofnever-endingdemandforhighermeasuringequipment,thesefactorsrequiretheuseofthenewfrequency

range,requiresabetteruseofexistingfrequencyrange.Aresult,thesearchforbettercontrol,inmostcases,bymeansoffrequencysynthesizerforfrequencygeneration.Thesedevicesuseagivenfrequency,fCofto

generateatargetfrequency（andphase）fOUTthegeneralrelationshipcanbesimplyexpressedas:

fOUT=εx×fC

Amongthem,thescalefactorεx,sometimesknownasthenormalizedfrequency.

Theequationisusuallygradualapproximationoftherealnumberalgorithms.Whenthescalefactorisarationalnumber,tworelativelyprimenumbers（outputfrequencyandreferencefrequency）thantheharmonic.However,inmostcases,εxmaybelongtoabroadersetofrealnumbers,theapproximationprocessiswithintheacceptablerangewillbetruncated

Thefrequencysynthesizerapracticalwaytoachieveisthedirectdigitalfrequencysynthesis（ofDDFS）,usuallyreferredtoasdirectdigitalsynthesis（DDS）.Thistechniqueusingdigitaldataprocessingtogenerateafrequencyandphaseadjustableoutput,theoutputandafixedfrequencyreferenceclocksourcefC.related.

DDSarchitecture,thereferenceorthesystemclockfrequencydividedbyascalefactortoproducethedesiredfrequency,thescalefactoriscontrolledbythebinarytuningwordprogrammable.

Inshort,directdigitalfrequencysynthesizertoconvertabunchofclockpulsesintoananalogwaveform,usuallyasinewave,trianglewaveorsquarewave.ShowninFigure1,itsmainparts:

thephaseaccumulator（toproducetheoutputwaveformphaseangledata）,relativetodigitalconverter,（abovethephasedatais

convertedtotheinstantaneousoutputamplitudedata）,anddigital-to-analogconverter（DAC）（themagnitudeofdataintoasampledanalogdatapoints）

Figure2-1DDSfunctionofthesystemblockdiagram.

Forthesinewaveoutput,relativetodigitalconverterisusuallyasinelookuptable（Figure2）.PhaseaccumulatorunitcountNarelativetothefrequencyoffC,accordingtothefollowingequation:

ThenumberofpulsesofthefC:

Mistheresolutionofthetuningword（24-48）

Ncorrespondstothesmallestincrementofphasechangeofthephaseaccumulatoroutputword

Figure2-2TypicalDDSarchitectureandsignalpath（withDACs）.

ChangingNwillimmediatelychangetheoutputphaseandfrequency,sothesystemhasitsowncontinuousphasecharacteristics,whichisoneofthekeyattributesofmanyapplications.Noloopsettlingtime,whichisdifferentfromtheanalogsystem,suchasphase-lockedloops（PLLs）.DACisusuallya

high-performancecircuit,designedspecificallyfortheDDScore（phaseaccumulatorandphaseamplitudeconverter）.Inmostcases,theresultsofthedevice（usuallysingle-chip）isgenerallyreferredtoasthepureDDSortheC-DDS.

ActualDDSdevicesaregenerallymultipleregisters,inordertoachieveadifferentfrequencyandphase

modulationscheme.Suchasphaseregister,theirstoragephaseofincreaseintheoutputphaseofthephaseaccumulator.Inthisway,thecorrespondingdelayoutputsinewavephaseinaphasetuningword.Thisisusefulforphasemodulationapplicationsforcommunicationsystems.Theresolutionoftheaddercircuitdeterminesthenumberofbitsofthephasetuningword,therefore,alsodecidedtodelaytheresolution.

IntegratedinasingledeviceontheengineofaDDSandaDAChasbothadvantagesanddisadvantages,however,whetherintegratedornot,needaDACtoproduceultra-highpurityhigh-qualityanalogsignal.DACwillconvertdigitalsinusoidaloutputtoananalogsinewavemaybesingle-endedordifferential.Someofthekeyre