直接数字频率合成技术中英文对照外文翻译文献.docx

直接数字频率合成技术中英文对照外文翻译文献.docx

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直接数字频率合成技术中英文对照外文翻译文献

（文档含英文原文和中文翻译）

中英文资料外文翻译文献

原文：

DDSdevicestoproducehigh-qualitywaveform:

asimple,efficientandflexible

Summary

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

Introduction

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

Frequencysynthesistask

Thegrowingcongestionofthespectrum,coupledwithlowerpowerconsumption,qualityofnever-endingdemandforhighermeasuringequipment,thesefactorsrequiretheuseofthenewfrequencyrange,requiresabetteruseofexistingfrequencyrange.Aresult,thesearchforbettercontrol,inmostcases,bymeansoffrequencysynthesizerforfrequencygeneration.Thesedevicesuseagivenfrequency,fCoftogenerateatargetfrequency（andphase）fOUTthegeneralrelationshipcanbesimplyexpressedas:

fOUT=εx×fC

Amongthem,thescalefactorεx,sometimesknownasthenormalizedfrequency.

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

DirectDigitalFrequencySynthesizer

Thefrequencysynthesizerapracticalwaytoachieveisthedirectdigitalfrequencysynthesis（ofDDFS）,usuallyreferredtoasdirectdigitalsynthesis（DDS）.Thistechniqueusingdigitaldataprocessingtogenerateafrequencyandphaseadjustableoutput,theoutputandafixedfrequencyreferenceclocksourcefC.related.DDSarchitecture,thereferenceorthesystemclockfrequencydividedbyascalefactortoproducethedesiredfrequency,thescalefactoriscontrolledbythebinarytuningwordprogrammable.

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

thephaseaccumulator（toproducetheoutputwaveformphaseangledata）,relativetodigitalconverter,（abovethephasedataisconvertedtotheinstantaneousoutputamplitudedata）,anddigital-to-analogconverter（DAC）（themagnitudeofdataintoasampledanalogdatapoints）

Figure1.DDSfunctionofthesystemblockdiagram.

Forthesinewaveoutput,relativetodigitalconverterisusuallyasinelookuptable（Figure2）.PhaseaccumulatorunitcountNarelativetothefrequencyoffC,accordingtothefollowingequation:

ThenumberofpulsesofthefC:

Mistheresolutionofthetuningword（24-48）

Ncorrespondstothesmallestincrementofphasechangeofthephaseaccumulatoroutputword

Figure2.TypicalDDSarchitectureandsignalpath（withDACs）.

ChangingNwillimmediatelychangetheoutputphaseandfrequency,sothesystemhasitsowncontinuousphasecharacteristics,whichisoneofthekeyattributesofmanyapplications.Noloopsettlingtime,whichisdifferentfromtheanalogsystem,suchasphase-lockedloops（PLLs）.DACisusuallyahigh-performancecircuit,designedspecificallyfortheDDScore（phaseaccumulatorandphaseamplitudeconverter）.Inmostcases,theresultsofthedevice（usuallysingle-chip）isgenerallyreferredtoasthepureDDSortheC-DDS.

ActualDDSdevicesaregenerallymultipleregisters,inordertoachieveadifferentfrequencyandphasemodulationscheme.Suchasphaseregister,theirstoragephaseofincreaseintheoutputphaseofthephaseaccumulator.Inthisway,thecorrespondingdelayoutputsinewavephaseinaphasetuningword.Thisisusefulforphasemodulationapplicationsforcommunicationsystems.Theresolutionoftheaddercircuitdeterminesthenumberofbitsofthephasetuningword,therefore,alsodecidedtodelaytheresolution.

IntegratedinasingledeviceontheengineofaDDSandaDAChasbothadvantagesanddisadvantages,however,whetherintegratedornot,needaDACtoproduceultra-highpurityhigh-qualityanalogsignal.DACwillconvertdigitalsinusoidaloutputtoananalogsinewavemaybesingle-endedordifferential.Someofthekeyrequirementsforlowphasenoise,excellentwideband（WB）andnarrowband（NB）,spurious-freedynamicrange（SFDR）,andlowpowerconsumption.Iftheexternaldevice,theDACmustbefastenoughtohandlethesignal,sothebuilt-inparallelportdeviceisverycommon.

DDSandothersolutions

Thefrequencyanalogphase-lockedloops（PLLs）,clockgenerator,andtheuseofFPGAdynamicprogrammingoftheoutputoftheDAC.Byexaminingthespectrumofperformanceandpowerofthesetechnologies,asimplecomparison,Table1showsthequalitativeresultsofthecomparison

Table1.DDSwithcompetingtechnologies-Advancedcompare

Powerconsumption

Spectralpurity

Remarks

DDS

Low

Middle

Easeoftuning

DiscreteDAC+FPGA

Middle

Middle-High

Withtuningcapabilities

AnalogPLL

Milddle

High

Difficulttuning

Phase-lockedloopisafeedbackloopanditscomponents:

aphasecomparator,adividerandapressure-controlledoscillator（VCO）,phasecomparatorreferencefrequencyandoutputfrequency（usuallytheoutputfrequencyisN）frequency）werecompared.TheerrorvoltagegeneratedbythephasecomparatorisusedtoadjusttheVCO,thustheoutputfrequency.Whentheloopisestablished,theoutputfrequencyand/orphasewiththereferencefrequencytomaintainapreciserelationship.PLLhaslongbeenconsideredinaparticularfrequencyrange,highfidelityandconsistentsignallowphasenoiseandhighspuriousfreedynamicrange（SFDR）areidealforapplications.

PLLcannotbepreciselyandquicklytuningthefrequencyoutputwaveform,andtheslowresponse,whichlimitstheirapplicabilityforfastfrequencyhoppingandpartofthefrequencyshiftkeyingandphaseshiftkeyingapplications.

Otherprograms,includingintegratedDDSenginefieldprogrammablegatearrays（FPGAs）-asyntheticsinewaveoutputwiththeoff-the-shelfDAC-thoughthePLLfrequency-hoppingproblemcanbesolved,butthereownshortcomings.Thedefectsofthemajorsystemsworkandinterfacepowerrequirements,highcost,largesize,andsystemdevelopersmustalsoconsidertheadditionalsoftware,hardwareandmemory.Forexample,usingtheDDSengineoptioninthemodernFPGAtogeneratethe10MHzoutputsignaldynamicrangeis60dBupto72kBmemoryspace.Inaddition,designersneedtoacceptandbefamiliarwiththesubtlebalanceDDScorearchitecture..

Fromapracticalpointofview（seeTable2）,thankstotherapiddevelopmentofCMOStechnologyandmoderndigitaldesigntechniques,aswellastheimprovementoftheDACtopology,DDStechnologyhasbeenabletoachieveunprecedentedlowpowerconsumptioninawiderangeofapplications,spectrumperformanceandcostlevels.AlthoughthepureDDSproductsinperformanceanddesignflexibilitytoachievethelevelofhigh-endDACtechnologyandFPGA,buttheadvantagesofDDSintermsofsize,powerconsumption,costandsimplicity,makingittheprimarychoiceformanyapplications.

Table2BenchmarkAnalysisSummary-frequencygenerationtechnique（<50MHz）

Phase-lockedloop

DAC+FPGA

DDS

Spectralperformance

High

High

Middle

Systempowerrequirements

High

High

Middle

Digitalfrequencytuning

No

Yes

Yes

Tuningresponsetime

High

Low

Low

Solutionsize

Middle

High

Low

Waveformflexibility

Low

Middle

High

Cost

Middle

High

Low

Designreuse

Middle

Low

High

Implementationcomplexity

Middle

High

Low

AlsobenotedthattheDDSdevicefordigitalmethodstoproducetheoutputwaveform,itcansimplifysomeofthearchitectureofthesolution,orthewaveformofdigitalprogrammingtocreatetheconditions.UsuallywithasinewavetoexplainthefunctionsandworkingprincipleoftheDDS,butusingmodernDDSICscaneasilygenerateatrianglewaveorsquarewave（clock）output,therebyeliminatingtheformercasethelookuptable,andthelattercasetheDACtheneedtointegrateasimpleandaccurateenough.

PerformanceandlimitationsoftheDDS

Imageandenvelope:

Sin（x）xxroll-off

TheactualoutputoftheDACisnotacontinuoussinewave,butaseriesofpulseswithasinusoidaltimeenvelope.Thecorrespondingspectrumisaseriesofimageandsignalaliasing.Imagealongthesin（x）/xenvelopedistribution（seeFigure3|margin|graph）.Theneedforthefiltertosuppressfrequenciesoutsidethetargetband,butcannotinhibitthehigh-levelinthepassbandaliasing（forexample,causedduetoDACnon-linear）

TheNyquistcriterionrequiresthateachcyclerequiresatleasttwosamplingpointsinordertorebuildthedesiredoutputwaveform.TheMirroringresponsearisingfromsamplingtheoutputfrequencyK,CLOCK×OUTInthisexample,whichCLOCK=2525MHzandfOUT=5MHz,thefirstandsecondmirrorfrequencyappearin（seeFigure3）fCLOCK×fOUT,​​o20MHzand30MHz.Thethirdandfourthm