关于vhdl的英文资料.docx

关于vhdl的英文资料.docx

《关于vhdl的英文资料.docx》由会员分享，可在线阅读，更多相关《关于vhdl的英文资料.docx（12页珍藏版）》请在冰豆网上搜索。

关于vhdl的英文资料

Introductiontosignalgenerator

Asignalgenerator,alsoknownvariouslyasatestsignalgenerator,functiongenerator,tonegenerator,arbitrarywaveformgenerator,digitalpatterngeneratororfrequencygeneratorisanelectronicdevicethatgeneratesrepeatingornon-repeatingelectronicsignals（ineithertheanalogordigitaldomains）.Theyaregenerallyusedindesigning,testing,troubleshooting,andrepairingelectronicorelectroacousticdevices.

Therearemanydifferenttypesofsignalgenerators,withdifferentpurposesandapplications（andatvaryinglevelsofexpense）;ingeneral,nodeviceissuitableforallpossibleapplications.Traditionally,signalgeneratorshavebeenembeddedhardwareunits,butsincetheageofmultimedia-PCs,flexible,programmablesoftwaretonegeneratorshavealsobeenavailable.

Functiongenerators：

Afunctiongeneratorisadevicewhichproducessimplerepetitivewaveforms.Suchdevicescontainanelectronicoscillator,acircuitthatiscapableofcreatingarepetitivewaveform.（Moderndevicesmayusedigitalsignalprocessingtosynthesizewaveforms,followedbyadigitaltoanalogconverter,orDAC,toproduceananalogoutput）.Themostcommonwaveformisasinewave,butsawtooth,step（pulse）,square,andtriangularwaveformoscillatorsarecommonlyavailableasarearbitrarywaveformgenerators（AWGs）.Iftheoscillatoroperatesabovetheaudiofrequencyrange（>20kHz）,thegeneratorwilloftenincludesomesortofmodulationfunctionsuchasamplitudemodulation（AM）,frequencymodulation（FM）,orphasemodulation（PM）aswellasasecondoscillatorthatprovidesanaudiofrequencymodulationwaveform.

Arbitrarywaveformgenerators

Arbitrarywaveformgenerators,orAWGs,aresophisticatedsignalgeneratorswhichallowtheusertogeneratearbitrarywaveforms,withinpublishedlimitsoffrequencyrange,accuracy,andoutputlevel.Unlikefunctiongenerators,whicharelimitedtoasimplesetofwaveforms;anAWGallowstheusertospecifyasourcewaveforminavarietyofdifferentways.AWGsaregenerallymoreexpensivethanfunctiongenerators,andareoftenmorehighlylimitedinavailablebandwidth;asaresult,theyaregenerallylimitedtohigher-enddesignandtestapplications.

Specialpurposesignalgenerators

Atonegeneratorandaprobeforlocatingaspecificpairofwiresamongstmany,forexampleinapunchblock.Inadditiontotheabovegeneral-purposedevices,thereareseveralclassesofsignalgeneratorsdesignedforspecificapplications.

Tonegeneratorsandaudiogenerators

Atonegeneratorisatypeofsignalgeneratoroptimizedforuseinaudioandacousticsapplications.Tonegeneratorstypicallyincludesinewavesovertheaudiofrequencyrange（20Hz–20kHz）.Sophisticatedtonegeneratorswillalsoincludesweepgenerators（afunctionwhichvariestheoutputfrequencyoverarange,inordertomakefrequency-domainmeasurements）,multitonegenerators（whichoutputseveraltonessimultaneously,andareusedtocheckforintermodulationdistortionandothernon-lineareffects）,andtonebursts（usedtomeasureresponsetotransients）.Tonegeneratorsaretypicallyusedinconjunctionwithsoundlevelmeters,whenmeasuringtheacousticsofaroomorasoundreproductionsystem,and/orwithoscilloscopesorspecializedaudioanalyzers.

Manytonegeneratorsoperateinthedigitaldomain,producingoutputinvariousdigitalaudioformatssuchasAES-3,orSPDIF.Suchgeneratorsmayincludespecialsignalstostimulatevariousdigitaleffectsandproblems,suchasclipping,jitter,biterrors;theyalsooftenprovidewaystomanipulatethemetadataassociatedwithdigitalaudioformats.

Thetermsynthesizerisusedforadevicethatgeneratesaudiosignalsformusic,orthatusesslightlymoreintricatemethods.

Videosignalgenerators

Avideosignalgeneratorisadevicewhichoutputspredeterminedvideoand/ortelevisionwaveforms,andothersignalsusedtostimulatefaultsin,oraidinparametricmeasurementsof,televisionandvideosystems.Thereareseveraldifferenttypesofvideosignalgeneratorsinwidespreaduse.Regardlessofthespecifictype,theoutputofavideogeneratorwillgenerallycontainsynchronizationsignalsappropriatefortelevision,includinghorizontalandverticalsyncpulses（inanalog）orsyncwords（indigital）.Generatorsofcompositevideosignals（suchasNTSCandPAL）willalsoincludeacolorburstsignalaspartoftheoutput.Videosignalgeneratorsareavailableforawidevarietyofapplications,andforawidevarietyofdigitalformats;manyofthesealsoincludeaudiogenerationcapability（astheaudiotrackisanimportantpartofanyvideoortelevisionprogramormotionpicture）.

Manyapplicationsrequirelow-frequencysignalgeneratorsthatcandeliverhigh-performance,high-resolutionsignals.ThisDesignIdeapresentsacircuitthatgeneratesfrequenciesof0to1MHz.Sinusoidal,triangular,andsquare-waveoutputsareavailable.Youcanachievefrequencyresolutionofbetterthan0.1Hzandphaseresolutionofbetterthan0.1°;thus,youcanprogramexactcoherentfrequencies.Thisfeatureisusefulindigitalmodulationandfrequency-tuningapplications.ThecircuitusestheADµC831andADC0832togeneratetherequiredfrequencies.YoucanprogramthemicrocontrollerfromeitheraPCoraUnix-basedworkstation.YouthenprogramtheADC0832usingathree-wireserialinterfaceviathemicrocontroller.Theinterfacewordis16bitslong.

YoucanprogramtheADC0832toprovidesinusoidal,triangular,andsquare-waveoutputsusing（direct-digital-synthesis）architecture.ThechipoperatesasanNCO（numericallycontrolledoscillator）usinganon-chip,28-bitphaseaccumulator,sine-coefficientROM,anda10-bitD/Aconverter.Youtypicallyconsidersinewavesintermsoftheirmagnitudeform,A（t）=sin（ωt）.Theamplitudeisnonlinearandis,therefore,difficulttogenerate.Theangularinformation,ontheotherhand,isperfectlylinear.Thatis,thephaseanglerotatesthroughafixedangleforeachunitintime.Knowingthatthephaseofasinewaveislinear,and,givenareferenceinterval（clockperiod）,youcandeterminethephaserotationforthatperiod:

ΔPhase=ωdt;ω=ΔPhase/dt=2πf,andf=（ΔPhase×fMCLK）/（2π）,wheredt=1/fMCLK,andfMCLKisthemasterclock..Usingthisformula,youcangenerateoutputfrequencies,knowingthephaseandmaster-clockfrequency.Thephaseaccumulatorprovidesthe28-bitlinearphase.Theamplitudecoefficientsoftheoutputsinewavearestoredindigitalformatinthesine-coefficientROM.TheDACconvertsthesinewavetotheanalogdomain.IfyoubypasstheROM,theADC0832deliverstriangularwaveformsinsteadofsinusoidalwaveforms.Asquare-waveoutputisalsoavailableonthepart.showsthevariouswaveformsavailablefromthesystem.Asshownin,thesinusoidal/triangularoutputwaveformsareavailableontheIOUTpin（Pin19）;andthesquarewaveoutputisavailableontheSIGN_BIT_OUTpin（Pin16）.YouprogramtheDDSbywritingtothefrequencyregisters.Theanalogoutputfromthepartisthen:

fOUT=fMCLK/228×（frequency-registerword）.

TheoutputsoftheDDShave28-bitresolution,soeffectivefrequencystepsontheorderof0.1Hzarepossibletoamaximumofapproximately1MHz.showsthetypicalwaveformoutputs.Twophaseregistersareavailablethatallow12-bitphaseresolution.Theseregistersphase-shiftthesignalby:

Phaseshift=2π/4096×（phase-registerword）.A50-MHzcrystaloscillatorprovidesthereferenceclockfortheDDS.TheoutputstageoftheDDSisacurrent-outputDACloadedbyanexternalresistor.A200Ωresistorgeneratestherequiredpeak-to-peakvoltagerange.Theoutputisac-coupledthroughcapacitorC1.TheMicroConvertercontainstwoon-chip,12-bitDACs.DAC1variesthecurrentthroughR5,adjustingthefull-scalecurrentoftheDDSviatheFSADJUSTpin.Theequationtocontrolthefull-scalecurrentoftheDDSDACis:

IOUT（full-scale）=18×I×R5.

DAC0,theinternalreferenceoftheMicroConverter,andopamp2allowforoffsetcontroloftheoutputvoltageoftheDDS.Youcanprogramthisdcoffsetto±10Vat10-bitresolution.WhenR1=R2andthegainofopamp2=8,thentheoutputofopamp2is:

VOUT=（DACoutput–（VREF/2））×8,yieldinga±10Vrange.

ResistorsR6throughR9allowforcontrolofgainthroughopamp3.Thegainoftheopampisafunctionofresistorswitching,whichyouenableusingtheRDRIVEpinavailableontheMicroConverter.Thisoperationallowsforaneffectiveprogrammable-outputamplitudeofapproximately±10Vp-p.Thus,thecircuitallowsforprogrammablesinusoidalandtriangularwaves,includingdcoffsets,andtheabilitytosetpeak-to-peakamplitudeofapproximately±10V.ThesquarewaveoutputontheSIGN_BIT_OUTpinhas0to5Vamplitude.Forlow-frequencyoperation,alowpassfilternormallyservestofilterreference-clockfrequencies,spurs,andotherimages.Forapplicationsinwhichtheoutputsignalneedsamplification,youshoulduseanarrowbandfiltertofilteroutunwantednoisebeforethegainstage.Athird-orderfilterwouldbegoodenoughtoremovemostoftheunwantednoise.Figure3showsatypicalspectralplotoftheoutput.Applicationsforthiscircuitrangefromsignal-waveformgenerationtodigitalmodulation.Youcanusethesysteminfrequency-sweepingand-scanningapplicationsandinresonanceapplicationsthatusethefrequencyasanexcitationsignaltodeterminecircuitresonanceWaveform—usuallyasinewave—bygeneratingatime-varyingsignalindigitalformandthenperformingadigital-to-analogconversion.BecauseoperationswithinaSignalgeneratordeviceareprimarilydigital,itcanofferfastswitchingbetweenoutputfrequencies,finefrequencyresolution,andoperationoverabroadspectrumof