外文翻译---借助 dds 的精密测量频率的一种替代方法

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1、AnalternativemethodofprecisefrequencybytheaidofaDDSContentsAmethodoffrequencymeasurementbasedonaclosedloopcomposedmainlyofaFrequencyComparator(FC)andaDirectDigitalSynthesizer(DDS)ispresentedinthispaper.TheDDSservesasreferencesinewavesignalgeneratoractingatoneoftheFC'sinputs.TheFCacceptst

2、hehard-limitedwaveformoftheDDSaswellastheunknownfrequency.Fromthecomparisonofthetwosignalsalogicoutputthatcontrolsanup/downcounterisproduced.Thecounter'soutputactingastheFrequencySettingWord(FSW)instructstheDDStoproduceanewsinewavecloserinfrequencytotheunknownone.Whentheloopsettles,theFS

3、Wgivesthedigitalestimateoftheunknownfrequency.AdvantageistakenfromtheinherenthighresolutionoftheDDSandnoiseimmunityoftheloop,todesignanequallypreciseandimmunefrequencymeter.Alltheadditionalassociatedstagesuptotheinstrument'sdisplayarepresented.1IntroductionThemostcommonlyusedfrequencymea

4、surementtechniqueadoptscountersthatcountthepulsesoftheunknownfrequencyduringapredefinedtimewindow(aperture).Apartfromthis,techniqueswherethepulsesofareferencefrequencyarecountedduringoneormoreperiodsoftheunknownonearealsocommon.Inthelattercase,theperiodinsteadofthefrequencyisestimated.So

5、mepapersin[1]intheliteraturedealwiththeproblemoflowfrequencymeasurementandarefocusinginthefrequencyrangeofcardiac(heart)signals(afewhertz)orinthemainsfrequency(50-60Hz).Thesetechniquesareactuallymeasuringtheperiodofthesignalsandusesomewaytocalculateitsreciprocal,thefrequency.In[2],thefre

6、quencyiscalculatedbythemethodoflook-uptables.Others[4-6]aremicroprocessorormicrocontrollerbased.Theabovemethodscanbecharacterizedasopen-loopmethodsi.e.digitalcountersareusedtocountduringapredefinedtinleintervalandcalculatetheresultafterwards.Itsclosed-loopformcharacterizestheproposedmeth

7、odinthispaper.Bytheterm"closed-loop"wedenotesomesortoffeedback.Awaveformwithaknown(controlled)frequencyisproducedwithinthecircuitandisfedbacktothefrequencycomparisonstagewhichconsecutivelyforcesittoapproximatetheunknown(input)frequency.Thedevicethatproducestheabovemention