Analternativemethodofprecisefrequencybytheaidofadds毕业英文翻译.doc

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1、AnalternativemethodofprecisefrequencybytheaidofaDDSContentsAmethodoffrequencymeasurementbasedonaclosedloopcomposedmainlyofaFrequencyComparator(FC)andaDirectDigitalSynthesizer(DDS)ispresentedinthispaper.TheDDSservesasreferencesinewavesignalgeneratoractingatoneoftheFC'sinputs.TheFCacceptsthehard-li

2、mitedwaveformoftheDDSaswellastheunknownfrequency.Fromthecomparisonofthetwosignalsalogicoutputthatcontrolsanup/downcounterisproduced.Thecounter'soutputactingastheFrequencySettingWord(FSW)instructstheDDStoproduceanewsinewavecloserinfrequencytotheunknownone.Whentheloopsettles,theFSWgivesthedigitales

3、timateoftheunknownfrequency.AdvantageistakenfromtheinherenthighresolutionoftheDDSandnoiseimmunityoftheloop,todesignanequallypreciseandimmunefrequencymeter.Alltheadditionalassociatedstagesuptotheinstrument'sdisplayarepresented.1IntroductionThemostcommonlyusedfrequencymeasurementtechniqueadoptscoun

4、tersthatcountthepulsesoftheunknownfrequencyduringapredefinedtimewindow(aperture).Apartfromthis,techniqueswherethepulsesofareferencefrequencyarecountedduringoneormoreperiodsoftheunknownonearealsocommon.Inthelattercase,theperiodinsteadofthefrequencyisestimated.Somepapersin[1]intheliteraturedealwith

5、theproblemoflowfrequencymeasurementandarefocusinginthefrequencyrangeofcardiac(heart)signals(afewhertz)orinthemainsfrequency(50-60Hz).Thesetechniquesareactuallymeasuringtheperiodofthesignalsandusesomewaytocalculateitsreciprocal,thefrequency.In[2],thefrequencyiscalculatedbythemethodoflook-uptables.

6、Others[4-6]aremicroprocessorormicrocontrollerbased.Theabovemethodscanbecharacterizedasopen-loopmethodsi.e.digitalcountersareusedtocountduringapredefinedtinleintervalandcalculatetheresultafterwards.Itsclosed-loopformcharacterizestheproposedmethodinthispaper.Bytheterm"closed-loop"wedenotesomesortof

7、feedback.Awaveformwithaknown(controlled)frequencyisproducedwithinthecircuitandisfedbacktothefrequencycomparisonstagewhichconsecutivelyforcesittoapproximatetheunknown(input)frequency.Thedevicethatproducestheabovemention