外文翻译-- 数字频率合成器

《外文翻译-- 数字频率合成器》由会员上传分享，免费在线阅读，更多相关内容在学术论文-天天文库。

1、附录2：外文原文，译文ModulatingDirectDigitalSynthesizerInthepursuitofmorecomplexphasecontinuousmodulationtechniques,thecontroloftheoutputwaveformbecomesincreasinglymoredifficultwithanalogcircuitry.Inthesedesigns,usinganon-lineardigitaldesigneliminatestheneedforcircuitboardadjustmentsoveryieldandtempera

2、ture.AdigitaldesignthatmeetsthesegoalsisaDirectDigitalSynthesizerDDS.ADDSsystemsimplytakesaconstantreferenceclockinputanddividesitdownatoaspecifiedoutputfrequencydigitallyquantizedorsampledatthereferenceclockfrequency.ThisformoffrequencycontrolmakesDDSsystemsidealforsystemsthatrequireprecisef

3、requencysweepssuchasradarchirpsorfastfrequencyhoppers.Withcontrolofthefrequencyoutputderivedfromthedigitalinputword,DDSsystemscanbeusedasaPLLallowingprecisefrequencychangesphasecontinuously.Aswillbeshown,DDSsystemscanalsobedesignedtocontrolthephaseoftheoutputcarrierusingadigitalphasewordinput

4、.Withdigitalcontroloverthecarrierphase,ahighspectraldensityphasemodulatedcarriercaneasilybegenerated.ThisarticleisintendedtogivethereaderabasicunderstandingofaDDSdesign,andanunderstandingofthespuriousoutputresponse.Thisarticlewillalsopresentasampledesignrunningat45MHzinahighspeedfieldprogramm

5、ablegatearrayfromQuickLogic.AbasicDDSsystemconsistsofanumericallycontrolledoscillator(NCO)usedtogeneratetheoutputcarrierwave,andadigitaltoanalogconverter(DAC)usedtotakethedigitalsinusoidalwordfromtheNCOandgenerateasampledanalogcarrier.SincetheDACoutputissampledatthereferenceclockfrequency,awa

6、veformsmoothinglowpassfilteristypicallyusedtoeliminatealiascomponents.Figure1isabasicblockdiagramofatypicalDDSsystemdesign.ThegenerationoftheoutputcarrierfromthereferencesampleclockinputisperformedbytheNCO.ThebasiccomponentsoftheNCOareaphaseaccumulatorandasinusoidalROMlookuptable.Anoptionalph

7、asemodulatorcanalsobeincludeintheNCOdesign.ThisphasemodulatorwilladdphaseoffsettotheoutputofthephaseaccumulatorjustbeforetheROMlookuptable.ThiswillenhancetheDDSsystemdesignbyaddingthecapabilitiestophasemodulatethecarrieroutputoftheNCO.Figure2