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1、AllAboutDirectDigitalSynthesisWhatisDirectDigitalSynthesis?Directdigitalsynthesis(DDS)isamethodofproducingananalogwaveform—usuallyasinewave—bygeneratingatime-varyingsignalindigitalformandthenperformingadigital-to-analogconversion.Becauseoperationswit
2、hinaDDSdeviceareprimarilydigital,itcanofferfastswitchingbetweenoutputfrequencies,finefrequencyresolution,andoperationoverabroadspectrumoffrequencies.Withadvancesindesignandprocesstechnology,today’sDDSdevicesareverycompactanddrawlittlepower.Whywouldon
3、euseadirectdigitalsynthesizer(DDS)?Aren’tthereothermethodsforeasilygeneratingfrequencies?Theabilitytoaccuratelyproduceandcontrolwaveformsofvariousfrequenciesandprofileshasbecomeakeyrequirementcommontoanumberofindustries.Whetherprovidingagilesourcesof
4、low-phase-noisevariable-frequencieswithgoodspuriousperformanceforcommunications,orsimplygeneratingafrequencystimulusinindustrialorbiomedicaltestequipmentapplications,convenience,compactness,andlowcostareimportantdesignconsiderations.Figure1.TheAD9833
5、-aone-chipwaveformgenerator.Manypossibilitiesforfrequencygenerationareopentoadesigner,rangingfromphase-locked-loop(PLL)-basedtechniquesforveryhigh-frequencysynthesis,todynamicprogrammingofdigital-to-analogconverter(DAC)outputstogeneratearbitrarywavef
6、ormsatlowerfrequencies.ButtheDDStechniqueisrapidlygainingacceptanceforsolvingfrequency-(orwaveform)generationrequirementsinbothcommunicationsandindustrialapplicationsbecausesingle-chipICdevicescangenerateprogrammableanalogoutputwaveformssimplyandwith
7、highresolutionandaccuracy.Furthermore,thecontinualimprovementsinbothprocesstechnologyanddesignhaveresultedincostandpowerconsumptionlevelsthatwerepreviouslyunthinkablylow.Forexample,theAD9833,aDDS-basedprogrammablewaveformgenerator(Figure1),operating9
8、at5.5Vwitha25-MHzclock,consumesamaximumpowerof30milliwatts.WhatarethemainbenefitsofusingaDDS?DDSdevicesliketheAD9833areprogrammedthroughahighspeedserialperipheral-interface(SPI),andneedonlyanexternalclocktogeneratesimplesinewaves.DDSdevicesarenowavai
