Analogfilterscanbefoundinalmosteveryelectronic
circuit.Audiosystemsusethemforpreamplification,
equalization,andtonecontrol.Incommunicationsys-
tems,filtersareusedfortuninginspecificfrequencies
andeliminatingothers.Digitalsignalprocessingsys-
temsusefilterstopreventthealiasingofout-of-band
noiseandinterference.
Thisapplicationnoteinvestigatesthedesignofanalog
filtersthatreducetheinfluenceofextraneousnoisein
dataacquisitionsystems.Thesetypesofsystemspri-
marilyutilizelow-passfilters,digitalfiltersoracombina-
tionofboth.Withtheanaloglow-passfilter,high
frequencynoiseandinterferencecanberemovedfrom
thesignalpathpriortotheanalog-to-digital(A/D)con-
version.Inthismanner,thedigitaloutputcodeofthe
conversiondoesnotcontainundesirablealiasedhar-
monicinformation.Incontrast,adigitalfiltercanbeuti-
lizedtoreducein-bandfrequencynoisebyusing
averagingtechniques.AN699Anti-Aliasing,AnalogFiltersforDataAcquisitionSystemsAuthor:BonnieC.BakerANALOGVERSUSDIGITALFILTERSMicrochipTechnologyInc.Asystemthatincludesananalogfilter,adigitalfilterorbothisshowninFigure1.WhenananalogfilterisINTRODUCTIONimplemented,itisdonepriortotheanalog-to-digitalconversion.Incontrast,whenadigitalfilterisimple-Analogfiltersca
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