在ADC电路，减少系统噪音的技术

Itmayseemthatdesigningalownoise,12-bitAnalog-to-Digital

Converter(ADC)boardorevena10-bitboardiseasy.Thisis

true,unlessoneignoresthebasicsoflownoisedesign.For

instance,onewouldthinkthatmostamplifiersandresistorswork

effectivelyin12-bitor10-bitenvironments.However,poordevice

selectionbecomesamajorfactorinthesuccessorfailureofthe

circuit.Another,oftenignored,areathatcontributesagreatdeal

ofnoise,isconductednoise.Conductednoiseisalreadyinthe

circuitboardbythetimethesignalarrivesattheinputofthe

ADC.Themosteffectivewaytoremovethisnoiseisbyusinga

low-pass(anti-aliasing)filterpriortotheADC.Includingby-pass

capacitorsandusingagroundplanewillalsoeliminatethistype

ofnoise.Athirdsourceofnoiseisradiatednoise.Themajor

sourcesofthistypeofnoiseareElectromagneticInterference

(EMI)orcapacitivecouplingofsignalsfromtrace-to-trace.TechniquesthatReduceSystemNoiseinADCCircuitsByBonnieC.Baker,MicrochipTechnologyInc.ANALOGDESIGNNOTEADN007Itmayseemthatdesigningalownoise,12-bitAnalog-to-DigitalIfthiscircuitisbuiltwithoutusinglownoiseprecautions,Converter(ADC)boardorevena10-bitboardiseasy.ThisisitisveryeasytoproduceanoutputsimilartoFigure2.true,unlessoneignoresthebasicsoflownoisedesign.ForHere,1024samplesweretakenattheoutputoftheADCinstance,onewouldthinkthatmostamplifiersandresistorswork(MCP3201)atadatarateof30ksps.Thesesampleshaveeffectivelyi