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1、BANDPASSSELECTIONFORBIOPOTENTIALAMPLIFIERSFrequencyRangesofVariousBiopotentialSignalsCommonbiopotentialsignalsAsshowninTable2.1,commonbiopotentialsignalsspantherangedcto10kHz.Underidealconditions,abiopotentialamplifierwithwidebandresponsewouldservemostapplications.However,thepresenceofco
2、mmon-modepotentials,electrodepolarization,andotherinterferingsignalsoftenobscurethebiopotentialsignalunderinvestigation.Assuch,thefrequencyresponseofabiopotentialamplifiershouldbetunedtothespecificspectralcontentexpectedfromtheapplicationathand.FrequencyRangesofVariousBiopotentialSignals
3、FrequencyRangesofVariousBiopotentialSignalsWIDEBANDBIOPOTENTIALAMPLIFIERThebiopotentialamplifiercircuitdescribedbytheschematicdiagramsofFigures2.2and2.3coversthecompletefrequencyrangeofcommonlyrecordedbiopotentialswithhighCMR.-3dBbandpassSpectralanalysisisthemostcommonwayofdeterminingthe
4、bandwidthrequiredtoprocessphysiologicalsignals.Forafirstestimate,however,therigorsofspectralanalysiscanbeavoidedsimplybyevaluatingthedurationsofhigh-andlow-frequencycomponentsofthesignal.Koide[1996]proposedamethodforestimatingthe-3dBbandpassbasedonacceptabledistortion.Astereotypicalintra
5、cellularsignalThedurationofthehighest-frequencycomponent,tHF,isestimatedfromastereotypicalsignaltobetheminimumriseorfalltimeofasignalvariation.Thedurationofthelowestfrequencycomponent,tLF,ontheotherhand,ismeasuredfromthetiltofthebaselineorofthelowest-frequencycomponentofinterest.Koideill
6、ustratedthiswithanexample.Figure2.1showsastereotypicalintracellularpotentialmeasuredfromthepacemakercellsinamammalianheartSAnode.Inthisexample,tHF=75msandtLF=610ms.UsingtheformulasofTable2.2,theamplificationsystemmusthavea3-dBbandpassof0.0026to41.3Hztoreproducethesignalwithnegligibledist
7、ortion(1%).Acceptabledistortion,usuallyconsideredtobe5%orlessforphysiologicalsignals,wouldrequireanarrower-3dBbandpass,of0.013to18.7Hz.Figure2.1AstereotypicalintracellularpotentialmeasuredfromthepacemakercellsinamammalianheartSAnodehasaminimumrisetimeoftHF=75msandatiltoft
