医学电子学课程学习

FrequencyRangesofVariousBiopotentialSignals第1页/共33页第一页，共34页。CommonbiopotentialsignalsAsshowninTable2.1,commonbiopotentialsignalsspantherangedcto10kHz.Underidealconditions,abiopotentialamplifierwithwidebandresponsewouldservemostapplications.However,thepresenceofcommon-modepotentials,electrodepolarization,andotherinterferingsignalsoftenobscurethebiopotentialsignalunderinvestigation.Assuch,thefrequencyresponseofabiopotentialamplifiershouldbetunedtothespecificspectralcontentexpectedfromtheapplicationathand.第2页/共33页第二页，共34页。FrequencyRangesofVariousBiopotentialSignals第3页/共33页第三页，共34页。FrequencyRangesofVariousBiopotentialSignals第4页/共33页第四页，共34页。WIDEBANDBIOPOTENTIALAMPLIFIERThebiopotentialamplifiercircuitdescribedbytheschematicdiagramsofFigures2.2and2.3coversthecompletefrequencyrangeofcommonlyrecordedbiopotentialswithhighCMR.第5页/共33页第五页，共34页。-3dBbandpassSpectralanalysisisthemostcommonwayofdeterminingthebandwidthrequiredtoprocessphysiologicalsignals.Forafirstestimate,however,therigorsofspectralanalysiscanbeavoidedsimplybyevaluatingthedurationsofhigh-andlow-frequencycomponentsofthesignal.Koide[1996]proposedamethodforestimatingthe-3dBbandpassbasedonacceptabledistortion.第6页/共33页第六页，共34页。AstereotypicalintracellularsignalThedurationofthehighest-frequencycomponent,tHF,isestimatedfromastereotypicalsignaltobetheminimumriseorfalltimeofasignalvariation.Thedurationofthelowestfrequencycomponent,tLF,ontheotherhand,ismeasuredfromthetiltofthebaselineorofthelowest-frequencycomponentofinterest.Koideillustratedthiswithanexample.Figure2.1showsastereotypicalintracellularpotentialmeasuredfromthepacemakercellsinamammalianheartSAnode.Inthisexample,tHF=75msandtLF=610ms.UsingtheformulasofTable2.2,theamplificationsystemmusthavea3-dBbandpassof0.0026to41.3Hztoreproducethesignalwithnegligibledistortion(1%).Acceptabledistortion,usuallyconsideredtobe5%orlessforphysiologicalsignals,wouldrequireanarrower-3dBbandpass,of0.013to18.7Hz.第7页/共33页第七页，共34页。Figure2.1AstereotypicalintracellularpotentialmeasuredfromthepacemakercellsinamammalianheartSAnodehasaminimumrisetimeoftHF=75msandatiltoftLF=610ms.The-3dBbandpassneededtoreproducethissignalwith1%distortionisof0.0026to41.3Hz.第8页/共33页第八页，共34页。Approximate-3dBFrequenciesRequired第9页/共33页第九页，共34页。Widebanddc-coupledbiopotentialamplifier

Figure2.2第10页/共33页第十页，共34页。Figure2.2Thiswidebanddc-coupledbiopotentialamplifierfrontendcoversthecompletefrequencyrangeofcommonlyrecordedbiopotentials.ABurr-BrownINA110AGICIAisdc-coupledtotheelectrodesviacurrent-limitingresistorsR22andR23andIS-1-3.3DPfaultcurrentlimiters.Capacitorsanddiodesareusedtoprotecttheamplifierfromhigh-frequencycurrents,suchasthoseusedinelectrosurgeryandablationproceduresaswellasfromhigh-voltagetransientssuchasthosethatmaybeexpectedfromdefibrillationandelectrostaticdischarge.第11页/共33页第十一页，共34页。第12页/共33页第十二页，共34页。Figure2.3TheoutputoftheISO107isolationamplifierisfedtoIC2B,whichhasitsgainselectablethroughswitchSW3.ThecircuitbuiltaroundIC2AnullsdcoffsetsautomaticallywhenSW1isclosed.Thefeaturesofthisbiopotentialamplifiermakeitanidealchoiceforrecordingcardiacmonophasicactionpotentials(MAPs)usingelectrodesindirectcontactwiththeheart.第13页/共33页第十三页，共34页。AC-COUPLEDINSTRUMENTATIONBIOPOTENTIAL

AMPLIFIERFRONTENDThecircuitofFigure2.5embodiestheclassicimplementationofamedium-impedance(10-MΩ)instrumentationbiopotentialamplifierbasedonthepopularAD521ICIAbyAnalogDevices.Thegainofthiscircuitisadjustablebetween10and1000andmaintainsaCMRofatleast110dB.第14页/共33页第十四页，共34页。第15页/共33页第十五页，共34页。Figure2.4Dcandverylowfrequencypotentialsarepreventedfrompropagatingbeyondthefront-endamplifierthroughatechniquecommonlyreferredtoasdcrejection.Here,IC4C,togetherwithR11andC17,areusedtooffsetIC1’sreferencetosuppressabaselinecomposedofcomponentsintherangedcto0.48Hz.第16页/共33页第十六页，共34页。AC-COUPLEDINSTRUMENTATIONBIOPOTENTIAL

AMPLIFIERFRONTENDTheheartofthecircuitisIC1,themonolithicICinstrumentationamplifier.Biopotentialsareac-coupledtotheamplifier’sinputsthroughC1andC2.Althoughinstrumentationamplifiershavedifferentialinputs,biascurrentswouldchargestraycapacitancesattheamplifier’sinput.Assuch,resistorsR1andR2arerequiredtoprovideadcpathtogroundfortheamplifier’sinputbiascurrents.Theseresistorslimittheimpedanceofeachinputto10MΩreferredtoground.Thehigh-passfilter,formedbytheac-couplingcapacitorandthebiasshuntresistoroneachoftheICIA’sinputs,hasa3-dBcutofffrequencyof0.12Hz.第17页/共33页第十七页，共34页。AC-COUPLEDINSTRUMENTATIONBIOPOTENTIAL

AMPLIFIERFRONTENDThegainofIC1isdeterminedbytheratiobetweenR3andR4.Usinga20-kΩmultiturnpotentiometer,andgiventhatthevalueoftherange-settingresistorR3is100kΩ,thedifferentialgainoftheamplifiercanbetrimmedbetween5and1000.TheoutputoffsetoftheamplifiercanbetrimmedthroughR5,which,atanygivengain,introducesanoutputoffsetequalandoppositetotheinputoffsetvoltagemultipliedbythegain.Thus,thetotaloutputoffsetcanbereducedtozerobyadjustingthispotentiometer.Theinstrumentationamplifierprovidesalow-impedanceoutput(0.1Ω)withapermissibleswingof10Vandcansourceorsinkupto10mA.第18页/共33页第十八页，共34页。Figure2.5第19页/共33页第十九页，共34页。Figure2.5Thisisaclassicmedium-impedance(10-MΩ)instrumentationbiopotentialamplifierbasedonthepopularAnalogDevicesAD521ICIA.Thegainisadjustablebetween10and1000andmaintainsaCMRofatleast110dB.The40-kHzsignalbandwidthmakesthisfrontendsuitableforrecordingEMGorECGsignalsorasageneral-purposehigh-impedanceac-coupledtransduceramplifier.第20页/共33页第二十页，共34页。BOOTSTRAPPEDAC-COUPLEDBIOPOTENTIALAMPLIFIERDirectaccouplingoftheinstrumentationamplifier’sinputsbywayofRChigh-passfiltersacrosstheinputsdegradestheperformanceoftheamplifier.Thispracticeloadstheinputoftheamplifier,whichsubstantiallylowersinputimpedanceanddegradestheCMRRofthedifferentialamplifier.Althoughunity-gaininputbufferscanbeusedtopresentahighinputimpedancetothebiopotentialsource,anyimpedancemismatchintheaccouplingofthesetoaninstrumentationamplifierstagedegradestheCMRperformanceofthebiopotentialamplifier.第21页/共33页第二十一页，共34页。Figure2.6第22页/共33页第二十二页，共34页。Figure2.6Thisbootstrappeddesignyieldsanac-coupleddifferentialamplifierthatretainsallofthesuperiorperformanceinherentindccoupledinstrumentationamplifiers.AcvoltagesfromtheoutputsoftheICIA’sdifferentialinputstagearefedtotheinvertinginputsoftheirrespectiveamplifiersviaC3andC4.ThiscausestheacvoltagedropacrossR1andR4tobevirtuallyzero.AccurrentflowthroughresistorsR1andR4ispracticallyzero,whiledcbiascurrentscanflowfreelytoground.第23页/共33页第二十三页，共34页。PASSIVEFILTERSThesimplestfiltersarethosethatcompriseonlypassivecomponents.Thesefilterscontainsomecombinationofresistive(R),capacitive(C),andinductive(L)elements.Theinductiveand/orcapacitivecomponentsarerequiredbecausetheseelementspresentvaryingimpedancetoaccurrentsatdifferentfrequencies.第24页/共33页第二十四页，共34页。Figure2.7第25页/共33页第二十五页，共34页。Figure2.7Inthisbiopotentialamplifier,biopotentialsareamplifiedbyaBurr-BrownINA128Uinstrumentationamplifier.R5,R6,R9,R10,andC22implementalow-passfilterwithacutoffofapproximately3.6kHz.Thebiopotentialamplifier’smainlow-passfiltersareimplementedbytwocascadedRCpassivefilterswithselectablecutofffrequency.IC4buffersthesignalsbetweenthecascadedsections.ThetwoRCsectionsareidentical,thereforesettingapoleatthesamefrequency.However,theeffectofthesecondRCcanbesuppressedbydisconnectingitscapacitorthroughswitchSW2.第26页/共33页第二十六页，共34页。Figure2.8第27页/共33页第二十七页，共34页。Figure2.8Thehigh-passfiltersfortheamplifierofFigure2.7areimplementedinessentiallythesamewayasthelow-passsections.Eachhigh-passsectionhascapacitors(C50andC53)whichopposecurrentflowwithanimpedancethatvariesinverselywithfrequencyandaresistorofselectablevaluethatshuntstheload.TheRCsectionsareidentical,t