醫(yī)學電子學課程學習

FrequencyRangesofVariousBiopotentialSignals第1頁/共33頁第一頁，共34頁。CommonbiopotentialsignalsAsshowninTable2.1,commonbiopotentialsignalsspantherangedcto10kHz.Underidealconditions,abiopotentialamplifierwithwidebandresponsewouldservemostapplications.However,thepresenceofcommon-modepotentials,electrodepolarization,andotherinterferingsignalsoftenobscurethebiopotentialsignalunderinvestigation.Assuch,thefrequencyresponseofabiopotentialamplifiershouldbetunedtothespecificspectralcontentexpectedfromtheapplicationathand.第2頁/共33頁第二頁，共34頁。FrequencyRangesofVariousBiopotentialSignals第3頁/共33頁第三頁，共34頁。FrequencyRangesofVariousBiopotentialSignals第4頁/共33頁第四頁，共34頁。WIDEBANDBIOPOTENTIALAMPLIFIERThebiopotentialamplifiercircuitdescribedbytheschematicdiagramsofFigures2.2and2.3coversthecompletefrequencyrangeofcommonlyrecordedbiopotentialswithhighCMR.第5頁/共33頁第五頁，共34頁。-3dBbandpassSpectralanalysisisthemostcommonwayofdeterminingthebandwidthrequiredtoprocessphysiologicalsignals.Forafirstestimate,however,therigorsofspectralanalysiscanbeavoidedsimplybyevaluatingthedurationsofhigh-andlow-frequencycomponentsofthesignal.Koide[1996]proposedamethodforestimatingthe-3dBbandpassbasedonacceptabledistortion.第6頁/共33頁第六頁，共34頁。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頁/共33頁第七頁，共34頁。Figure2.1AstereotypicalintracellularpotentialmeasuredfromthepacemakercellsinamammalianheartSAnodehasaminimumrisetimeoftHF=75msandatiltoftLF=610ms.The-3dBbandpassneededtoreproducethissignalwith1%distortionisof0.0026to41.3Hz.第8頁/共33頁第八頁，共34頁。Approximate-3dBFrequenciesRequired第9頁/共33頁第九頁，共34頁。Widebanddc-coupledbiopotentialamplifier

Figure2.2第10頁/共33頁第十頁，共34頁。Figure2.2Thiswidebanddc-coupledbiopotentialamplifierfrontendcoversthecompletefrequencyrangeofcommonlyrecordedbiopotentials.ABurr-BrownINA110AGICIAisdc-coupledtotheelectrodesviacurrent-limitingresistorsR22andR23andIS-1-3.3DPfaultcurrentlimiters.Capacitorsanddiodesareusedtoprotecttheamplifierfromhigh-frequencycurrents,suchasthoseusedinelectrosurgeryandablationproceduresaswellasfromhigh-voltagetransientssuchasthosethatmaybeexpectedfromdefibrillationandelectrostaticdischarge.第11頁/共33頁第十一頁，共34頁。第12頁/共33頁第十二頁，共34頁。Figure2.3TheoutputoftheISO107isolationamplifierisfedtoIC2B,whichhasitsgainselectablethroughswitchSW3.ThecircuitbuiltaroundIC2AnullsdcoffsetsautomaticallywhenSW1isclosed.Thefeaturesofthisbiopotentialamplifiermakeitanidealchoiceforrecordingcardiacmonophasicactionpotentials(MAPs)usingelectrodesindirectcontactwiththeheart.第13頁/共33頁第十三頁，共34頁。AC-COUPLEDINSTRUMENTATIONBIOPOTENTIAL

AMPLIFIERFRONTENDThecircuitofFigure2.5embodiestheclassicimplementationofamedium-impedance(10-MΩ)instrumentationbiopotentialamplifierbasedonthepopularAD521ICIAbyAnalogDevices.Thegainofthiscircuitisadjustablebetween10and1000andmaintainsaCMRofatleast110dB.第14頁/共33頁第十四頁，共34頁。第15頁/共33頁第十五頁，共34頁。Figure2.4Dcandverylowfrequencypotentialsarepreventedfrompropagatingbeyondthefront-endamplifierthroughatechniquecommonlyreferredtoasdcrejection.Here,IC4C,togetherwithR11andC17,areusedtooffsetIC1’sreferencetosuppressabaselinecomposedofcomponentsintherangedcto0.48Hz.第16頁/共33頁第十六頁，共34頁。AC-COUPLEDINSTRUMENTATIONBIOPOTENTIAL

AMPLIFIERFRONTENDTheheartofthecircuitisIC1,themonolithicICinstrumentationamplifier.Biopotentialsareac-coupledtotheamplifier’sinputsthroughC1andC2.Althoughinstrumentationamplifiershavedifferentialinputs,biascurrentswouldchargestraycapacitancesattheamplifier’sinput.Assuch,resistorsR1andR2arerequiredtoprovideadcpathtogroundfortheamplifier’sinputbiascurrents.Theseresistorslimittheimpedanceofeachinputto10MΩreferredtoground.Thehigh-passfilter,formedbytheac-couplingcapacitorandthebiasshuntresistoroneachoftheICIA’sinputs,hasa3-dBcutofffrequencyof0.12Hz.第17頁/共33頁第十七頁，共34頁。AC-COUPLEDINSTRUMENTATIONBIOPOTENTIAL

AMPLIFIERFRONTENDThegainofIC1isdeterminedbytheratiobetweenR3andR4.Usinga20-kΩmultiturnpotentiometer,andgiventhatthevalueoftherange-settingresistorR3is100kΩ,thedifferentialgainoftheamplifiercanbetrimmedbetween5and1000.TheoutputoffsetoftheamplifiercanbetrimmedthroughR5,which,atanygivengain,introducesanoutputoffsetequalandoppositetotheinputoffsetvoltagemultipliedbythegain.Thus,thetotaloutputoffsetcanbereducedtozerobyadjustingthispotentiometer.Theinstrumentationamplifierprovidesalow-impedanceoutput(0.1Ω)withapermissibleswingof10Vandcansourceorsinkupto10mA.第18頁/共33頁第十八頁，共34頁。Figure2.5第19頁/共33頁第十九頁，共34頁。Figure2.5Thisisaclassicmedium-impedance(10-MΩ)instrumentationbiopotentialamplifierbasedonthepopularAnalogDevicesAD521ICIA.Thegainisadjustablebetween10and1000andmaintainsaCMRofatleast110dB.The40-kHzsignalbandwidthmakesthisfrontendsuitableforrecordingEMGorECGsignalsorasageneral-purposehigh-impedanceac-coupledtransduceramplifier.第20頁/共33頁第二十頁，共34頁。BOOTSTRAPPEDAC-COUPLEDBIOPOTENTIALAMPLIFIERDirectaccouplingoftheinstrumentationamplifier’sinputsbywayofRChigh-passfiltersacrosstheinputsdegradestheperformanceoftheamplifier.Thispracticeloadstheinputoftheamplifier,whichsubstantiallylowersinputimpedanceanddegradestheCMRRofthedifferentialamplifier.Althoughunity-gaininputbufferscanbeusedtopresentahighinputimpedancetothebiopotentialsource,anyimpedancemismatchintheaccouplingofthesetoaninstrumentationamplifierstagedegradestheCMRperformanceofthebiopotentialamplifier.第21頁/共33頁第二十一頁，共34頁。Figure2.6第22頁/共33頁第二十二頁，共34頁。Figure2.6Thisbootstrappeddesignyieldsanac-coupleddifferentialamplifierthatretainsallofthesuperiorperformanceinherentindccoupledinstrumentationamplifiers.AcvoltagesfromtheoutputsoftheICIA’sdifferentialinputstagearefedtotheinvertinginputsoftheirrespectiveamplifiersviaC3andC4.ThiscausestheacvoltagedropacrossR1andR4tobevirtuallyzero.AccurrentflowthroughresistorsR1andR4ispracticallyzero,whiledcbiascurrentscanflowfreelytoground.第23頁/共33頁第二十三頁，共34頁。PASSIVEFILTERSThesimplestfiltersarethosethatcompriseonlypassivecomponents.Thesefilterscontainsomecombinationofresistive(R),capacitive(C),andinductive(L)elements.Theinductiveand/orcapacitivecomponentsarerequiredbecausetheseelementspresentvaryingimpedancetoaccurrentsatdifferentfrequencies.第24頁/共33頁第二十四頁，共34頁。Figure2.7第25頁/共33頁第二十五頁，共34頁。Figure2.7Inthisbiopotentialamplifier,biopotentialsareamplifiedbyaBurr-BrownINA128Uinstrumentationamplifier.R5,R6,R9,R10,andC22implementalow-passfilterwithacutoffofapproximately3.6kHz.Thebiopotentialamplifier’smainlow-passfiltersareimplementedbytwocascadedRCpassivefilterswithselectablecutofffrequency.IC4buffersthesignalsbetweenthecascadedsections.ThetwoRCsectionsareidentical,thereforesettingapoleatthesamefrequency.However,theeffectofthesecondRCcanbesuppressedbydisconnectingitscapacitorthroughswitchSW2.第26頁/共33頁第二十六頁，共34頁。Figure2.8第27頁/共33頁第二十七頁，共34頁。Figure2.8Thehigh-passfiltersfortheamplifierofFigure2.7areimplementedinessentiallythesamewayasthelow-passsections.Eachhigh-passsectionhascapacitors(C50andC53)whichopposecurrentflowwithanimpedancethatvariesinverselywithfrequencyandaresistorofselectablevaluethatshuntstheload.TheRCsectionsareidentical,t