心电采集系统中模拟电路的设计英文文献.docx
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心电采集系统中模拟电路的设计英文文献.docx
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心电采集系统中模拟电路的设计英文文献
ECGacquisitionsysteminanalogcircuitdesign
ECGastheheartelectricalactivityintheperformanceofbodysurface,thesignalisweak,thespectralrangeof0.05~200Hz,voltageamplitudeis0~5mV[1],thesignalsourceimpedanceofthousandstohundredsofthousandsofEuropeEuropeandtherewerealotofnoise,sotheECGacquisitionsystemcanbetherationaldesignoftherightofthekeycomponentsofECG.ECGmeasurementconditionsisquitecomplex,inadditiontosubject,includingelectromyography,respiratorywavesignal,EEGsignalinterferenceandotheroutsideinterferenceinvivohasalsobeen50HZelectricity,baselinedrift,electrodecontactandinterferencewithotherelectromagneticdevicesinvitroTherefore,thestrongnoiseinterferencehowtoeffectivelysuppressavarietyofECGacquisitionsystemwillbethekeytothedesign.
1ECGacquisitionsystem
CompleteECGacquisitionsystemincludesanaloganddigitaltwoparts[2],whichsimulatesomeofthemajortocompletethepickupECGsignals,amplificationandfiltering,theanalogportionofthedigitalpartwillreceivetheECGsignalanalysisandprocessingtohealthcarepersonnelarriveatacorrectdiagnosis,theECGacquisitionsystemintheanalogcircuitsintheECGmonitoringsystemplaysanimportantrole.ECGacquisitionsystemstructureshowninFigure1.
Figure1.TheoverallstructureofECGacquisitionsystem
CarriedonbythespecialelectrodesinthehumanECGsignalpickupthefirstamplifiedbytheinitialpre-amplifier,andavarietyofinterferencesignalsinacertaininhibitionintotheband-passfiltertofiltertheECGsignalinterferenceoutsidethefrequencyrange,andthenfilteredbythemainamplifierwillamplifythesignalfurthertotherightrange,andthenfilteredby50Hznotchfilterfrequencyinterference,aresimulatedECGsignalwillbeconvertedintotheADsystem,analog-digitalconversion,convertedintodigitalsignalsAfterthecentralprocessingunitresponsibleforthesubsequentanalysisandprocessing.
2preamplifiercircuit
PickedupfromthebodysurfaceECGgenerallyonlyafewmillivolts,inordertoimproveitsresolutiondisplayandprocessinginthebackend,youfirstneedtoamplifythesignal.ECGacquisitionprocess,thepre-amplifierthegreatestimpactontheECG,ECGtoimprovetheperformanceoftheamplificationofpreamplifiercannotchoosetoolarge(generallylessthan20),otherwisetheywillbeduelargerinterferencesignal(refertotheelectrodepolarizationvoltage),causingtheamplifierobstruction.
FortheECG,theacquisitionofthesignalsaredifferentialmodesignals,sotheamplifierisadifferentialamplifiercircuitstructure,themostcommonistheuseoflow-noise,highinputimpedance,highCMRR,highgainandinterferencestrongabilityinparallelwiththedifferentialamplifiercircuit,knownasthethreeopampinstrumentationamplifier,thissystemusesacommonintegratedoperationalamplifierLM324amplifiertoconstitutesuch.LM324isanintegratedoperationalamplifier4,ascheapandeasytouse,itiswidelyusedincontrolandsignalamplificationprocessed.Wearecarefullydesignedandrepeatedinthelaboratoryexperiments,usingLM324circuitcomposedofsuccessfulamplificationoftheECGsignalprocessing,itsmaintechnicalindicatorscanmeettherequirements.LM324caneitheruseasinglepowersupply,youcanalsousethedualpowersupply,powersupplyvoltagehasbeenusedfromthe+5V±15V,anddrivewithlowpowerconsumption,eachgroupofdifferentialgainamplifiercanreach100dB.Throughtherationaldesignofperipheralcircuits,makingtheLM324amplifierasthemaindevicecanmeetthehighmagnification,highstabilityamplificationofECGprocessingrequirements.
Itisworthmentioningthat,LM324'slowcurrentnoise,especiallyfortheapplicationofECG,ithasaverygoodDCCharacteristics:
inputoffsetvoltageislessthan5mV,theinputoffsetvoltagedriftislessthan7uV/℃,theinputbiascurrentlessthan40nA,commonmoderejectionratioof100dB,anditslowpower,lowpower(aslowas3V),andotherfeaturestostreamlinepackageisbattery-poweredportableECGmonitoringsystemanexcellentchoice.AmplificationcircuitshowninFigure2.
Figure2Designoftheamplifierconsistsoftwocomponents,U1CandU1Dconstitutethefirststageofthedifferentialinputandoutputstage,U2Adifferentialratioforthebasiccircuit,thetotalvoltagegainAu,isequaltotheproductoftwo-stagegain.Thefirststageusesthesamephaseasinput,ahigherinputresistance,U1CandU1Dopampselectionofthesamecharacteristics,sothattheircommon-modevoltageoutputvoltageanddriftareequal,thenthroughtheseconddifferentialfractionalU2Acircuitcomposedofcancanceleachotherout,andtheseconddifferentialamplifiercircuitwillbepointdifferentialinputsingleendedoutputchangingtoadapttotheneedsofgroundload.Afterthetwo-stagecascadecircuit,theyaremutuallyreinforcing,sothatcombinationofthiscircuithashighinputimpedance,voltagegainadjustmentisconvenient,commonmoderejectionishighandoffsetdrift,andaseriesofadvantages.InordertoimproveCMRRandreducetemperaturedrifteffects,andfurtherimprovethecircuitperformance,measuringamplifierwithsymmetricalstructure,ieafewcarefullyselectedexternalresistorR10,R11,R12,R13,R14,R15,R16andregulationofRW2,makestheR11=R12,R13=R14,R16=R15+adjustedRW2.SobyadjustingthesizeofanexternalresistorRW2caneasilychangethemeasurementofamplifiergain.
Removalofthebodytocarrycommunicationmodeinterferenceisaneffectivemethodistousetherightlegdrivecircuit[3],intheFigure2system,therightlegRLsideisnotdirectlygrounded,buttheamplifieroutput.Shieldedfromthedriveroutputcommonmodevoltagedetection,itisthereversebytheauxiliaryamplifierU0amplified,andthenthroughthefeedbackresistorR1totherightleg,rightlegdrivethusbethenameofthatdisplacementcurrentisnotflowingintothehumanbodyland,buttheflowofR1andauxiliaryamplifieroutputofU0.ButrightlegdrivecircuitoftheACinterferencevoltagefeedbackloop,whiletheACcurrentflowsthroughthebodymayhavebecomeunsafe,thecurrentlimitingresistorisnotverysmall,usuallytakingmorethan1MinEurope,whereR1isasecurityprotection,betweenwhenthepatientandtohighvoltage,theauxiliaryamplifiersaturationU0,rightlegdrivecircuitdoesnotwork,U0equivalenttogrounding,theresistorR1sincethentolimitprotection.Interferencesignalsenttotherightlegdriveamplifierinvertingamplifier,drivenrightlegelectrodeRLreachedforthedepthofinterferencesignalisanegativefeedback,whicheffectivelyweakensthehumanbodysensingthecommonmodeinterferencesignals.
3mainamplifierandfiltercircuit
ThemainECGamplificationandfiltercircuitshowninFigure3.Detectionsignalasthemaininterferenceinthesignalsbetweentheelectrodeplatesandthepolarizationvoltage,50Hzfrequencyinterference,theinstrumentaroundtheinternalnoiseandelectromagneticinterferenceequipmentandsoon.ToobtainaclearECGsignalstability,filterdesignisalsocritical,especially50Hzbandstopfilterisparticularlyimportant.CollectedfromtheECG,200Hzsignalisstrongerthantheinterference,andinterferencesignalsbelow0.05Hzrelativelyweak,sotakethefirstfiltercircuitinthelow-passfilteroutsignalsbelow200Hz,andthentakethewayofhigh-passtofilteroutthepolarizationvoltageandhighfrequencyinterference.InthecircuitU2Bandresistors,capacitors,composedofband-passfilter,whilethecircuitwithhighinputimpedance[4].FiltercircuitusingRCcouplingcircuit,highinputimpedancelowoutputimpedance,andinputandoutputbetweenthegoodisolation.Itsroleismainlytopre-amplifieracrosstheDCvoltageandDCpolarizationvoltage,coupledECG.InordertoensurethatnodistortionofECGcoupledtothenextlevel,mustbecoupledRC.RCproductofthelargerlow-frequencyresponseoftheamplifierthebetter,butincreasetheRCvaluescannotbeunlimited,becausetheRvalueislimitedbytheinputimpedance,Cistoolargenotonlylargeinsizeandincreaseinleakagecurrentcanalsocausedrift,butalsochargeanddischargetimewillbeextendedloop.ECGbodylowfrequencyfiltercircuitwiththeRCactivefiltercaneffectivelyavoidthegeneral-purposeintegratedcircuitoperationalamplifierasthebandwidthisnarrowandnotsuitableforhighfrequencyrangeofdefects.
4levelliftcircuit
AmplifiedECGsignalafterfilteringwillbesenttoA/Dconverteranalogtodigitalconversion,andthesystemchosenADconverterisasingle5VsupplytheMAX187,sotheneedtoaddafilteraftertheupliftofthecircuitlevel,theECGsignalraisedtotherangeof0~+5V.Circuitdesignisverysimple,showninFigure4.
Circuit-leveluplift
Figure4
5Analysis
ThroughthismethodsuccessfullydesignedandimplementedtheanalogECGacquisitionsystemcircuit,whichissimpleandreliablecircuit-leveluplift,amplifierwithhighgain,highinputimpedance,highCMRR,lownoise,lowdrift,rightbandwidthanddynamicrangecharacteristics,thecircuitcanbeinstrongbackgroundnoise,thesensorsurfacewithoutdistortionbytheweakECGsignaldetectedandenlarged,upliftedtotheextentappropriate,toobtainbettershowninFigure5ECGFig.
ECGmeasured
Figure5
ThetestprovedthatthedesignpaperECGacquisitioncircuitcanbeclinicallyvaluableECGdata,ECGfollow-uptreatmenttoprovideareliableguarantee.
Thisviewofinnovation:
overcomingthetraditionalECGinstrumentation
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