心电采集系统中模拟电路的设计英文文献.doc

心电采集系统中模拟电路的设计英文文献.doc

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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

ECGacquisitioncircuitsimulation

ADconversion

Levelofuplift

Enlarge

Filtercircuit

Preamplifier

ECG

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.

Preamplifiercircuit

Figure2

Figure2Designoftheamplifierconsistsoftwocomponents,U1CandU1Dconstitutethefirststageofthedifferentialinputandoutputstage,U2Adifferentialratioforthebasiccircuit,thetotalvoltagegainAu,isequaltotheproductoftwo-stagegain.Thefirststageusesthesamephaseasinput,ahigherinputresistance,U1CandU1Dopampselectionofthesamecharacteristics,sothattheircommon-modevoltageoutputvoltageanddriftareequal,thenth