Analog-Fundamentals-of-the-ECG-Signal-Chain

AnalogFundamentalsoftheECGSignalChainPreparedBy:MatthewHannTILinearApplicationsEngineerAnalogFundamentalsoftheECGSignalChain•WhatisBiopotential?•WhatisECG?•TheEinthovenTriangle•LeadConfigurationDefinitionsandPurpose•AnalogLeadDerivation•ModelingtheElectrodeInterface•InputFilteringandDefibrillationProtection•Isolation•TheINAfrontend•ACvs.DCcoupling•RLDriveAmplifierSelectionandDesign•INApostGain+AnalogFiltering•A/Dconversionandfiltering•ADS1298Introduction,Features,andAdvantagesWhatisaBipotential?WhatisaBiopotential?AnElectricPotentialMeasuredBetweenLivingCellsBiopotentialsfromCellsElectricalSignalsFromtheBodyEVERYCELLISLIKEALITTLEBATTERYRestingPotentialTimeVoltage+20mV-70mVActionPotentialReversedPotentialDepolarizationRepolarization0VHUMANCELL-70mVIONSVoltsNaKCa++++Cl-NaKCa++++Cl-WhatisECG?BiopotentialsfromCells-ElectrodesDIAGNOSTICMONITORElectrodesConvertIonicSignalsFromTheBodyIntoElectricalSignalsinWiresECGBPTEMPRESPIONStoELECTRONSCONVERTERNaKCl++-e-e-e-WhatisECG?WhatisECG?VentricularDepolarizationAtrialDepolarizationAMeasureoftheElectricalActivityoftheHeartHeartValveContributiontoECGWaveformPressuresignalhasslowerrise30HzBW,25harmonicsECGsignalhasfasterrise100-150HzBW,70harmonics120mmHgVesselMaximumPressureHead60mmHgVesselRelaxation1mVp-pLeftHeartContractsLeftHeartRelaxesECGandBloodPressureWavesWhatisECG?ActualECG-Normal24mmx1sec/25mm=0.96sec/beat=1/0.96sec=1.04bps62BPMatrest24mm,0.96secChartSpeed:25mm/sec10mm=1mV10mm=0.4sec1mVCal10mm,1mVp-pBASELINEordcDRIFTChargingTimeConstantofHighPassFilterandChangingElectrodeHalf-CellPotentialWhatisECG?ECGIrregularTracingsDuetoExternalArtifactsBaselineordcDriftMuscleShaking50/60HzPick-UpBaselinedcInstabilityWhatisECG?ModelingtheElectrodeInterfaceElectricalCharacteristicsIncludeaDYNAMICResistance,Capacitance,andOffsetVoltageRuRe’Ce’Rs’RdCdVe’WhatisECG?AnalogLeadDerivationECGEinthovenTriangle,1907I=VLA-RL–VRA-RL3DerivedLeadsI,II,IIIRLRefEinthoven’sLawInelectrocardiogramatanygiveninstantthepotentialofanywaveinLead2isequaltothesumofthepotentialsinLeadIandIII.II=VLL-RL–VRA-RLIII=VLL-RL–VLA-RL3BodyElectrodesAnalogLeadDerivation*LeadsareavoltagepotentialmeasurementwithrespecttoacommonreferenceAnalogLeadDerivationRRARLARLLTheWilsonCentral(WCT)ProvidesChestLeadReferenceatCenteroftheEinthovenTriangle3WCTRRARALALLRRAWCTRALALL3Assuming:*DrawingTakenFromBioelectromagnetism,JaakoMalmivuoandRobertPlonseyAnalogLeadDerivationTheWilsonCentralistheAVERAGEpotentialbetweenRA,LA,andLLTheWilsonCentralisusedtoderiveareferencepotentialfortheChestLeads,V1–V6RRARLARLLVWCTRALALL3AnalogLeadDerivationChestLeadSignalsProvideDifferentInformationatDifferentCross-SectionalAnglesAnalogLeadDerivationTheGoldbergerTerminalrepresentstheAUGMENTEDleadderivationfromtheWCTVLL2LLRALA3RA’LA’LL’WCT’VaVfLLWCTaVf.2LLLARA2*DrawingTakenFromBioelectromagnetism,JaakoMalmivuoandRobertPlonsey*ExampleDerivationforAVLAnalogLeadDerivationWhatisthePurposeofAlltheLeads?EachleadprovidesuniqueinformationabouttheECGOutputSignalMultipleAnglesGiveaBetterThan2-DPictureoftheECGOutputStandardsElectrodesNeeded1LeadLA,RA3LeadLA,RA,LL6LeadsLA,RA,LL12LeadsLA,RA,LL,V1-6IEC60601–2–51(Diagnostic)LeadConfigurationsECGInputFiltering,DefibrillationProtection,andIsolationECGInputFilteringandProtectionExample:LEADIProtectionwithInputFiltering+Vs+Vs-Vs-VsCdiffCCMCCMCFCFRProt1RProt1RProt2RProt2LARANE2HNE2HProtectionDiodesZenerDiodeCdiff=10xCcmNeonGasLampsProtectAgainstDefibrillationVoltagesSeriesResistanceLimitsInputCurrentCF,Ccm,andCdiff+RprotformHPFZenerDiodeECGInputandDefibrillationProtectionTINASimulationCircuitForDefibrillationPulseVCCVCCVCCVcmNR211kR251kC647nR201kC847nR241k63.4k63.4k33pC1933p330p63.4k63.4k33p5+ECGp+ECGn33p+VpulseNe2LampNe2LampA+IinPA+IinNVLamp1Vlamp2R3100mVout-+-+VCVS11NE2HLampsCdiff=10xCcmClampingDiodesECGModelECGProtectionCircuitZenerDiodeECGInputandDefibrillationProtectionInputCurrent,Voltage,andOutputResponseto3000VDefibrillationPulseTime(s)0.005.00m10.00mIinN-310.84u0.00IinP0.00271.43uVLamp10.0040.19Vlamp2-40.190.00Vout0.006.53DefibPulse0.003.00kTheINAFrontEndTheINAFrontEndKeyFeaturesoftheINAFrontEndInputBiasCurrentInputImpedanceInputCurrentNoiseInputVoltageNoisePowerConsumptionDC/ACCMRR*Important*InputOffsetVoltageInputOffsetVoltageDriftGainErrorNonlinearityPSRRNotAsImportant*DCErrorssuchasVOSareswampedoutbytheOffsetsIntroducedbytheSkin-ElectrodeContactsTheINAFrontEndVrefVrefR211kR251kC6100pR14100kR191kC747nR201kV40C8100pR22100kR231kC947nR241kV50R163.4kR363.4kC1833pC1933pR463.4kR563.4kC1033pC1233pC20330p+ECGp-+-+INA1VoutnVVn12VnoisefAIn12In_fAIdealSimulationCircuitwithCurrentandVoltageNoiseSourcesECG+SkinImpedanceElectrodeImpedance+OffsetInputCM+DifferentialFilteringIdealINAFrontEndTFrequency(Hz)1.0010.00100.001.00kTotalnoise(V)0.004.00u8.00u12.00u16.00u20.00u24.00u28.00u32.00uTheINAFrontEndSimulationShowingOutput-ReferredTotalRMSNoisevs.Bandwidth(G=1-10)TTime(s)8.37m366.11m723.85mVoltage(V)2.502.502.51TheINAFrontEndSimulationsShowingOutput-ReferredECGSignal(G=1-10)Snaps