脑电波检测电路

WirelessNon-contactCardiacandNeuralMonitoringYuM.Chi,PatrickNgDepartmentofElectricalandComputerEngineeringUniversityofCalifornia,SanDiego9500GilmanDriveLaJolla,CA92093m1chi,[e-mail],JosephKangDepartmentofBioengineeringUniversityofCalifornia,SanDiego9500GilmanDriveLaJolla,[e-mail]tofComputerScienceandEngineeringUniversityofCalifornia,SanDiego9500GilmanDriveLaJolla,[e-mail]tmentofBioengineeringUniversityofCalifornia,SanDiego9500GilmanDriveLaJolla,[e-mail]siologicalmonitoringwillbeakeydrivingforceintheupcomingwirelesshealthrevolution.CardiacandbrainsignalsintheformofECGandEEGaretwocrit-icalhealthindicatorsthatdirectlybenetfromlong-termmonitoring.Despiteadvancementsinwirelesstechnologyandelectronicsminiaturization,however,theuseofwirelesshomeECG/EEGmonitoringisstilllimitedbytheinconve-nienceanddiscomfortofwetadhesiveelectrodes.Wehavedevelopedawirelessbiopotentialinstrumenta-tionsystemusingnon-contactcapacitiveelectrodesthatop-eratewithoutskincontact.Thesensorscanbeembeddedwithincomfortablelayersoffabricforunobtrusiveuse.Alloftheissuesrelatingtothedesignoflownoise,highperfor-mancecapacitivesensorsarediscussedalongwithfulltech-nicaldetails,circuitschematicsandconstructiontechniques.Thenon-contactelectrodehasbeenintegratedintobothawearableECGchestharnessaswellaEEGheadband.Wehavealsodesignedacompact,battery-powered,wirelessdataacquisitionsystemtointerfacewithmultipleelectrodesandmonitorpatientcardiacandneuralsignalsinrealtime.Experimentaldatashowsthatthenon-contactcapacitiveelectrodeperformcomparabletoAg/AgClelectrodesusingourspecialchestharnessandheadbandstoensuretight,movement-freeelectrodepositioning.GeneralTermsEEG,ECG,WirelessHealth,CapacitiveSensorsPermissiontomakedigitalorhardcopiesofallorpartofthisworkforpersonalorclassroomuseisgrantedwithoutfeeprovidedthatcopiesarenotmadeordistributedforprofitorcommercialadvantageandthatcopiesbearthisnoticeandthefullcitationonthefirstpage.Tocopyotherwise,torepublish,topostonserversortoredistributetolists,requirespriorspecificpermissionand/orafee.WirelessHealth2010,October57,2010,SanDiego,USACopyright2010ACM978-1-60558-989-3...$10.00.1.INTRODUCTIONBrainandcardiacbiopotentialsignalsintheformofEEGandECGaretwocriticalphysiologicalindicatorsthataredirectlysuitedforlong-termwirelesshealthmonitoring.Yetdespiteadvancementsinwirelesstechnologyandelectronicsminiaturization,however,theuseEEG/ECGhasstillbeenlargelylimitedbytheinconvenienceanddiscomfortofcon-ventionalwetcontactelectrodes.Forhomeuse,clinicalgradeadhesiveelectrodesareoftencitedasirritatinganduncomfortableleadingtolowusagecompliance.Asanalternative,dryelectrodes[1][2]havestartedbecomingmuchmorecommon-place.However,likewetelectrodes,dryelectrodesstillrequiredirectelectricalcontacttotheskin.Inaddition,dryelectrodes,whichdonothavethebenetofaconductivegel,aremuchmoresensitivetotheconditionoftheskinandarehighlysusceptibletomotionartifacts.Forfuturewirelesshealthsystems,alessobtrusivesensorisneededtomatchtheadvancementsmadeinwirelesstechnology.Incontrasttowetanddrycontactsensors,non-contactcapacitiveelectrodesdonotrequireanohmicconnectiontothebody.Thisoersnumerousadvantagessincenon-contactelectrodesrequirezeropreparation,arecompletelyinsensitivetoskinconditionsandcanbeembeddedinsideagarmentforacompletelyunobtrusive,patient-friendlysys-tem.Whiletheconceptofnon-contactbiopotentialsensorsisnotnew,withtherstworkingdevicereporteddecadesago[3],apracticaldeviceforpatientusehasyettomateri-alize.Morerecently,severalauthorshavepresentedresultsfromdesignsutilizingthelatestincommerciallyavailablediscretelownoiseampliers[4][5][6],includingsomewire-lessdesigns[7].Overtheyears,manycleverdesignshaveappeared,someproprietary.However,nothinghasreallyprogressedbeyondthe'labprototype'stage.Inaddition,generalknowledgeaboutcapacitivesensorsandhowtodesignandconstructthemarescarceinliterature.Inthispaper,weattempttoaddresstheseshortcomingsbypresentingthefulldesigns,includingalltherelevantdetailsintheanalogfront-end,ï+ï+ï+ï+Vref10nFѥ)1M10k1001M1nF10kLMP7702/A10kѥ)1M1nFï+ï+ï+Vref10nFѥ)1M10k1001M1nF10kï+10k10kѥ)VrefVcmCLOCKDATACONVERTAinADS7685Ain16bADCCONVERTDATACLOCKElectrode1Electrode2CapacitiveDRLDifferentialChannel1DifferentialChannel2N-ElectrodesN-ChannelsLMP7702/BLMP7702/ALMP7702/BLMP7704/ALMP7704/BLTC6081/ALTC6081/BADS768516bADCPIC24microcontroller100kBodyInsulationFigure1:FullschematicofwirelessECG/EEGsystem.ThecapacitiveelectrodePCBcontainsthefront-endamplier.Dierentialgain,digitization,activegroundinganddigitalprocessing/wirelessiscontainedonseparatebaseunit.AmplifierSnapConnectorActiveShield(innerlayer)SensingPlate(bottom)Figure2:Pictureofthenon-contact,capacitiveelec-trode.ThesensorismanufacturedonastandardPCB,whichcontainstheampliercircuitsonthetopandthesensingplateonthebottom.forahigh-quality,contactless,wirelessECG/EEGmonitor.Inaddition,wecharacterizethesystem-levelperformancebydirectlycomparingthecapacitiveele