Level-shifter

Abstract—Highvoltage(15V)driversareintegratedintotheVLSIchipforMEMSapplicationwiththedevelopmentofSOCtechnology.Thepre-drivercircuit,whichgeneratesthepull-upandpull-downsignal,ismainlyavoltagelevelshiftercircuit.Itconvertsthelowvoltagecontrolsignaltohighvoltagecontrolsignal.ConventionalvoltagelevelshiftercircuitusinghighvoltageNMOSandhighvoltagePMOSoperateswellon0.8umprocess.However,withthecontinuousprocessshrinking,conventionalvoltagelevelshiftercircuitisnotsuitableforhighvoltagepowersupplyduetothereducedbreakdownvoltageofthehighvoltagedevices.Althoughstackedhighvoltagedevicescanbeappliedtosolvethisissue,thecircuitwillhaveDCleakagecurrentandtheinternalhighvoltageswingproblem.Thispaperdescribesanewlowvoltagetohighvoltageconvertercircuit.Byusingallthelowvoltagedevices,theDCleakagecurrentandthehighvoltageswingnodehavebeeneliminated.Thiscircuitisfabricatedin0.35SOIprocess.Bothsimulationandtestresultsvalidateitsoperationsforcontrollinghighvoltagedrivers.I.INTRODUCTIONighvoltage(15V)driversareintegratedintotheVLSIchipforMEMSapplicationwiththedevelopmentofSOCtechnology.ThehighvoltagedriversusuallyapplyhighvoltageNMOS(HVNMOS)andhighvoltagePMOS(HVPMOS)asthepull-upandthepull-downdevice.Thepre-drivercircuit,whichgeneratesthepull-upandpull-downcontrolsignal,ismainlyavoltagelevelshiftercircuit.ItgeneratestheHVNMOScontrolsignalandconvertsthelowvoltagecontrolsignaltohighvoltageHVPMOScontrolsignal.Reliability,andthelowpowerconsumption,especiallythelowDCcurrentaremajorconcernsforapracticalpre-drivercircuit.Previousresearchofthevoltageshiftercircuit[1]usinghighvoltageNMOSandhighvoltagePMOSoperateswellon0.8umprocess.However,withthecontinuousprocessshrinking,breakdownvoltageofthosehighvoltagedevices,especiallythePdevice,alsoreduces.Inordertomaintainthehighoperationvoltage,stackeddevicescanbeusedinthepre-driver[2][3].ThevoltageshiftercircuitusingstackedHVdevices,ontheotherhand,willexperienceDCleakagecurrentandfurtherincreasetheoverallpowerconsumption.Atthesametime,theinternalnodesoftheconventionalvoltageshiftcircuithavelargevoltageswing(changesfromGNDtothepowersupply).Thislargevoltageswingwillincreasethecomplexityofthelayout.Itmayevenaffectthereliabilityofthecircuitduetothehighelectricfield.ThispaperdescribesanewlowvoltagetohighvoltageconvertercircuitwithoutDCleakagecurrent.Italsoreducesthevoltageswingoftheinternalnodes.II.HVDEVICESTRUCTUREANDTHEDRIVERCIRCUITThehighvoltagedevicescanbemanufacturedusingstandarddigitalcommercialprocessusingspeciallayouttechniques[4].Fig.1showsthecrosssectionofahighvoltagedevice.ThelightlydopedN-wellregion(N-)createsadriftpath.ThebreakdownvoltagewillbeincreasedduetothereducedconcentrationlevelnearthePNjunctionasshowninthefollows[2]:22)(MaxDADAsiENqNNNBV+≅ε(1)Whereεsiisthedielectricpermittivityofsilicon,NAisthedopingconcentrationoftheacceptorsofP-typematerial,NDisthedopingconcentrationofthedonorsintheN-typematerial,qisthechargeofanelectron(1.602E-19coulombs),andEMaxisthecriticalelectricfieldforsilicon.Atthesametime,thefieldoxideisappliedintheHVdevicetoprotectthegatefromthehighelectricalfield.N+SourceP-N-N+GateOxideDrainGateFieldOxideFig.1.CrosssectionofahighvoltageNMOS.Fig.2showsahighvoltagedrivercircuitusingaHVNMOSandaHVPMOS.Thedraintosourcebreakdownvoltage(Vds)isveryhighforthesedeviceswhilethegatetosourcebreakdownvoltage(Vgs)ismuchlower.Forthe0.35umprocessusedinthisresearchproject,theVgsbreakdownvoltageofHVNMOSisabout5VandtheVdsbreakdownvoltageishigherthan15V.LowvoltagesignalcanbeusedtodrivetheHVNMOSdirectly.FortheHVPMOS,theVsgbreakdownvoltageofHVNMOSisalsoabout5VwhiletheVsdbreakdownvoltageisabout10V.Inthisproject,thecontrolsignalfortheHVNMOSvariesfrom0and3V.ThecontrolsignalforHVPMOSshouldclosetopowersupply(HVCC)toavoidhighVsgvoltage.ThecontrolsignalisdesigntovaryfromALowVoltagetoHighVoltageLevelShifterCircuitforMEMSApplicationDongPan1,3,Member,IEEE,HarryW.Li2,andBogdan.M.Wilamowski3,Fellow,IEEE1MicronTechnology,Inc.,Boise,ID837162UniversityofIdaho,ElectricalandComputerEngineeringDepartment,Moscow,ID838443UniversityofIdaho,CollegeofEngineering,800ParkBlvd.Suite200Boise,ID83712HHVHVHVCCOutP_ctrN_ctrGNDHVCC-3VHVCC3VFig.2.Ahighvoltagedrivercircuitanditscontrolsignals.HVCC-3VtoHVCC.Thus,specialpre-drivercircuitmustbeusedtogeneratethecontrolsignals.III.ACONVENTIONALVOLTAGELEVELSHIFTERCIRCUITAconventionalvoltageshiftercircuitisshowninFig.3.ItappliestwoHVNMOSandtwoHVPMOSdevices.TwobiasvoltagesareusedtolimitthevoltageswingoftheOut_l1andOut_h1nodes.Whentheinputishigh,M2turnsonandpullsdowntheOut_l1nodetoGND.ThegeneratedlargeVgsofM4willturnontheM4andpullthenodeMID1toGND.M6andBias_hwillkeepOut_h1lowerthanbiash+|Vthp|(IfOut_h1ishigherthanbiash+|Vthp|,M6willturnonandpullthenodeOut_h1downtobiash+|Vthp|).Thecross-coupledtransistorM7andM8operatelikeacurrentsensecircuit[5].Itwillfurtherpulldownthevoltageofout_h1nodetoaboutBias_h.Onthecontrary,whentheinputislow,theOut_h1outputwillbehighandtheOut_l1willbelow.ThemaximumvoltagesacrossthedrainandsourceoftheHVPMOSandtheHVNMOSinFig.3areclosetoHVCC.IfHVCCishigherthanthe