DEVICE FOR PROTECTION AGAINST EXCEEDING THE SAFE OPERATING AREA

Abstract

A control circuit comprising a rail terminal, an input terminal, an output terminal, a first switching device with a control gate connected to the input terminal, a second switching device configured to withstand a first maximum voltage, and a third switching device configured to withstand a second maximum voltage. The first is a first node, the second switching device is connected between the rail terminal and a first node, the second switching device is connected between the first node and a second node, and the third switching device is connected between the second node and the output terminal.The control circuit further includes a bypass circuit coupled between the output terminal and the second node, in parallel with the third switching device, and configured to limit the voltage at the third switching device across the second switching device as well as to limit the voltage across the third switching device during activation of the first switching device.

Description

BE2025 / 5024 2 ofsuchadrivercircuitwouldbeexpandedandoptimizedcomparedtoconventionalcircuitsof similararea. Theproblemforwhichthepresentinventionoffersasolution,isillustratedbytheFigures1a-1b, whichshowrespectivelyacircuitschematicpriorartdrivercircuitandtheevolutionwithtimeof5 thevoltageonthedifferentnodesinsaidpriorartdrivercircuit.Moreprecisely,thedrivercircuitof Figure1aisoneofthesmallestimplementationsofastackeddriverarchitecture,whereintwo switchingdevicesS1andS2areconnectedinseriessothatthevoltageisdistributedoverthetwo switchingdevices.InthespecificimplementationofFigure1a,theswitchingdevicestaketheform ofanNMOStransistor,whereinthefirsttransistorS1iscoupledbetweenarailterminaldenotedby10 RAIL,andanodedenotedbyMID,whereasthesecondtransistorS2iscoupledbetweenthenode MIDandanoutputterminaldenotedbyPAD.ThegateofthefirsttransistorS1iscoupledtoan inputterminalTX,whereasthegateofthesecondtransistoriscoupledtoaprotectionterminalPROT whichdeliversafixedDC-voltagetosaidgate.InthesimpleimplementationofFigure1a,thetwo transistorsS1andS2haveidenticalmaximumtoleratedvoltagevaluesVmax.Therailterminaliskept15 at0V,andfixedDC-voltagevaluedeliveredtothegateofthesecondtransistorS2bytheprotection terminalPROTischosenequalorclosetoVmax. Figure1bshowstheevolutionovertimeofthevoltagesVpad(thevoltageontheoutputterminal PAD)andVmid(thevoltageonthenodeMID),whenattimet=0bothtransistorsS1andS2areina switchedoffstateandtheoutputterminaliskeptatavoltageofabouttwicethevalueVmax,whereas20 atapointintimet1bothtransistorsareactivated.SaidactivationcausesboththevoltagesVpadand Vmidtodropto0V,yetsaidvoltagedropproceedsmuchmorerapidlyforVmidthanforVpadsince theloadcapacitanceconnectedtotheoutputterminalPADistypicallymanytimeslargerthanthe capacitanceconnectedtothenodeMID.Indeed,theformermaycompriseexternalcapacitances whereasthelatteronlyconsistofon-chipcapacitances.Asaresult,thevoltageoverthesecond25 transistorS2,whichyieldsthedifferencebetweenVpadandVmid,increasesfromavalueclosetoVmax attimet1toamaximalvalueexceedingVmaxatthepointintimewhenVmidreaches0V.TheSOA conditionsarethusexceededsincethesecondtransistorS2experiencesavoltagebeyondits maximumtoleratedvoltagevalue,therebycreatingasevereriskofdamageordegradationtosaid secondtransistor.30 AnaïvewaytobypassthisproblemwouldbetoincreasethecapacitiveloadofthenodeMIDto approximatelymatchthecapacitiveloadoftheoutputterminal,forexamplebycouplingthenode MIDtoanexternalcapacitiveelement.Assuch,itsdischargeprocesswouldproceedslower,ideally atthesamepaceasthedischargeoftheoutputterminal.Inthatcase,thelower-lyingofthetwo35 voltagegraphsinFigure1bwouldbealteredtobecomelesssteep,ideallyparalleltothehigher-lying 2025 / 5024 BE2025 / 5024 3 voltagegraph,andthevoltageoverthesecondtransistorS2,definedastheverticaldistancebetween thetwographs,wouldatanypointintimeremainbelowthemaximumvalueVmax.However,such anexternalcapacitiveelementrepresentsanundesirableoff-chipconnectiontotheMIDnode,and correspondswithanundesirablyincreasedsurfacearea,notablysincetheoutputterminaltypically correspondswithaverylargecapacitance.Moreover,theloadcapacitanceoftheoutputterminal5 mightvarysignificantlywithtime,makingitimpossibleforthedrivertosuitablycontrolsaid capacitanceandthusrenderingthisnaïvesolutioninfeasible.Finally,drivercircuitswhichallowfor arapiddischargearegenerallypreferableoverslowlydischargingcircuitslikethenaïvelyproposed circuitwithanadditionalexternalcapacitiveelement. 10 Analternativesolutiontothisproblem,knownfromthepriorart,hasbeendescribede.g.inB. Serneelsetal,“AHigh-VoltageOutputDriverinaStandard2.5V0.25µmCMOSTechnology”, 2004IEEEInternationalSolid-StateCircuitsConference,SanFransico,2004(DOI: 10.1109 / ISSCC.2004.1332636).Herein,Figure7.8.2showsacircuitschematicofadrivercircuit withthreeNMOStransistorsconnectedinseries.ComparedtothecircuitofFigure1a,notonlya15 thirdNMOStransistor,butalsoelaborateadditionalcircuitrycoupledtosaidthirdtransistorwas added.Saidadditionalcircuitryisneededforthethirdtransistor,whichcannolongerbebiasedby aDCvoltage,tosensethevoltageontheoutputterminal.However,suchadditionalcircuitrycomes attheexpenseofnotonlyaddingsurfacearea,butalsonegativelyimpactingtheimpedanceofthe outputterminalandreducingthemaximumachievableswitchingspeedofthedrivercircuit.20 SUMMARY TheobjectofembodimentsoftheinventionistoprovideadrivercircuitwithincreasedSafe OperationArea(SOA)comparedtoconventionalcircuitsofsimilararea,whilstreducingtheabove-25 describeddisadvantagesofexistingtechnologies. Accordingtoafirstaspect,adrivercircuitisprovided,comprisingarailterminal,aninputterminal, anoutputterminal,afirstswitchingdevicewithacontrolportcoupledtotheinputterminal,asecond switchingdeviceconfiguredtowithstandafirstmaximumvoltage,andathirdswitchingdevice30 configuredtowithstandasecondmaximumvoltage.Herein,therailterminalmayforexamplebea groundterminal,apowerterminal,aVSSterminaloraVDDterminal.Thefirstswitchingdeviceis coupledbetweentherailterminalandafirstnode,thesecondswitchingdeviceiscoupledbetween thefirstnodeandasecondnode,andthethirdswitchingdeviceiscoupledbetweenthesecondnode andtheoutputterminal.Thedrivercircuitfurthercomprisesabypasscircuitwhichiscoupled35 betweentheoutputterminalandthesecondnodeinparallelwiththethirdswitchingdevice,and 2025 / 5024 BE2025 / 5024 4 whichisconfiguredtolimitboththevoltageoverthesecondswitchingdeviceandthevoltageover thethirdswitchingdevice,inparticularsothatthevoltageoverthesecondswitchingdevicedoes notexceedthefirstmaximumvoltageandthevoltageoverthethirdswitchingdevicedoesnotexceed thesecondmaximumvoltage,duringactivationofthefirstswitchingdevice. 5 SuchadrivercircuithasincreasedSafeOperationArea(SOA)comparedtoconventionalcircuitsof similararea,inthesensethatthecircuitisconfiguredtoswitchvoltagelevelswhichexceedthe maximumtoleratedvoltagevaluesoftheindividualcomponentdevices,whilstguaranteeingthat noneofthesecomponentdevicesexceedsitsmaximumtoleratedvoltage.Herein,bymaximum toleratedvoltageofadeviceitismeantthemaximalvaluethevoltageoverthedevicemayattain10 withoutriskofdamageordegradationofthedeviceand / oroftheotherdevicesoftheintegrated circuit,and / orwithoutriskofunreliabledevicefunctionality.Saidfirstmaximumvoltageandsecond maximumvoltagethusrefertothemaximumtoleratedvoltageofthesecondandthirdswitching devicerespectively. SaidincreaseoftheSOAisachievedinthefollowingway.Sincethethreeswitchingdevicesare15 mutuallycoupledinthedescribeddrivercircuit,theyareoperatedtogether,inthesensethatwhen thefirstswitchingdeviceswitchesonandthusstartstoconduct,thisforcesthesecondswitching device,andeventuallyalsothirdswitchingdevice,tosubsequentlyswitchonaswell.Asaresult,a decenton-stateisachievedwhereinallswitchingdevicesareclosed,whereaswhenthefirst switchingdeviceswitchesoff,acurrentcannolongerflowfromthesecondorthirdswitchingdevice20 sothatallswitchingdevicesaredeactivatedandanoff-stateisattained.However,duringactivation ofthefirstswitchingdevice,whenthedrivercircuitswitchesfromtheoff-statetotheon-state,the switchingdeviceclosesttotheoutputterminal,i.e.thethirdswitchingdevice,riskstoexperiencea voltagethatexceedsitsmaximumtoleratedvoltagevalueduetothefactthattheoutputterminal dischargesmuchmoreslowlythanthefirstnodeduetoitshigherloadcapacitance.SuchaSOA25 overshootispreventedbythebypasscircuit.Indeed,thisbypasscircuitiscoupledbetweentheoutput terminalandthesecondnodeinparallelwiththethirdswitchingdevice,andthusprovidesaparallel currentpathforthedischargecurrentfromtheoutputterminaltoflowtothesecondnode.Compared toconventionaldrivercircuitswiththreeswitchingdeviceswhichlacksuchabypasscircuit,this thushastheadvantagethatsaiddischargecurrentisnolongerforcedsolelythroughthethird30 switchingdevice,butmayalso,orevenprimarily,runthroughthebypasscircuit.Thisprovidesfor amoreevendistributionofsaiddischargecurrent,andthusofthecorrespondingvoltagedrop, betweenthesecondandthirdswitchingdevice.Herein,thebypasscircuitistunedsuchthatthe voltagedropoverthethirdswitchingdeviceontheonehandisnotsohighthatthethirdswitching deviceexceedsitsmaximumtoleratedvoltagevalue(thesecondmaximumvoltage)andthusitsSOA35 boundaries,butontheotherhandisalsosufficientlyhighforthevoltagedropoverthesecond 2025 / 5024 BE2025 / 5024 5 switchingdevicenottoexceedthefirstmaximumvoltage.Asaresult,noneoftheswitchingdevices exceedsitsSOAboundariesduringthetransitionfromoff-statetoon-state,andthussafeoperation isguaranteed,evenwhenthevoltagebetweentheoutputterminalandtherailterminalduringthe off-statepriortosaidtransitionexceededtheindividualmaximumtoleratedvoltagevalues.Inother words,thebypasscircuithastheeffectofenablingtoincreasetherobustnessonthedrivercircuit5 withouttherebyriskingdamageordegradationoftheconstituentcircuitdevicesand / or malfunctioningofthedrivercircuit. Assuch,thedescribeddrivercircuitsaccommodatesfortheneed,asreferredtoabove,fordriver circuitsconfiguredtoswitchvoltagelevelswhichexceedthemaximumtoleratedvoltagevaluesof theindividualconstituentdeviceswithoutovershootingitsSafeOperationArea.Manypotential10 applicationsarise.Forexample,suchadrivercircuitallowstoreconcileoutdatedprotocolsinvolving highvoltagerangeswithnewertechnologiesthatindividuallydonotsupportsuchvoltageranges. Furthermore,physicalconstraintssuchasminimumvoltagesrequiredforlight-emittingdiodesmight necessitateexceedingatechnology'smaximumtoleratedvoltage.Evenincaseswherealternative deviceswithsufficientvoltagetoleranceitexist,itmaybebeneficialtosticktodeviceswithlower15 voltagetolerance,duetoapplicationrequirementsorfunctionaladvantagesofthelowervoltage tolerantdevices.Forinstance,despitetheirlowervoltagetolerance,coretransistorsmaybe preferableoverthickgatetransistors,sincetheyperformbetterconcerningspeedandradiation hardness.Similarly,employinglower-voltageratedtransistorsmaybeastrategyforavoidingthe additionalmasksandincreasedcostsassociatedwithhighervoltagedevices,likedoublediffusion20 MOS(DMOS)transistors.Thecommondenominatorbetweenthesedifferentpotentialapplications istheadditionalflexibilitygainedbyenablingtheimplementationofdrivercircuitswhereinhigh voltagesareexpectedtoarise,withtransistorsorotherdevicesconfiguredforoperationonlyatlower voltages. Theproposeddrivercircuitsavoidorreducethedisadvantagesassociatedwiththepriorartsolutions25 mentionedabove,namelytheundesirablyslowdischargeandhighsurfaceareaassociatedwith couplingthefirstnodetoanexternalcapacitance,andthedetrimentalimpactonswitchingspeed, outputterminalimpedanceandrequiredsurfaceareaassociatedwithcouplingthethirdswitching devicetoadditionalcircuitryconfiguredfortrackingtheoutputterminalvoltage.Inparticular,the describeddrivercircuitmaybeimplementedwithasmallnumberofconstituentdevices,andthus30 withlowsurfacearea(siliconarea).Moreover,duringtheoff-statethedrivercircuitisreducedtoa simplestackedarchitectureofthefirstandsecondswitchingdevices,liketheoneofthepriorart circuitofFigure1a,andthushasthesamefunctionaladvantagesassuchasimplestack.Indeed, whenallswitchingdevicesareswitchedoff,thebypasscircuitprovidesanimpedanceparalleltothe thirdswitchingdevice,whichislowerthantheimpedanceofanopenswitch,sothatthesecondnode35 2025 / 5024 BE2025 / 5024 6 isnormallychargeduptothesamevoltagevalueastheoutputterminal,whilenocurrentcanrun throughtheopenthirdswitchingdevice. Inapreferredembodiment,thedrivercircuitfurthercomprisesaprotectionterminal,whereinthe secondswitchingdevicehasacontrolportwhichiscoupledtotheprotectionterminalandthethird5 switchingdevicehasacontrolportwhichiscoupledtotheprotectionterminal. WhensuchaprotectionterminaliscoupledtoafixedDCvoltagesource,saidprotectionterminal mayservetomaintainboththecontrolportofthesecondswitchingdeviceandthecontrolportof thethirdswitchingdeviceatafixedDCvoltage.Thishastheadvantagethatnoadditionalbiasing10 circuitryisneededtokeepthecontrolportvoltageofthethirdswitchingdeviceconstant,inthesense thatoneandthesameterminalmaybeusedtocontrolboththecontrolportofthesecondswitching deviceandthecontrolportofthethirdswitchingdevice. Inapreferredembodiment,thebypasscircuitisconfiguredtoconductacurrentwhenthevoltage15 oversaidbypasscircuitexceedsathresholdvoltage. Indeed,atthebeginningofthetransitionfromoff-statetoon-state,whenthefirstandsecond switchingdeviceshavejustswitchedon,suchabypasscircuitoffersapathwayforthehighdischarge currentscorrespondingwiththedischargeoftheloadcapacitanceoftheoutputterminal,toflow20 towardsthesecondnode.Herein,saidthresholdvoltageispreferablytunedtoavaluebelowthe initialoutputterminalvoltage,i.e.belowthevalueofthevoltagebetweentheoutputterminaland therailterminalduringoff-state.Thisensuresthatduringthedropofthevoltageontheoutput terminaloversaidthresholdvoltage,saiddischargecurrentmayrunfromtheoutputterminaltothe secondnodethroughthebypasscircuit,orthroughboththebypasscircuitandthethirdswitching25 device.Theextenttowhichthisdischargecurrentisdividedoverthebypasscircuitandthethird switchingdevicethendependsontheirrelativeconductivities. Inembodimentswhereinthebypasscircuithasathresholdvoltage,thebypasscircuitispreferably configuredtohaveafirstconductivitywhichishigherthantheconductivityofthethirdswitching30 device,whenthevoltageoverthebypasscircuitishigherthanthethresholdvoltage,andtohavea secondconductivitywhichislowerthanthefirstconductivity,whenthevoltageoverthebypass circuitislowerthanthethresholdvoltage. Forexample,thebypasscircuitmaybeconfiguredhavealowimpedanceandalowresistancewhen thevoltageoverthebypasscircuitishigherthanthethresholdvoltage,andtohaveahighimpedance35 andahighresistancewhenthevoltageoverthebypasscircuitislowerthanthethresholdvoltage. 2025 / 5024 BE2025 / 5024 7 Forexample,thebypasscircuitmaybeavoltagetriggeredortransienttriggeredelectrostatic discharge(ESD)clamp,suchasasiliconcontrolledrectifier(SCR)ESDclamp. Assuch,thedischargeofthesecondnodemaybesubdividedintoarapidfirstphaseandaslow secondphase.Indeed,atthebeginningofthetransitionfromoff-statetoon-state,whenthefirstand5 secondswitchingdeviceshavejustswitchedon,ahighdischargecurrentisforcedtopassthrough boththebypasscircuitandthethirdswitchingdevice,resultinginadropofthevoltageontheoutput terminalfromahighinitialvaluethatexceedsthethresholdvoltage,ultimatelytowardsthevoltage oftherailterminalwhichiskeptat0V.Duringthefirstphasewhereintheoutputterminalvoltage decreasesfromsaidinitialvaluetowardsthedifferencebetweensaidinitialvalueandthethreshold10 voltage,thebypasscircuitinsuchanembodimentwillhaveafirstconductivity,i.e.ahigher conductivitythanthethirdswitchingdevice,orequivalentlyaloweradmittancethanthethird switchingdevice.Consequently,saiddischargecurrentisrapidlyconductedthroughthebypass circuit,whileonlyasmallfractionofsaidcurrentpassesthroughthethirdswitchingdevice.Once theoutputterminalvoltageislowenoughforthebypasscircuitvoltagetoreachthevalueofits15 thresholdvoltage,asecondphaseisinitiatedwhereinthebypasscircuithasasecondconductivity whichislowerthanthefirstconductivity,forexampleasecondconductivitywhichislowerthanthe conductivityofthethirdswitchingdevice.Thismeansthattheremainingdischargecurrentwill conducttoasmallerextentthroughthebypasscircuit,andwillforexamplemainlyconductthrough thethirdswitchingdevice,withonlyasmallfractionofsaidcurrentpassingthroughthebypass20 circuit,sothatsaidsecondconductingphasewillbeslowerthantherapidfirstphase.Eventually, theoutputterminalvoltagewillstagnateat0Vwhenitsloadcapacitancehascompletelydischarged. Inanadvantageousembodiment,eachofthefirstswitchingdevice,thesecondswitchingdeviceand thethirdswitchingdevicecomprisesatransistor,preferablyaMOStransistor,andeachcontrolport25 isformedbythegateorbaseofthetransistor. Indeed,transistorsmayserveasswitchingdevicesinadrivercircuit,inthattheymaybetriggered toswitchon,andthusattainanactivatedstate,whenasufficientvoltagesurgeisdeliveredtotheir gateorbase,andtoswitchoff,andthusattainadeactivatedstate,whenthereceivedgateorbase30 voltageceasestosuffice.Notethatifaprotectionterminalasdescribedispresentinsuchan embodiment,whichprotectionterminaliscoupledtoafixedDCvoltagesource,thisallowsto maintainthegateorbasevoltagesofboththesecondandthirdswitchingdeviceatafixedDC voltage. 35 2025 / 5024 BE2025 / 5024 8 Inanexemplaryembodiment,eachofthefirstswitchingdevice,thesecondswitchingdeviceand thethirdswitchingdeviceisaMOStransistor,andtheoutputterminaliscoupledtothedrainofthe thirdswitchingdevice,thesecondnodeiscoupledbetweenthesourceofthethirdswitchingdevice andthedrainofthesecondswitchingdevice,thefirstnodeiscoupledbetweenthesourceofthe secondswitchingdeviceandthedrainofthefirstswitchingdevice,thesourceofthefirstswitching5 deviceiscoupledtotherailterminal,andthebypasscircuitiscoupledbetweenthedrainofthethird switchingdeviceandthesecondnode. Suchamutualcouplingofthedifferentdevicesallowsforasimpleimplementationwithfew constituentsandlowsurfacearea.Inparticular,thethreeswitchingdevicesmaysimplybeconnected10 inseries,resultinginastackeddriverarchitecturewhereinduringthetransitionfromoff-statetoon- state,thevoltageisdividedoverthethreetransistorsthatserveasswitchingdevices.Still,as explainedaboveinreferencetothepriorartcircuitofFigure1a,aconventionalstackeddrive architecturewhichlacksthedescribedbypasscircuitfailstomaintaineachtransistorinitsSOA conditionswhentheinitialvoltagebetweentheoutputterminalandtherailterminal,priortosaid15 transition,exceedsthemaximumtoleratedvoltagesoftheindividualtransistors.However,instacked driverarchitecturesprovidedwithasuitablytunedbypasscircuit,theSOAboundariesofthesecond andthirdswitchingdevicesarenotexceededduringsaidtransition,evenwhentheinitialvoltage dropbetweentheoutputterminalandthefirstnodeexceededthefirstandsecondmaximumvoltage, sincesaidvoltagedropisthensuitablydistributedoverthesecondandthirdswitchingdevice.20 Preferably,thebypasscircuitcomprisesatleastonediode. Indeed,adiodeisaprimeexampleofadevicewithathresholdvoltage,inthesensethatits exponentialcurrent-voltagecharacteristichastheeffectthatforvoltagesexceedingitsthreshold25 voltage,thediode’sresistanceisnegligible,whereasforvoltagesbelowsaidthresholdvoltage,the diode’sresistanceisvirtuallyinfinite.Asaresult,diodesconductveryfastabovetheirthreshold voltage,andalmostdonotconductbelowtheirthresholdvoltage.Whenthebypasscircuitthus comprisesatleastonediode,thetransitionfromoff-statetoon-stateproceedsasfollows. Thetransitionfromoff-statetoon-stateisinitiatedwhentheinputterminalswitchesonthefirst30 switchingdevice,causingthevoltageonthefirstnodetodrop.Consequently,thesecondswitching deviceisalsoswitchedon,therebygivingrisetoavoltagedroponthesecondnodeandcausingthe diodetostartconducting.Duringthisfirstphaseofthetransition,thefirstandsecondswitching devicearethusclosedwhilethethirdswitchingdeviceremainsopen,andthedischargecurrent associatedwiththedischargeoftheloadcapacitanceoftheoutputterminalrunssolelythroughthe35 bypasscircuit,whereinthediodeconductssaidcurrentveryrapidly,anddoesnotrunatallthrough 2025 / 5024 BE2025 / 5024 9 thethirdswitchingdevice.Assuch,theoutputterminalvoltagedecreasesrapidlyfromitsinitial valuetoavaluelowenoughforthediodecircuitvoltagetoreachitsthresholdvoltage.Oncesaid voltagereachesthediodethresholdvoltage,thediodesubstantiallyceasestoconduct,therebygiving risetoasecondphasewhereintheremainingdischargecurrentissubstantiallyforcedthroughthe thirdswitchingdevice,whichisthustriggeredtoswitchon.Inthissecondphase,thecircuitno5 longerbenefitsfromthehighdiodeconductivityabovethresholdvoltage,sothatthedischarge proceedsmuchmoreslowlyduringsaidsecondphase. Itshouldbenotedthatthebypasscircuitmayalsoconsistofastringorstackofdiodes,inwhich casetheroleofthethresholdvoltageofthebypasscircuitisplayedbythesumofthethreshold voltagesofthedifferentdiodes.10 Inafirstpreferredembodimentwhereinthebypasscircuitcomprisesatleastonediode,thethird switchingdeviceisanNMOStransistor,andadiodeoftheatleastonediodehasananodewhichis coupledtotheoutputterminal,andhasacathodewhichiscoupledtothesecondnode. Inanalternative,secondpreferredembodimentwhereinthebypasscircuitcomprisesatleastone15 diode,thethirdswitchingdeviceisaPMOStransistor,andadiodeoftheatleastonediodehasan anodewhichiscoupledtothesecondnode,andhasacathodewhichiscoupledtotheoutputterminal. Whenadiodeiscoupledtothesecondnodeandtotheoutputterminalinthisway,itisforward biasedduringthetransitionfromoff-statetoon-stateandthusallowstoconductacurrentfromthe20 outputterminaltothesecondnode(whenthebypassedthirdswitchingdeviceisanNMOStransistor) respectivelyfromthesecondnodetotheoutputterminal(whenthebypassedthirdswitchingdevice isaPMOStransistorandthecurrentdirectionisthusreversed),therebycontributingtothedischarge oftheloadcapacitanceoftheoutputterminal. 25 Inanexemplaryembodimentwhereinthebypasscircuitcomprisesatleastonediode,thedriver circuitcomprisesanelectrostaticdischarge(ESD)clampcoupledbetweentheoutputterminaland therailterminal,andadiodeoftheatleastonediodefunctionsalsoasadiode,forexampleaholding diode,oftheelectrostaticdischargeclamp. 30 SuchembodimentsarebeneficialforapplicationswhereinanESDclampbetweentheoutput terminalandtherailterminalisrequired,irrespectiveofthepurposeofincreasingtheSafeOperation Area.Indeed,forsuchapplications,thepresentedembodimenthastheadvantagethatnoadditional diodeisneededfortheimplementationofthebypasscircuit:onemaysimplyre-useadiodeofthe ESDclamp,forexampletheholdingdiodeoftheESDclamp,as(partof)thebypasscircuit.This35 2025 / 5024 BE2025 / 5024 10 hastheadvantagethatnoadditionalsurfacearea(siliconarea)isconsumedfortheimplementation ofthebypasscircuit. Inanexemplaryembodiment,thebypasscircuitcomprisesaresistiveelement.Forexample,the bypasscircuitmayconsistofaresistiveelement,ormaycomprisebotharesistiveelementanda5 diode.Indeed,aresistiveelementmayhelptoachievethesamepurposeasadiodewhencoupled betweentheoutputterminalandthesecondnodeinparallelwiththethirdswitchingdevice,inthat itwillcreateaparallelpathwayforthedischargecurrentfromtheoutputterminaltothesecondnode, whichistherebynotentirelyforcedthroughtheotherwisevulnerablethirdswitchingdevice.When suitablytuned,sucharesistiveelementmaythushavetheeffectofsuitablydividingthevoltagedrop10 overthesecondandthirdswitchingdeviceswithoutsurpassingtheirrespectiveSOAboundaries. Forexample,thebypasscircuitmaycompriseorconsistofaMOStransistorconfiguredtohavea lowconductivitywhenthevoltageoversaidMOStransistorislowerthanacertainthresholdvoltage, andtohaveahighconductivitywhenthevoltageoversaidMOStransistorishigherthansaid thresholdvoltage.15 Otherexamplesofbypasscircuitssolelyconsistingofresistiveelementsandnotcomprisingdiodes, maynothaveathresholdvoltage,andconsequentlymaynotgiverisetodischargepatternswitha firstrapidphaseandasecondslowphaseliketheonedescribedaboveforbypasscircuitswitha diode,butratherexhibitamoregradualevolutionofthevoltageonthesecondnodewithtime. Inanadvantageousembodimentwithaprotectionterminal,thedrivercircuitfurthercomprisesa20 voltagelimitingcircuitwhichiscoupledbetweenthefirstnodeandtheprotectionterminal,and whichisconfiguredtolimitthevoltagebetweentheprotectionterminalandthefirstnode,wherein thevoltagelimitingcircuitpreferablycomprisesadiodeoraMOStransistor. Indeed,suchavoltagelimitingcircuitguaranteesagoodcontrolofthefirstnodeduringtheoff-state25 andduringthetransitionformon-statetooff-state,byallowingexcessivecurrentwhichriskstobuild uponthefirstnodewhenthefirstandsecondswitchingdevicesswitchoff,todischargethrough saidvoltagelimitingcircuittowardstheprotectionterminal.Therebythevoltagebetweenthefirst nodeandtheprotectionterminalissuitablycontrolled,andmoreoverthevoltageoverthefirst switchingdeviceislimited,inparticularsothatitdoesnotexceedthemaximumtoleratedvoltage30 ofsaidfirstswitchingdevice.Herein,itmaybepreferabletoimplementsaidvoltagelimitingcircuit withaforwardbiaseddiode,sincesuchadiodehasexcellentconductivityandthusallowsforarapid discharge,aslongasthevoltageitexperiences,exceedsitsthresholdvoltages. Nosuchadditionalvoltagelimitingcircuitryisneededforbiasingthesecondnode,sinceawell- controlledbiasingofthesecondnodeisalreadyensuredbythebypasscircuit.35 2025 / 5024 BE2025 / 5024 11 Inafirstexemplaryembodimentwithavoltagelimitingcircuit,thesecondswitchingdeviceisan NMOStransistorandthevoltagelimitingcircuitcomprisesadiode,withananodewhichiscoupled tothefirstnode,andwithacathodewhichiscoupledtotheprotectionterminal. Inanalternative,secondexemplaryembodimentwithavoltagelimitingcircuit,thesecondswitching deviceisaPMOStransistorandthevoltagelimitingcircuitcomprisesadiode,withananodewhich5 iscoupledtotheprotectionterminal,andwithacathodewhichiscoupledtothefirstnode. Indeed,whenadiodeiscoupledtothefirstnodeandtotheprotectionterminalinthisway,itis forwardbiasedduringthetransitionfromon-statetooff-stateandthusallowstoconductacurrent fromthefirstnodetotheprotectionterminal(whenthesecondswitchingdeviceisanNMOS transistor)respectivelyfromtheprotectionterminaltothefirstnode(whenthesecondswitching10 deviceisaPMOStransistorandthecurrentdirectionisthusreversed),therebycontributingtothe dischargeofthefirstnodeandthuslimitingthevoltagebetweenthefirstnodeandtheprotection terminal. Inathirdexemplaryembodimentwithavoltagelimitingcircuit,thesecondswitchingdeviceisan15 NMOStransistorandthevoltagelimitingcircuitcomprisesaPMOStransistorwhichhasasource, adrain,agateandabulk,whereinthesourceand / orthebulkofsaidPMOStransistoriscoupledto theprotectionterminal,thedrainofsaidPMOStransistoriscoupledtothefirstnodeandthegateof saidPMOStransistoriscoupledtoacontrolcircuit. Inanalternative,fourthexemplaryembodimentwithavoltagelimitingcircuit,thesecondswitching20 deviceisaPMOStransistorandthevoltagelimitingcircuitcomprisesanNMOStransistorwhich hasasource,adrain,agateandabulk,whereinthesourceand / orthebulkofsaidNMOStransistor iscoupledtotheprotectionterminal,thedrainofsaidNMOStransistoriscoupledtothefirstnode andthegateofsaidNMOStransistoriscoupledtoacontrolcircuit. Insaidthirdandfourthexemplaryembodiment,thePMOSorNMOStransistorinthevoltage25 limitingcircuitmayforexamplehaveitsgatecoupledtotheinputterminal,and / ormayhaveits sourceand / orbulkcoupledtothegateofthesecondswitchingdevice. Inanadvantageousembodiment,thebypasscircuitisconfiguredandconnectedtocreatean additionalcurrentpathbetweentheoutputterminalandtherailterminal,and / ortocreatean30 additionalcurrentpathbetweentheoutputterminalandthefirstnode. Suchanadditionalcurrentpathbetweentheoutputterminalandtherailterminalhastheadvantage thatthedischargecurrentassociatedwiththedischargeoftheloadcapacitanceoftheoutputterminal isnolongerforcedtopassinitsentiretythroughtheswitchingdevices.Rather,acertainfractionof35 saiddischargecurrentmaybeconductedbysaidadditionalcurrentpath,whereastheremaining 2025 / 5024 BE2025 / 5024 12 fractionpassesthroughtheswitchingdevices.Asaresult,thedischargingprocessoftheload capacitanceoftheoutputterminalisbeingspedup,leadingtolowerimbalancesbetweenthefirst andthesecondswitchingdevice. Asimilareffectmaybeattributedtoanadditionalcurrentpathbetweentheoutputterminalandthe firstnode,inthatitallowsforacertainfractionofsaiddischargecurrenttopassthroughthefirst5 switchingdevicebutnotthroughthesecondandthirdswitchingdevice,therebydistributingtheload capacitance,tobedischargedduringthetransitionfromoff-statetoon-state,moreevenlybetween theswitchingdevices.Comparedtoembodimentswithanadditionalcurrentpathtowardstherail terminal,embodimentswithanadditionalcurrentpathtowardsthefirstnodehavetheeffectof slowingdownthedischargeprocess.Indeed,contrarytotheformerembodiments,thelatter10 embodimentsforcethefractionofsaiddischargecurrentthatdoesnotpassthroughthesecondand thirdswitchingdevice,tostillpassthroughthefirstswitchingdeviceinsteadofpassingdirectlyto therailterminal.Assuch,thedischargeprocessisstillbeingspedupcomparedtoembodimentswith noadditionalcurrentpaths,yetisslowerthanthedischargeprocessforembodimentswithan additionalcurrentpathtowardstherailterminal.Onemayalsocombinebothtypesofadditional15 currentpaths. Inanexemplaryembodimentwithanadditionalcurrentpathbetweentheoutputterminalandthe railterminaland / orwithanadditionalcurrentpathbetweentheoutputterminalandthefirstnode, thebypasscircuitcomprisesabipolartransistorhavingacollectorcoupledtotherailterminalorto20 thefirstnode,anemittercoupledtotheoutputterminalandabasecoupledtothesecondnode. Indeed,suchaconfigurationallowsafractionofthedischargecurrentassociatedwiththedischarge oftheloadcapacitanceoftheoutputterminal,torunfromtheoutputterminalviathebaseofthe bipolartransistortothecollectorofthebipolartransistorandinthiswaytoeithertherailterminal orthefirstnode,dependingonwhichofthesesaidcollectoriscoupledto.Inanexemplary25 embodiment,thebypasscircuitmaycompriseastringorstackofseveralbipolartransistors,wherein forexampleafirstbipolartransistormayhaveacollectorcoupledtotherailterminal,whereasa secondbipolartransistormayhaveacollectorcoupledtothefirstnode.Thereby,bothanadditional currentpathfromtheoutputterminaltotherailterminal,andanadditionalcurrentpathfromthe outputterminaltothefirstnode,arebeingcreated.30 Inanexemplaryembodiment,thedrivercircuitfurthercomprisesoneormoreswitchingdevices coupledbetweenthefirstnodeandthesecondswitchingdevice. Infact,thefirstswitchingdevicemaybereplacedbyanystackorseriesconnectionofswitching devices,whereinsaidstackmayhavearbitrarylength,withoutsignificantlycompromisingthe35 bypasscircuit’seffectofexpandingthedrivercircuit’sSafeOperationArea(SOA). 2025 / 5024 BE2025 / 5024 13 Inanexemplaryembodiment,thedrivercircuitfurthercomprisesoneormoreswitchingdevices coupledbetweenthethirdswitchingdeviceandtheoutputterminal. Insuchembodiments,thedrivercircuitcomprisesastackorseriesconnectionofswitchingdevices, whereinthebypasscircuitisthuscoupledinparallelwithaswitchingdevicewhichisnotnecessarily5 directlyconnectedtotheoutputterminal,andwhichdoesnotnecessarilylieclosesttotheoutput terminalcomparedtotheotherswitchingdevicesinthestack.Embodimentswhereintheswitching devicebypassedbythebypasscircuitistheswitchingdeviceclosesttotheoutputterminalare generallypreferred,forthereasonthatitissaidswitchingdeviceclosesttotheoutputterminalwhich isthemostvulnerableagainstSOAovershoot.Nevertheless,incertainsituationsitmaybedesirable10 tocouplethebypasscircuitinparallelwithadifferentswitchingdevicewhichisnotclosesttothe outputterminal,forexampleinthesituationwhensaidswitchingdeviceiscoupledtoahighly capacitivenode,forexampletoanodewhichiscoupledtoahighexternalcapacitance. 15 BRIEFDESCRIPTIONOFTHEFIGURES Theaccompanyingdrawingsareusedtoillustratepresentlypreferrednon-limitingexemplary embodimentsofdevicesofthepresentinvention.Theaboveandotheradvantagesofthefeatures andobjectsoftheinventionwillbecomemoreapparent,andtheinventionwillbebetterunderstood20 fromthefollowingdetaileddescriptionwhenreadinconjunctionwiththeaccompanyingdrawings, inwhich: Figure1aisacircuitschematicofaconventionaldrivercircuitwithastackeddriverarchitecture; Figure1bisagraphoftheevolutionwithtimeofthevoltageontheoutputterminalandthevoltage onaparticularnode,inthedrivercircuitofFigure1a;25 Figure2aisacircuitschematicofadrivercircuitaccordingtoafirstembodiment; Figure2bisagraphoftheevolutionwithtimeofthevoltageontheoutputterminal,thevoltageon afirstnodeandthevoltageonasecondnode,inthedrivercircuitofFigure2a; Figure3isacircuitschematicofadrivercircuitaccordingtoasecondembodiment; Figure4aisacircuitschematicofthedrivercircuitofFigure3,whereineachswitchingdeviceisan30 NMOStransistor; Figure4bisacircuitschematicofadrivercircuitaccordingtoathirdembodiment,whereineach switchingdeviceisaPMOStransistor; Figure5aisacircuitschematicofadrivercircuitaccordingtoafourthembodiment; Figure5bisacircuitschematicofadrivercircuitaccordingtoafifthembodiment;35 2025 / 5024 BE2025 / 5024 14 Figure6aisacircuitschematicofthedrivercircuitofFigure5a,whereinthebypasscircuitisa diode; Figure6bisacircuitschematicofthedrivercircuitofFigure5b,whereinthebypasscircuitisa diode; Figure6cisacircuitschematicofthedrivercircuitofFigure5a,whereinthebypasscircuitisa5 diode,forexampletheholdingdiode,ofanESDclamp; Figures7a-7earecircuitschematicsofadrivercircuitaccordingtoembodimentswithanadditional currentpath; Figures8aand8barecircuitschematicsofadrivercircuitaccordingtoembodimentswithfour switchingdevicesandonebypasscircuit,respectivelywithfiveswitchingdevicesandtwobypass10 circuits. DETAILEDDESCRIPTIONOFEMBODIMENTS Inthefollowingdescriptions,commonnumericaldesignationsmaybeusedforsimilar,15 correspondingpartsacrossmultiplefigures. Figure2ashowsacircuitschematicofadrivercircuitaccordingtoageneralembodiment,consisting ofarailterminalRAIL,aninputterminalTX,anoutputterminalPAD,afirstswitchingdeviceS1 withacontrolportG1coupledtotheinputterminalTX,asecondswitchingdeviceS2andathird20 switchingdeviceS2bis.Herein,thesecondswitchingdeviceS2mayormaynothaveacontrolport, andisconfiguredtowithstandafirstmaximumvoltageV1,andthethirdswitchingdeviceS2bis mayormaynothaveacontrolport,andisconfiguredtowithstandasecondmaximumvoltageV2. Therailterminalmayforexamplebeagroundterminal,apowerterminal,aVSSterminaloraVDD terminal.25 Thefirst,secondandthirdswitchingdevicesareconnectedinseries,inthatthefirstswitchingdevice S1isconnectedbetweentherailterminalRAILandafirstnodeN1,thesecondswitchingdeviceS2 isconnectedbetweenthefirstnodeN1andasecondnodeN2,andthethirdswitchingdeviceS2bis isconnectedbetweenthesecondnodeN2andtheoutputterminalPAD.Thedrivercircuitfurther comprisesabypasscircuit100whichisconnectedbetweentheoutputterminalPADandthesecond30 nodeN2inparallelwiththethirdswitchingdeviceS2bis,andwhichisconfiguredtolimitboththe voltageoverthesecondswitchingdeviceS2andthevoltageoverthethirdswitchingdeviceS2bis, inparticularsothatthevoltageoverthesecondswitchingdeviceS2doesnotexceedthefirst maximumvoltageV1andthevoltageoverthethirdswitchingdeviceS2bisdoesnotexceedthe secondmaximumvoltageV2,duringactivationofthefirstswitchingdeviceS1.Theswitching35 devicesS1,S2andS2bis,aswellasthebypasscircuit100,arerepresentedasarectangularboxto 2025 / 5024 BE2025 / 5024 15 emphasizethatFigure2arepresentsageneralembodiment,inthatmanydifferentimplementations ofsaidswitchingdevicesS1,S2,S2bisandsaidbypasscircuit100maybechosen.Figures4a,5a and6arepresentafewsuchchoices. ItmaybecleartothereaderthattheembodimentofFigure2amustnotbeconsideredaslimitedto5 thesimpleseriesconnectionspresented,butmayratheralsocompriseothercomponentsanddevices, suchasresistorsordiodes,whichmaybeaddedtothedescribeddrivercircuit,alongtheshown currentpathsoralongadditionalcurrentpathsthatmaybeaddedtothecircuit,withoutsignificantly alteringitsfunctionality. 10 IntheembodimentofFigure2a,thethreeswitchingdevicesS1,S2andS2bisareconnectedinseries, sothattheyareoperatedtogetherinthesensethatwhenthefirstswitchingdeviceS1switcheson andthusstartstoconduct,thisforcesthesecondswitchingdeviceS2,andeventuallyalsothird switchingdeviceS2bis,tosubsequentlyswitchonaswell.Asaresult,adecenton-stateisachieved whereinallswitchingdevicesareclosed,whereaswhenthefirstswitchingdeviceS1switchesoff,a15 currentcannolongerflowfromthesecondorthirdswitchingdevicesothatallswitchingdevices aredeactivatedandanoff-stateisattained.However,duringactivationofthefirstswitchingdevice S1,whenthedrivercircuitswitchesfromtheoff-statetotheon-state,theswitchingdeviceclosest totheoutputterminal,i.e.thethirdswitchingdeviceS2bis,riskstoexperienceavoltagethatexceeds itsmaximumtoleratedvoltagevalueV2duetothefactthattheoutputterminalPADdischarges20 muchmoreslowlythanthefirstnodeN1duetoitshigherloadcapacitance.SuchaSOAovershoot ispreventedbythebypasscircuit100.Indeed,thisbypasscircuit100iscoupledbetweentheoutput terminalPADandthesecondnodeN2inparallelwiththethirdswitchingdeviceS2bis,andthus providesaparallelcurrentpathforthedischargecurrentfromtheoutputterminalPADtoflowto thesecondnodeN2.Comparedtoconventionaldrivercircuitswiththreeswitchingdeviceswhich25 lacksuchabypasscircuit,thisthushastheadvantagethatsaiddischargecurrentisnolongerforced solelythroughthethirdswitchingdeviceS2bis,butmayalso,orevenprimarily,runthroughthe bypasscircuit100.Thisprovidesforamoreevendistributionofsaiddischargecurrent,andthusof thecorrespondingvoltagedrop,betweenthesecondswitchingdeviceS2andthirdswitchingdevice S2bis.Herein,thebypasscircuit100istunedsuchthatthevoltagedropoverthethirdswitching30 deviceS2bisontheonehandisnotsohighthatthethirdswitchingdeviceS2bisexceedsits maximumtoleratedvoltagevalue(thesecondmaximumvoltageV2)andthusitsSOAboundaries, butontheotherhandisalsosufficientlyhighforthevoltagedropoverthesecondswitchingdevice S2nottoexceedthefirstmaximumvoltageV1.Asaresult,noneoftheswitchingdevicesexceeds itsSOAboundariesduringthetransitionfromoff-statetoon-state,andthussafeoperationis35 guaranteed,evenwhenthevoltagebetweentheoutputterminalPADandtherailterminalRAIL 2025 / 5024 BE2025 / 5024 16 duringtheoff-statepriortosaidtransitionexceededtheindividualmaximumtoleratedvoltage values. Indeed,letusassumeforsimplicitythatthemaximumtoleratedvoltagevaluesofthesecond switchingdeviceS2andthethirdswitchingdeviceS2bis,whichwehavecalledthefirstmaximum5 voltageV1andthesecondmaximumvoltageV2respectively,areequal.Letusdenotesaid maximumtoleratedvoltagebyVmax.Assumemoreoverthatduringtheoff-state,thevoltageonthe outputterminalPADyieldsapproximatelytwicethevalueofthefirstmaximumvoltageVmax,and thatthefirstnodeN1iskeptatafixedDCvoltageequaltoorslightlylowerthansaidfirstmaximum voltageVmax.Thelattermayforexamplebeachievedbycouplingacontrolportofthesecond10 switchingdeviceS2toafixedDCvoltagesource,aswillbeexplainedbelowinreferencetoFigure 3. Figure2brepresentstheevolutionwithtimeofthevoltageontheoutputterminalPAD,denotedby Vpad,ofthevoltageonthefirstnodeN1,denotedbyVN1,andofthevoltageonthesecondnodeN2,denotedbyVN2,whenattimet=0allswitchingdevicesareswitchedoff,yetattimet1thefirst15 switchingdeviceS1isbeingactivated.Herein,thevoltageVN1playstheroleofthevoltageVmidin thepriorartreferenceofFigure1b. Asexplainedabove,VN1andVpadremainconstantatrespectivelyVmaxandtwotimesVmaxpriorto theactivation,i.e.upuntilthepointintimet1.Byvirtueofthebypasscircuit100,thesecondnode N2iskeptatthesamevoltageastheoutputterminalPADduringtheoff-state.Indeed,whenall20 switchingdevicesareswitchedoff,thebypasscircuit100providesanimpedanceparalleltothethird switchingdeviceS2bis,whichislowerthantheimpedanceofanopenswitch,sothatthesecond nodeN2ischargeduptothesamevoltagevalueastheoutputterminalPAD,whilenocurrentcan runthroughtheopenthirdswitchingdeviceS2bis.Therefore,upuntilthepointintimet1,thesecond nodeN2alsoremainsataconstantvoltageoftwotimesthevalueVmax.25 Whenatthepointintimet1thefirstswitchingdeviceS1isswitchedonduetothesignalitreceives fromtheinputterminalTX,thevoltageonthefirstnodeN1startstodrop,ascurrentmaynowrun fromthefirstnodeN1viathefirstswitchingdeviceS1towardstherailterminalRAIL.Thistriggers thesecondswitchingdeviceS2toswitchonaswell.LikeinthepriorartcircuitofFigures1a-1b, thevoltageontheoutputterminalPADdecreasesaswellwithtime,yetmuchslowerthanthevoltage30 onthefirstnodeN1sincetheoutputterminalPADcorrespondswithamuchhigherloadcapacitance. ThevoltageonthesecondnodeN2experiencesadecreaseaswell,subdividedinarapidfirstphase andaslowsecondphase.Duringsaidrapidfirstphase,thedischargecurrentfromtheoutputterminal PADtothesecondnodeN2ismainlyforcedtopassthroughthebypasscircuit100,whichforsuch highvoltagevalueshasamuchhigherconductivitythanthethirdswitchingdeviceS2bis.Said35 dischargecurrentisthusrapidlyconductedthroughthebypasscircuit100,causingthevoltageon 2025 / 5024 BE2025 / 5024 17 thesecondnodeN2todropalmostinstantaneouslytoacertaincriticalvaluebelowitsinitialvalue oftwotimesVmax.Saidcriticalvaluecorrespondswithathresholdvoltagevalueforthebypass circuit100,inthesensethatsaidbypasscircuit100almostceasestoconductwhensaidvoltageis reached.Forexample,ifthebypasscircuit100consistsofastackofdiodes,saidvaluecorresponds withthesumoftherespectivediodethresholdvoltages.Sincethedischargecurrentcanthen5 substantiallynolongerpassthroughthebypasscircuit100,thethirdswitchingdeviceS2bisis triggeredtoswitchonandconductsaiddischargecurrent,whilethebypasscircuitconductsvery poorlyorevendoesnotconductatall.Thiscorrespondswithasecond,slowdischargephase, whereinthesecondnodeN2dischargesatthesamepaceastheoutputterminalPAD,whichismuch slowerthanthedischargepaceofthefirstnodeN1.Atacertainpointintimet2,thefirstnodeN110 attainstherailterminalvoltage(0V),whilethesecondnodeN2andtheoutputterminalPADhave notyetreachedsaidvalue.Atthattime,thevoltageoverthesecondswitchingdeviceS2,which correspondstothedifferencebetweenthevoltagesVN2andVN1,attainsitshighestvalue. Nevertheless,saidsecondswitchingdeviceS2doesnotsurpassitsSOAboundaries,sincethebypass circuit100ofFigure2aistunedinsuchawaythatVN2hassufficientlydecreasedduringtherapid15 firstphasethatatthepointintimet2,VN2doesnotexceedthemaximumtoleratedvoltageVmax.On theotherhand,VN2hasnotdecreasedtoomucheitherduringsaidrapidfirstphase,andinparticular hasdecreasedbylessthanthevalueVmax,sothatthedifferencebetweenthevoltagesVpadandVN2, whichyieldsthevoltageoverthethirdswitchingdeviceS2bis,doesnotexceedVmaxeither. Consequently,eachofthedifferentswitchingdevicesremainswithinitsSOAconditionsduringthe20 transitionfromoff-statetoon-state,eventhoughtheinitialvoltagevaluebetweentheoutputterminal PADandtherailterminalRAILwastwiceashighastheindividualmaximumtoleratedvoltages. Saidtuningofthebypasscircuit100correspondstosuitablychoosinghowtoimplementthebypass circuit100,infunctionofthemaximumtoleratedvoltagevaluesofthedifferentswitchingdevices. Forexample,whenthebypasscircuit100consistsofastackofdiodes,thenumberofdiodesinsaid25 stackischoseninsuchawaythatthesumofthediodethresholdvoltagesliesbelowthesecond maximumvoltageV2,yetishighenoughforthevoltageoverthesecondswitchingdeviceS2to remainbelowthefirstmaximumvoltageV1. Otherimplementationsofthebypasscircuit100,forexamplewithresistiveelementsinsteadof diodes,arepossibleaswell.Forexample,thebypasscircuit100maycompriseorconsistofaMOS30 transistorwhichisconfiguredtohavealowconductivitywhenthevoltageoversaidMOStransistor islowerthanacertainthresholdvoltage,andtohaveahighconductivitywhenthevoltageoversaid MOStransistorishigherthansaidthresholdvoltage.Otherembodimentsmaynotexperiencesuch aseeminglyinstantaneousvoltagedropasintherapidphaseinFigure2b,butwillrathershowa muchmoregradualdecreaseofVN2towards0V.35 2025 / 5024 BE2025 / 5024 18 Inthedescribedembodiment,themaximumtoleratedvoltagesofthesecondswitchingdeviceS2 andthirdswitchingdeviceS2bis,i.e.thevaluesV1andV2,wereidentical.Forexample,switching devicescorrespondingwithrecenttransistortechnologiestypicallyhavemaximumtoleratedvoltage valuesofforexample0.9V,or1.8V,or2.5VHowever,inotherembodimentsthesevaluesV1and V2maybesignificantlydistinct.Inparticular,thecircuitdoesnotneedtobeimplementedwiththree5 identicalswitchingdevices,butmaybeimplementedwithforexampleonehigh-voltage-MOS transistorandtwolow-voltage-MOStransistors.Generally,thedescribedbypasscircuit100,when suitablytuned,managestoprotectthecircuitagainstSOAovershoot,whentheoff-statevoltage betweentheoutputterminalPADandtherailterminalRAILdoesnotexceedthesumofthe maximumtoleratedvoltageofthefirstswitchingdeviceS1andthemaximumtoleratedvoltageof10 thesecondswitchingdeviceS2,soforexamplewhensaidoff-statevoltagedoesnotexceed1.8V, incaseallswitchingdevicesS1,S2andS2bisare0.9V-transistors,whensaidoff-statevoltagedoes notexceed3.6V,incaseallswitchingdevicesS1,S2andS2bisare1.8V-transistors,andwhensaid off-statevoltagedoesnotexceed5V,incaseallswitchingdevicesS1,S2andS2bisare2.5V- transistors.15 Figure3showsacircuitschematicofadrivercircuitaccordingtoageneralembodiment.In comparisonwiththeembodimentofFigure2a,aprotectionterminalPROThasbeenadded,the secondswitchingdeviceS2hasbeenequippedwithacontrolportG2,thethirdswitchingdevice S2bishasbeenequippedwithacontrolportG2bis,andbothcontrolportsG2andG2bisare20 connectedtotheprotectionterminalPROT.Herein,theswitchingdevicesS1,S2andS2bis,aswell asthebypasscircuit100,arerepresentedasarectangularboxtoemphasizethatFigure3represents ageneralembodiment,inthatmanydifferentimplementationsofsaidswitchingdevicesS1,S2, S2bisandsaidbypasscircuit100maybechosen. WhensuchaprotectionterminalPROTiscoupledtoafixedDCvoltagesource,saidprotection25 terminalPROTmayservetomaintainboththecontrolportG2ofthesecondswitchingdeviceS2 andthecontrolportG2bisofthethirdswitchingdeviceS2bisatafixedDCvoltage.Thishasthe advantagethatnoadditionalbiasingcircuitryisneededtokeepthecontrolportvoltageofthethird switchingdeviceS2bisconstant,inthesensethatoneandthesameterminalmaybeusedforbiasing boththecontrolportG2ofthesecondswitchingdeviceS2andthecontrolportG2bisofthethird30 switchingdeviceS2bis. Figure4ashowsacircuitschematicofadrivercircuitaccordingtoanadvantageousembodiment.In comparisonwiththegeneralembodimentofFigure3,eachofthefirstswitchingdeviceS1,the secondswitchingdeviceS2andthethirdswitchingdeviceS2bishasbeenimplementedasanNMOS35 transistor,andtheirrespectivecontrolportsG1,G2andG2biscorrespondwiththegatesofsaid 2025 / 5024 BE2025 / 5024 19 transistors.TheembodimentofFigure4acanbeobtaineduponmodifyingthepriorartcircuitof Figure1abyaddinganNMOStransistorS2bisasathirdswitchingdeviceinseriesbetweenthe secondswitchingdeviceS2andtheoutputterminalPAD,couplingthegateofthesaidthirdNMOS transistorS2bistotheprotectionterminalPROT,andaddingabypasscircuit100betweentheoutput terminalPADandthesecondswitchingdeviceinparallelwiththethirdswitchingdeviceS2bis,5 whereinsaidbypasscircuit100isconfiguredtolimitboththevoltageoverthesecondswitching deviceS2andthevoltageoverthethirdswitchingdeviceS2bis,inparticularsothatthevoltageover thesecondswitchingdeviceS2doesnotexceedthefirstmaximumvoltageV1andthevoltageover thethirdswitchingdeviceS2bisdoesnotexceedthesecondmaximumvoltageV2,duringactivation ofthefirstswitchingdeviceS1.Notethatthebypasscircuit100isstillrepresentedasarectangular10 boxtoemphasizethatmanydifferentimplementationsofsaidbypasscircuit100maybechosen. Atransistorformsanaturalchoiceofswitchingdeviceinadrivercircuit,inthattheymaybe triggeredtoswitchon,andthusattainanactivatedstate,whenasufficientvoltagesurgeisdelivered totheirgateorbase,andtoswitchoff,andthusattainadeactivatedstate,whenthereceivedgateor15 basevoltageceasestosuffice.SimilarlyasintheembodimentofFigure3,theprotectionterminal PROTmaybecoupledtoafixedDCvoltagesourcesoastomaintainafixedDCvoltageonthegate G2ofthesecondswitchingdeviceS2aswellasonthegateG2bisofthethirdswitchingdevice S2bis. NotethatthecircuitofFigure4ahasasimpleimplementationwithfewconstituentsandthuslow20 surfacearea. Herein,thefirst,secondandthirdswitchingdevicemaygenerallybeofcomparabledimensions, unlessthefixedDCvoltagedeliveredtotheprotectionterminalPROTissignificantlylow,inwhich casethefirstswitchingdeviceS1mayhaveslightlysmallerdimensionsthanthesecondswitching deviceS2andthethirdswitchingdeviceS2bis.25 Figure4bshowsacircuitschematicofthedrivercircuitthatformstheanalogofthecircuitofFigure 4a,whereineachoftheswitchingdevicesS1,S2andS2bisisnowaPMOStransistorinsteadofan NMOStransistor.TheskilledpersonunderstandsthatcomparedtoFigure4a,theorderofthe differentcomponentshasbeenreversedinordertomaintaintheconventionthatthecurrentruns30 fromthetoptothebottomofthefigure.However,thefunctionalityoftheembodimentofFigure4b isanalogoustothatofFigure4a. Figure5ashowsacircuitschematicofadrivercircuitaccordingtoanadvantageousembodiment. SaidembodimentcorrespondswiththeembodimentofFigure4awhereinavoltagelimitingcircuit35 200hasbeenaddedbetweenthefirstnodeN1andtheprotectionterminalPROT.Moreprecisely,in 2025 / 5024 BE2025 / 5024 20 theembodimentofFigure5asaidvoltagelimitingcircuit200consistsofadiode201,withananode whichiscoupledtothefirstnodeN1,andwithacathodewhichiscoupledtotheprotectionterminal PROT.Figure5bshowsacircuitschematicofthedrivercircuitthatformstheanalogofthecircuit ofFigure5a,whereineachoftheswitchingdevicesS1,S2andS2bisisnowaPMOStransistor insteadofanNMOStransistor.Herein,thevoltagelimitingcircuit200betweenthefirstnodeN15 andtheprotectionterminalPROTconsistsofadiode201,withananodewhichiscoupledtothe protectionterminalPROT,andwithacathodewhichiscoupledtothefirstnodeN1. Suchavoltagelimitingcircuit200guaranteesawell-controlledbiasingofthefirstnodeN1during theoff-stateandduringthetransitionformon-statetooff-state,byallowingexcessivecurrentwhich riskstobuilduponthefirstnodeN1whenthefirstswitchingdeviceS1andthesecondswitching10 deviceS2switchoff,todischargethroughsaidvoltagelimitingcircuit200towardstheprotection terminalPROT.TherebythevoltagebetweenthefirstnodeN1andtheprotectionterminalPROTis suitablycontrolled,andmoreoverthevoltageoverthefirstswitchingdeviceislimited,inparticular sothatitdoesnotexceedthemaximumtoleratedvoltageofsaidfirstswitchingdevice.Herein,said voltagelimitingcircuit200isimplementedwithaforwardbiaseddiode201,sincesuchadiodehas15 excellentconductivityandthusallowsforarapiddischarge,aslongasthevoltageitexperiences, exceedsitsthresholdvoltages. OtherexamplesofavoltagelimitingcircuitincludevoltagelimitingcircuitscomprisingaMOS transistor202.Forexample,whenthesecondswitchingdeviceS2isanNMOStransistor,thevoltage limitingcircuit200maycompriseaPMOStransistor202whichhasasource,adrain,agateanda20 bulk,whereinthesourceand / orthebulkofsaidPMOStransistor202iscoupledtotheprotection terminalPROT,thedrainofsaidPMOStransistor202iscoupledtothefirstnodeN1andthegate ofsaidPMOStransistor202iscoupledtoacontrolcircuit,forexampletotheinputterminalTX. Alternatively,whenthesecondswitchingdeviceS2isaPMOStransistor,thevoltagelimitingcircuit 200maycompriseanNMOStransistor202whichhasasource,adrain,agateandabulk,wherein25 thesourceand / orthebulkofsaidNMOStransistor202iscoupledtotheprotectionterminalPROT, thedrainofsaidNMOStransistor202iscoupledtothefirstnodeN1andthegateofsaidNMOS transistor202iscoupledtoacontrolcircuit,forexampletotheinputterminalTX. NosuchadditionalvoltagelimitingcircuitryisneededforbiasingthesecondnodeN2,sinceawell- controlledbiasingofthesecondnodeN2isalreadyensuredbythebypasscircuit100.30 Figure6ashowsacircuitschematicofadrivercircuitaccordingtoapreferredembodiment,which correspondswiththeembodimentofFigure5awhereinthebypasscircuit100ischosentobeasingle diode101.Figure6bshowsacircuitschematicofthedrivercircuitthatformstheanalogofthe circuitofFigure6a,whereineachoftheswitchingdevicesS1,S2andS2bisisnowaPMOS35 transistorinsteadofanNMOStransistor. 2025 / 5024 BE2025 / 5024 21 Itispreferabletoimplementthebypasscircuit100withadiode101,asadiodeisaprimeexample ofadevicewithathresholdvoltage,inthesensethatitsexponentialcurrent-voltagecharacteristic hastheeffectthatforvoltagesexceedingitsthresholdvoltage,thediode’sresistanceisnegligible, whereasforvoltagesbelowsaidthresholdvoltage,thediode’sresistanceisvirtuallyinfinite.Asa result,diodesconductveryfastabovetheirthresholdvoltage,andalmostdonotconductbelowtheir5 thresholdvoltage.Whenthebypasscircuit100thuscomprisesatleastonediode101,thetransition fromoff-statetoon-stateproceedsasfollows. Thetransitionfromoff-statetoon-stateisinitiatedwhentheinputterminalTXswitchesonthefirst switchingdeviceS1,causingthevoltageonthefirstnodeN1todrop.Consequently,thesecond switchingdeviceS2isalsoswitchedon,therebygivingrisetoavoltagedroponthesecondnodeN210 andcausingthediode101tostartconducting.Duringthisfirstphaseofthetransition,thefirst switchingdeviceS1andsecondswitchingdeviceS2arethusclosedwhilethethirdswitchingdevice S2bisremainsopen,andthedischargecurrentassociatedwiththedischargeoftheloadcapacitance oftheoutputterminalPADrunssolelythroughthebypasscircuit100,whereinthediode101 conductssaidcurrentveryrapidly,anddoesnotrunatallthroughthethirdswitchingdeviceS2bis.15 Assuch,theoutputterminalvoltagedecreasesrapidlyfromitsinitialvaluetoavaluelowenough forthediodevoltagetoreachitsthresholdvoltage.Oncesaidvoltagereachesthediodethreshold voltage,thediode101substantiallyceasestoconduct,therebygivingrisetoasecondphasewherein theremainingdischargecurrentissubstantiallyforcedthroughthethirdswitchingdeviceS2bis, whichisthustriggeredtoswitchon.Inthissecondphase,thecircuitnolongerbenefitsfromthe20 highdiodeconductivityabovethresholdvoltage,sothatthedischargeproceedsmuchmoreslowly duringsaidsecondphase. Itshouldbenotedthatthebypasscircuit100mayalsoconsistofastringorstackofdiodes101,in whichcasetheroleofthethresholdvoltageofthebypasscircuitisplayedbythesumofthethreshold voltagesofthedifferentdiodes101.Typicaldiodethresholdvoltagevaluesrangefrom0.5Vto0.925 V,forexample0.7V.Thementionedtuningofthebypasscircuit100thenamountstochoosingthe numberofdiodes101inthestackinsuchawaythatsaidsumofdiodethresholdvoltagesliesbelow themaximumtoleratedvoltageV2ofthethirdswitchingdeviceS2bis,yetisstillhighenoughfor thevoltagedropoverthesecondswitchingdeviceS2duringtransitionfromoff-statetoon-state,doesnotexceedthemaximumtoleratedvoltageV1ofthesecondswitchingdeviceS2.30 Suchastackofdiodeshastheadvantagethatcomparedtoasinglediode101,itisgenerally configuredtowithstandahighervoltagedrop.Ontheotherhand,thehigherthenumberofdiodes implementedinthebypasscircuit100,thehigheralsotherequired(silicon)surfacearea.Therefore, itispreferabletoimplementthebypasscircuit100withthesmallestnumberofdiodes101suchthat theabove-mentionedcriterionregardingthevoltagesdropsduringthetransition,isfulfilled.35 2025 / 5024 BE2025 / 5024 22 Otherexamplesofbypasscircuits100includebypasscircuitscomprisingresistiveelements,suchas MOStransistorswhichareconfiguredtohavealowconductivitywhenthevoltageoversaidMOS transistorislowerthanacertainthresholdvoltage,andtohaveahighconductivitywhenthevoltage oversaidMOStransistorishigherthansaidthresholdvoltage.Forexample,thebypasscircuit100 maycompriseorconsistofaMOStransistorwhosegateiscoupledwithitssource,suchthatits5 conductivityisessentiallyzerowhenthevoltageoversaidMOStransistorliesbelowathreshold voltage,andisveryhighwhenthevoltageoversaidMOStransistorliesabovesaidthresholdvoltage. Figure6cshowsacircuitschematicofadrivercircuitaccordingtoapreferredembodiment,which correspondswiththeembodimentofFigure6a,modifiedinthatthediode101thatconstitutesthe10 bypasscircuit100isnotastand-alonediode,butratherformspartofanESDclamp120.Indeed,the drivercircuitofFigure6cisequippedwithanESDclamp120coupledbetweentheoutputterminal PADandtherailterminalRAIL,saidESDclamp120consistingofadiode101,forexamplea holdingdiode,andoneormoreclampingdevices110,whereinsaiddiode101iscoupledbetween theoutputterminalPADandthesecondnodeN2inparallelwiththethirdswitchingdeviceS2bis,15 soastoserveasthebypasscircuit100. SuchembodimentsarebeneficialforapplicationswhereinanESDclamp120betweentheoutput terminalPADandtherailterminalRAILisrequired,irrespectiveofthepurposeofincreasingthe SafeOperationArea.Indeed,forsuchapplications,theembodimentofFigure6chastheadvantage thatnoadditionaldiodeisneededfortheimplementationofthebypasscircuit100:onemaysimply20 re-useadiodeoftheESDclamp120,forexampletheholdingdiode101oftheESDclamp120,as (partof)thebypasscircuit100.Thishastheadvantagethatnoadditionalsurfacearea(siliconarea) isconsumedfortheimplementationofthebypasscircuit100. Figures7a-7eshowcircuitschematicsofadvantageousembodimentsofadrivercircuit,wherein25 additionalcurrentpaths300,310havebeenaddedbetweentheoutputterminalPADandrespectively therailterminalRAIL(Figure7a),thefirstnodeN1(Figure7b),andboththerailterminalRAIL andthefirstnodeN1(Figure7c).Moreprecisely,inFigures7a-7b,comparedtotheembodimentof Figure2a,thebypasscircuit100isequippedwithoneadditionalterminal,whichisconnectedto respectivelytherailterminalRAILandthefirstnodeN1,therebyformingrespectivelytheadditional30 currentpath300andtheadditionalcurrentpath310.InthedrivercircuitofFigure7c,twosuch additionalterminalshavebeenadded,oneofwhichiscoupledwiththerailterminalRAILviathe additionalcurrentpath300,whereastheotheroneiscoupledwiththefirstnodeN1viatheadditional currentpath310. 35 2025 / 5024 BE2025 / 5024 23 Suchanadditionalcurrentpath300betweentheoutputterminalPADandtherailterminalRAIL hastheadvantagethatthedischargecurrentassociatedwiththedischargeoftheloadcapacitanceof theoutputterminalPADisnolongerforcedtopassinitsentiretythroughtheswitchingdevicesS1, S2andS2bis.Rather,acertainfractionofsaiddischargecurrentmaybeconductedbysaidadditional currentpath300,whereastheremainingfractionpassesthroughtheswitchingdevicesS1,S2and5 S2bis.Asaresult,thedischargingprocessoftheloadcapacitanceoftheoutputterminalPADis beingspedup,leadingtolowerimbalancesbetweenthefirstswitchingdeviceS1andthesecond switchingdeviceS2. Asimilareffectmaybeattributedtoanadditionalcurrentpath310betweentheoutputterminalPAD andthefirstnodeN1,inthatitallowsforacertainfractionofsaiddischargecurrenttopassthrough10 thefirstswitchingdeviceS1butnotthroughthesecondswitchingdeviceS2andthethirdswitching deviceS2bis,therebydistributingtheloadcapacitance,tobedischargedduringthetransitionfrom off-statetoon-state,moreevenlybetweentheswitchingdevices.Comparedtoembodimentswithan additionalcurrentpath300towardstherailterminalRAIL,embodimentswithanadditionalcurrent path310towardsthefirstnodeN1havetheeffectofslowingdownthedischargeprocess.Indeed,15 contrarytotheformerembodiments,thelatterembodimentsforcethefractionofsaiddischarge currentthatdoesnotpassthroughthesecondswitchingdeviceS2andthirdswitchingdeviceS2bis, tostillpassthroughthefirstswitchingdeviceS1insteadofpassingdirectlytotherailterminalRAIL. Assuch,thedischargeprocessisstillbeingspedupcomparedtoembodimentswithnoadditional currentpaths,yetisslowerthanthedischargeprocessforembodimentswithanadditionalcurrent20 path300towardstherailterminalRAIL.Onemayalsocombinebothtypesofadditionalcurrent paths300and310,asinFigure7c. Figure7dshowsanexemplaryembodimentwithanadditionalcurrentpath300betweentheoutput terminalPADandtherailterminalRAIL,whereinthebypasscircuit100comprisesabipolar25 transistorhavingacollectorcoupledtotherailterminalRAIL,anemittercoupledtotheoutput terminalPADandabasecoupledtothesecondnodeN2.Similarly,Figure7eshowsanexemplary embodimentwithanadditionalcurrentpath310betweentheoutputterminalPADandthefirstnode N1,whereinthebypasscircuit100comprisesabipolartransistorhavingacollectorcoupledtothe firstnodeN1,anemittercoupledtotheoutputterminalPADandabasecoupledtothesecondnode30 N2. Whenthefirst,secondandthirdswitchingdevicesS1,S2andS2bisareallNMOStransistors,said bipolartransistormaybeaPNPtransistor,asisthecaseinFigures7dand7e.Whensaidswitching devicesareallPMOStransistors,likeintheembodimentofFigures4band5b,anadditionalcurrent path300or310maycompriseanNPNbipolartransistor.Indeed,aconfigurationasinFigures7d-35 7eallowsafractionofthedischargecurrentassociatedwiththedischargeoftheloadcapacitanceof 2025 / 5024 BE2025 / 5024 24 theoutputterminalPAD,torunfromtheoutputterminalPADviathebaseofthebipolartransistor tothecollectorofthebipolartransistorandinthiswaytoeithertherailterminalRAIL(Figure7d) orthefirstnodeN1(Figure7e),dependingonwhichofthesesaidcollectoriscoupledto. Inanexemplaryembodiment,thebypasscircuit100maycompriseastringorstackofseveralbipolar transistors,whereinforexampleafirstbipolartransistormayhaveacollectorcoupledtotherail5 terminalRAIL,whereasasecondbipolartransistormayhaveacollectorcoupledtothefirstnode N1.Thereby,bothanadditionalcurrentpath300fromtheoutputterminalPADtotherailterminal RAIL,andanadditionalcurrentpath310fromtheoutputterminalPADtothefirstnodeN1,are beingcreated,therebyforminganimplementationoftheembodimentofFigure7c. 10 Finally,thedrivercircuitmayfurthercompriseoneormoreswitchingdevicescoupledbetweenthe firstnode(N1)andthesecondswitchingdevice,suchasinFigure8a,and / ormayfurthercomprise oneormoreswitchingdevices(S3,S3bis)coupledbetweenthethirdswitchingdevice(S2bis)and theoutputterminal(PAD),suchasinFigure8b. Moreprecisely,Figure8ashowsacircuitschematicofadrivercircuitaccordingtoanembodiment,15 whereinfourswitchingdeviceshavebeenimplemented.ComparedtotheembodimentofFigure2a, theprotectionterminal,secondnode,andsecondandthirdswitchingdevicehavebeenrenamedto PROT3,N3,S3andS3bis,anintermediatenodeN2hasbeenadded,whichiscoupledtothesource ofthesecondswitchingdeviceS3,anintermediateswitchingdeviceS2,intheformofanNMOS transistor,hasbeenaddedbetweenthefirstnodeN1andtheintermediatenodeN2,andthegateof20 theintermediateswitchingdeviceS2iscoupledtoanintermediateprotectionterminalPROT2. Similarly,Figure8bshowsacircuitschematicofadrivercircuitaccordingtoanembodiment,whereinfiveswitchingdeviceshavebeenimplemented.Moreprecisely,comparedtothe embodimentofFigure2a,afirstadditionalswitchingdeviceS3,asecondadditionalswitchingdevice S3bis,anadditionalprotectionterminalPROT3andanadditionalbypasscircuit100’havebeen25 added,whichareconnectedinastackbetweentheoutputterminalPADandthesecondswitching deviceS2bis,inthesamewayasthestackofthesecondandthirdswitchingdevicesS2,S2bis,the protectionterminalPROT2andthebypasscircuit100,iscoupledbetweentheformerstackandthe firstnode. 30 Saidembodimentsshowthattheobjectoftheinventionisalsoimplementableindrivercircuits which,irrespectiveoftheinvention,arealreadyequippedwithastackofmorethantwoswitching devices.Insuchcircuits,abypasscircuit100or100’canservetoreducethenumberofswitching devicesinthestackbyonedevice,andthusalsoreducetheassociatedcomplexityandsizeofthe biasingcircuitry,inthesensethatinsteadofimplementinganadditionalswitchingdeviceinorder35 tosufficientlydividethevoltagedropcorrespondingwiththedischargeoftheoutputterminalPAD, 2025 / 5024 BE2025 / 5024 25 abypasscircuit100or100’isaddedandcoupledinparallelwiththeswitchingdeviceclosesttothe outputterminalPAD. Insuchstackeddrivercircuits,abypasscircuit100maybeimplementedateverydistinguishable “block”oftwoswitchingdevices,inthesamewayasinFigures2a-7e.However,suchabypass circuit100willbemostusefulandhavethebiggestimpactwhenimplementedattheblockclosest5 totheoutputterminalPAD.Indeed,sincetheoutputterminalPADistheterminalwiththelargest loadcapacitancethatneedstobedischarged,itistheswitchingdeviceclosesttosaidoutputterminal PADwhichisatthehighestriskofexceedingitsSOAconditions. Insuchalargestackedcircuit,thefunctionalityofthebypasscircuit100,100’isanalogoustothat ofthebypasscircuit100intheembodimentsofFigures2a-7e,inthatthebypasscircuit(s)guarantee10 thatallconstituentswitchingdevicesremainwithinSOAconditionswhentheoff-statevoltage betweentheoutputterminalPADandtherailterminalRAILisnohigherthanthesumofthe maximumtoleratedvoltagesofthefirstswitchingdeviceS1,theintermediateswitchingdeviceS2 andthesecondswitchingdeviceS3(Figure8a),respectivelythesumofthemaximumtolerated voltagesofthefirstswitchingdeviceS1,thesecondswitchingdeviceS2andthefirstadditional15 switchingdeviceS3(Figure8b). However,itshouldbenotedthatinsuchlargestackedcircuits,itisnolongerpossibletokeepall switchingdevicesatafixedDCgatevoltage.Indeed,whiletheprotectionterminalPROT2farthest fromtheoutputterminalPADmaybestillbecoupledtoafixedDCvoltagesource,therebykeeping theintermediateswitchingdeviceS2(Figure8a)respectivelythesecondandthirdswitchingdevices20 S2andS2bis(Figure8b),whicharecoupledtotheprotectionterminalPROT2,atafixedDCgate voltageV0,thisisnolongerpossiblefortheprotectionterminalPROT3closesttotheoutputterminal PAD,andthusfortheswitchingdevicesS3andS3biswhicharecoupledtoPROT3.Instead,the latterprotectionterminalPROT3maybecoupledtoavoltagesourcewhichswitchesbetweentwo DCvoltagesVAandVBdependingonthevalueofthevoltageontheoutputterminalPAD.For25 example,saidvoltagesourcemaydeliverafirstDCvoltageVAwhenthevoltageontheoutput terminalPADishigh,andasecond,higherDCvoltageVBwhenthevoltageontheoutputterminal PADislow.WhenallswitchingdevicesinthestackhavethesamemaximumtoleratedvoltageVmax, e.g.1.8V,thevoltageV0ontheprotectionterminalPROT2farthestfromtheoutputterminalPAD maybeequaloressentiallyequaltoVmax,andthevoltagesVAandVBbetweenwhichtheprotection30 terminalPROT3closesttotheoutputterminalPADisconfiguredtoswitch,maybeequalor essentiallyequaltorespectivelyVmaxandtwotimesVmax,i.e.forexample1.8Vand3.6V. ThesecondandthirdswitchingdevicesS3andS3bis(Figure8a),respectivelythefirstadditional andsecondadditionalswitchingdevicesS3andS3bis,