A precision CMOS bandgap reference - web.mit.edu

1 1014 IEEEJOURNALOFSOLID-STATECIRCUITS, , , , ,threep-tubresistors,andoneop-amparenece ssarytoproduceareferencewithfixedvoltage of than2percent,whilekeepingthermaldriftbel ow40ppm/ ~ Cto125 ,atmodestcostincircuitcomplexity, ,thevoltagereferenceisoftenapotentiallym osttroublesomecomponentsinceitmustproduc eatemperaturestable,processinvariant, , ;however,theabsolutemagnitudeofoutputisp oorlycontrolledbecauseitdependsontheaccu racyofdepletionandenhancementimplants[1] .Inthebandgapreferences,wheretheoutputis derivedfromthevoltagedifferenceoftwodiod esforwardbiasedbyratioedcur-rents,bothth ethermaldriftandtheabsolutevalueoftheout putcanbecontrolledwithprecision[2] [4].ACIVfOSbandgapvoltagereferencewhichu sesbipolar-likesource-to-draintransferch aracteristicsofMOStran-sistorinweakinver sionwasreported[5],[6]. [7] , ,1983;revisedJuly13, ,MurrayHI1l, ,Honeywell, [8]usestemperaturedependentp-tubresistor stoprovidebiascurrentstothereferencediod es,whicharetheemitter-basejunctionsofthe bipolartran-sistorsformedbythen+ ,thebasiccircuitandthecriteriafortempera turecompensa-tionarepresented, , , , (7 )andacrossdiode2isV2(T),thentheoutputcan beexpressedasvout=A(vl(T)-v2(T))+B(v2(T) )=avl(T) bv2(T)(1) [4].

2 Thesearederivedfordevicesbiasedbyeithert emperatureindependentconstantcurrent1,or currentswhichvarywithtemperatureasT , (1) ,andresistorsRl,R2,andR3isthebandgapcirc uitwhichproducesafixedvoltageVOut= , $ :PRSCISIONCMOSBANDGAPREFERENCE1015 DDThevoltagedropattemperatureTisgivenbyT TFig. [9].proposedbyKuijk[8], ,YeandTsividis[9]havedemonstratedthiscon figuration,andaconfigurationpro-ducingap ositiveoutputvoltage, (2)Inladditiontothegainofthecircuit,whic hisde-terminedbytheratioofresistorsR~and R~,themagni-tudeandtheratioofthebiascurr entsisdeterminedbytheratioofresistorsRIa ndR~: (T)=n[vG(T +(?)ln(*) 7)wherenisthenonidealityfactor,VG(T)isth ebandgapvoltageattemperatureT,kistheBolt zmannconstant,qistheelectroncharge,Aisan ormalizingconstantrelatedtothegeometryof thedevice,and~ (T) [10]givestheempiricalexpressionfortheban dgapvalueex-trapolatedfromphysicalmeasur ementovertemperattnx? (T)=VGO+~T($)whereVGO= ,anddVG/dT= 4 (l),subjecttotheconditionthatthetemperat urecoefficientattempera-tureT=TOiszero,d YOutdT~.]

3 ~,=o.(9)ThevalueoftheoutputvoltageVOut(T O)isuniqueandgivenby[()kTOvout(To)=nVGO+ qVOU, Vi(T)II(T)=R1(4)(B-l+T (ZHH=O)) 10)VOut Vi(T)_VOut V(T)12(T)=R R+;.(5)332 Inthisimplementation,however,thebiasingc urrentsII(T)and12(T)aretemperaturedepend entbecauseofthevariationofVI(T)andV2(T), andtoalesserextentbecaluseofthevariation ofVOutwithrespecttotempera-ture,Thecondi tionsforthetemperaturecompensationofthis circuitwithtemperatureindependentRI,Rz,a ndR~are{&enin[8]. ~= ~followingdifferentialequation:TdVOut--v o~t+%lwdT++W+ vgo=o.(11)Itisimportanttonoticethattheva lueofVOut(TO)asgivenin(10),andthebandgap temperatureresponseasgivenin(11)dependso nlyonphysicaldiodeparametersnand~,andres istortemperaturecoefficient(1/R)(dR/dT). resistorsapproximatelydoubletheirresista nceforatern--peraturein;reaiefrom-Oto100 C. emittervoltageV~eofaShockley sequation,forqV>>nkT, (6)substratecollector,p-tubbase,andn+ , , , ,similartotheonegivenin[6],thereferenced evicecanoperateatlargerbiasingcurrent, ,eachunittransistorwith20pmX20pmemitter, ,werecharacterizedtoobtainthevalueofpara me-tersnand~necessarytopredictthevoltage dropacrossthereferencedeviceasgivenin(7) .]}

4 Thevalueofnwasdeterminedbymeasuring1 ,andthenfittingthemeasuredvoltageusing(7 ), , ~parameterdirectly,theprecise1 ,becauseaminorinaccuracy( C)intemperaturemeasurementofthereference s,canleadtolargeerrorsinestimateof~.When thesemeasurementsaremadeondevicesplacedo nawaferprober,anuncertaintyintemperature betweenthethermo-coupleinthewaferchuck,a ndthewaferitselfcanalsocausesignificante rrorsinthevalueof~.Anewindirectmethodofm easurementwasusedindeterminingthevalue~. Aprecisionop-ampwithlowinputoffsetandhig hopen-loopgain,andasetofprecisiondiscret eresistorswhosevalueswereindividuallymea sured, ,andthevaluesofdiscreteresistorsweresele cted ~ ~= (7),and(8),togeneratethe1 V ,andtheresistancevaluesRI,R~,andR~,thepr ogramsolvesiterativelyforbiaspointsVIand V2,andoutputvoltageV&until,VOU,-V1(R1(T) ,T)_VOU, V2(R3(T),T)R~(T)RI(T) R2(T)+R3(T) RI(T) (12)-4284-1:s88- x ~= ~=4, ,4,700I.,,,00~8080100120 TEMPERATURE(UC) :~edresistorbandgapcircuittodeterminethe vatueof, ~ ,andmoreprecisedeterminationof~.

5 , ~mtwintubCMOS technologyis-3 , p-typesiliconsamples[11] , , ,forap-tubresistor,R(T)=ROT22(13)MICEIEJ DAANDKIM:PRECISIONCMOSBANDGAPREFERENCE10 17100-90-80 70 R,60 50-R240-30- R= ~o,,lnT( K) ~ ,[l\(dR} (14)andthepropercompensation,accordingto formula(10),occurswhenI&tatTOis[(3P++(H) out(~O) ~ GO+ C,wheretheresistanceofbiasingresistorsva riesasT22,thevalueof/3= ,andthevalueofTois50 (To)is ,andthetemperaturevariationofP&over100 :1yieldingvoltagedifferenc~(Vl-Vz)-80mVa t25 (1)is10and9, :p-tubdoping,resistormismatch,referenced iodemismatch, ,whichresultsintheop-ampoffseterror, , ,3006-4, 5> +00 TEMF3 SRATURE( C) , ,.(16)Therefore,forafractionalerrorinimp lantdosedN,/iV,,thefractionalerroronthep -tubresistancedR/Ris;dR dN$ - RN, (17)Forthen-p-nbipolardevicebiasedwithfi xedV~G,thecollectorcurrentisproportional tothenumberofimpuri-ties/unitareaintheba se[12](alsoknownasGurnmelnumber).Forthed evicewithionimplantedp-tubbase,thisnumbe risequaltotheiopimplantdoseN.))]]

6 Therefore,I-h~qvh,/kT(18)sandtheVbedropa crossthereferencedeviceisV-~ln(lN~).be(1 9)ThechangeinVb~ofthereferencedeviceduet othep-tubionimplanterroriskTdN,dVbe= qN~ (20)Thedopingofthep-tubinthetwintubCMOS processcanbecontrolledto+ , , ,DECEMBER1984implantdoseshouldresultina+ ,or+ (19)thevariationofthevoltageacrosstheref er-encedevicebiasedbythep-tubresistorres ultingfromthechangesinV~,andthebiascurre ntis[1kTdNdIdV1=dV2=y@+Fs(21)Forbiascurr ent1inthecircuit,V&t VbgI=R (22)thechangeincurrentdIisdVOut dVbedI=~ (%,-%)dRR2(23)for10%resistancevariation, thefirsttermin(23) ~__IRandusing(17),(21),and(24)(12kTdN,dV 1=dV2= 9% (24)(25)Thebandgapoutputvoltagechangeist hendVOutl=adV1-bdV,=(a-b)dV1=dV1.(26)The totalvariationoftheoutputvoltageduetovar iationinthep-tubdopingis(27)The+10percen terrorinthep-tubimplantwillresultin+ ~ , (28)wherethevalueofa= ~ , ~canbematchedaccuratelybecausetheycanber atioedbyanexactintegerfactor,and- ~.A;~ x x x-x-x-~-x-x~ s> :31-x-x-x-x_x x-x-x-x-x-x.)]

7 ,,),~020406060100 TEMPERATURE[ C) !0,2MV----P-TUBIMPLANTERRORMO%-X-RESISTO RRATloMISMATCHttOA ,Sensitivityofoutputvoltagetoprocessingv ariationsalsobecauseRIandR~haveanidentic ~ ~andR~ismorelikelytooccursincetheseresis torsareratioedbyanonin-tegernumber,andbe causeRzisbiasedatadifferentpotentialfrom thesubstratethanRIandR~.Therefore,onlyR~ /l?., )mismatchofR~,andRzis (%++l-d(%,=d(a(v-(29) ,for1percentresistancemismatchingand80mV differencebetweenVIandV2,withR,/Rz=10the outputvoltageerrorisdVOut3H= #(V1 V2)=8mV.(30)2,Theabovediscussionillustra tedthatexcludingtheoffseterroroftheop-am pthevariousprocessingvariationscanaffect theoultputvoltageofthebandgapcircuitbyab out+15 mV,thesheetresistivityofbiasingresistors wasvariedby~10percentandtheratioofresist orswasmismatchedby~ ,whichincludestheoffseterroroftheop-amp, givesthefollowingrelationforJ& bv2+Cvo,(31)whereaandbaregivenin(2)and(3 ),VO,istheoffset,and(ic= 1+5=.aRz (32) ,c=10;thus, ,R~,andR~.))]

8 This, ,resistorsRIandR~areidenticallybiasedwit hrespecttothesubstrate, ,neglectingtheinfluenceofbiascurrent,the voltagecoefficientsofRIandR~shouldbeiden tical(33)Aftertediousalgebra,using(l),(2 ),(3),(4),(5),(7),and(33)onecancomputeth etotalvariationoftheoutputvoltagetobe-[- dVOutR31dR3dV&=1:2#(VI-V,) RzR3d<upsupr1(34) L l. ~J12345678910V~up(VOLTS) (~u~).Thefirstterminbracketsdependsondifferencesbe-tweenvoltagecoefficientsofresistancebetweenRI(orR~)andR~ (ThiscurveisshownforanarbitrarycurrentapproximatingoperatingpointofR~ )OnthiscurvethebiasvoltagesaremarkedforresistorsR~ (-=10-3),thefirsttermin(34) .Thesecondtermin(34) , ~;cribedin[13].Thetesterusesasecondop-ampwithp-tubresistorsR~andR~ , ,includingthesecondop-ampandresistorsR~andR5, , , , ,DECEMBER1984 QIq~ ----SIMULATIONp .,..d~1->2, 1\\\,..\\\\.., ..,.,.-!.:3020Io20406080100 TEMPERATURE( C).,. ,,circuitaftercompensationfortheop-ampof fset.,.. ,,.,.,,,.:,.$.]

9 : ,,.::. ,..,,, ,,0,.., .. :.,,..~ ,o~ 0~-IZ90- 0 > Aa A_A A A5-1,300 >0----------------------------~--------- ---------n:=:==-_--=~r=..*..---*offsetco ntributionwasmeasuredbygroundingemitters of-!310 Q,andQ2throughinternalpadsandmeasuringth eout-q n 0 !wT080901mbetterthan2mVfromOto125 ( C)Morecompletemeasurementsofcircuitsondi fferent~~~~~)LOT#l\ BEFCRECOMPENSATION chipsitesofasinglewafershowthattheoffset com------AFTERCOMPENSATION pensatedoutputvoltagevariationis3mVatroo mtemper-~~~ ~}LOT# ~.zfn)LOT# ,thelargestcontributiontotheoutputerrorl ikelyduetoomissioninanalysisoftheinfluen ceofbiascomesfromtheinputoffsetoftheCMOS summingop-amp. currentont] ~ ,theoutputofthese~ancellingte& ~.025V,whiletheworst-casetemperaturedrif tis7mVfromOto125 ~ ,orbyoffsetcancelingtech-extremecasesofl argeoffseterrors,theoffsetitselfmaybeniq ues[14].temperature-dependent, , ,observedonsmallper-dependentresistorsan dnaturallyoccurringn-p-nhi-polarcentageo fsamples, :PRSCISIONCMOSBANDGAPREFERENCE areshowntobeindependentofthedesignparame terssuchascurrentvaluesandtheirratios,re sistorvalues, ~ ~ ~.

10 025 Vwithtemperaturestabilitybetterthan7mVfr omOto125 ,whichproducespositiveoutputisshownin[9] . , [1][2][3][4][5][6][7][8][9]. , , , , AnewNMOS temperature-stablevoltagereference, , , , , NewdevelopmentsinICvoltageregulators, ~, , , , Asimplethree-terminatICbandgapreference, , , 393? , :Wiley, , AlowvoltageCMOS bandgaprefer-ence, , , , MOStransistorsoperatedinthelateralbipola rmodeandtheirapplicationinCMOS technology, , , , Aprecisioncurvature-compensatedCMOS bandgapreference, , , , , Aprecisionreferencevoltagesource; , , , , BandgapvoltagereferencesourcesinCMOS technology, , , , 25, [10][11][12][13][14] , AccurateanafysisoftemperatureeffectsinIC V~,characteristicswithapplicationstoband gapreferencedevices, , , , , Areviewofsomechargetransportpropertiesof silicon, Solid-StateElectron.,VOL20, , ,PhysicsofSemicortductor~evices, :Wiley, , Low-powerhigh-driveCMOS operationalamplifiers, , , , , Alow-noisechopper-stabilizeddifferential switched-capacitorfilteringtechnique; , , , ,Poland, ,Ston~Brook,in1972, ,NewHaven,CT, ,Allentown,PA, ,BellLabs,MurrayHill,NJ, , , ,Seoul,Korea,in1973and1975,respectively, ,Minneapolis,MN,in1979and1980, ,heworkedasaProcessEngineerattheKoreaIns tituteofScienceandTechnology,Seoul,Korea , ,hewasaLinearCMOSD esigner~articir)atinzin.