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A precision curvature-compensated CMOS …

634 IEEEJOURNALOFSOLID-STATECIRCUITS, , ,DECEMBER1983 APrecisionCurvature-CompensatedCMOSB andgapReferenceBANG-SUPSONG,STUDENTMEMBE R,IEEE, ,FELLOW,IEEEAb.~tract +5 Vpowersupplies, , [1],thebandgapreferencing(BGR) [2] [5].InCMOS technology,theBGRtechniquehasbeendirectl yapplied[6] [8].How-ever,thedevelopmentofahigh-perfo rmanceCMOS band-gapreferencehasbeenhinderedbysevera llimitingfactorsattributabletothepeculia ritiesofthebipolardevicesavail-ableinast andardCMOS process, ,andem-bodiescurvaturecompensationanddif ferentialoffsetManuscriptreceivedApril6, 1983;revisedAugust3, ,IBMC orporation, ,MurrayHill,NJ07974, ,ElectronicsResearchLaboratory,Universit yofCali-fornia,Berkeley, , , (commonlycalledPTAT)whilethequadratictem peraturecorrectionvoltageisproportionalt otheabsolutetemperaturesquared(PTAT2). (CDS)technique[9]. , , ~noisecomponentofaCMOS opampalongwithitsoffset,thedominantnoise sourceisthethermalnoiseofaCMOS opampwhichisdesignedtobeontheorderof100p V(rms) , , , $ :PRECISIONCURVATURE-COMPENSATEDCMOSBANDG APREFERENCE6351R2R3v0sVref0I1,+12V,ef=VB E+(I+%)(AVBE+Vo~)I[~Q, ,inann -wellCMOS process,thep+diffusioninthen--well, (a).]

634 IEEE JOURNAL OF SOLID-STATE CIRCUITS, ... A Precision Curvature-Compensated CMOS Bandgap Reference BANG-SUP SONG ... proportional to the absolute ...

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Transcription of A precision curvature-compensated CMOS …

1 634 IEEEJOURNALOFSOLID-STATECIRCUITS, , ,DECEMBER1983 APrecisionCurvature-CompensatedCMOSB andgapReferenceBANG-SUPSONG,STUDENTMEMBE R,IEEE, ,FELLOW,IEEEAb.~tract +5 Vpowersupplies, , [1],thebandgapreferencing(BGR) [2] [5].InCMOS technology,theBGRtechniquehasbeendirectl yapplied[6] [8].How-ever,thedevelopmentofahigh-perfo rmanceCMOS band-gapreferencehasbeenhinderedbysevera llimitingfactorsattributabletothepeculia ritiesofthebipolardevicesavail-ableinast andardCMOS process, ,andem-bodiescurvaturecompensationanddif ferentialoffsetManuscriptreceivedApril6, 1983;revisedAugust3, ,IBMC orporation, ,MurrayHill,NJ07974, ,ElectronicsResearchLaboratory,Universit yofCali-fornia,Berkeley, , , (commonlycalledPTAT)whilethequadratictem peraturecorrectionvoltageisproportionalt otheabsolutetemperaturesquared(PTAT2). (CDS)technique[9]. , , ~noisecomponentofaCMOS opampalongwithitsoffset,thedominantnoise sourceisthethermalnoiseofaCMOS opampwhichisdesignedtobeontheorderof100p V(rms) , , , $ :PRECISIONCURVATURE-COMPENSATEDCMOSBANDG APREFERENCE6351R2R3v0sVref0I1,+12V,ef=VB E+(I+%)(AVBE+Vo~)I[~Q, ,inann -wellCMOS process,thep+diffusioninthen--well, (a).]

2 Therefore,itisnotpossibletosensethecolle ctorcurrentdirectlyasinthebipolarbandgap referencesoastoreducetheerrorduetothefin itecurrentgain[3],[4].Inap -wellprocess, , , -diffusionresistorinthen -wellandtheCMOS opampisassumedtohaveaninfinitegainwithth eoffsetvoltageofVO,. ,andbothareintheforwardactiveregion,theo utputvoltageofthereferenceisgivenby(1~ef =vBE+1+:(AVBE+V&)1(1)whereVBEistheemitte r-basevoltageoftransistorQ1,AVBE isthedifferencebetweentheemitter-basevol tagesoftransistorsQ1andQ2,andVO, (b).Ifthesearetakenintoaccount,thetransi storemitter basevoltageisgivenby1rb11 VBE=F Jn#+F ~ln~+ A&(2)S1l+FlwhereVTisthethermalvoltagekT/ q,11istheemittercurrentoftransistorQ1,Is listhesaturationcurrentoftransistorQl,& ,thecurrentsensedandcontrolledbyBaseEmit tertP+h+%(a)y-AV,E+?-1rb/AI&II(b) ,(a)Substratep-n-ptransistorprofile.(b) +FlAVBE=V~lnA+V~ln$+V~ln~1 rlbid1+T2(3) ,andiftheemittercurrentsofthetransistors areinfactequal,thenonlythefirsttermsin(2 )and(3) ,becauseoftherelativelypoorperformanceof cmos -compatibledevices, ,mul-tipliedbythegainfactor(1+R~/R1),whi chistypicallyontheorderof10, , , , ,non-PTAT componentsintheoutputdueto636 IEEEJOURNALOFSOLID-STATECIRCUITS, , , ,isindependentoftemperature,theresulting temperaturecoefficienterrorduetoa5mVVO$, forexample,isapproximately(11++Vo,TCerro r=110X5mV~,fTO= C.))

3 (4)Thatis,atemperaturecoefficientontheor derof132 ,ineffectdecreasingthegainfactor(1+R2/R1 )asimpliedby(l). ,however, ,R2,andR3haveazerotemperaturecoefficient , ~~ (2)and(3)aretaken,theV~~isgivenbyVJnAV~~ =V~ln#-=V~ln~S11S1V~lnA=VJnRl(%)Rl(To)~s l V inRI(T)(5)whereTOisthereferencetemperatu re, ~~variationthatresultswhenthereisnoresis tortemperaturecoefficient,andthesecondis thatwhichresultswhenatemperaturecoeffici entispresent,Furtherinsightcanbeobtained byexpandingthissecondtermasaTaylorseries intempera-tureaboutTO,andneglectinghighe rorderterms: BE= BEl,dezd T;$$~(T-To)-VT&$$T-TO) (6). , ,(6)canbeusedtoshowthata1000ppm/0 CresistorTCwouldresultina cerrOr=(l+wwb*+@+2a(7)Forexample,assumin ga2kflbaseresistancewith1000ppm/0 CTC,a30 PAPTAT biascurrentlevel,a/3of150,anda~TCof7000p pm/0C,anoutputTCof , , ,thebipolartransistorshaveinfinitecurren tgain,zerointrinsicbaseresistance,andhav eperfectexponentialjunctionrelationships ,andthebandgapofsiliconvarieslinearlywit htemperature,theoutputvoltageistypically givenby[10]()V,c~=VgO+V~(4 n a)l+ln$(8)0whereVgOistheextrapolatedsili conbandgapatOK,nistheexponentofthemobili tyvariationinthebaseofthebipolartransist or(typicallyabout0,8),aistheexponentofth etemperaturevariationofthebiascurrent(1f orPTAT biascurrent,forexample),andTOisthetemper atureatwhichthereferenceoutputtemperatur ecoefficientiszero, (21)derivedintheAppendixisthemoregeneral formof(8).

4 Thisrelationillustratesthewell-knownfact thatevenforanidealbandgapwithanoptimally chosenTO, , ,aswellaslinearlywithtemperature[11],[12 ].Thishigherordertemperaturevariationadd sacurvatureterm, 55 Cto125 (4 n a)in(8)couldbemadezero, ~~directly[5].Severalauthorshaveproposed simplyaddinginhigherordertem-perature-de pendenttermsintheoutputtocancelthePTAT2t ermoftheoutputvoltagevariation[4]. , ,curvaturecompensation,alreadywidelyappl iedinbipolarreferences, , ~~tocanceloutthelineartemperaturevariati onofV~~.AfterthePTAT correctionvoltageisadded,thereferenceout putV,efwillexhibitmostlythequadratictemp eraturevariationasshowninFig, ;isaddedtothattocanceloutthequadratictem peraturevariationof1 ~~,thefinalreferenceoutputV, ~,FV;~vrefI1 Emi! (notseated).ITempIndep[TllIIDC urrentGeneratorb----lI, , (TI)while1~ ~ ,thereferenceoutputV,~fisgivenbywhere(9) vT1nA+2v& )+M:r+ 10)TheinclusionofthePTAT2voltagemeanstha tthetrimprocedureforthereferenceconsists oftwosteps,onetogivethecorrectoutputvolt agefortheuncompensatedreference, (set1~tozero), , , , ,itismostconvenienttodothiswithacombinat ionofacapacitorarraytoadjusttheCz/C1rati o, , ~ , ~causestheemittercurrentsoftransistorsQ6 andQ, , ,thevoltagedevelopedacrosstheresistorRIi sPTAT andthecurrentZ~ ~ OisnotcriticalbecauseitaffectsonlythePTA T2componentoftheoutputvoltage(notPTAT).]

5 TheTIvoltageVOisdevelopedacrossR3andthec urrent10throughR~ ,thecurrentratio1~/10iseasilytrimmedbyR~ .InthepresenceofthemismatchesofMl M2andJ411 BEl,deil+~vT+~v;+~(14)where~=~++,(vT-vT) T+2yJ5vJ#vm,o0110C2R3V~lnA 4cRv~ +5VV. 3 (15)110 Theconstanturepresentsthestandarddeviati on(%) , ,thetempera-turecoefficientuncertaintyre sultingfromthemismatchvoltagesis50timess mallerthantheuncertaintycausedbytheopamp offsetofexistingdesignsgivenby(4). , ,alltheMOSswitchesareclosedtoSONGANDGRAY :PRECISIONCURVATURE-COMPENSATEDCMOSBANDG APREFERENCE639s, (c) (a)c?Firstoffset-storagemode.(b)Secondof fset-storagemoe.(c) $andS2,thechannelchargesareinjectedintot heopampsummingnodestoloadthecapacitorsCl andCz,Thechargeinjec-tiondifferentialvol tageVflduetothemismatchofswitchesS1andS2 issampledacrossClandC2alongwiththeoffset voltageVO, ,thefirstgainstagechargesthecouplingcapa citortocompensatefortheinputdifferential voltageVI,AftertheswitchesS3andSdareopen ed,twostagesareconnectedinafeedbackampli ficationmode,andtheamplificationofAV~~ta kesplacebythecapacitorratioC2 , :1)moderategainforeachstage(100to300);2) singledominantpoleperstage;3)inherentzer osystematicoffsetvoltage;and4)capacitord rivingcapability(15pFforonestageand100pF fortwostages).

6 TransistorsMlp MITperformsalevelshiftandadifferentialto single-endedconversion, ,thelowerpartcomposedoftransistorsJ4d MjisnotcascodedwhiletheupperpartIv& ,eachopampisstabilizedbyconnectingafrequ encycom-M,911 IkII4iMeM12M9M13UI~111M,eI[IM6M,I iii K5W 2FF+P+ ~.pensationcapacitorbetweenthehighimpeda ncenodeandtheacground~,.Whenthetwoopamps arecascadedandthefeedbackloopclosedaroun dthecompositeamplifier, , ,tocompensateforthedifferencebetweenthec ollectorcurrentandtheemittercurrent, (a).However, (b). , ,whilethelatterismorestraightforwardtopr edictgivendevicegeomet~.Theapproachtaken hereistoincludealumpedresistorR~O~Pmadeo fthesamen -=(+3-+(16)Fortheprocessusedhere, , , ,DECEMBER1983~.iJ(a)(b) (a)lBreturning.(b) +,.INTRINSICRESISTANCE~ ? ~?1 +ExtrinsicCompensationResistance -w,,,~.%iw=%, b=rbl rb,lACOMPENSATIONRESISTANCE(a)(b) (a) (b) (100) , , [referencewhichusesacapacitor-ratioampli ficationhasthecancellationsofoffset,base currentandbaseresistance, ,theType111[ , (a)Outputsyncclock.)]]]

7 (b) ,thefirst-ordercorrectedandsecond-orderc or-rectedV,,f sat250 Cwerefoundtobe61mV, , ,theparametersJ&l,Vg02,and4 n , , , ~ :PREC1S1 ONCURVATURE-COMPENSATEDCMOSBANDGAPREFERE NCE64 ITABLEISTATISTICSOFMEASUREDTEMPERATURECO EFFICIENTSOF7 SAMPLES(ppm C)Standardoto70 ~ 55to125 ,[mV)-5~p:TypeI1II50050I00 TEMPERATURE( C) , *lmVat25 CTCSeeTableIPower12mWwith+5 VsupplyLoad100pFcapacitorCycletime5ps+PS RR50dB(de) PSRR60dB(de)ClockRR75dBOutputnoise400pV( 500kHz)pensation, (PSRR),thebaseofallp-n-ptransis-torsshou ldbebiasedataconstantvoltagerelativetoth enegativesupplyline,Otherwise,thebasewid thmodulation(Earlyeffect)willlimitthePSR R ofthereference,Thecriticalaspectofthedes ignisthesubstratep-n-ptransistorbecauset hen , , , , ,theobservedemitterareareductionduetothe basecrowdingisinsignificantoverthe1to100 PAemitter(a)1I\IIitIIIIIIIUB=rL(b) (a)Aunitcell.(b)Drawndime]sionsofaunitce ll(~m). ~ ,intheemittercurrentrangeover100pA, ,intheemittercurrentrangebelow1PA,thecur rentgain~ + , ,eachn -well(base)wassurroundedbythep+diffusion (collector) , , ,DECEMBER1983 TABLEIIITEMPERATUJWDATAOFDIFFUSEDFWSISTO RSANDp-n-pTRANSISTORS(-55to125 c)StandardDiffusedResistors:MeanDeviatio nMinimumMaumumSheetresistance(Q/square) * ** * , :Currentgain/?

8 AtIE=30pA1758391273 TCoffl*650387254717792*TCunrtisppm/0C.** Rand6 RarecomposedOf40and240squaresof6pm-widep + ,respectively, , (6)andneglectinghigherorders,thefor-ward -biaseddiodevoltageisgivenby[10]V~~=Vg V~[(4 n a)lnT lnEG]+HV~ LV~(17)whereVgisthebandgapofsiliconwhich isafunctionofbasedoping[13]andtemperatur e[11],[12],nandaareparametersillustrated in(8),EandGaretheparameterswhosemagnitud eareinsignificantinthetemperatureanal-ys is[10],andHandLaredefinedfrom(6)H=T1dROR dTTOand(18)(19)Thatis,ifthebiascurrentva riationandthesiliconband-gapcurvaturedis cussedinSectionsIIandIIIareincluded,theV ~~in(17) , ~~in(17)iscompensatedbyaddingthefirst-or dercorrectionvoltageKVTtoV~~,thereferenc eoutputV, +KVT=Vg V~(4 n a)lnT-t(K+H+h13G)vT LV;.(20)Byequatingthederivativeoffi,fatT Otozeroandeliminatingtheunknownconstants ,weobtaindVg- +vT 4-n-a)(l+ln~) f= g s[11].From(21),thenominalvoltageatTOisth erefore reflTO=Vgol+ TO(4 n ~)+LV~(22)wheredVgvgol=vg(To) ~To= (23)ToAscommonlycalled,V,Olisthelinearly -extrapolatedSibandgapvoltageatT= (22) :PRECISIONCURVATURE-COMPENSATEDCMOSBANDG APREFERENCE643V~~in(17) ~andthesecond-ordercorrectionvoltageFV~t oV~~,thereferenceoutputVr~fis~ef=VBE+KVT +Fv;=~ V~(4 n a)ln7 +(K+H+lnEG)V~+(F L)V~.

9 (24)Byequatingthefirst-orderandthesecond -orderderiva-tivesofV,, ,whered%1d2 VgdTTOT ~dT2()Tz1 2;To()+VT(4 fr-a)ln$++$.(25)0thenominalvoltageatTOis ~eflTo=vgo2+~VT~4 n (.X)(26)dVg1d2 VgJ &2=vg(To) ~TTo+y~T:= (27)NowVg02isthequadratically-extrapolat edSibandgapvoltageatT= (23).ThetheoreticalvalueofVg(OK) [12].Thebiascurrentvariationnolongeraffe cts(26) ,theintermediatevoltageatTOis1d2Vg(V,,+K VT)lTO=Vgo2+~~T:-LV;.(28)ToCorresponding ly,themagnitudeofthePTAT2voltageFV~atTOi sobtainedbysubtracting(28)from(26):1d2 VgFV;ITO=;VTO(4 n a) 2dT2T:+LV;.(29) (29) ,thefinalV~~fgivenby(25)isindependentoft heseinstabilitiesasfarastheirtemperature variationsarecompensatedproperly.[1][2][ 3][4][5][6][7][8][9][10][11],[12][13] , NewdevelopmentsinICvoltageregulators, , , , , Aprecisionreferencevoltagesource, , , , , Asimplethree-terminafbandgapreference, , , , , Acurvaturecorrectedmicro-powervoltageref erence, , , , , , , Anewcurvature-correctedbandgapreference, , , 1143, , ACMOS voltagereference, , , , , Alow-voltageCMOS bandgapreference, , , 577, , , ,Jr.

10 , Anintegratedsingle-chipPCMvoicecodecwith filters, , , ~ , , , , Char-acterizationofsurfacecannelCCDimage arraysatlowlightlevels, Temperaturedependenceoftheband~apinSi, , , , , , AccurateanafysisoftemperatureeffectsinIc V~Fcharacteristicswithapplicationtobandg apreferencesource,; , , , , MeasurementsofbandgapnarrowingmSibipolar tranwstors, Solid-StateElectron., , ,1976.~,,,/,,.~$:,Bang-SupSong(S 79)wasborninKunsan,,,,,$~< ; ,:Korea,in1973, ~, , engineeringfromtheKoreaAdvancedInstitute +,,,,:ofScience,Korea,in1975, ~.,%..inelectricalengineeringfromtheUniv ersityof1%<,rCalifornia,Berkeley, , ..,researchstaffintheElectronicsandCommu nica-tionsDivisionoftheAgencyforDefenseD evel-opment, ,hewasagraduatestudentattheUniversityofT exas, ,heisworkingatBellLaboratones,MurrayHill , (S 65 M69 SM76 F 80)wasborninJonesbo;o;AK,onDecember8, ,MS., ,Tucson,AZ,in1963,1965,and1969, ,FairchildSemiconductor,PaloAlto,CA,wher ehewasinvolvedintheapplica-tionofnewtech nologiesforanalogintegratedcircuits, ,UniversityofCalifornia,Berkeley, ,electro-thermalinteractionsinintegrated circuits,devicemodeling,telecommuni-cati onscircuits, ,theEuropeanSolid-StateCircuitsConferenc e, ,andasProgramChairmanofthe1982 IntemationafSotid-StateCircuitsConferenc e.


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