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学号201100303050

姓名黄欢宣

指导教师黄庆南

2015年4月2日

ANovelBuilt-inCMOSTemperatureSensorforVLSICircuits

WangNailong,ZhangShengandZhouRunde

（InstituteofMicroelectronics,TsinghuaUniversity,Beijing100084,China）

Abstract:

AnoveltemperaturesensorisdevelopedandpresentedespeciallyforthepurposeofonlinethermalmonitoringofVLSIchips.Thissensorrequiresverysmallsiliconareaandlowpowerconsumption,andthesimulationresultsshowthatitsaccuracyisintheorderof018℃.TheproposedsensorcanbeeasilyimplementedusingregularCMOSprocesstechnologies,andcanbeeasilyintegratedtoanyVLSIcircuitstoincreasetheirreliability.

Keywords:

temperaturesensor;

thermaltestability;

frequencyoutput.

EEACC:

1265A;

2560;

2570D

CLCnumber:

TN47　　　Documentcode:

A　　　ArticleID:

025324177（2004）0320252205

1　Introduction

Duetotheadvancesinthefabricaionprocessfieldofintegratedcircuits,thecomponentdensityandtheoverallpowerdissipationofthehighperformanceVLSIchipsincreasecontinuously.Atthebeginningofthiscentury,thepowerdissipatedinasinglechiphasexceeded100W,andtightlypackedchipassembliesasthemultichipmodulescanevendissipatethousandswatts.Therefore,thethermalstateofintegratedcircuitshasbeenalwaysagreatproblemconcernedandisconsideredasabottleneckinincreasingtheintegrationofelectronicsystems.Toovercomethisproblem,manyresearchersdevelopedlow2powerdesigntechniquesforVLSIsystems.Inordertoavoidthermaldamages,continuousthermalmonitoringshouldbeappliedduringboththeproductionreliabilitytestingandthefieldoperation.AnefficientwayistobuildtemperaturesensorsintoallVLSIchips,withtheappropriatecircuitryprovidingeasyreadout.Insomeearlierworks,theresearchersusedtheparasitic,lateralorsubstratebipolartransistors,whichcanberealizedinmostoftheCMOSprocesses,asthermalsensors.TheseareusuallyPTATsensors.TheweaknessofthesesenorsisthatthebipolarstructuresarenotwellcharacterizedinaMOSprocess.Thus,althoughtheycanprovideasatisfiectsolutionforagivenprocess,thecircuitscannotberegardedasageneralCMOSapproachandcannotbewidelyused.

2　Problemformulation

Therearevarioustemperaturesensorssuitableforthermalstateverificationofintegratedcircuitmicrostructuressuchasthermoresistors,pnjunctions,andtheexploitationoftheweakinversionofMOStransistors.Ourobjectiveistoconvertthetemperaturetoanoscillatingsignaltomakeitcompatibletodigitalcircuitdesignmethodandfacilitatetheevaluationofthetemperaturesensed.AtemperaturesensorbasedonaringoscillatorisintroducedinRef.,thiscellguaranteesaaccuracyof3℃thatismarginallyacceptableasachiptemperaturesensorbutthesiliconarearequiredisratherbig.AMOStemperaturecontrolledoscillatorisusedasasensortomonitorthethermalstateofmicroelectronicstructuresinRef.However,thissensorrequiresabout10to15mWpowertodrivethethermaldelaylineandthedissipatertransistor.

Toovercometheseinconveniences,wethinkthatthetemperaturesensorstobeusedasbuiltinunitsforVLSIcircuitsonlinethermalmonitoringshouldmeetsomespecialrequirementsasfollows:

（1）Nearlylinearityinatemperaturerange（usually0~100℃）;

（2）Lowpowerconsumption（nomorethan1mW）;

（3）Simplestructureandsmallsiliconarea（usuallynomorethan40transistors）;

（4）Easyreadoutresultswithfavorablydigitaloutputsignal（e.g.,thefrequencyofasquarewavewhichcarriesthetemperatureinformation）;

（5）Easy（onepoint）calibration;

（6）Highaccuracy（intheorderof2℃orless）;

（7）CompatibilitywiththepresentCMOSprocess;

Consideringthegivenrequirements,wepresentanewbuiltintemperaturesensormeetingalltheaboverequirements

3　Built-inthermalmonitoringsensor

OurnewtemperaturesensorisavoltagecontrolledrelaxationoscillatorbasedtemperaturesensorshowninFig.1.Thecircuitconsistsoftwoparts,avoltageoutputsensorandarelaxationoscillator.

Fig.1　Temperaturesensordesignedbasedona

voltage2controlledrelaxationoscillator

3.1　Voltage-outputsensor

OurvoltageoutputsensorcircuitexploitsthetemperaturedependenceofthemosimportantparameteroftheMOStransistor,namely,thethresholdvoltage（VT）.Thethresholdvoltagehasanegativetemperaturecoefficientas:

VT（T）=VT（T0）+a（T-T0）

（1）

whereaisthetemperaturecoefficientwithatypicalvalueof-118mVö

KinCMOS0135Lm5Vtechnology;

VT（T0）isthevalueofthethresholdvoltageattemperatureT0.AsshowninFig.1,thevoltageoutputsensorisathresholdvoltagereferencecell.ThepchanneltransistorsP1,P2constituteacurrentmirror.ThecurrentoftransistorN1ismirroredtotansistorsN2,N3,andN4.ThevoltagedroponthesetransistorsisfedbacktothegateofN1.Foreasycalculating,wechooseasamesizeofthetransistorsN2,N3,andN4（BN2=BN3=BN4）,andwechooseappropriatesizeoftheothertransistorstoensurethatthetransistorsP1,P2,N1,N2,N3,andN4areallinthestateofsaturation.Thentheoutputvoltagesofthissensorareindirectproportiontothethresholdvoltageandlinearwithtemperatureandtheirvaluesare:

VH=VT（1+2KP12KP12-3KN12）=k1VT

（2）

VL=VT（1+2KN12KP12-3KN12）=k2VT（3）

where

isdeterminedbytheratiobetweenthegatesizesofthenchanneltransistorN1andN2,and

istheratioofthegatesizesofthepchanneltransistorP1andP2.

　Byadjustingthesizesofthetransistors,wefound

shouldbebiggerthanthreetimesof,whenthetransistorsP1,P2,N1,N2,N3,andN4areallinthestateofsaturation.Theadvantagesofthiscircuitarrangemetarethesimplicityandthestableoutput.AnimportantfeatureisthattheoutputvoltagesofVHandVLarepracticallyindependentofthesupplyvoltage（VDD）.

3.2　Voltage-controlledrelaxationoscillator

Thequickinterfacingoftheanalogue,currentoutputsensorwiththedigitalenvironmentisnotasimpletask.Toovercomethisproblemweuseavoltagecontrolledrelaxationoscillatorasthevoltagefrequencyconverter.Theoutputsignalofthisconverterisasquarewave,thefrequencyofwhichcarriesthetemperatureinformation.Thisfrequencycanbeeasilyturnedintoadigitalnumberbycountingthesquarewavepulsesinaprescribedtimewindow.AsshowninFig.1,thecurrentoftheresistorismirroredusingthetransistorsP3,P4,P5,N5,N6toprovidethesamesourceandsinkcurrentstochargeanddischargethecapacitorC.Assumingtheinitialvalueofthefoscislogic0,thenthetransistorP6isonandthetransistorN7isoffcausingthecapacitorCtobechargedusingthesourcecurrentIuntilVcexceedstheupperthresholdVH.Whenthisoccurs,theoutputlatchtogglesandthelogicvalueoffoscbecomeslogic1,whichinturnmakesthetransistorP6offandthetransistorN7on.ThismakesthecapacitorCtobedischargedbythesinkcurrentuntilthecapacitrvoltagefallsbelowalowerthresholdVLatwhichtimetheentirecyclerepeats.Neglectingthedelayofthecomparators,latchandtransistorsP6andN7,theoscillationcycletimeshouldbe:

　AsthecurrentissmallandtheWö

LratioofthetransistorP3ischosentobebiginthisdesign,theVgspcanbeapproximatedtothethresholdvoltageofthetransistorP1andtherefoethecurrentcanbeapproximatedby

　AndthetemperaturedependenceoftheresistorRsis

wherekisthetemperaturecoeficientoftheresistor,withtypicalvaluek=255×

10-6ö

℃forpolysiliconsheetresistorintheCMOS0135Lm5Vtechnology.Therefore,theoscillationcycletimeisfoundtobe

　Thisequationimpliesthatthecycletimeoftherelaxationoscillatorisnearlylinearwithtemperature,andthenthefrequencyoftheoscillatoris

4　Simulationresultsanddiscussion

ThesimulationresultofthevoltageoutputthermalsensorisillustratedinFig.2,andthevariaionoftherelaxationoscillatorbasedsensoroscillationcycletimeandfrequencyversusthechiptemperatureisshowninFig.3.Toevaluateabuildinthermalsensor,therearethreeimportantcharacteristics:

accuracy,sili2conarea（transistornumber）,andpower

dissipation.ThecharacteristicsofourvoltagecontrolledrelaxationoscillatorbasedsensorisshowninTable1:

5　Conclusion

Inthispaper,apracticalandefficientbuiltintemperaturesensorforthermalmonitoringoftheintegratedcircuitsisintroduced.Themainadvantagesofthepresentedchiptemperaturesensorsarelowsiliconarea,lowpowerdissipation,digitaloutputinformofoscillationfrequency,highaccuracy,andeasilyimplementedusingregularCMOSprocesstechnologies.Therefore,thissensorcanbeeasilyintegratedtoanyVLSIcircuitstoincreasecircuitsreliability.

References

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473

[2]　NebelW,MermetJ.Lowpowerdesignindeepsubmicronelectronics.Boston:

KluwerAcademicPublishers,1997,Chapter4.1

[3]　MontaneE,BotaSA,SamitierJ.Acompacttemperaturesen2sorofa110LmCMOStechnologyusinglateralPNPtransistors.In:

ProcTHERMINIC’96Workshop,1996:

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[4]　BianchiRA,KaramJM,CourtoisB.CMOScompatibletem2peraturesensorbasedonthelateralbipolartransistorforverywidetemperaturera