低功耗智能便携式温度测量仪研究报告翻译.docx
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低功耗智能便携式温度测量仪研究报告翻译.docx
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低功耗智能便携式温度测量仪研究报告翻译
Anultra-low-powerCMOStemperaturesensorforRFIDapplications
Abstract:
Anultra-low-powerCMOStemperaturesensorwithanalog-to-digitalreadoutcircuitryforRFIDapplicationswasimplementedina0.18mCMOSprocess.Toachieveultra-lowpowerconsumption,anerrormodelisproposedandthecorrespondingnoveltemperaturesensorfront-endwithanewdouble-measuremethodispresented.Analog-to-digitalconversionisaccomplishedbyasigma-deltaconverter.Thecompletesystemconsumesonly26A@1.8Vforcontinuousoperationandachievesanaccuracyof±0.65◦Cfrom–20to120◦Caftercalibrationatonetemperature.
Keywords:
CMOStemperaturesensor。
erroranalysis。
digitaloutput。
lowpower。
RFID
DOI:
10.1088/1674-4926/30/4/045003EEACC:
1205。
1065H
1.Introduction
RFIDtechnologyhasattractedprofoundattention.Notcontentwithobjectidentificationonly,peopleareseekingformorefunctionsprovidedbyRFIDsystems.Oneofthemostattractiveapplicationsistorealizereal-timetemperaturesensingbyintegratingatemperaturesensorintotheRFIDtag.However,thereexistsomechallengingfeaturesforthesensor.First,thetemperaturesensormustbeon-chipandeasytocalibratetominimizethecost.Second,thepowerconsumptionofthesensorisstringentlylimited.Third,thetemperaturesensorshouldachievehighaccuracyinthewholetemperaturesensingrange.Severalpapershavereportedtemperaturesensordesigns.However,thesecaneithernotberealizedinlow-costCMOStechnologyortheyconsumetoomuchpowerforcontinuousoperation.Inthispaper,anoveldesignofaCMOStemperaturesensor,whichofferslowpower,lowcostandhighaccuracy,isproposed.Anerrormodelforthissensorisdeveloped.Also,thearchitecturalimprovementsofthetemperaturesensor,whichincludesasensorfrontendandasigma-deltaADC,isgiven.
2.Errormodel
ThemostimportantcandidateforaCMOStemperaturesensoristhebipolartransistor,whichcanberealizedasaparasiticdeviceinstandardCMOStechnology.AlmostallCMOStemperaturesensorsfollowtheprincipleofthegeneralarchitectureofthebandgapreferenceasillustratedinFig.1.
Thedifferenceofthetwobase-emittervoltagesisdirectproportionaltotheabsolutetemperature(PTAT>,asgivenby
Therefore,thetemperaturecanbemeasuredbycomparingwiththereferencevoltage,whichistheoreticallytemperatureindependent.Nevertheless,severalerrorsareinherentinsuchacircuit,andthustheaccuracygreatlydependsontheprocessparameters.AtypicaltestresultfortheerrorsofCMOStemperaturesensorispresentedinRef.andlistedinTable1.
Asshown,theerrorsofthisbandgapreferencecircuitareduetotheoffsetoftheopamp(Vos>,thespreadintheabsolutevalueofthebase–emittervoltage∂(Vbe>,thespreadintheabsolutevalueoftheresistors∂(Rsh>,themismatchofthebipolartransistor∂(Vos,Q>,andthemismatchoftheresistors∂(ΔR>,respectively.
AtemperaturesensorerrormodelwasbuiltaccordingtothetestresultsdescribedinTable1withtheerrorsourcesbeingexpressedas
whereVT=kT/q.Thedifferencebetween,representingthe∂(Vbe>ofthebipolartransistorQ1,and,representingthe∂(Vbe>ofthebipolartransistorQ2,denotesthemismatchofthebipolartransistors∂(Vos,Q>.∂(Rsh>:
R=R(1+∂R>:
∂(Rsh>ofresistorsR1andR2,respectively,denotesthemismatchoftheresistors∂(ΔR>.Thesimulationoftheerrors∂(Vos>and∂(Vos,Q>areillustratedinFigs.2(a>and2(b>,respectively,whensettingtheratioofI1andI2tobeatypicalvalueofeight.TheresultsmatchedwellwiththedatagiveninTable1.Figure2(c>shows∂(Vos>and∂(Vos,Q>asfunctionsoftemperature.Asshown,theerrorvaries±2.5◦Cintherangeof−20to120◦C.BasedonEqs.(2>–(4>,thereferencevoltageandthetemperaturedependentvoltageillustratedinFig.1aregivenby
whereAisacoefficient.Itisshownthatthereferencevoltageisaffectedby∂(Vos>,∂(Vos,Q>,∂(ΔR>,and∂(Vbe>,whilethetemperaturedependentvoltageisonlyaffectedby∂(Vos>,∂(Vos,Q>,and∂(ΔR>.
3.Architectureimprovement
AsillustratedinFig.3,thetemperaturesensorfrontendgeneratesthetemperaturedependentvoltage,whichis
theinputsignalofasecond-ordersigma-deltaADC.ThereferencevoltageforΣΔADCisgeneratedfromtheRFIDtag.AfterΣΔADCdigitalizes,thedigitalcircuitcalculatesthedifferenceoffortwoworkingmodesofthefrontendcircuit.
3.1CMOStemperaturesensorfrontend
temperaturesensorfront-end,asillustratedinFig.4.Theoutputvoltageisalsotemperaturedependentandgivenby
TheSwitch2controlsthevalueofI1.I1isfourtimeslargerthanI2whentheSwitch2isclosed.WhiletheSwitch2isopen,I1isthreetimeslargerthanI2.Sothedifferenceofbetweentwoworkingmodesis
Theresultimpliesagoodperformanceofthisnewdoublemeasuremethod.Theonlyerrorofthevoltagedifference,whichisproportionaltotheabsolutetemperature,comesfromthemismatchoftheresistances,namely∂(ΔR>,whichiswellcontrolledinCMOStechnology.
However,isdigitalizedbyΣΔADCbycomparingitwith.Sotheaccuracyofalsodependsontheprecisionofthereferencevoltage,whichisprovidedbyabandgapcircuitintheRFIDtag.AsseenfromEq.(4>,itisdifficulttokeepconstantoveralargetemperaturerangeandusuallyrequirescomplexcalibrationssuchassecondordercurvaturecorrection.Fortunately,thefactthattemperaturesensingandrecordingisdiscreteintimealleviatesthisdemand.By
comparingfortwoworkingmodeswiththesamereferencevoltage,thedifferencevoltagecanbepreciselymeasuredwhenisequalinjusttwocasesratherthanrequiringtobeexactlythesameoverthewholemeasuredtemperaturerange.Thus,acalibrationforisnolongernecessary.AsisshowninEq.(6>,theproposedtemperaturesensorfrontendhastheadvantageofbetterimmunitytothemainerrorsof∂(Vos>,∂(Vos,Q>,∂(Vbe>,and∂(Rsh>.Asigma-deltaADCfollowingthecircuitisdesignedtodigitizethefortwoworkingmodes.
3.2ADconverter
Thesigma-deltaADChasbeenproventobeverysuitableinlowfrequency,highperformancecases.Inourapplication,thesignalalmostactsasaDCsignal.Asecond-ordersigma-deltaADCischosenforitslowcomplexityandmoderateaccuracyof10bits.
Nevertheless,theoffsetinthesigma-deltamodulatorwouldinfluencetheDCsignal.AsshowninFig.6,theoutputvoltagewouldincludetheoffsetvoltageoftheopampwhensamplingtheinputsignalinasample-and-hold(S-H>circuit.Theoutputvoltageisgivenby
beingclosedoropen,wecanwrite
TheoffsetvoltageoftheopampiscancelledautomaticallyanddoesnotinduceadditionalerrorswhenconvertingtheanalogDCsignaltothedigitaldomain.
3.3Architectureerrorsimulation
Theproposedarchitectureovercomestheerrorsourcesof∂(Vos>,∂(Vos,Q>,∂(Vbe>,and∂Rsh>describedintheerrormodel.AsillustratedinFig.7,thetemperatureerrorinthemostinterestedrangeof–20to50◦Cisnegligible.Theremainingerror∂(ΔR>causeda±0.65◦Cvariationintherangeof−20to120◦CduetothemismatchofR1andR2.
4.Measurementresults
ThewholeCMOStemperaturesensorisimplementedinSMIC0.18mprocess.ThemicrographofthisproposedsensorisshowninFig.8.Thecompletecircuitoccupies0.9mm2(excludingbondpads>.
Themeasuredresultsfortheproposedtemperaturesensor,whichareillustratedinFig.9,matcheswellwiththesimulationresults.Aftercalibrationatonetemperature,thevariationoftheerrorislessthan±0.65◦Cfrom–20to120◦C.TomeetthestringentlimitofpowerconsumptionoftheRFIDtag,thesensorwithdigitaloutputconsumesonly26A@1.8Vforcontinuousoperation,ofwhich6Aisconsumedbythesensorfront-endand20Abythesigma-deltaconverter.
Table2comparesthepowerconsumption,theinaccuracyandcalibrationconditionwithpreviousworks.Manytemperaturesensorsprovideanadditionallow-powerworkingmodeinwhichthesensorisnormallyshutdownandonlypowersupwhennecessary.Asthetimeforonetemperaturemeasurementisusuallyonlyseveraltenmicroseconds,theaveragepowerconsumptionisfarlessthanthepeakone.Forcontinuousoperationthepowerconsumptionshouldbelimitedto50AforRFIDapplications.Ourworkalsoprovidesanadditionallow-powerworkingmodecontrolledbySwitch1inFig.4.Thepresentedtemperaturesensorperformsaswellassensorspresentedinpreviousworksoverawidetemperaturerange,butachievesmuchlowerpowerconsumptionforcontinuousoperation.
5.Conclusion
ThetemperaturesensorwithdigitaloutputforRFIDapplicationsofferslimitedpowerconsumption,lowcostandhighaccuracy.AnoveldesignofaCMOStemperaturesensorispresented.Comparedwithtraditionalpower-hungryerrorcancellationtechnologiessuchasDynamicElementMatching
(DEM>ofbiascurrent,theproposedsensorfront-endwithasecond-ordersigma-deltaADCovercomesthecircuiterrorsbymeansofanewdouble-measuremethodandconsumesonly26A@1.8Vforcontinuousoperation.Aftercalibrationatonetemperature,thesensorachievesanaccuracyof±0.65◦Cinthemeasuredtemperaturerangefrom–20to120◦C.
Acknowledgments
TheauthorswouldliketothankLeeYangofSMIC(Shanghai>forchipfabricationsupport.
References
[1]SotoMA,SahuPK,RueckC,etal.DistributedtemperaturesensorsystembasedonRamanscatteringusingcorrelationcodes.ElectronLett,2007,43(16>:
862
[2]BakkerA,HuijsingJH.MicropowerCMOStemperaturesensorwithdigitaloutput.IEEEJSolid-StateCircuits,1996,31(7>:
933
[3]TuthillM.Aswitched-current,switched-capacitortemperaturesensorin0.6umCMOS.IEE
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- 功耗 智能 便携式 温度 测量仪 研究 报告 翻译
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