外文翻譯-外文文獻(xiàn)-英文文獻(xiàn)-溫度傳感器芯片簡化設(shè)計

TemperatureSensorICsSimplifyDesignsWhenyousetouttoselectatemperaturesensor,youarenolongerlimitedtoeitherananalogoutputoradigitaloutputdevice.Thereisnowabroadselectionofsensortypes,oneofwhichshouldmatchyoursystem'sneeds.Untilrecently,allthetemperaturesensorsonthemarketprovidedanalogoutputs.Thermistors,RTDs,andthermocoupleswerefollowedbyanotheranalog-outputdevice,thesilicontemperaturesensor.Inmostapplications,unfortunately,theseanalog-outputdevicesrequireacomparator,anADC,oranamplifierattheiroutputtomakethemuseful.

Thus,whenhigherlevelsofintegrationbecamefeasible,temperaturesensorswithdigitalinterfacesbecameavailable.TheseICsaresoldinavarietyofforms,fromsimpledevicesthatsignalwhenaspecifictemperaturehasbeenexceededtothosethatreportbothremoteandlocaltemperatureswhileprovidingwarningsatprogrammedtemperaturesettings.Thechoicenowisn'tsimplybetweenanalog-outputanddigital-outputsensors;thereisabroadrangeofsensortypesfromwhichtochoose.ClassesofTemperatureSensorsFourtemperature-sensortypesareillustratedinFigure1.Anidealanalogsensorprovidesanoutputvoltagethatisaperfectlylinearfunctionoftemperature(A).InthedigitalI/Oclassofsensor(B),temperaturedataintheformofmultiple1sand0sarepassedtothemicrocontroller,oftenviaaserialbus.Alongthesamebus,dataaresenttothetemperaturesensorfromthemicrocontroller,usuallytosetthetemperaturelimitatwhichthealertpin'sdigitaloutputwilltrip.Alertinterruptsthemicrocontrollerwhenthetemperaturelimithasbeenexceeded.Thistypeofdevicecanalsoprovidefancontrol.

Figure1.SensorandICmanufacturerscurrentlyofferfourclassesoftemperaturesensors.

"Analog-plus"sensors(C)areavailablewithvarioustypesofdigitaloutputs.TheVOUTversustemperaturecurveisforanICwhosedigitaloutputswitcheswhenaspecifictemperaturehasbeenexceeded.Inthiscase,the"plus"addedtotheanalogtemperaturesensorisnothingmorethanacomparatorandavoltagereference.Othertypesof"plus"partsshiptemperaturedataintheformofthedelaytimeaftertheparthasbeenstrobed,orintheformofthefrequencyortheperiodofasquarewave,whichwillbediscussedlater.

Thesystemmonitor(D)isthemostcomplexICofthefour.InadditiontothefunctionsprovidedbythedigitalI/Otype,thistypeofdevicecommonlymonitorsthesystemsupplyvoltages,providinganalarmwhenvoltagesriseaboveorsinkbelowlimitssetviatheI/Obus.Fanmonitoringand/orcontrolissometimesincludedinthistypeofIC.Insomecases,thisclassofdeviceisusedtodeterminewhetherornotafanisworking.Morecomplexversionscontrolthefanasafunctionofoneormoremeasuredtemperatures.Thesystemmonitorsensorisnotdiscussedherebutisbrieflymentionedtogiveacompletepictureofthetypesoftemperaturesensorsavailable.Analog-OutputTemperatureSensorsThermistorsandsilicontemperaturesensorsarewidelyusedformsofanalog-outputtemperaturesensors.Figure2clearlyshowsthatwhenalinearrelationshipbetweenvoltageandtemperatureisneeded,asilicontemperaturesensorisafarbetterchoicethanathermistor.Overanarrowtemperaturerange,however,thermistorscanprovidereasonablelinearityandgoodsensitivity.Manycircuitsoriginallyconstructedwiththermistorshaveovertimebeenupdatedusingsilicontemperaturesensors.

Figure2.Thelinearityofthermistorsandsilicontemperaturesensors,twopopularanalog-outputtemperaturedetectors,iscontrastedsharply.

Silicontemperaturesensorscomewithdifferentoutputscalesandoffsets.Some,forexample,areavailablewithoutputtransferfunctionsthatareproportionaltoK,othersto°Cor°F.Someofthe°Cpartsprovideanoffsetsothatnegativetemperaturescanbemonitoredusingasingle-endedsupply.

Inmostapplications,theoutputofthesedevicesisfedintoacomparatororanA/Dconvertertoconvertthetemperaturedataintoadigitalformat.Despitetheneedfortheseadditionaldevices,thermistorsandsilicontemperaturesensorscontinuetoenjoypopularityduetolowcostandconvenienceofuseinmanysituations.DigitalI/OTemperatureSensorsAboutfiveyearsago,anewtypeoftemperaturesensorwasintroduced.Thesedevicesincludeadigitalinterfacethatpermitscommunicationwithamicrocontroller.TheinterfaceisusuallyanI2CorSMBusserialbus,butotherserialinterfacessuchasSPIarecommon.Inadditiontoreportingtemperaturereadingstothemicrocontroller,theinterfacealsoreceivesinstructionsfromthemicrocontroller.Thoseinstructionsareoftentemperaturelimits,which,ifexceeded,activateadigitalsignalonthetemperaturesensorICthatinterruptsthemicrocontroller.Themicrocontrolleristhenabletoadjustfanspeedorbackoffthespeedofamicroprocessor,forexample,tokeeptemperatureundercontrol.

Thistypeofdeviceisavailablewithawidevarietyoffeatures,amongthem,remotetemperaturesensing.Toenableremotesensing,mosthigh-performanceCPUsincludeanon-chiptransistorthatprovidesavoltageanalogofthetemperature.(Onlyoneofthetransistor'stwop-njunctionsisused.)Figure3showsaremoteCPUbeingmonitoredusingthistechnique.Otherapplicationsutilizeadiscretetransistortoperformthesamefunction.

Figure3.Auser-programmabletemperaturesensormonitorsthetemperatureofaremoteCPU'son-chipp-njunction.

Anotherimportantfeaturefoundonsomeofthesetypesofsensors(includingthesensorshowninFigure3)istheabilitytointerruptamicrocontrollerwhenthemeasuredtemperaturefallsoutsidearangeboundedbyhighandlowlimits.Onothersensors,aninterruptisgeneratedwhenthemeasuredtemperatureexceedseitherahighoralowtemperaturethreshold(i.e.,notboth).ForthesensorinFigure3,thoselimitsaretransmittedtothetemperaturesensorviatheSMBusinterface.Ifthetemperaturemovesaboveorbelowthecircumscribedrange,thealertsignalinterruptstheprocessor.

PicturedinFigure4isasimilardevice.Insteadofmonitoringonep-njunction,however,itmonitorsfourjunctionsanditsowninternaltemperature.BecauseMaxim'sMAX1668consumesasmallamountofpower,itsinternaltemperatureisclosetotheambienttemperature.Measuringtheambienttemperaturegivesanindicationastowhetherornotthesystemfanisoperatingproperly.

Figure4.Auser-programmabletemperaturesensormonitorsitsownlocaltemperatureandthetemperaturesoffourremotep-njunctions.

ControllingafanwhilemonitoringremotetemperatureisthechieffunctionoftheICshowninFigure5.Usersofthispartcanchoosebetweentwodifferentmodesoffancontrol.InthePWMmode,themicrocontrollercontrolsthefanspeedasafunctionofthemeasuredtemperaturebychangingthedutycycleofthesignalsenttothefan.Thispermitsthepowerconsumptiontobefarlessthanthatofthelinearmodeofcontrolthatthispartalsoprovides.BecausesomefansemitanaudiblesoundatthefrequencyofthePWMsignalcontrollingit,thelinearmodecanbeadvantageous,butatthepriceofhigherpowerconsumptionandadditionalcircuitry.Theaddedpowerconsumptionisasmallfractionofthepowerconsumedbytheentiresystem,though.

Figure5.Afancontroller/temperaturesensorICuseseitheraPWM-orlinear-modecontrolscheme.

ThisICprovidesthealertsignalthatinterruptsthemicrocontrollerwhenthetemperatureviolatesspecifiedlimits.Asafetyfeatureintheformofthesignalcalled"overt"(anabbreviatedversionof"overtemperature")isalsoprovided.Ifthemicrocontrollerorthesoftwareweretolockupwhiletemperatureisrisingtoadangerouslevel,thealertsignalwouldnolongerbeuseful.However,overt,whichgoesactiveoncethetemperaturerisesabovealevelsetviatheSMBus,istypicallyusedtocontrolcircuitrywithouttheaidofthemicrocontroller.Thus,inthishigh-temperaturescenariowiththemicrocontrollernotfunctioning,overtcouldbeusedtoshutdownthesystempowersuppliesdirectly,withoutthemicrocontroller,andpreventapotentiallycatastrophicfailure.

ThisdigitalI/Oclassofdevicesfindswidespreaduseinservers,batterypacks,andhard-diskdrives.Temperatureismonitoredinnumerouslocationstoincreaseaserver'sreliability:atthemotherboard(whichisessentiallytheambienttemperatureinsidethechassis),insidetheCPUdie,andatotherheat-generatingcomponentssuchasgraphicsacceleratorsandhard-diskdrives.Batterypacksincorporatetemperaturesensorsforsafetyreasonsandtooptimizechargingprofiles,whichmaximizesbatterylife.

Therearetwogoodreasonsformonitoringthetemperatureofahard-diskdrive,whichdependsprimarilyonthespeedofthespindlemotorandtheambienttemperature:Thereaderrorsinadriveincreaseattemperatureextremes,andaharddisk'sMTBFisimprovedsignificantlythroughtemperaturecontrol.Bymeasuringthetemperaturewithinthesystem,youcancontrolmotorspeedtooptimizereliabilityandperformance.Thedrivecanalsobeshutdown.Inhigh-endsystems,alertscanbegeneratedforthesystemadministratortoindicatetemperatureextremesorsituationswheredatalossispossible.Analog-PlusTemperatureSensors"Analog-plus"sensorsaregenerallysuitedtosimplermeasurementapplications.TheseICsgeneratealogicoutputderivedfromthemeasuredtemperatureandaredistinguishedfromdigitalI/Osensorsprimarilybecausetheyoutputdataonasingleline,asopposedtoaserialbus.

Inthesimplestinstanceofananalog-plussensor,thelogicoutputtripswhenaspecifictemperatureisexceeded.Someofthesedevicesaretrippedwhentemperaturerisesaboveapresetthreshold,others,whentemperaturedropsbelowathreshold.Someofthesesensorsallowthetemperaturethresholdtobeadjustedwitharesistor,whereasothershavefixedthresholds.

ThedevicesshowninFigure6arepurchasedwithaspecificinternaltemperaturethreshold.Thethreecircuitsillustratecommonusesforthistypeofdevice:providingawarning,shuttingdownapieceofequipment,orturningonafan.

Figure6.ICsthatsignalwhenatemperaturehasbeenexceededarewellsuitedforover/undertemperaturealarmsandsimpleon/offfancontrol.

Whenanactualtemperaturereadingisneeded,andamicrocontrollerisavailable,sensorsthattransmitthereadingonasinglelinecanbeuseful.Withthemicrocontroller'sinternalcountermeasuringtime,thesignalsfromthistypeoftemperaturesensorarereadilytransformedtoameasureoftemperature.ThesensorinFigure7outputsasquarewavewhosefrequencyisproportionaltotheambienttemperatureinKelvin.ThedeviceinFigure8issimilar,buttheperiodofthesquarewaveisproportionaltotheambienttemperatureinkelvins.

Figure7.AtemperaturesensorthattransmitsasquarewavewhosefrequencyisproportionaltothemeasuredtemperatureinKelvinformspartofaheatercontrollercircuit.

Figure8.ThistemperaturesensortransmitsasquarewavewhoseperiodisproportionaltothemeasuredtemperatureinKelvin.Becauseonlyasinglelineisneededtosendtemperatureinformation,justasingleoptoisolatorisrequiredtoisolatethesignalpath.

Figure9,atrulynovelapproach,allowsuptoeighttemperaturesensorstobeconnectedonthiscommonline.Theprocessofextractingtemperaturedatafromthesesensorsbeginswhenthemicrocontroller'sI/Oportstrobesallthesensorsonthelinesimultaneously.Themicrocontrolleristhenquicklyreconfiguredasaninputinordertoreceivedatafromeachofthesensors.Thedataareencodedastheamountoftimethattranspiresafterthesensorsarestrobed.Eachofthesensorsencodesthistimeafterthestrobepulsewithinaspecificrangeoftime.Collisionsareavoidedbyassigningeachsensoritsownpermissibletimerange.

Figure9.Amicrocontrollerstrobesuptoeighttemperaturesensorsconnectedonacommonlineandreceivesthetemperaturedatatransmittedfromeachsensoronthesameline.

Theaccuracyachievedbythismethodissurprisinglyhigh:0.8°Cistypicalatroomtemperature,preciselymatchingthatoftheICthatencodestemperaturedataintheformofthefrequencyofthetransmittedsquarewave.Thesameistrueofthedevicethatusestheperiodofthesquarewave.

Thesedevicesareoutstandinginwire-limitedapplications.Forexample,whenatemperaturesensormustbeisolatedfromthemicrocontroller,costsarekepttoaminimumbecauseonlyoneoptoisolatorisneeded.ThesesensorsarealsoofgreatutilityinautomotiveandHVACapplications,becausetheyreducetheamountofcopperrunningoverdistances.AnticipatedTemperatureSensorDevelopmentsICtemperaturesensorsprovideavariedarrayoffunctionsandinterfaces.Asthesedevicescontinuetoevolve,systemdesignerswillseemoreapplication-specificfeaturesaswellasnewwaysofinterfacingthesensorstothesystem.Finally,theabilityofchipdesignerstointegratemoreelectronicsinthesamedieareaensuresthattemperaturesensorswillsoonincludenewfunctionsandspecialinterfaces.

中文翻譯溫度傳感器芯片簡化設(shè)計當(dāng)選擇一個溫度傳感器時，將不再局限于模擬輸出或數(shù)字輸出設(shè)備。現(xiàn)在有的傳感器類型，會讓你有很大的選擇空間。在市場上的所有的溫度傳感器提供模擬輸出。熱敏電阻、RTDs和熱電偶是另一種模擬輸出設(shè)備，硅溫度傳感器。在大多數(shù)應(yīng)用程序中，不幸的是，這些模擬輸出設(shè)備需要比較器、ADC或在他們的輸出放大器。因此，當(dāng)更高的級別，集成的變得可行，數(shù)字接口的溫度傳感器成為可用。這些芯片在多種形式出售，從簡單信號在特定溫度時的設(shè)備已超過那些報告同時提供警告在升溫設(shè)置的遠(yuǎn)程和本地的溫度。選擇現(xiàn)在不是簡單地之間模擬輸出和數(shù)字輸出的傳感器；有范圍廣泛的傳感器類型可供選擇。溫度傳感器的種類圖1。傳感器和IC制造商目前提供溫度傳感器的四的類。在圖1中舉例說明四種溫度傳感器類型。一種理想的模擬傳感器提供輸出電壓，這是一個完美的線性溫度（A）的功能。在數(shù)字I/O類的傳感器(B)中，溫度多1和0的表單中的數(shù)據(jù)傳遞到微控制器，通常是通過串行總線。沿著相同的總線，數(shù)據(jù)被發(fā)送到溫度傳感器的微控制器，通常設(shè)置的警報針的數(shù)字輸出將旅行的溫度限制。警報中斷微控制器時已經(jīng)超過溫度限制。這種類型的設(shè)備，還可以提供風(fēng)扇控制。"模擬正量"傳感器(C)被應(yīng)用在多種類型的數(shù)字輸出上。當(dāng)超過特定溫度的時候，Vout對溫度曲線是一個數(shù)字輸出。在這種情況下，增加到模擬溫度傳感器的“正信號”只不過是一個比較器的參考電壓。其他的類型“正信號”部分在以頻率和方波的形式儲存以后被延遲，這些將會在以后討論。系統(tǒng)監(jiān)視器（D）是四種類型當(dāng)中最復(fù)雜的集成電路。除了功能由數(shù)字I/O類型提供外，當(dāng)電壓上升或下降到通過I/O總線設(shè)置的極限的時候這類型裝置的監(jiān)測系統(tǒng)會報警。風(fēng)扇監(jiān)控和/或控制包含在這種類型中的集成電路。在某些情況下，此類設(shè)備用于決定一個風(fēng)扇是否正在工作。更多復(fù)雜控制風(fēng)扇如一或更多量過的溫度的功能。系統(tǒng)監(jiān)視器傳感器這里不討論，但簡短提到溫度傳感器的類型。模擬輸出溫度傳感器熱電阻和硅溫度傳感器被廣泛地應(yīng)用在模擬輸出溫度傳感器上。圖2清楚地顯示當(dāng)需要時電壓和溫度的線性關(guān)系，硅溫度傳感器是比熱敏電阻好得多。在狹窄的溫度范圍之內(nèi)，熱敏電阻可以提供合理的線性和良好的敏感特性。許多構(gòu)成原始電路的熱敏電阻已經(jīng)被硅溫度傳感器代替。圖2。熱敏電阻和硅溫度傳感器這兩個模擬輸出溫度探測器的比較。硅溫度傳感器有不同的輸出刻度和偏移量。例如，與絕對溫度成比例的輸出轉(zhuǎn)換功能，還有其他與攝氏溫度和華氏溫度成比例。攝氏溫度部分提供一種組合以便溫度能被單端補給傳感器測試。在大多數(shù)應(yīng)用程序中，這些裝置的輸出被裝入一個比較器或A/D轉(zhuǎn)換器的溫度數(shù)據(jù)轉(zhuǎn)換為數(shù)字格式。這些附加的裝置，熱電阻和硅溫度傳感器繼續(xù)被使用是由于在很多情況下它的成本低和使用方便。數(shù)字I/O溫度傳感器大約在五年前，一種新型溫度傳感器出現(xiàn)了。這種裝置包括一個允許與微控制器進(jìn)行通信的數(shù)字接口。接口通常是I2C或SMBus的串行總線，但其他的串行接口，如SPI是共用的。除了要報告的微控制器，溫度讀數(shù)，該接口也從微控制器接收指令。這些指令通常溫度限制，如果超出，將中斷微控制器的溫度傳感器在集成電路上的數(shù)字信號。然后微控制器可以調(diào)整風(fēng)扇速度，或減慢微處理器的速度，例如，保持溫度在控制下。這種類型裝置有多樣性的特點。遠(yuǎn)程溫度傳感，為了能夠遠(yuǎn)程測量，大多數(shù)的高效處理器提供一個溫度的模擬電壓芯片晶體。（晶體管的兩個p-n結(jié)僅被使用）。圖3顯示了一個使用這種技術(shù)檢測的處理器。其他應(yīng)用利用離散的晶體管實現(xiàn)相同的功能。圖3。設(shè)計的溫度傳感器可遠(yuǎn)程測試處理器芯片上的p-n結(jié)溫度。這種類型的傳感器的另一個重要特征是測量溫度在高或低極限外有中斷微控制器的能力（包括在圖3中所示的傳感器）。在其他的傳感器上，當(dāng)測量的溫度超過極限的時候，它會產(chǎn)生一個高或低的溫度門限，對於在圖3中的傳感器，那些極限經(jīng)由SMBus接口被傳送到溫度傳感器。如果溫度移動到周圍畫線范圍上面或下面，報警信號會中斷處理器。在圖4中畫一種類似的裝置。而不是監(jiān)測一個p-n結(jié)溫度，它會檢測四個結(jié)和其內(nèi)部的溫度。因為Maxim的MAX1668消耗很小的能量