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1、ReturnNextPreviousContentsEnd番茄花园-ElectronicCircuitsandApplications Still waters run deep.流静水深流静水深,人静心深人静心深 Where there is life,there is hope。有生命必有希望。有生命必有希望ReturnNextPreviousContentsEndChapterThreePhysicalElectronicsOfTransistorsChapterThreePhysicalElectronicsOfTransistorsContentsuActivedevicesandC
2、ontrolElementsuBipolarTransistorsasControlElementsuField-EffectTransistorsasControlElementsReturnNextPreviousContentsEnd3.0ActivedevicesandControlElements(1)3.0ActivedevicesandControlElements(1)1.Whatisanactivedevice有源器件有源器件?Anactivedeviceisadevicecapableofcontrollingtheflowofelectricalenergyfromaso
3、urcetoaload.Ifanactivedeviceistobeusefulforincreasingthepowerlevelofsignal,thenthepowerrequiredatthecontrolinputsmustbemuchlessthanthepowerdeliveredtotheload,thebalancecomingfromthedcpowersources.Thecombinationoftheactivedeviceanditsassociatedpowersourcethenfunctionsasanamplifier,andissaidtohavepowe
4、rgain.Theop-ampisanactivedevice.2.Whatisacontrolelement控制器件控制器件?Acontrolelementisanetworkelementthatcanbeusedforthecontrolofpowerflow.Acontrolelementnormallyrequiresatleastthreeelectricalterminals,withthev-icharacteristicattheoutputterminalpairbeingdependentonthevoltageorcurrentattheotherterminals.T
5、hetransformisacontrolelement.ReturnNextPreviousContentsEnd3.0ActivedevicesandControlElements(2)3.0ActivedevicesandControlElements(2)3.TransistorandclassificationThetransistorismadefromsemiconductor.Itisthemostwidelyusedactivedeviceinmodernelectroniccircuits.Transistorscanbedividedintotwogeneralcateg
6、ories:uBipolartransistor(BJT)双极性晶体管双极性晶体管uField-effecttransistor(FET)场效应晶体管场效应晶体管ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(1)3.1BipolarTransistorsasControlElements(1)3.1.1ThePhysicalBasisofTransistorOperationInjection注入注入,Diffusion扩散扩散,andCollection收集收集Atypicalbipolartransi
7、storstructureisshownasItconsistsofap-typecentralregion,calledthebase基区基区,whichissandwichedbetweentwon-typeregions,calledtheemitter发射区发射区andthecollector集电区集电区.ThisarrangementisknownasanNPNtransistor.Itisalsopossibletoconstructacomplementaryform,thePNPtransistor,byusingp-typematerialfortheemitterandco
8、llectorregionsandn-typematerialforthebase.Ineithercase,thebipolartransistorconsistsoftwop-njunctionsthatshareacommonregion,thebase,betweenthem.ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(2)3.1BipolarTransistorsasControlElements(2)Tounderstandhowthebipolartransistoroperatesasa
9、controlelement,wecandrawonourunderstandingofthep-njunctiondiodedevelopedinSection7.3.Inthediodeaforwardbiasproducesasignificantcurrentresultingfromanetflowofholesandelectronsfromtheregionswheretheyaremajoritycarrierstotheregionwheretheyareminoritycarriers.Thisinjectionprocessisreviewedschematicallyi
10、nfollowingfigure.ThetotalterminalcurrentI isgivenbythesumofthetwocurrentcomponentsarisingfromtheholeflowandtheelectronflow.ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(3)3.1BipolarTransistorsasControlElements(3)Underreversebias,thep-njunctiondiodeischaracterizedbyasmallsaturat
11、ioncurrent,arisingfromthecollectionofminoritycarriersfromtheirrespectiveregionsbytheelectricfieldinthespace-chargelayer.Themagnitudeofthisreversesaturationcurrentdependsontheavailableconcentrationofminoritycarriers,andissmallinthediode.Thebipolartransistorworksasacontrolelementbycombininginjectionat
12、oneofitsp-njunctionswithcollectionattheotherp-njunction.ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(4)3.1BipolarTransistorsasControlElements(4)Inthenormalgainortheactivegainregion放大区放大区ofoperation,theemitter-basejunctionismaintainedinforwardbias,andthecollector-basejunctionis
13、heldinreversebias.Bydopingtheemitterregionmuchmoreheavilythanthebase,mostoftheinjectionofminoritycarriersismadetooccurintothebasesideofthejunction.Thus,underforwardbiasconditions,thereisalargebuildupofminoritycarriers(electronsinanNPNtransistor,holesinaPNPtransistor)onthebasesideoftheemitter-basejun
14、ction.Whilethisbuildupofelectronconcentrationistakingplaceattheemitterendofthebaseregion,thereverse-biasedcollector-basejunctionkeepstheconcentrationofminorityelectronsverylowatthecollectorendofthebaseregion.Thiscombinationofaforwardbiasattheemitter-basejunctionandareversebiasatthecollector-basejunc
15、tionthusestablishesalargeconcentrationgradientofminoritycarriersacrossthebaseregion.Normalthermalmotions,therefore,produceadiffusiveflowofminorityelectronsthroughthebaseregion,fromtheemitterend,wheretheyareinexcess,tothecollectorend,wheretheyaresweptacrossthecollector-basejunctionintothecollectorreg
16、ion.ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(5)3.1BipolarTransistorsasControlElements(5)ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(6)3.1BipolarTransistorsasControlElements(6)Abovefigureillustratesthisflowofelectronsfromtheemittertothebasebyinjectio
17、n注入注入,acrossthebasebydiffusion扩散扩散,andintothecollectorbycollection收集收集.Nearlyalltheelectronsenteringthebaseregionfromtheemitterreachthecollector.Asmallfraction,however,recombine复合复合withholestoformcompletecovalentbonds.Becauseofthisrecombinationprocess,andbecauseoftheinjectionofholesfromthebasetothee
18、mitter,someholesmustbesuppliedtothebaseviathebaseterminal.Theseholescannotbesuppliedfromthecollectorbecausetheyaretheminoritycarrierthere,andarefewinnumbers.Insummary,thecollector-basejunctionbehavesasareverse-biaseddiodewhosesaturationcurrentiscontrolledbytheinjectionofelectronsattheemitter-basejun
19、ction.Thecollectorcurrentisindependentofthecollector-basevoltage,providedthatareversebiasisestablishedatthecollector-basejunction.Thus,thebasicpropertyofacontrolelement,inthiscasethedependenceoftheoutput(collector)currentonaninputvariable(emittercurrentoremitter-basevoltage)hasbeendemonstrated.Retur
20、nNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(7)3.1BipolarTransistorsasControlElements(7)3.1.2 Circuit Symbols and Terminal Variables for Bipolar Transistors1.NPNbipolartransistor2.PNPbipolartransistorTheonlydifferencebetweenNPNandPNPdevicesymbolsisthedirectionofthearrowontheemitter
21、lead,whichindicatestheactualdirectionofforwardcurrentintheemitter-basejunction.Thereferencedirectionsfortheterminalcurrentsarealldefinedenteringthedevice,irrespectiveofthedirectionofpositive current flow.Thus at least one of the terminals current must bealgebraicallynegative.Thevoltagesubscriptsdeno
22、tetheterminalsbetweenwhichthevoltageismeasured,withthefirstsubscriptindicatingthepositivereferenceterminalandthesecondthenegativereferenceterminal.ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(8)3.1BipolarTransistorsasControlElements(8)3.1.3 Regions of Transistor OperationSince
23、thetransistorhasthreeterminals,therearesixpossiblewaystoconnectitinagivencircuit.InputOutputConnectionInputOutputConnectionB-EC-ECommon-emitterC-EB-ENousingB-CE-CCommon-collectorE-CB-CNousingE-BC-BCommon-baseC-BE-BNousingTherearefourregionsoftransistoroperation.1.Active-Gainregion放大区放大区E-Bjunctionis
24、forwardbiasedC-Bjunctionisreversebiased2.Saturationregion饱和区饱和区E-BjunctionisforwardbiasedC-Bjunctionisforwardbiased3.Cutoffregion截止区截止区E-BjunctionisreversebiasedC-Bjunctionisreversebiased4.Reverseregion反向区反向区E-BjunctionisreversebiasedC-BjunctionisforwardbiasedReturnNextPreviousContentsEnd3.1BipolarT
25、ransistorsasControlElements(9)3.1BipolarTransistorsasControlElements(9)3.1.4 v-i Characteristics of BJT1.TheinputcharacteristicofBJTTheinputcharacteristicofatransistorissimilartothatofadiode,whichcanbeexpressedas(IBS0).ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(10)3.1Bipolar
26、TransistorsasControlElements(10)2.TheoutputcharacteristicofBJTInactiveregion,therearetherelationshipsofcurrentsWhere,F is the forward short-circuit common-base current gain.It is apositive number whose magnitude is slightly less than 1.F is the forwardshort-circuit common-emitter current gain.It is
27、a positive number whosemagnitudecanbequitelarge.ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(11)3.1BipolarTransistorsasControlElements(11)3.1.5 Maximum Voltage and Current Limits1.MaximumpowerdissipationPD,max(中国标准表示为PCM)Aswasthecasefordiodes,thetemperatureriseofatransistorpro
28、ducedbyinternalpowerdissipationultimatelylimitstheallowedvoltagesandcurrents.Themaximumpermissiblepowerdissipationforagiventransistorwilldependonitsphysicalsize,itsmethodofconstructionandmounting,andthemaximumexpectedambientoperatingtemperature.Evaluationofthesethermalparameterswillproduceamaximumpo
29、werdissipationratingtothedeviceunderthegivensetofoperatingconditions.Thisratingservestolimitthemaximuminternaltemperatureofthestructuretoasafelevel,usuallyfrom150Cto200Cinsiliconunits.Becausethe Fisclosedto1,intheactive-gainregion,nearlyallthepowerdissipationoccursatthecollector-basejunction.Thepowe
30、rdissipationofatransistorisTheoperatingregionofatransistorwhosepowerdissipationislessthanthePD,max iscalledsafeoperatingregion安全工作区安全工作区.ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(12)3.1BipolarTransistorsasControlElements(12)2.C-Esustainingvoltage(CE耐压耐压)VCEO(中国标准表示为中国标准表示为U
31、(BR)CEO)Whenthebaseisopened,iftheC-Evoltageisincreasedtomagnitudethattheavalanchemultiplicationoccurs,thevalueofC-Evoltageiscalledthesustainingvoltagebetweencollectorandemitter.3.MaximumcollectorcurrentIC,max(中国标准表示为中国标准表示为ICM)Themaximumvalueofcollectorcurrentthatatransistorcancarryislimitedbythecur
32、rentcarryingcapacityofthefinewireusedtoconnecttheactiveregionsofthedevicetoitsterminalleads.Ifexcessivecurrentoccurs,thiswirewillmelt,causinganopencircuitatoneormoreofthedeviceterminals.ReturnNextPreviousContentsEnd3.1BipolarTransistorsasControlElements(13)3.1BipolarTransistorsasControlElements(13)3
33、.1.6TransistorOperationintheReverseRegionThebipolartransistorisasomewhatsymmetricaldevice,sincearegionofonetypeofsemiconductorisplacedbetweentworegionsofanoppositelydopedsemiconductor.ThusitisperfectlypossibletointerchangetherolesofcollectorandemitterandoperatethetransistorinreversewiththeEmitter-Ba
34、sejunctionreverse-biasedandtheCollector-Basejunctionforward-biased.Normally,however,theemitterandcollectorarefabricatedverydifferently,withtheresultthatsuperioramplifyingcharacteristicsareobtainedinthenormalconnection,andverypooramplifyingcharacteristicsareobtainedinreverseregion.Nevertheless,transi
35、storcharacteristicsdocontinueintothethirdquadrant(thereverseregion),andacurrentgain Rcanbedefinedthereanalogousto Fintheactive-gainregion.Inourcoursewegenerallyignorereverse-regionoperation,asitisencounteredrelativelyrarelyinsignal-processingcircuits.ReturnNextPreviousContentsEnd3.2Field-EffectTrans
36、istorsasControlElements(1)3.2Field-EffectTransistorsasControlElements(1)InChapter7wefoundthatthecurrentandvoltageinann-typesemiconductorbarwerelinearlyrelatedthroughtheconductanceofthebarSincetheconductanceGinthetwo-terminalbarisaconstant,thereisnopossibilityofutilizingthebarasacontrolelement.Howeve
37、r,throughamorecomplexstructure,itbecomespossibletovarytheconductancebetweentwoterminalsinresponsetoathird-terminalcontrolvoltage,andthisformsthebasicmechanismofoperationforthegroupofsemiconductorcontrolelementsknownasfield-effecttransistors(FETs).Examinationofaboveequationshowsthatiftheconductanceof
38、abaristobecontrolled,therearetwopossiblewaysinwhichitmaybeaccomplished.Eitherthecarrierconcentrationnorthegeometry(A/L)mustbemaderesponsivetovoltage.Theelectroniccharge qisafundamentalconstantnotsubjecttocontrol,andthemobility eisalsoanindependentconstantinthefirst-orderanalysisofFETsReturnNextPrevi
39、ousContentsEnd3.2Field-EffectTransistorsasControlElements(2)3.2Field-EffectTransistorsasControlElements(2)3.2.1 Junction Field-Effect Transistors 结型场效应晶体管结型场效应晶体管AschematicdiagramofanN-typechanneljunctionFET(N沟道沟道结型场效应晶体管结型场效应晶体管)isshownasItoperatesonthebasisofvaryingthecross-sectionalareaofasemicon
40、ductorbar.Thebasicbarisshownasn-type,andthisportionofthedeviceiscalledthechannel.Theterminalsattheendsofthebararelabeledsourceanddrain.Alongonesideofthebarisap-typeregion,whichformsap-njunctionalongthelengthofthebar.Thep-regionistermedthegateandisconnectedtothethirdorcontrolterminalofthestructure.Th
41、isgeneralformofFETisknownasthejunctionfield-effecttransistorJFET.AJFET(junctionfield-effecttransistor)isaunipolar,voltage-controlledtransistorthatusesaninducedelectricalfieldtocontrolcurrent.ThecurrentthroughtheJFETiscontrolledbyitsgatevoltage,vGS.Themorenegativethevoltage,thesmallerthecurrent.AJFET
42、consistsofalengthofn-typeorp-typedopedsemiconductormaterialcalledachannel.Theendsofthechannelarecalledthesourceandthedrain.Inann-channelJFET,thegateisp-typematerialsurroundingthechannel.Inap-channeldeviceitisn-typematerial.TherearetwotypesofJFET:N-channelJFETandP-channelJFETReturnNextPreviousContent
43、sEnd3.2Field-EffectTransistorsasControlElements(3)3.2Field-EffectTransistorsasControlElements(3)金属氧化物场效应金属氧化物场效应晶体管（简称晶体管（简称MOS管）Inthisstructureametalgateelectrodeisspacedfromtheconductingchannelbyathininsulator.Tworegions,moreheavilydopedthanthechannelanddenotedn+,serveasthesourceanddraincontracts.
44、Typically,theinsulatorisalayerofsiliconoxideapproximately0.1micron(微米微米)thick,growndirectlyonthen-typesiliconsurface.Thisstructureiscalledtheinsulator-gatefield-effecttransistor(IGFET),orthemetal-oxide-semiconductor(MOS)field-effecttransistor.Thep-typesubstrate(基片基片)isrequiredtogivetheassemblysuffic
45、ientphysicalsizeandstrengthforhandlinganddoesnotplayadirectroleintheelectricalperformance.3.2.2 Metal-Oxide-Semiconductor Field-Effect TransistorsReturnNextPreviousContentsEnd3.2Field-EffectTransistorsasControlElements(4)3.2Field-EffectTransistorsasControlElements(4)TheMOSFETsubstrateisusuallyconnec
46、tedtoitsmostnegativelybiasedpart,usuallythesourcelead.AnN-channelMOSFEThasaninward-pointingsubstratearrow.AP-channelMOSFEThasanoutward-pointingarrow.N-channelandP-channelMOSFETareidenticalexcepttheirvoltagepolaritiesarereversed.TherearetwomaincategoriesofMOSFET:uDepletionMOSFET耗尽型耗尽型MOSFETuEnhanceme
47、ntMOSFET增强型增强型MOSFETReturnNextPreviousContentsEnd3.2Field-EffectTransistorsasControlElements(5)3.2Field-EffectTransistorsasControlElements(5)1.EnhancementMOSFET增强型增强型MOS场效应管场效应管AnenhancementMOSFEThasnophysicalchannelbetweenthedrainandthesource,unlikethedepletionMOSFET.Instead,thesubstrateextendsallt
48、hewaytothesilicondioxide(SiO2)layer.AnenhancementMOSFETworksonlywithpositivegate-sourcevoltages.Apositivegate-sourcevoltageaboveaminimumthresholdvalue(VT)createsaninversionlayerofchargesinthesubstrateregionadjacenttotheSiO2layer.Theconductivityofthisinducedchannelisenhancedbyincreasingthegate-source
49、voltageonthepositiveside.EnhancementMOSFETsareextensivelyusedindigitalcircuitsandlarge-scaleintegration(LSI)applications.ReturnNextPreviousContentsEnd3.2Field-EffectTransistorsasControlElements(6)3.2Field-EffectTransistorsasControlElements(6)2.DepletionMOSFET耗尽型耗尽型MOS场效应管场效应管LikeaJFET,adepletionMOSF
50、ETconsistsofalengthofP-type(foraP-channelMOSFET)orN-type(foranN-channelMOSFET)semiconductormaterialcalledthechannel,whichisformedonasubstrateoftheoppositetype.Thissubstratereducesthechannelbetweenthedrainandthesource.Freeelectronsfromthesourcetothedrainhavetopassthroughthisnarrowchannel.Thetwoendsof