模电英文课件ch3.1.ppt
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模电英文课件ch3.1.ppt
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Ch3.TheBipolarJunctionTransistor3.1.1TransistorStructure3.1.2NPNTransistor:
Forward-ActiveModeOperation3.1BasicBipolarJunctionTransistor3.1.3Current-VoltageCharacteristic3.1.4BJTMainParametersCh3.TheBipolarJunctionTransistor3.0PreviewWediscusstheDCandACanalysisanddesignofbipolarcircuits.Diodesareusefulinwaveshapingandswitchingcircuits,butnotcapableofamplifyingcurrentsorvoltages.Transistoriscapableofcurrentandvoltageamplification,itisathree-terminaldevice_Revolution.Transistorhastwoclasses,oneisthebipolartransistor,whichhastwomajortypes,otheristhefiled-effecttransistor(FET).Webegintointroducethephysicalstructureandoperationofthebipolartransistor.3.1BasicBipolarJunctionTransistor(BJT)3.1.1TransistorStructureTherearetwotypesofbipolartransistor:
NPNandPNP.B-EjunctionB-CjunctionBaseterminalEmitterterminalCollectorterminalEmitterCollectorBaseSymbol3.1.1TransistorStructureFeatureoftransistorstructureCrosssectionofNPNbipolarTransistor(3)Basemustbeverynarrow.
(1)Impuritydopingconcentrationinemitterregionismuchlargerthanothertworegions.
(2)Areaofcollectorregionisbiggerthanthatofemitter.3.1.2NPNTransistor:
Forward-ActiveModeOperationAmplificationconditionItiscalledtheforward-activeoperatingmode,oractiveregion.1.Transferprocessofcarriersinnpn
(1)Emitterregionemitelectronsintobase.
(2)Collectorregioncollectelectronsinjectedbasefromemitter.(3)B-Evoltagecontrolscollectorcurrent.Iftransistorisusedasanamplifyingdevice.B-Ejunctionisforwardbiased.B-Cjunctionisreversebiased.NPNbipolartransistorbiasedintheforward-activemode3.1.2NPNTransistor:
Forward-ActiveModeOperation1.Transferprocessofcarriers3.1.2NPNTransistor:
Forward-ActiveModeOperationTherearetwotypesofcarriers,electronsandholescontributingtothecurrent,sothetransistoriscalledbipolarjunctiontransistor(BJT).EmitterCurrentVT_thermalvoltageIES_emitterleakagecurrent2.CurrentrelationshipsIE=IB+IC,IC=InC+ICBO,IB=IB-ICBOTransferprocessofcarriersWeknowfromtransferprocessofcarriersgenerallyICICBO-common-basecurrentgain,onlydependongeometriesandconcentration,norelationwithvoltages.Generally=0.90.992.CurrentrelationshipssinceIE=IB+IC,IC=InC+ICBO,iscommon-emittercurrentgain,also,onlydependongeometriesandimpurityconcentration,independentofB-CandB-Evoltages.Generally500,B-Cisreversebiased,someelectronsbegintosweepintocollector,recombinationdecreasesinbase,soIBreducesundersamevBE,curveshiftstoright。
(1)whenvCE=0V,itissameasforwardexponentialrelationofadiode。
Common-emittercircuit3.1.3Current-VoltageCharacteristics2.TheoutputCharacteristicofCEiC=f(vCE)iB=const3.1.3Current-VoltageCharacteristics2.OutputcharacteristicofCE(Transistorcharacteristic)iC=f(vCE)iB=constSaturation:
iCiscontrolledbyvCE,iCincreasesrapidlyasvCEincreases,andvCE0.7V(Silicon)。
B-Eisforwardbiased,B-Cisforwardbiased,too,orvoltageofreversebiasedisverysmall.Fourregionsforcharacteristic3.1.3Current-VoltageCharacteristics2.OutputcharacteristicofCE(Transistorcharacteristic)iC=f(vCE)iB=constFourregionsforcharacteristicCut-off:
iCisnearlyzero,Cut-offregionisunderiB=0。
vBEVB(turninvoltage),B-Cisreversebiased。
3.1.3Current-VoltageCharacteristics2.OutputcharacteristicofCE(Transistorcharacteristic)iC=f(vCE)iB=constFourregionsforcharacteristicBreakdown:
Reverse-biasvoltageofB-Cincreasestoomuch,B-Cjunctionbegintobreakdown.3.1.3Current-VoltageCharacteristics2.OutputcharacteristicofCE(Transistorcharacteristic)iC=f(vCE)iB=constFourregionsforcharacteristicForward-activemode:
iCandiBarerelatedbyiC=iB.Curvesareparallelandequidistance.B-Eisforwardbiased,B-Cisreversebiased.3.1.3Current-VoltageCharacteristics2.TheoutputCharacteristicofCEroVA/ICCurrent-voltagecharacteristicsforthecommon-emittercircuit,showingtheEarlyvoltage3.1.3Current-VoltageCharacteristics3.TheoutputCharacteristicofCBWhytheVCBcanbenegative?
3.1.4BJTMainParameters1.CurrentGain
(1)Common-emitterdccurrentgainFF=(ICICEO)/IBIC/IBvCE=const3.1.4BJTMainParameters1.CurrentGain
(2)Common-emitteraccurrentgain=IC/IBvCE=const3.1.4BJTMainParameters1.CurrentGain(3)Common-basedccurrentgainFF=(ICICBO)/IEIC/IEWhenICBOandICEOareverysmall,F,F.(4)Common-baseaccurrentgain=IC/IEVCB=const3.1.4BJTMainParameters2.Reverse-biasLeakageCurrents
(2)Collector-emitterleakagecurrentICEOICEO=(1+F)ICBO
(1)Collector-baseleakagecurrentICBOInmostinstancesinthistext,leakagewillbecompletelynegligible.ICBOisthecollectorleakagecurrentincommon-baseconfiguration,whentheemitterisanopencircuit.ICEO3.1.4BJTMainParameters3.BreakdownVoltageBVCBOCollector-basejunctionbreakdownvoltageinopen-emitterconfiguration。
BVCEOBr
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