5 HW Solns
EE203:HomeworkAssignment#3
HOMEWORKDUE:05/18/2010(inclass)
Problem#1:(3ptseach)
a. Forauniformlydopedn++p+nbipolartransistorinthermalequilibriumsketchtheenergy
banddiagramandtheelectricfieldthroughthedevice.
b. Sketchtheminoritycarrierprofileinapnjunctioninforwardbiasandreversebias
neglectinggenerationandrecombinationinthedepletionregion.Labelrelevantvalues.
c. InaBJTbiasedinforwardactiveregion,thebasecurrentisiB=6.0uA,thecollectorcurrent
isiC=510uA.Determine,F,andiE.
ANSWER:IE+IC+IB=0thereforeIE=516uA.=85.F=0.9883
d. InaBJT,theemitterisgenerallymoreheavilydopedthanthebase.Whyisthisimportant
todeviceoperation?
ANSWER:Theemitterismoreheavilydopedthatthebasetokeeptheminoritycarrierinjection
ratiofromEtoBhigherthanBtoE.
e. Whatisthebiasontheemitterbaseandbasecollectorjunctionsifabipolarjunction
transistorisintheforwardactivecondition?
ANSWER:ThebiasontheEBjunctionispositiveandthebiasontheBCjunctionisnegative.
f. Whatarethefouroperatingmodesofabipolarjunctiontransistor?Howarethetwopn
junctionsbiasedforeachoperationmode?
ANSWER:forwardactive(VBE>0,VBC<0),saturation(VBE>0,VBC>0),cutoff(VBE<0,VBC<0),
andreverseactive(VBE<0,VBC>0)
g. InawelldesignednpnBJT,whichislargerthewidthofthebaseortheminoritycarrier
diffusionlengthinthebase?
ANSWER:Theminoritycarrierdiffusionlengthislargerthanthewidthofthebase.
i. Inwords,whatisthebasetransportfactorinapnpBJT?
ANSWER:Thebasetransportfactoristhefractionofinjectedminoritycarriersthatmakeit
acrossthebase.
h. Listthreecontributionstothebasecurrent.
ANSWER:(1)currentfromtherecombinationofinjectedminoritycarriersfromtheemitter,(2)
currentfromminoritycarriersinjectedfromthebasetotheemitter,(3)currentfromtheholes
sweptintothebasebythereversebiasBCjunction.
j. YouneedtomakeanequationsheetfortheEE203midterm.Youareonlyallowed10
equations.Whichequationswouldyouputonyoursheet?
ANSWER:Any10equationsrelevanttothefirst5weeksofclass.
Problem #3:
Problem #3
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