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ID:56990542
大小:381.00 KB
页数:25页
时间:2020-07-25
《微电子学伯克利Lecture 课件.ppt》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、Lecture6OUTLINEPNJunctionDiodesReverseBreakdownLargeandSmallsignalmodelsReading:Chapter2.2-2.3,3.2-3.4BipolarJunctionTransistors:Chapter4DepletionWidthatEquilibriumV(x)xa-bV00--(1)--(2)--(3)V(a)=0V(-b)=V0;BuiltinpotentialReverseBreakdownMechanismsZenerbreakdo
2、wnoccurswhentheelectricfieldissufficientlyhightopullanelectronoutofacovalentbond(togenerateanelectron-holepair).Avalanchebreakdownoccurswhenelectronsandholesgainsufficientkineticenergy(duetoaccelerationbytheE-field)in-betweenscatteringeventstocauseelectron-ho
3、lepairgenerationuponcollidingwiththelattice.ReverseBreakdownAsthereversebiasvoltageincreases,theelectricfieldinthedepletionregionincreases.Eventually,itcanbecomelargeenoughtocausethejunctiontobreakdownsothatalargereversecurrentflows:breakdownvoltageParallelPN
4、JunctionsSincethecurrentflowingacrossaPNjunctionisproportionaltoitscross-sectionalarea,twoidenticalPNjunctionsconnectedinparallelacteffectivelyasasinglePNjunctionwithtwicethecross-sectionalarea,hencetwicethecurrent.SmallandLargeSignalModels-BasicConceptExampl
5、e:DiodeDCBiasCalculationsVx=1VConstant-VoltageDiodeModelforLarge-SignalAnalysisIfVD6、model:keypointsThisexampleshowsthesimplicityprovidedbyaconstant-voltagemodeloveranexponentialmodel.Usinganexponentialmodel,iterationisneededtosolveforcurrent.Usingaconstant-voltagemodel,onlylinearequationsneedtobesolved.Small-SignalAnalysisSmall-signalanalysi7、sisperformedataDCbiaspointbyperturbingthevoltagebyasmallamountandobservingtheresultinglinearcurrentperturbation.IftwopointsontheI-Vcurveareveryclose,thecurvein-betweenthesepointsiswellapproximatedbyastraightline:DiodeModelforSmall-SignalAnalysisSincethereisal8、inearrelationshipbetweenthesmall-signalcurrentandsmall-signalvoltageofadiode,thediodecanbeviewedasalinearresistorwhenonlysmallchangesinvoltageareofinterest.Small-SignalResistance(orDynami
6、model:keypointsThisexampleshowsthesimplicityprovidedbyaconstant-voltagemodeloveranexponentialmodel.Usinganexponentialmodel,iterationisneededtosolveforcurrent.Usingaconstant-voltagemodel,onlylinearequationsneedtobesolved.Small-SignalAnalysisSmall-signalanalysi
7、sisperformedataDCbiaspointbyperturbingthevoltagebyasmallamountandobservingtheresultinglinearcurrentperturbation.IftwopointsontheI-Vcurveareveryclose,thecurvein-betweenthesepointsiswellapproximatedbyastraightline:DiodeModelforSmall-SignalAnalysisSincethereisal
8、inearrelationshipbetweenthesmall-signalcurrentandsmall-signalvoltageofadiode,thediodecanbeviewedasalinearresistorwhenonlysmallchangesinvoltageareofinterest.Small-SignalResistance(orDynami
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