[模拟cmos集成电路设计].design.of.analog.cmos.integrated.circuits.-.behzad.razavi

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1、Chapter2BasicMOSDevicePhysicsInstudyingthedesignofintegratedcircuits,oneoftwoextremeapproachescanbetaken:(1)beginwithquantummechanicsandunderstandsolid-statephysics,semiconductordevicephysics,devicemodeling,andfinallythedesignofcircuits;(2)treateachsemiconductor

2、deviceasablackboxwhosebehaviorisdescribedintermsofitsterminalvoltagesandcurrentsanddesigncircuitswithlittleattentiontotheinternaloperationofthedevice.Experienceshowsthatneitherapproachisoptimum.Inthefirstcase,thereadercannotseetherelevanceofallofthephysicstodesi

3、gningcircuits,andinthesecond,he/sheisconstantlymystifiedbythecontentsoftheblackbox.Intoday'sICindustry,asolidunderstandingofsemiconductordevicesisessential,moresoinanalogdesignthanindigitaldesignbecauseintheformer,transistorsarenotconsideredassimpleswitchesandma

4、nyoftheirsecond-ordereffectsdirectlyim-pacttheperformance.Furthermore,aseachnewgenerationofICtechnologiesscalesthedevices,theseeffectsbecomemoresignificant.Sincethedesignermustoftendecidewhicheffectscanbeneglectedinagivencircuit,insightintodeviceoperationprovesi

5、nvaluable.Inthischapter,westudythephysicsofMOSFETsatanelementarylevel,coveringthebareminimumthatisnecessaryforbasicanalogdesign.TheultimategoaIisstilltodevelopacircuitmodelforeachdevicebyformulatingitsoperation,butthisisac-complishedwithagoodunderstandingoftheun

6、derlyingprinciples.AfterstudyingmanyanalogcircuitsinChapters3through13andgainingmotivationforadeeperunderstandingofdevices,wereturntothesubjectinChapter16anddealwithotheraspectsofMOSoperation.WebeginourstudywiththestructureofMOStransistorsandderivetheirWchar-act

7、eristics.Next,wedescribesecond-ordereffectssuchasbodyeffect,channel-lengthmodulation,andsubthresholdconduction.WethenidentifytheparasiticcapacitancesofMOSFETs,deriveasmall-signalmodel,andpresentasimpleSPICEmodel.Weas-sumethatthereaderisfamiliarwithsuchbasicconce

8、ptsasdoping,mobility,andpnjunctions.