ogIC

Chapter1Devices-MOSFETVersion-II,2012, WhatisElectronic

Circuits(Netlist)=ElementsElementsordevices:PrimaryorBasicCellinthe元器件在電路中的基礎地位和決定性元器件的選擇+連接關系(結構)+參數(量化ElementsStructure&itsOperationStateSmall/Larger

Elements(

Active有源PN

Passive無源simplePassive:Twoterminals;linear;BiasingtoprovideactivedevicesoperationpointActive:ExceptDiode,threeormoreterminals(Why?)Staticbiasingnecessary,Generallynonlinear;Onlyactivedevicewithmorethantwoterminalscanbeusedamplifying,andseriousconditionsneededforlinear Passive:

,Ohmlaw:RL LR W 選擇電阻類型(結構/材料:RS),設計圖形Application,VtoBranchCircuitCurrentCurrentBasing.GoodinApplication,ItoCurrentCurrentVoltageBasing,Poorin

電阻自身的設簡單, 主要考慮在電路中的電流定義、電位調節，設定合適的工作點和匹配條 Passive:LinearCapacitance&

CCS

(W

Inductance:LLt tC和L功能上表現為對偶特

CdVC

L

Lagersignal& 描Smallsignal& 描

XC

XL電容上電壓不能突變,電壓電感上電流不能突變,電流紋

IC中至少C不可避免,電路頻時域大信號Start-upPulseOSCDelayDC Simplestactiveelement:PN PN/Diode--正向導通(電壓近似鉗位),反向截止直至擊穿電流性--擴散電流,I-V指數規律V-I對數率顯著非線性 )1] Vln(IPN S

S

SIS0反向飽和電流與反偏電壓無關,但隨PN結面積而增熱電壓,理想正溫度系數電

kT26mV@ 電 能Question:PN結在電路里有何具體應用直流 ，穩壓，鉗位，電平移位交流：低阻高頻極點、交流短路，結電容變容效應拓展應用：MOSDiode電流 Active:BipolarJunctionTransistor

結構兩個背靠背PN,發射結正偏集電結反偏三端口非線性電流性質:本質上仍是PN結電流!發射結正偏提供擴散電流Ie;基極復合形成IB；IBIE集電結反偏對Ie按比例收集,形成VCB正偏或零偏,收集系數隨偏壓線性變化導致IC隨反偏電壓線性變化

exp(VBEV CV CQuestion:畫出BJT輸出特性曲線,與MOS輸出特性比較形似而內在機制不同,應用可類比、借鑒

FourTerminals:Gate(G),Source(S),Drain(D),Substrate特點:PN結反偏天 橫向:對原理:柵壓(縱向電場)感應電荷，形成反型溝道、溝道電阻(開啟)漏壓(橫向電場)驅動溝道電阻,形成溝道電流;兩維電場增強型耗盡型本質強反型下為漂移電流定律成立(修正弱反型下為擴散電流； Dimension:WidthLengthRatio

工藝規范制造,設計確定形狀和尺PlateCap,Controlled

簡單看就是可變非線性 DeviceSymbol:two

VoltageControltype Currentdirectiontype Substrate-ReverseBiased,抑制襯底PN結電流P:方向向外;N:DefinitionDrain& Source:提供載流子;Drain:收集載流Circuit(CurrentPMOS:s/bulk,high,NMOS:s/bulk,

NMOS:DtoPMOS:StoDrain:N/PMOS

DCI-Vequationsindifferentregion;DCParametersinMOSFET.

DCCurrent:InducedCharger ChargerinChannelinducedbyGateVoltage(dxwithVx

Vx

LinearapproximationofVxaroundxVx ,dxLx

0;

TotalQinvinChannelinducedbyFieldL dQ

VDS

V)WL

VGDVTH xC )1 x

VGS

DCCurrentindifferent

ElectricalFiled,mobility

tL,

ELDrift

EQinvVDS

inv

LinearCurrent,

W 1V2 kCox kk'(W VGS 過驅 k(V 1V2

導通電阻 (on)VDS

k線性電流飽和漏

1k2, DS

Process/Gaink

Width-LengthW/

Overdrive

Threshold襯底偏置AC:背柵

VTHVTHVTH0 2f2q2f2q0Si

2/2Explain:Usuallyinversebiased,NMOS:VBS<0;PMOS:溝道調制效

1k2(1 ), ,

MOSFET更關注在飽和恒流區的應用-不可替代 溝道調制效應–對飽和漏電流修

LLL(1L)L(1 等效W/L

(W W(1 )W(1VDS L(1 引入溝道調制系數,理想等效厄利電壓V,理想V

1,

A(W

1k2(1 )

1k2(1VDSA DS A實際輸出電流與VGS,VDS兩種電壓均有關;VGS(主控),VDS(輔控 非線性

Operationregion

工作區域的限定與兩VGS:截止-弱反型(亞閾)-過渡-強反型；VDS:線性-過渡-D端溝道未夾斷,VGD=VG-VD=VGS- 飽和恒D端溝道夾斷VGDVTHVDSVGS-VTHVDSVDS到達臨界點后,多余VDS降落在漏漏耗盡層中,溝道電阻形狀不變,漏收集電流系數飽和為1,電流近似恒定.

OverdriveVoltage

飽和

1

2IDSk2IDSkQuestion:=0時電流IDS=0或者說,強反型飽和電流模型在當IDS0時,一定可進入弱反型亞進入過渡區和亞閾區后,可使0甚至<0Question:如何判斷在弱反型下的漏飽和恒流臨界條件

SubthresholdorWeak -100mV左兩種電流成份并存:VGS感應的載流子梯度形成VDS橫向電場驅動形成漂 exp(VGSVTH)[1exp(VDS 當VDS>>3VT時,濃度梯度大,但載流子總量小，擴達到輸出電流飽和條件 柵控電壓調制為主的擴散電流分

)Iexp(VGS D

SimilartoBJT,亞閾的MOSFET可視為BJT(I-V功能特性)觀特征:電流小,或小電流易工作WI區,n>1亞閾斜率

ACRelated&ComefromDCACParametersinMOSFET:Small

AC

ACparametersarederivedbyDCI-V AC:gm&柵壓、漏壓對輸出小

io1

線性

@

Constan

d d

@VGSConstan

io

線性疊交流參數與直流I-V方程有關,由直流工作點定義最關心飽和區的交流參數 存在gm和gd的非對稱,可放大?

gm&gdunbalancedforpossible

gm(SI)k

2I

k

I

1

&

大信號下一定產生非Whatis

/2

VA0L 高

IDS

恒流信號放大:定性/定量

io

gmgd

gm/

Review:MOSFETOperation Digital:x-yTurn-on；Cut-yx

og:x-y第一象Turn-CurrentVoltageStrong/Weak og:R,ConstantI,Constant

MOSDiode:VoltageSource 飽和/線性臨界線右平移類似PN結I-V定T T

r1

低

gm

恒壓 VDSVGS1

m m

輸出阻抗轉變恒流恒壓o oSmallSignalEquivalent 低頻等效電路,忽略電容柵-源電柵-漏覆蓋(Miller)電容漏-源輸出(負載)電容MOSDiode:G-D短路,gmVgs=gmVds受控源等效1/gm總輸出導納gT=gm+gd,總輸出阻抗Question:IsLreductionreallybenefit ogNegative:LroGainPositive:LCgsfT

io Vgs

小尺寸,精度

fT

Twotransistors:Parallel&

(W

(L

)M1L

L)M

(W/ (W/同類MOS串、

Large

M M

Exe:利用等效W/L,判斷MA,MB狀態Result:MB:Saturation;MA: 定義法證明,或復合管等效W/L法證明Alwaystruewithoutrelatedwithtwo復合管:一個MOS管拆分為若圖形尺寸效應:W/L相同的復合管和單有差異！W/L相同但W,L不同的單管有差異 Discussion:Operationstatues

HowcanaMOSFETinCircuitwithazeroCut-off,VGS<<VTH,SwitchTurn-on,VGS>VTH,VDS=0,similarasRwithThesaturatedcurrentisalwayslargerthanthelinearcurrentTrue,ifVGSfortwotransistorsaretheUncertain,ifVGSfortwoMOSFETsaredifferent,ThelinearcurrentwithlargeVGSmaybelargerthanthatthesaturatedcurrentwithsmallVGS.Thetransistorwithsmallcurrent(suchas0.1uA)isalwaysinW.I.No,W/Lshouldbeconsidered,smallW/LresultinalargeevenwhenIDSissmall,thusstillinS.I.;ForaparticularW/L,theMOSFETcanmoreenteringintoW.I.whenIDSis

UniqueI-VmodelofMOSFETinAll

1k'WV

1n

WV S

ox IDS<<IS0,說明<<VT,進入弱反型，否則強反型,附近為過度區,統一的端口歸一化電流模型,與夾斷電壓Vp,溝道電位VD或VSf(r {1f(r

VS(D)

VGn

亞閾斜輸出

IFIRIS0(ifir

電流相減的物理依據和好處適合各個偏置工作區域,與原獨立模型

數學近似

1if(r1if(r

VS(D)

11if1ir1i1lnxSVDS, 1i1

x

Vx1if1V ln[11if1V

1 ln1 1,

VxVSor ln1if1if1iR

ln

VS,

Sd Sd

ln[1xS]ln[1xd

ln VplnxSVDS,

統一模型的應用：跨導gm,輸出導納

11if(rgmS(d

2IF(

2IS0

1if(r1if(r 2IS0

VpVS)]2IS0

nk

2kI 2kI 2IS0ln[1exp(VpVS)]2IS0exp(Vp) i

2ISir

)0

,g -

2VDSISV 強反型線V

T

統一模型的應

1if11if

VpVS)]Vp

if>>1,強反

Vp-

V

V

1ifDS 1ifif<<1,弱反

1ln[1exp(VpVS)]exp(VpVS)1i1iV-V 1111 1]

1] )[1exp(DS 根據exp(-VDS/VT)==1/A的飽和條

VlnVln

1

1](2

1i1i反1i1i

1/AgmS/

Whatto MOSFETStructureisdefinedbyProcessOnlytodesignbothinparameterandstructureParameter:W/L,andW,Application:ConnectionofterminalswithinorbetweenMaindeviceandcircuit靜態工作點IDS

VGS

VDS阻抗參

,1/圖形參 W/工藝參 k頻率參

W

1

SPICEModel,HandCalculation&

Level1~3

k’,VTH,(VA),,n, --模擬電路性能與采用的工藝密切相關,同一工藝也有參數工藝角:N-PMOS(tt,ss,ff,sf, R(typical,slow,

仿真技術很DC直流工作AC交流小信號(頻率瞬態、噪聲特性匹配失調,仿真精度

ComparisonofMOS&

CurrentControlCurrentSourceLargeoutputcurrentdrivingcapability,greatFastspeedduetoandhighgmandlargecurrent VoltageControlCurrentSource(VCCS)Lowvoltage&lowpowerconsumptionHighintegration(gm

(gm

(gm/IC

(1/ / /

DS Although(gm/I)MOSinW.I.isthesameasthatofBJT,butthecurrentIislimited(cannotbetoolarge),sothatgmforMOSisremainlower,andinhighcurrentthecurrentefficientisseriouslyreduced.

DC:I-Vcharacter,Non-linearBehavior;Determinedtheoperationpoint.AC:smallsignalcharacter,gm,gd,rd,LinearCompletedthelinearForsmallsignal,MOStreatedaslinearwhichisDCpointForlargersignal,MOStreatedasnon-linearnoneedforoperationDigital:Largersignalnon-linear,anykind