1Digital Integrated Circuits © Prentice Hall 1995InverterCMOS INVERTERDigital Integrated Circuits © Prentice Hall 1995InverterLast LectureMetrics for qualifying digital circuits»Cost» Reliability» Speed (delay)»Performance2Digital Integrated Circuits © Prentice Hall 1995InverterToday’s lectureThe CMOS inverter at a glanceAn MOS transistor model for manualanalysisThe VTC of the CMOS inverterDigital Integrated Circuits © Prentice Hall 1995InverterThe CMOS Inverter: A First GlanceVDDVinVoutCL3Digital Integrated Circuits © Prentice Hall 1995InverterCMOS InvertersPolysiliconInOutMetal1VDDGNDPMOSNMOS2λλλλDigital Integrated Circuits © Prentice Hall 1995InverterSwitch Model of CMOS TransistorRon|VGS|<|VT||VGS|>|VT||VGS|4Digital Integrated Circuits © Prentice Hall 1995InverterCMOS Inverter: Steady State ResponseVDDVDDVoutVoutVin=VDDVin=0RonRonVOH=VDDVOL=0VM=Ronp)f(Ronn,Digital Integrated Circuits © Prentice Hall 1995InverterCMOS Inverter: Transient ResponseVDDVoutVin=VDDRonCLtpHL= f(Ron.CL)=0.69RonCLtVoutVDDRonCL10.5ln(0.5)0.365Digital Integrated Circuits © Prentice Hall 1995InverterCMOS PropertiesFull rail-to-rail swingSymmetrical VTCPropagation delay function of loadcapacitance and resistance of transistorsNo static power dissipationDirect path current during switchingDigital Integrated Circuits © Prentice Hall 1995InverterThe MOS TransistorPolysiliconAluminum6Digital Integrated Circuits © Prentice Hall 1995InverterMOS Transistors -Types and SymbolsDSGDSGGSDDSGNMOSEnhancementNMOSPMOSDepletionEnhancementBNMOS withBulk ContactDigital Integrated Circuits © Prentice Hall 1995InverterThreshold Voltage: Conceptn+n+p-substrateDSGBVGS+-DepletionRegionn-channel7Digital Integrated Circuits © Prentice Hall 1995InverterThe Threshold VoltageDigital Integrated Circuits © Prentice Hall 1995InverterThe Body Effect-2.5 -2 -1.5 -1 -0.5 00.40.450.50.550.60.650.70.750.80.850.9VBS (V)VT (V)8Digital Integrated Circuits © Prentice Hall 1995Inverter0 0.5 1 1.5 2 2.50123456x 10-4VDS(V)ID(A)VGS= 2.5 VVGS= 2.0 VVGS= 1.5 VVGS= 1.0 VCurrent-Voltage RelationsA good ol’ transistorQuadraticRelationshipResistive SaturationVDS=VGS-VTDigital Integrated Circuits © Prentice Hall 1995InverterTransistor in Linearn+n+p-substrateDSGBVGSxLV(x)+–VDSIDMOS transistor and its bias conditions9Digital Integrated Circuits © Prentice Hall 1995InverterTransistor in Saturationn+n+SGVGSDVDS>VGS-VTVGS-VT+-Pinch-offDigital Integrated Circuits © Prentice Hall 1995InverterCurrent-Voltage RelationsLong-Channel Device10Digital Integrated Circuits © Prentice Hall 1995InverterA model for manual analysisDigital Integrated Circuits © Prentice Hall 1995InverterCurrent-Voltage RelationsThe Deep-Submicron EraLinearRelationship-4VDS(V)0 0.5 1 1.5 2 2.500.511.522.5x 10ID(A)VGS= 2.5 VVGS= 2.0 VVGS= 1.5 VVGS= 1.0 VEarly Saturation11Digital Integrated Circuits © Prentice Hall 1995InverterVelocity Saturationξ(V/µm)ξc= 1.5υn(m/s)υsat= 105Constant mobility (slope = µ)Constant velocityDigital Integrated Circuits © Prentice Hall 1995InverterPerspectiveIDLong-channel deviceShort-channel deviceVDSVDSATVGS-VTVGS = VDD12Digital Integrated Circuits © Prentice Hall 1995InverterIDversus VGS0 0.5 1 1.5 2 2.50123456x 10-4VGS(V)ID(A)0 0.5 1 1.5 2 2.500.511.522.5x 10-4VGS(V)ID(A)quadraticquadraticlinearLong ChannelShort ChannelDigital Integrated Circuits © Prentice Hall 1995InverterAunified modelfor manual analysisSDGB13Digital Integrated Circuits © Prentice Hall 1995InverterSimple Model versus SPICE0 0.5 1 1.5 2 2.500.511.522.5x 10-4VDS(V)ID(A)VelocitySaturatedLinearSaturatedVDSAT=VGTVDS=VDSATVDS=VGTDigital Integrated Circuits © Prentice Hall 1995InverterAPMOSTransistor-2.5 -2 -1.5 -1 -0.5 0-1-0.8-0.6-0.4-0.20x 10-4VDS(V)ID(A)Assume all variablesnegative!VGS = -1.0VVGS = -1.5VVGS = -2.0VVGS = -2.5V14Digital Integrated Circuits © Prentice Hall 1995InverterTransistor Modelfor Manual AnalysisDigital Integrated Circuits © Prentice Hall 1995InverterThe Transistor as a SwitchVGS ≥ VTRonSDIDVDSVGS=VDDVDD/2 VDDR0Rmid15Digital Integrated Circuits © Prentice Hall 1995InverterThe Transistor as a Switch0.5 1 1.5 2 2.501234567x 105VDD (V)Req (Ohm)Digital Integrated Circuits © Prentice Hall 1995InverterThe Transistor as a Switch16Digital Integrated Circuits © Prentice Hall 1995InverterThe Sub-Micron MOS TransistorThreshold VariationsSubthreshold ConductionParasitic ResistancesLatch-upDigital Integrated Circuits © Prentice Hall 1995InverterThreshold VariationsVTLLong-channel thresholdLow VDSthresholdThreshold as a function ofthe length (for lowVDS)Drain-induced barrier lowering(for low L)VDSVT17Digital Integrated Circuits © Prentice Hall 1995InverterSub-Threshold Conduction0 0.5 1 1.5 2 2.510-1210-1010-810-610-410-2VGS(V)ID(A)VTLinearExponentialQuadraticTypical values for S:60 .. 100 mV/decadeThe Slope FactorDigital Integrated Circuits © Prentice Hall 1995InverterParasitic ResistancesWLDDrainDraincontactPolysilicon gateDSGRSRDVGS,eff18Digital Integrated Circuits © Prentice Hall 1995InverterFuture Perspectives25 nm MOS transistor (Folded Channel)Digital Integrated Circuits © Prentice Hall 1995InverterVoltage TransferCharacteristic19Digital Integrated Circuits © Prentice Hall 1995InverterPMOS Load LinesVDSpIDpVGSp=-5VGSp=-2VDSpIDnVin=0Vin=3VoutIDnVin=0Vin=3Vin=VDD-VGSpIDn=-IDpVout=VDD-VDSpVoutIDnVin=VDD-VGSpIDn=-IDpVout=VDD-VDSpDigital Integrated Circuits © Prentice Hall 1995InverterCMOS Inverter Load CharacteristicsIn,pVin=5Vin=4Vin=3Vin=0Vin=1Vin=2NMOSPMOSVin=0Vin=1Vin=2Vin=3Vin=4Vin=4Vin=5Vin=2Vin=320Digital Integrated Circuits © Prentice Hall 1995InverterCMOS Inverter VTCVoutVin1234512345NMOS linPMOS offNMOS satPMOS satNMOS offPMOS linNMOS satPMOS linNMOS linPMOS satDigital Integrated Circuits © Prentice Hall 1995InverterSimulated VTC0.0 1.0 2.0 3.0 4.0
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