1Digital Integrated Circuits © Prentice Hall 1999InverterVoltage TransferCharacteristicDigital Integrated Circuits © Prentice Hall 1999InverterPMOS Load LinesVDSpIDpVGSp=-5VGSp=-2VDSpIDnVin=0Vin=3VoutIDnVin=0Vin=3Vin = VDD-VGSpIDn = - IDpVout = VDD-VDSpVoutIDnVin = VDD-VGSpIDn = - IDpVout = VDD-VDSp2Digital Integrated Circuits © Prentice Hall 1999InverterCMOS Inverter Load CharacteristicsIDnVoutVin = 2.5Vin = 2Vin = 1.5Vin = 0Vin = 0.5Vin = 1NMOSVin = 0Vin = 0.5Vin = 1Vin = 1.5Vin = 2Vin = 2.5Vin = 1Vin = 1.5PMOSDigital Integrated Circuits © Prentice Hall 1999InverterCMOS Inverter VTCVoutVin0.5 1 1.5 2 2.50.5 1 1.5 2 2.5NMOS resPMOS offNMOS satPMOS satNMOS offPMOS resNMOS satPMOS resNMOS resPMOS sat3Digital Integrated Circuits © Prentice Hall 1999InverterSwitching Threshold as afunction of Transistor Ratio1001010.80.911.11.21.31.41.51.61.71.8MV (V)Wp/WnDigital Integrated Circuits © Prentice Hall 1999InverterDetermining VIH and VILVOHVOLVinVoutVMVILVIHA simplified approach4Digital Integrated Circuits © Prentice Hall 1999InverterInverter Gain0 0.5 1 1.5 2 2.5-18-16-14-12-10-8-6-4-20Vin (V)gainDigital Integrated Circuits © Prentice Hall 1999InverterGain as a function of VDD0 0.05 0.1 0.15 0.200.050.10.150.2Vin (V)Vout (V)0 0.5 1 1.5 2 2.500.511.522.5Vin (V)Vout(V)Gain=-15Digital Integrated Circuits © Prentice Hall 1999InverterSimulated VTC0 0.5 1 1.5 2 2.500.511.522.5Vin (V)Vout(V)Digital Integrated Circuits © Prentice Hall 1999InverterImpact of Process Variations0 0.5 1 1.5 2 2.500.511.522.5Vin (V)Vout(V)Good PMOSBad NMOSGood NMOSBad PMOSNominal6Digital Integrated Circuits © Prentice Hall 1999InverterPropagation DelayDigital Integrated Circuits © Prentice Hall 1999InverterCMOS Inverter Propagation DelayApproach 1VDDVoutVin = VDDCLIavtpHL = CL Vswing/2IavCLkn VDD~7Digital Integrated Circuits © Prentice Hall 1999InverterCMOS Inverter Propagation DelayApproach 2VDDVoutVin = VDDRonCLtpHL = f(Ron.CL)= 0.69 RonCLtVoutVDDRonCL10.5ln(0.5)0.36Digital Integrated Circuits © Prentice Hall 1999InverterDynamic Behavior of MOS TransistorDSGBCGDCGSCSBCDBCGB8Digital Integrated Circuits © Prentice Hall 1999InverterThe Gate CapacitanceDigital Integrated Circuits © Prentice Hall 1999InverterGate CapacitanceSDGCGCSDGCGCSDGCGCCut-offResistive SaturationMost important regions in digital design: saturation and cut-off9Digital Integrated Circuits © Prentice Hall 1999InverterGate CapacitanceWLCoxWLCox22WLCox3CGCCGCSVDS/(VGS-VT)CGCD0 1CGCCGCS = CGCDCGCBWLCoxWLCox2VGSCapacitance as a function of VGS(with VDS = 0)Capacitance as a function of the degree of saturationDigital Integrated Circuits © Prentice Hall 1999InverterDiffusion Capacitance10Digital Integrated Circuits © Prentice Hall 1999InverterJunction CapacitanceDigital Integrated Circuits © Prentice Hall 1999InverterLinearizing the Junction CapacitanceReplace non-linear capacitance bylarge-signal equivalent linear capacitancewhich displaces equal charge over voltage swing of interest11Digital Integrated Circuits © Prentice Hall 1999InverterCapacitances in 0.25 µmCMOS processDigital Integrated Circuits © Prentice Hall 1999InverterComputing the CapacitancesVDDVDDVinVoutM1M2M3M4Cdb2Cdb1Cgd12CwCg4Cg3Vout2FanoutInterconnectVoutVinCLSimplifiedModel12Digital Integrated Circuits © Prentice Hall 1999InverterThe Miller EffectVinM1Cgd1Vout∆V∆VVinM1Vout∆V∆V2Cgd1“A capacitor experiencing identical but opposite voltage swings at both its terminals can be replaced by a capacitor to ground, whose value is two times the original value.”Digital Integrated Circuits © Prentice Hall 1999InverterCMOS InvertersPolysiliconInOutMetal1VDDGNDPMOSNMOS1.2 µm=2λ13Digital Integrated Circuits © Prentice Hall 1999InverterComputing the
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