# Design and Implementation of VLSI Systems (EN0160)

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Design and Implementation of VLSI Systems (EN0160). Sherief Reda Division of Engineering, Brown University Spring 2007. [sources: Weste/Addison Wesley – Rabaey Pearson]. Last time Gate layouts and stick diagrams This time MOS transistor theory (ideal case). - PowerPoint PPT Presentation

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• Design and Implementation of VLSI Systems(EN0160)Sherief RedaDivision of Engineering, Brown UniversitySpring 2007[sources: Weste/Addison Wesley Rabaey Pearson]

• Lecture05: MOS transistor theoryLast timeGate layouts and stick diagrams

This timeMOS transistor theory (ideal case)

• gate-oxide-body sandwich = capacitorOperating modes Accumulation Depletion InversionThe charge accumulated is proportional to the excess gate-channel voltage (Vgc-Vt)

• The MOS transistor has three regions of operationCut off Vgs < Vt

• How to calculate the current value?MOS structure looks like parallel plate capacitor while operating in inversionGate oxide channelQchannel = CVC = oxWL/tox = CoxWL (where Cox=ox/tox)V = Vgc Vt = (Vgs Vds/2) Vt

• Carrier velocity is a factor in determining the currentCharge is carried by electronsCarrier velocity v proportional to lateral E-field between source and drainv = E called mobilityE = Vds/LTime for carrier to cross channel:t = L / v

• I=Q/tNow we knowHow much charge Qchannel is in the channelHow much time t each carrier takes to cross

• In linear mode (Vgs > Vt & Vds < Vgs-Vt)For a given Vgs, Ids is proportional (linear) to Vds

• In saturation mode (Vgs > Vt and Vds Vgs-Vt)Now drain voltage no longer increases current

• Operation modes summary 0.6 micron process tox = 100 m = 350 cm2/V*s Vt = 0.7 V W/L = 4/2 l

• PMOS is similar

• What happens when we construct a INV (PMOS+NMOS)?

• Inverter voltage transfer functionABCED

• SummaryThis lectureIdeal transistor modeling

Next lectureNon ideal transistor modeling

• Inverter current transfer function

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