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Design and Implementation of VLSI Systems EN0160

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Design and Implementation of VLSI Systems EN0160

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    2. Lecture05: MOS transistor theory Last time Gate layouts and stick diagrams This time MOS transistor theory (ideal case)

    3. gate-oxide-body sandwich = capacitor

    4. The MOS transistor has three regions of operation Cut off Vgs < Vt

    5. How to calculate the current value? MOS structure looks like parallel plate capacitor while operating in inversion Gate – oxide – channel Qchannel = CV C = eoxWL/tox = CoxWL (where Cox=eox/tox) V = Vgc – Vt = (Vgs – Vds/2) – Vt

    6. Carrier velocity is a factor in determining the current Charge is carried by electrons Carrier velocity v proportional to lateral E-field between source and drain v = µE µ called mobility E = Vds/L Time for carrier to cross channel: t = L / v

    7. I=Q/t Now we know How much charge Qchannel is in the channel How much time t each carrier takes to cross

    8. In linear mode (Vgs > Vt & Vds < Vgs-Vt)

    9. In saturation mode (Vgs > Vt and Vds = Vgs-Vt)

    10. Operation modes summary

    11. PMOS is similar

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

    13. Inverter voltage transfer function

    14. Summary This lecture Ideal transistor modeling Next lecture Non ideal transistor modeling

    15. Inverter current transfer function

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