Berkeley ELENG 105 - Lecture 14 (9 pages)

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Lecture 14



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Lecture 14

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Pages:
9
School:
University of California, Berkeley
Course:
Eleng 105 - Microelectronic Devices and Circuits
Microelectronic Devices and Circuits Documents

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EECS 105 Fall 2001 Lecture 14 R T Howe Lecture 14 Last time MOS field effect transistor MOSFET currentvoltage characteristics Today Square law MOSFET model Linear MOSFET model Dept of EECS University of California at Berkeley EECS 105 Fall 2001 Lecture 14 R T Howe Finding ID f VGS VDS Approximate inversion charge QN y drain is higher than the source less charge at drain end of channel Dept of EECS University of California at Berkeley EECS 105 Fall 2001 Lecture 14 R T Howe Inversion Charge Q N y Q N y 0 Q N y L QN y 0 Cox VGS VTn Average inversion charge QN y L Cox VGD VTn VGD VGS VDS Dept of EECS University of California at Berkeley EECS 105 Fall 2001 Lecture 14 R T Howe Drift Velocity and Drain Current Long channel assumption use mobility to find v v y n E y n V y nVDS L Substituting I D WvQN Dept of EECS University of California at Berkeley EECS 105 Fall 2001 Lecture 14 R T Howe Square Law Characteristics Boundary what is ID SAT Dept of EECS University of California at Berkeley EECS 105 Fall 2001 Lecture 14 R T Howe The Saturation Region When VDS VGS VTn there isn t any inversion charge at the drain according to our simplistic model Why do curves flatten out Dept of EECS University of California at Berkeley EECS 105 Fall 2001 Lecture 14 R T Howe Square Law Current in Saturation Current stays at maximum where VDS VGS VTn VDS SAT ID Measurement ID increases slightly with increasing VDS model with linear fudge factor ID SAT Dept of EECS University of California at Berkeley EECS 105 Fall 2001 Lecture 14 R T Howe Linear MOSFET Model Channel inversion charge neglect reduction at drain Velocity saturation defines VDS SAT Esat L constant Drain current vsat n I D SAT WvQN W vsat Cox VGS VTn Esat 104 V cm L 0 12 m VDS SAT 0 12 V Dept of EECS University of California at Berkeley EECS 105 Fall 2001 Lecture 14 R T Howe Linear MOSFET in Saturation I D SAT vsatWCox VGS VTn 1 nVDS Implication of weaker dependence on VGS Dept of EECS University of California at Berkeley



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