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Unformatted text preview: 6.012 - Electronic Devices and Circuits Lecture 13 - Large-Signal Models - Outline Announcements Handout - Lecture Outline and Summary Review MOSFET model: gradual channel approximation iD { 0 )2 /2a K (vGS VT K (vGS VT avDS/2)vDS for for for (Example: n-MOS) (vGS VT)/a 0 vDS (cutoff) 0 (vGS VT)/a vDS (saturation) 0 vDS (vGS VT)/a (linear) with K (W/L)eCox*, VT = VFB 2fp-Si + [2eSi qNA(|2fp-Si| vBS)]1/2/Cox* and a = 1 + [(eSi qNA/2(|2fp-Si| vBS)]1/2 /Cox (frequently a 1) Comparison of MOSFET and BJT models and characteristics Refined device models Charge stores: 1. Junction diodes 2. BJTs 3. MOSFETs The Early Effect: 1. Base-width modulation in BJTs: wB(vCE) 2. Channel-length modulation in MOSFETs: L(vDS) Extrinsic parasitics: Lead resistances, capacitances, and inductances Clif Fonstad, 10/03 Lecture 13 - Slide 1 The gradual channel approximation - review Electrostatics problem in x-direction to find qn*(y) as a function of vGS, vBS, and vCS(y) Drift problem in y-direction to relate iD to vGS, vDS, and vBS S n+ 0 vGS 0 G + iG vDS D iD n+ x p-Si vBS + B iB L y iD (vGS ,v DS ,v BS ) = W v * me Cox vGS - VT (v BS ) - a DS v DS L 2 iD inc. vGS When vDS reaches (vGS - VT)/a, the channel vanish...
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This note was uploaded on 07/20/2009 for the course CSAIL 6.012 taught by Professor Prof.cliftonfonstadjr. during the Fall '03 term at MIT.

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