NSUB_Calculation

NSUB_Calculation - Square law model with channel length mod...

Info iconThis preview shows pages 1–9. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Square law model with channel length mod µn Cox W ID = (VG S Vt )2 1 + n 2 L 24443 1444 4 4 ID s at [ (VDS Vef f )] ID-sat term (at pinchoff) + "extra" Square law model with channel length modulation µn Cox W 2 ID = VG S Vt ) 1 + ( n 2 L 24443 1444 4 4 I D sat [ (VDS Vef f )] • Fractional extra part is (VDS-Veff) • Meaning of : Fractional change in current ID per volt change in VDS • Problem: depends on L – Want parameter for SPICE model that works for all L What causes change? Where does come from? • Change in effective channel length L • One way to reduce : longer L • Change L represents smaller fraction Revisit modified square law VDS L ID ID = µ n Cox W 2 VG S Vtn ) ( 2 L µ n Cox W 2 ID + ID = (VG S Vtn ) L 2 L ID VDS ID Revisit modified square law • Rewrite in fractional change terms • Use 1 1 x 1+ x ID 1+ ID µ n Cox = ID 1+ ID 2 W L1 L L (VG S Vtn ) 2 (small x) • Relate L to known L; measured ID; change in ID µC W ID L 2 = n ox (VG S Vtn ) 1+ ID L 12 L 2444 444 3 ID L=L ID ID L also given by semiconductor physics ... • Voltage drop VDS across depleted region L with doping density NSUB • Equate L L= 2K S 0 VD S qN SU B ID 2K S 0 VDS = ID qN SU B NSUB NSUB parameter for SPICE • Solve for NSUB N SU B = 2K S 0 VDS 2 ID qL ID • KS Silicon dielectric constant 1 .8 1 • NSUB Substrate doping units / 3 cm Sanity check 1 1 to 1 1 / 3 : E+ 4 E+ 7 cm • VDS from activetriode edge to “large” VDS • Caution:consistent length units on L, NSUB, 0 Example VDS-ID data from lab for P-channel MOSFET: Example: Calculate NSUB ID VDS N SU B = 2(11.)(88 8 .5E 12)(1.3V ) 9 2 6E (1. 19) (1E 6) 4 µA 8 50 0 µA 3 = 2.3E + 21 [ m 7 3 N SU B = 2.73E + 21[ m = 2.73E + 15[cm ] 3 • For CD4007, L = 10µm = 1.0E-5m • VDS for largest VDS data point – Minimize effect of measurement error ...
View Full Document

This note was uploaded on 10/13/2009 for the course ECE 4902 taught by Professor Mcneill during the Spring '01 term at WPI.

Page1 / 9

NSUB_Calculation - Square law model with channel length mod...

This preview shows document pages 1 - 9. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online