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prelim2

prelim2 - ECE 3150 2nd Prelim Exam April 7 2009 When you...

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ECE 3150 2 nd Prelim Exam April 7, 2009 When you are asked to explain a question briefly, I am only expecting 1-3 short sentences . Any wrong information you put down can be subject to point deduction, whether it is relevant to the question. For a NPN transistor in forward active, I E = I F0 (exp(V BE /V T ) – 1)(1+V CB /V A ) , where B i B n F N n W D qA I 2 0 2245 , V T = k B T/q , W B is the base width, N B is the base doping, D n is the electron diffusivity, and V A is the Early voltage. I E = I B + I C , I C = α I E = β I B . For nMOSFET with the threshold voltage V th , the drain current I D in the linear and saturation regions above threshold ( V GS > V th ) are: (notice that C ox μ ch = k n ) ( 29 ( 29 ( 29 saturation 2 2 linear 2 2 2 ' 2 2 ' 2 th GS Dsat DS OV n th GS ch ox D th GS Dsat DS DS DS th GS n DS DS th GS ch ox D V V V V V k L W V V C L W I V V V V V V V V k L W V V V V C L W I - = = - = - = < - - = - - = μ μ And in the saturation region, the quasi-static circuit model can be approximated as: For nMOSFET below the threshold voltage, ( 29 T th GS T DS V V V κ V V th D e e I L W I / / ) 1 ( 2 - - - = and ox si C C m + 2245 1 1 κ , where I th is the current at V GS =V th in the EKV model. The small signal parameters can be approximated as: g m = κ I D /V T , r o = V A /I D and A vo = κ V A /V T . CS CS with R S CG CD R in 1/g m + R L /A vo R out ( R L load) (r o ||R L ) (r o ||R L )+A vo R S (r o ||R L ) 1/g m || (r o ||R L ) A v ( R L load) - g m (r o ||R L ) - g m (r o ||R L )/(1+g m R S ) g m (r o ||R L ) 2245 1 MOSFET Diff pair operation range: OV id OV V v V 2 2 max , < < - , and the small signal transconductance gain at small v id can be evaluated from: = 2 id OVcm d v V I i .

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