prelim207 - ECE 315 2 nd Prelim Exam November 13, 2007 When...

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Unformatted text preview: ECE 315 2 nd Prelim Exam November 13, 2007 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 bipolar junction diode, I D = I (exp(V D /V T ) 1) , with + = D i p p A i n n N n L D N n L D qA I 2 2 and V T = k B T/q . The minority injection level at the edge of the depletion region can be approximated by p n = p n0 exp( V D /V T ), which is valid for both forward and reverse biases. 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 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- = =- =- = < -- = -- = And in the saturation region, the quasi-static circuit model can be approximated as: For V GS < V th , if V DS > 3V T , ( 29 ( 29 T th GS th D V V V I I / exp- 2245 , where I th is the current at V GS =V th in EKV model. V T is the thermal voltage at 26mV at room temperature. The small signal parameters can be approximated as: g m = I D /V T , r o = V A /I D and A vo = 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 For a CS amplifier with a R L and C L load and an input resistance of R sig , the time constant can be estimated by R sig (C gs + (1+A v )C gd ) + (R L ||r o ) C L ....
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prelim207 - ECE 315 2 nd Prelim Exam November 13, 2007 When...

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