This preview shows pages 1–3. Sign up to view the full content.
This preview has intentionally blurred sections. Sign up to view the full version.View Full Document
Unformatted text preview: ECE 3150 2 nd Prelim Exam Solution Spring, 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 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 = I E = 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 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 nMOSFET below the threshold voltage, ( 29 T th GS T DS V V V V V th D e e I L W I / / ) 1 ( 2--- = and ox si C C m + 2245 1 1 , 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 = 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 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 . For the 5-transistor differential amplifier with a current mirror active load, A vo = g mn (r on ||r op ) , similar to a single-stage CS amplifier. s A vo = g m r o = 2V A /V OV V A is the early voltage. +- v in r o g m v in v out +- D G S S 1 For all problems, we will use the CMOS parameters as k n = n C ox = 0.4mA/V 2 , k p = p C ox = 0.2mA/V 2 , V An =V Ap =20V, V thn =|V thp | = 0.5V, n = p = 0.6, I thn = 1 A and I thp = 0.5 A. V DD = 4V. 1. We will design CS amplifiers below with appropriate sizing. (a) Design a CS NMOS amplifier, complete with the PMOS current mirror with an I REF of 0.1mA (3 pts) . Make V OV of NMOS and PMOS the same, give the W/L for all transistors if the small- signal output resistance of this single-stage amplifier needs to be 10k and A v = 20. Box your answers (4 pts) . (b) With all the same design specifications, repeat (a) with PMOS amplifier and NMOS current mirror. Give the circuits and all transistor sizing (4 pts) . Is this amplifier inverting (1 pts) ?...
View Full Document
- Spring '07