Homework Assignment #4

EE 477 Spring 2013 Professor Parker

Hardcopies due in the course boxes on the third floor of EEB 10 AM 2/25/13

Ecopies due 10 AM 2/25/13 using the "Assignment" Function on DEN

Solution will be posted at 4 PM Monday so you can review it before the Tues. Midterm

Assume for the problems below that V_dd = 1.8 v, V_tp0 is -.7 v. and V_tn0 is .7 V. V_tpbodyeffect is -.9 v. and V_tnbodyeffect is .9 V.

Assume ß_n (k_n)= 219.4 W/L µ A(microamps)/V² and ß_p (k_p)= 51 W/L µ A/V²

1. a) (15 %) Why is it important to have the PMOS and NMOS transistor betas in an inverter close to equal? Give two main reasons.

b) (5 %) What is the main reason larger chips (dies) are more expensive than smaller ones?

2. (10 %) Assume that an inverter is on segment B of the input/output transfer curve. If V_in = 0.8V, what is the minimum value of V_out that would allow the inverter to remain in the B segment after reaching steady state?

3. (10%) Now assume that an inverter is on segment E of the input/output transfer curve. Assume beta_n = beta_p. The input voltage is V_in = 1.2V. Show that the PMOS transistor is in cutoff. What is the maximum output voltage V_out that would allow the inverter to remain in segment E?

4. (10%) Why does the NMOS transistor output a weak 1 when used as a pass transistor?

5. a) (10%) An inverter has the transistors sized so that as the input falls from Vdd to Gnd, a current spike occurs when V_in = 0.85V. What is the ratio of beta_p to beta_n ?

b) (10%) What are the dimensions of the PMOS transistor in this inverter if the NMOS transistor is unit size?

6. (15%) Assume an inverter is on segment D of the input/output transfer curve. If the ratio of beta_p to beta_n = 2, what is the minimum value of V_in that would allow the inverter to remain in segment D?

7. (7%) Explain why there is a design rule for poly gate extension. What can happen if this rule is violated?

8. (8 %) Draw the shape of the channel of a PMOS transistor operating in saturation. Why is the channel in this shape?