EEL3304: Exam 2

NAME:     March 19, 1997

This exam is open-book, open-notes, and open-calculator. There are three problems and one extra credit problem on this exam. Make sure you completely finish the first three problems before you start the extra credit.

Make sure you fill in the blanks with your final numerical answers (with proper units!) and make sure that all of your work is shown. You have exactly two hours for this exam. Good luck!

1. (40 points) Answer the following questions assuming that the transistor is biased in the active region ( V) and has a large . As usual, , , and are small ac signals. Use the following component values: , , , , and F.
   1. (15 points) Compute the DC operating point assuming that .

      Answer summary:
      
      

      
      

      
      

      
      

      
      

      
      

      

   2. (5 points) Compute and for this operating point.

                   
      

   3. (5 points) Draw the complete small signal model. (Assume is large for all of the parts of this problem).

   4. (5 points) Find the small signal gain / .

      
      

   5. (5 points) Find the input resistance .

      
      

   6. (5 points) Find the small signal gain / .

      
      

2. (40 points) For the MOS transistor, assume that , and is very large.
   1. (15 points) Compute the DC operating point for the MOSFET

      Answer summary:

      
      

      
      

      
      

      
      

   2. (5 points) Compute .

      
      

   3. (5 points) Draw the small signal model. Do not include -assume that is large for all of the parts of this problem.

   4. (5 points) Compute the gain .

      
      

   5. (5 points) Find the input resistance .

      
      

   6. (5 points) Find the output resistance . As usual, do not include the load resistor in your calculation.

      
      

3. (20 points) Short answer
   1. (5 points) Sketch a transistor current-voltage characteristic that defines graphically. Don't forget to label each axis.

   2. (5 points) Sketch a transistor current-voltage characteristic that defines graphically. Don't forget to label each axis.

   3. (5 points) Which of the following amplifiers typically has a higher voltage gain when biased to the same current level: a common source MOS amplifier or a common emitter BJT amplifier? Why?
   4. (5 points) Which of the following amplifiers typically has a higher input impedance when biased to the same current level: a common source MOS amplifier or a common emitter BJT amplifier? Why?

4. Extra Credit (5 points) Derive an analytic expression for the input impedance of the following circuit. You cannot neglect but assume that .

   

   (analytic expression)