EEL3304: Exam 1

NAME:     February 5, 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.

WARNING: Sometimes you may be given numbers that you do not need.

Please show all of your work. You have exactly two hours for this exam. Good luck!

1. (40 points)

   

   1. (10 points) Derive assuming an ideal, infinite-gain opamp. Hint: you should get a single time-constant solution. Make sure that your answer makes sense for DC.

   2. (10 points) Sketch the magnitude of the frequency response vs.\ frequency (in Hz) for , , , and C=0.1nF. Be sure to include numerical values such as the DC gain and the 3dB point (in Hz).

   3. (10 points) If is a 1 Volt step input at t=0, write an expression for . Also, sketch . Label all interesting points on the graph.

   4. (10 points) If we assume that the op amp has a slew rate (SR) of . Again sketch . Label all interesting points on the graph.

2. (40 points)

   

   1. (20 points) Derive for all possible values of . Assume ideal operation of all diodes and opamps, and .

   2. (10 points) Sketch vs and label all important points and slopes.

   3. (10 points) Now use the diode plus battery model instead of the ideal diode. Assume a voltage drop of 0.7V for the forward biased diode. Sketch vs , label all important points and slopes.

3. (20 points) Answer each of the following with a few short sentences, derivation and/or sketch. There are four short answer problems.
   1. (5 points) Why do we use small signal analysis?
   2. (5 points) Assume a constant 0.7V is applied to forward bias a diode. As the temperature increases, will the current through the diode increase, decrease, or stay the same? Why?

   3. (5 points) Which circuit most likely has a higher input impedance: a circuit using an opamp in an inverting configuration or a noninverting configuration? Why?

   4. (5 points) Why do we typically want the output impedance of a circuit to be low? (Be clear! What exactly would the problem be if the output impedance was too high?)

4. (5 points) EXTRA CREDIT-No partial credit will be given.

   

   Sketch the vs transfer characteristic for the above circuit. Label all important numerical values on the graph. The op amp is infinite gain and ideal except it saturates at the power rails. and . Show all your work.