EE Interview Questions 3

Posted by bob on November 13, 2013

Here are four more questions, continuing our series of typical questions that an electrical engineering candidate might encounter.  It is fair to note that my experience and candidates were all in the area of digital/analog/microcomputer design and definitely not Power Engineers.

The question numbers are continued from the previous blog posts.

7)      We can have resistors with resistance (DC) from 0 ohms to millions of ohms.  Yet when we build a Printed Circuit Board (PCB) we typically only see trace impedances (AC) ranging from maybe 10 to 200 ohms.

  1. Why do we see such a limited range of impedance in our PCBs?
  2. What are the factors that control the characteristic impedance of a PCB trace?
  3. Which factor has the biggest direct effect on trace impedance?
  4. Why does anybody care what the impedance of a trace might be?

8)      In general terms, what is the advantage of a twisted pair of copper conductors as a transmission line?

  1. How is it different from two separate parallel wires?
  2. In what way might a coaxial (shielded) cable be better?

9)      Let’s assume you have something like a processor or system-on-a-chip.  We will call that IC1 and let’s suppose that the datasheet says we need 3 bypass capacitors on a particular power supply rail: a 47pF ceramic capacitor, a 100uF aluminum electrolytic capacitor, and a 0.1uF multilayer ceramic capacitor.

  1. Which capacitor do you want to place closest to IC1?
  2. Which capacitor do you place in the next closest position?
  3. Which capacitor do you place in the third closest position?
  4. Explain your choices; what are you trying to control here?

10)      The circuit below is typically called an emitter-follower circuit. 

  1. What is the primary advantage of a circuit like this?
  2. What is the typical voltage gain (Vout/Vin) of this circuit?
  3. What is the approximate input impedance seen at Vin?
  4. What is the approximate output impedance seen at Vout?

There you go.  Ten questions that might seem easy or might seem difficult.

Do you have a favorite interview question that somebody has asked you?

Comments and criticisms are always welcome.