EE Interview Questions 1

Posted by bob on November 13, 2013

Here are a couple of typical interview questions I might ask an electrical engineering candidate during a job interview.  Before we get started on my questions, it is normal for me to run through the candidate's resume and ask a few questions about the experiences they have had previously.  This allows the candidate to talk about things in which they should have some confidence.  I would probably tell the candidate that there is not necessarily a single "right" (correct) answer to any of my technical questions.  Indeed, the questions tend to be somewhat open-ended and are designed to let me understand what kinds of problems and solutions this candidate has already encountered.

One of my favorite warm-up exercises is simply to show the candidate a circuit board or collection of parts that I have been working with recently.  I will ask them to tell me what they see.  The idea here is simply to get a quick understanding of the electrical parts they recognize.  Even very inexperienced engineers will quickly identify some ICs, resistors, capacitors, (some) inductors, and major groupings such as power supplies.  Some parts such as thin-film resistor networks might not be so easily identified.

Then it is time to start sketching stuff on blank paper.

1)      Let’s suppose you have a basic embedded microprocessor (microcontroller) system that includes a main chip (processor/controller,) a flash EPROM, a RAM, and some I/O devices.  You have already loaded the EPROM with code, but the system does not appear to be running when you power it up.  (It does not do what you expect it to do.) 

  1. Where do you start debugging?  (What things do you check first?) 
  2. Why do you look at these things first?
  3. If these things all seem perfect, where do you look next?

2)      Now let’s look at the signals between this processor and the read/write (RAM) memory connected to that processor.  We will assume that there are some address lines, some data lines, and some control lines.  The datasheets for the processor and memory show a control line (perhaps something like a Chip Select, a Write Strobe, or a Row Address Strobe (something like CS, WR, RAS).  Those datasheets show nice, perfect waveforms like the example shown below.

But we know from real life and looking at oscilloscope images, waveforms are never this clean. 

  1. What might you expect this waveform to really look like on your oscilloscope? 
  2. What kinds of signal problems can we expect to find in most systems? 
  3. As you show each change-from-perfect, explain what can cause that particular impairment to happen to our signal.






(Draw your waveform above here, showing the various problems (impairments) that happen to real signals.)


3)      Okay, we have talked about some signal impairments (meaning signal integrity problems) that can happen to our control signal waveform between these two devices.

  1. What is the simplest change I can make to a circuit to improve the signal integrity? 
  2. Why (or how) does this work? 
  3. What are other, more complicated methods we could use? 
  4. What are the worst things we might do here?

So there are three questions.  Was that so bad?  The responses you might give are intended to give me a quick idea of how much of this work you have done or seen before.  It also tends to reveal if you know how to "show your work" while sketching and talking about an idea.

Remember, this is just an opportunity to test yourself against some arbitrary questions.  If you don't understand what I am getting at for any question, then it is time to do a little research and then discuss your ideas with a fellow student or coworker.  But please don't email me and ask for "the answers."  (See my previous rant.)