Did you get as far as discussing what's happening with regard to the electric field near the gates of the transistors as they're switching or did you, perchance, skip a few levels of abstraction that you or the interviewers don't understand especially well?
I kept my answer to about five minutes, so no to the transistors, although I started with a switch closing in the mouse or keyboard, so I was able to give some sense of a lower level.
