The first interview was personality-based. The second interview included some personality questions with a technical question or two. I had one second interview on campus and the other was via webcam.

It's not really the questions that are difficult; it's more about how aggressive they can be. However, people have received offers without answering correctly, so I'm guessing it depends on who interviews you.

What is the difference between a BJT and a MOSFET?

BJT has leakage current in the gate, however, I said MOSFET has infinite gate resistance and BJT has Rpi as the base resistance. This was considered incorrect.

What does this digital circuit do?

It was a DFF with Q* plugged into D, and Q is the output. It was a frequency divide by two system.

How to make sure voltage from the first system gets to the second system?

First system is plugged into the base of a BJT, and the collector is plugged into the second system. The answer was to add a pull-up resistance, which is VDD in series with a resistor, connected to the collector.

I gave plenty of working answers, but none were considered correct.