Remember basic transistor physics? Let's see if you really do.
I've often railed on these pages about how the de-emphasis of basic engineering fundamentals such as physics, including semiconductor physics, has damaged undergraduate EE students. This quiz is to show you that, if you had the benefit of such courses, you were paying attention, and learned more as you progressed in your career, if that path included circuit design.
Most of the questions shouldn't require any calculation other than mental arithmetic to come up with the correct answer in a matter of seconds.
If you never got to design any real-world transistor circuits, it's likely that you will have some difficulty. Remember, all answers only need to be within "engineering accuracy," that is, within 1% or so. I've used this as my favorite interview question for many years for anyone claiming extensive bipolar junction transistor (BJT) circuit design experience. I've also turned the tables, and (at the end of the interview) asked the person interviewing me these same questions. Hint: The Diode Equation is the key!
All of the questions relate to the simple circuit in the schematic below. Assume no loading of the output and C1 is large (e.g., treat as an AC short circuit). Ambient temperature is 25°C. Q1 is a silicon BJT (2N3904). The schematic appears on all question pages so you won’t have to keep jumping back to see it. Answers appear on the last page.
1. The DC voltage at Vout is 11.0 VDC. What is the small-signal mid-band AC gain?
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