Nov 20 2008
Moment of truth is tomorrow
I will find out whether or not I passed my qual tomorrow. For most people, in this two week window when you take your qual, it does not matter when you take your qual, you will still be freaking out because you don’t find out if you passed until it’s all over. So if you were one of the first ones to take it, you’d have to wait a whole two weeks to find out whether or not you passed. If you took it on the very last day, you would find out the next day, but you would have been waiting this whole time to take your qual and you just want to get it over with.
During the time between after you take your qual and when you find out, you may over analyze things that you or your committee may have said. Here’s one example…I just derived rpi for a BJT and it is beta/gm.
Prof: Is beta a small signal parameter or a large signal parameter?
Me: Hmm, good question. Pause. I believe it is small signal.
Prof: But if it were small signal, doesn’t that mean that…I don’t remember what he said.
Me: Hmm. strange. Give me a few more seconds to think about it. Yeah, you are right, it is large signal.
Prof: What?!
Aw crud, is beta small signal?
Me: Okay okay hold on. Uh.
Prof: Nevermind. Next question.
You see, that was not good. Seriously, that kind of sucked. How could I not know if beta is a small signal parameter or a large signal parameter? Why did he say nevermind? Did he conclude that it’s game over for me and decided to move on? I shrugged it off. But when I went back to my office, I told my officemates what had happened and we debated it.
Me: So is beta small signal or large signal?
Grad student #1: It’s small signal, man.
Me: Oh, I guess I was right. He tricked me. But no, it can’t be small signal.
Grad student #2: No, it’s small signal.
Me: If beta is small signal, then what is the collector current if I know the base current? Isn’t it beta times Ib?
Grad student #2: I don’t know what it is, but I know that beta is small signal.
Me: No, that’s bogus, look here in this device physics textbook, beta = IC/IB. Capital letters. This thing is large signal.
Grad student #1: Look, what’s the gm of a MOS? It consists of large signal parameters but gm is a small signal parameter?
Me: Dude man, of course small signal parameters consist of large signal parameters. All of them are like that. But just because something consists of large signal parameters does not mean it is small signal.
Then all of a sudden it made sense why that prof said nevermind. Beta is both small signal and large signal, just as the small signal model of a resistor is the same as the large signal model of a resistor. That prof did not want to continue to press the question because it would only make him look like a fool.
As for wondering if I passed, I am fairly certain that I did, but for these kind of things, you just never know for sure. All I know is that I did not have any major missteps during my qual but ultimately the decision is not mine. I feel pretty good about it, but I am not celebrating yet. I will say that I’ve been sleeping well and I have very little doubt that I passed. Given what I know, I’d place my odds of failing at 9 to 1 against. Something crazy had to have happened in order for me to fail. Perhaps they hated my qual paper and thought it was trash. Or maybe I unknowingly pissed one of my committee members off.