Difficulty using Q(Tg) for NISM on DC-DC POL's where impedance peak is <~30mOhm
In Welcome to the Forum
Jun 29, 2022
Thanks for the feedback, so I guess I have some follow-up questions. So from my understanding, the Q(Tg) plot is essentially related to the S21 magnitude by some derivative. This means that the tiny, but sharp, blips in the impedance are responsible for the massive Q(Tg) spikes. In general, I noticed that as I increased the number of points in my measurement, the more definition these blips got, the sharper they would get as well, resulting in increasingly large Q(Tg) peaks. I also notice that these blips shift around from measurement-to-measurement, my main suspicion is that they might be caused by changes in the load of the POL adding noise to my measurement, or causing small shifts in the loop gain of the converter (since the bode plot I've measured isn't constant over load). It seems to me that these blips can be generally ignored, but one area where I could see a problem coming up is where I have a less well-behaved DC-DC converter. If I increase the number of points of my measurement, I think I might be worried about these sharp "fake" peaks blowing out the true, lesser peak. Could there maybe be an issue where I might want to set an upper limit on the number of samples I take to reduce the impact of the small blips?