Ken Kundert

Andrew, people often think of strobing as a data reduction technique. It almost never is, and if you think of it that way you can miss its true power.
I have found that strobing is useful for two things.
The most common is the FFT where it is used as a way to eliminate interpolation error. For this case, if you line things up just right, then you are free to use strobeoutput=all, however if you are not super careful and do not line things up just right, then using strobeoutput=all can reintroduce interpolation errors. This is easy to do because if you output all points it is hard to know which points are the strobe points, and it is also very difficult to know where the FFT is placing its sample points. This is a very error prone process where improvements the the environment would go a long way towards making FFT measurements easier and more accurate. What is needed is perhaps three things: 1. the best would be for environment to tell the simulator it is running and FFT and configure strobing so that the simulator places the points precisely where the FFT needs them. This is a rather obvious need that has been overlooked for a very long time. 2. without that, it would be nice if the simulator had the option to produce two data files, one with only the strobe points and one with all points. Then you could plot both and see exactly where the strobe points are, and what is happening between the strobe points (you generally want to be able to adjust strobe start so that strobe/sample points fall at the end of the cycle; this is easier if you can see both sets of points). 3. It would be great if the FFT produced two outputs as well, the time domain wafeform and the frequecy domain spectrum. That way a user could confirm that the FFT samples were placed where they are suppose to be (they could graphically confirm this important fact). And with 2, the user could confirm that the stobe points and the FFT sample points were aligned. It would be possible to do this with a Inverse FFT.
The second use of strobing is to suppress large periodic variations so as to be able to see small perturbations. For example, I often use strobing or sampling at the clock frequency when observing the output of switching power regulators as a way of suppressing the clock ripple. It makes my measurements much more sensitive and repeatable. I do the same with mixers, where I sample at the LO frequency.
Ken
