Steve wrote a rather lengthy message, including:
? ?"I read phase margin as the absolute difference between the reading for phase at the UGF and 0 or 180/-180 whichever is closer."
It can't be either/or.? It must be only one of them, depending on how you have kept track of polarities.? Phase margin can be >90 degrees, so it's not the one that is closer (which forces it to be <90 degrees).
The fact that you added a minus sign to the thing being plotted, adds -180 degrees to the phase plot.
? ?"[Incidentally, a few days ago LTspice produced the plot in Phase and Gain Margin - old.jpg. ...
? ? At this stage I can only (very gingerly) conclude that this resulted from the update to LTspice.? Eek...]"
It's very unlikely.
There probably was a difference between your circuits.? But they can be hard to find.? Sometimes, comparing the .net files makes it easier to find their differences.
One problem with visually comparing schematics, is that attributes can be made not visible.
? ?"...?problems with the schematic no longer recognising .inc statements ..."
That should not have happened either, and points to something being wrong in the schematic, or with the included files themselves.? Typo?
Sorry, your questions are very complicated and it's late.? I'll try to write more later.
Andy
