Re: timestep size effect (surprising?)
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Helmut is correct.? The unexpected behavior is due to LTspice's waveform viewer trying to "connect the dots" using curves, and when it does that, the trace appears to go negative.
If you take the original simulation (without "plotwinsize=0") and right-click > View > Mark Data Points, you'll see that the actual data points don't go negative (*).? But the curve LTspice draws between the dots does swing negative.? Note that LTspice doesn't use a linear interpolation between points.? It uses curves.? If it used only linear interpolation, it would have avoided the problem of swinging negative, but it makes things look somewhat "ragged" so the curves are preferred.
(*)? Actually, one of the savedpoints did go negative, just a little, but I think that is another artifact of LTspice's waveform compression algorithm.? LTspice does not only discard waveform points it doesn't need, it apparently also modifies the values that it stores at the points that it keeps.? This was news to me.
Regards,
Andy
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