Re: [IBIS-Users] input stimulus for extracting IBIS VT curves

I disagree that the edge should be "as fast as possible".

For the IBIS models used in HSPICE, my recollection is that HSPICE
treats it as a switch, waiting until the (digital) input waveform
crosses a threshold, then switching the IBIS model. The edge rate of
that digital stimulus waveform therefore shouldn't matter ... except
that very slow edge rate causes a known time delay before the IBIS
modeled device switches, and extremely fast edge rates might make the
simulation run slow or lead to convergence problems. Theoretically
it's good to make it fast so that it works like an instantaneous
binary switch, but there could be practical problems if you try to do
that.

For the transistor (SPICE) models, ideally you should attempt to match
the actual waveform (edge rate and amplitude) that is at that point
inside the IC, NOT the "fastest possible edge rate". Hopefully that
is what the IBIS modeler did too. Using a faster edge rate than what
those transistors normally see, makes it unrealistic.

Andy

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