Subject: RE: [IBIS-Users] IBIS Info.
From: Ingraham, Andrew (Andrew.Ingraham@compaq.com)
Date: Thu Mar 14 2002 - 09:04:02 PST
> When you say the pulldown curve gives the I/V characteristics when the
> output is in the low state, but with Clamps subtracted; do you mean that
> the physical clamping circuit should be removed from the spice netlist
> when performing the S2IBIS2 generation?
Personally, I would prefer not to remove the physical clamping circuit from the netlist. There might be interactions of some sort, or elements not in the actual clamping circuit that also clamp or conduct in the high impedance state. Stephen Peters' description is the way I'd do it. It makes sure that the Pulldown + Clamp data really adds up to the total current in the low state.
When you do the subtraction to get the Pulldown and Pullup data, it is not uncommon for the result to be non-monotonic. The IBIS check program will complain, because it checks for non-monotonicity of the individual tables, rather than summing them back together. What really matters is the total current after summing, not the separate tables.
Andy
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