Subject: [IBIS-Users] IBIS Model for Coupled, Differential Pins
From: Dolese, John (John_Dolese@or.mxim.com)
Date: Fri May 24 2002 - 13:34:52 PDT
When I make an IBIS model of differential pins such as an LVDS output I want
to know how our customers will interpret the VI and VT data I give them. It
occurs to me that I should take the VI curves with a differential voltage
applied about the common mode voltage. This will give the odd mode impedance
of the pin pair. Does the signal integrity software keep track of both pins
so that if an odd mode reflection occurs both pins will be excited together?
In short if the odd mode impedance is 50 Ohms and the single ended impedance
is 100 Ohms, which do I report?
I have seen the single pin spice model template used in the ibis to spice
converter from Intusoft. Is there a template somewhere for differential
inputs and outputs? Such a templated would clear up any ambiguity about how
the ibis data is interpreted.
Another thing I'm wondering is about Resistance_Matrix. Are the resistors in
this matrix lumped between the lead inductance and the package pin
capacitance the same as r_pkg? It seems more reasonable that any conductance
between pins would occur on the die side of l_pkg.
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