[IBIS-Users] {Spam?} {Filename?} LVDS IBIS model - simulation issue

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Hi,

I am making IBIS models for LVDS (low voltage differential signal) IO 
buffer.
To model an LVDS buffer I created the following test circuit, assigned 
the generated IBIS model to both buffers, set one buffer as inverted output.


*Problem:*
In the image below the YELLOW waveform is what I saw and the PURPLE 
waveform is what I expected to see.

YELLOW = IBIS model
PURPLE = Spice ( reference ) model

Here is combined pullUp (yellow) and pullDown (green) IV curves 
(actually it is spice curves from which IV tables were derived):


Lets assume that simulator tries to find operational point for LVDS 
buffer driving high. Then for the non-inverted buffer a point (Vp, Ip) 
will be taken from pullUp table, for the inverted buffer a point (Vn, 
In) from pullDown table, the following conditions should be satisfied: 
Ip = In, Vp - Vn = Ip*50. On the image above it is seen that there are 2 
points satisfying the condition: Vp =~  1.45V and Vp =~ 2.2V. Seems that 
something like that happened during simulation and simulator got to the 
second point. (BTW, there are 60 points for the region 0.9 - 1.6V and 10 
points for the region 1.6-2.5V in the IBIS model IV tables).

*Question:*
What can be done to resolve this situation? Should IV tables or another 
IBIS structures be modified and how? I am making *ibis ver. 4.2* models.

Thanks,
Andrey

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