[SI-LIST] Re: Can I get this from an IBIS model?

Doug,

The [Pullup] and [Pulldown] tables are, effectively, impedance tables, since
they are constructed as instantaneous voltage-current points. For a brief
period of time at the start of a transition from one state to the other,
both the pullup and pulldown tables are contributing to the overall current
at the IBIS model pin. However, if this is ignored the impedance of the
buffer while driving the line to the high state can be determined from the
pullup table and the impedance to drive the line to the low state can be
determined from the pulldown table. Through the transition, the
instantaneous impdedance will, most likely, be found to be not constant, as
you might expect.

Regards,
Tony

-----Original Message-----
From: Doug Brooks [mailto:doug@xxxxxxxxxx]
Sent: Saturday, September 28, 2002 12:06 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Can I get this from an IBIS model?



Suppose I have an IBIS model, but not the physical part. Is there a way I 
can determine the output impedance of the device (and if different, the 
output impedance for each digital state) from the IBIS model itself?

I know I can build a simulation and solve for the output impedance that 
way, but can I get it from the IBIS model itself without going through the 
simulation step? . And if so, where in a model do I look?

Thanks for any help.

Doug Brooks

____________________________________________________________________________
___
UltraCAD Design announces availability of its new book "Signal Integrity 
Issues in PCB Design"
Details at  www.ultracad.com


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