Subject: [IBIS-Users] Comments on IBIS Spec Version 4.1
From: Timothy Coyle (timothy.coyle@sun.com)
Date: Thu Jul 31 2003 - 12:51:57 PDT
Hi,
The following are some comments/feedback I have on IBIS version 4.1. My comments are not necessarily on the new
additions to version 4.1, but some things that could be changed/modified in previous versions.
- Page 17, under keyword diff pin, it states that if it is a differential input than vdiff overrides and supercedes need for Vinh and
Vinl parameters. But on page 22 it states that for any Input model type if Vinh and Vinl are not defined the parser gives a warning. When people
create a differential buffer, most are not concerned with the single-ended signal. I have seen a lot of people define the Vinh and Vinl as the
differential thresholds (say +/- 100mv for LVDS) because they think these will be applied to the differential signal. I think some more clarification
is needed here when someone is using an Input as a differential input.
- page 24, under keyword model, the Cref and Rref subparamter paragraph.(last paragraph) I have always taken issue with the way this is worded.
I do not think propogation delay should be used - some people will confuse this with the time it takes from the input to the output, which is not
correct for IBIS. I think we should say in order for simulators to calculate flight time correctly, a timing load is need to determine the time
it takes the output buffer to reach Vmeas. Some people refer to this as time to Vmeas.
- pg 53, under keyword Rising/Falling waveform, last paragraph stating that V/T curve assumes die capacitance included. Then it goes on
to say that this can lead to numerical errors with C_comp in simulators. I am under the impression that for an output buffer model that the
simulator will compensate for the die capacitance being in the V/T curves. Maybe this needs more clarification?
Regards,
Tim
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