Re: Use of femto scaling in IBIS models

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Mike,

Thanks for the information. This issue is clearly an oversight on my part.
When I wrote our tool that automates the process of generating IBIS models, I
didn't check what the valid prefixes are in IBIS, so I coded my program to use
all known prefixes available in the engineering world. Since then, I have a
newer revision of the tool which uses engineering notation in the tables (only).

Due to time limitations, I cannot commit to fix all the earlier models. One way
of getting around the fA problem is to edit the file to be version 2.1, since it
is legal in that spec.

However, I question whether this is a spec or parser issue. I parsed the 1.1
IBIS file in question with both parsers just now, and neither one of them gave
me an error. If this is illegal in 1.1, both parsers should have given me an
error. This is why these prefixes slipped in to start out with...

At one time we were debating whether in cases like this, when the parser didn't
agree with the spec, which one should take precedence. If I remember correctly
we voted for the parser. In this light, the Intel models are not illegal.
(Someone correct me if I am wrong).

So the question is, should we fix the parser, or change the spec to allow for
all prefixes. In my opinion it doesn't make sense to have to say 0.01 pA for 10
fA and so on. Even though these kind of numbers are usually noise and outside
the usually measurable range, I would still allow them for the sake of
consistency and completeness. You never know, someone might even need them in
some cases... (especially with capacitances).

Arpad
================================================================================

Ibisians,

I have recently found a problem in the parser which affects both
versions of the parser when parsing version 1.x IBIS models which
contain values scaled using the femto(f) prefix.

As far as I know this only affects Intel models as everyone else
uses unscaled number in engineering/scientific format.

According to the IBIS 1.1 spec, the prefix f is not
a legal prefix, pico is the smallest allowed. As the Intel model is
set as version 1.1 it is not a valid IBIS model.
Also the IBIS2.1 parser does not pick it up as it uses the IBIS v1.1
parser checker.

Illegal scale characters in the IBIS file are set to ' ' i.e. scale=1.0
without any error message.

I fiexed it by adding the character f to the known_scales array
i.e Mkmunp -> Mkmunpf
If the IBIS version in the file is set to 2.1 it will work OK
as f is recognised.

This should only affect simulated models, as measured models are
somewhat difficult to measure to that degree of accuracy.
I did once see currents of magnitude e+41 in an Intel model which I
presumed was simulated otherwise most of California would have been
blacked out!

Here is a supplementary question. Why is not having the same file
name as that in the file classified as an error rather than a warning?
Even if the file has the right name and you access it through a full
path name you get the error.

Regards

Mike

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Subject: Use of femto scaling in IBIS models
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