[SI-LIST] Re: Yet another IBIS issues
- From: "Hassan O. Ali" <hassan@xxxxxxxx>
- To: "Gil Gafni" <gil.gafni@xxxxxxxx>,"Si-List" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 12 Apr 2004 16:17:38 -0400 (EDT)
Gil,
Please find my answers inline based on the little I know about IBIS.
On Apr 12, "Gil Gafni" <gil.gafni@xxxxxxxx> wrote:
>
> Hello Experts
>
> I know IBIS model is a "hot topic" on the IS list. I still have some
> issues that I would like to have you opinions so I will have better
> closure -
>
> Few questions:
> * If I take an HSPICE model of a buffer and its equivalent IBIS model
> 1. Will they have the same "buffer delay"?
No.
> 2. Is "buffer delay" is at all defined with IBIS models?
Yes and No.
Vmeas, Rload, Cload parameters defined in IBIS files, provide an AC test load
for buffer-
delay extraction. The test load is usually the one used to extract AC
parameters
provided in the device's data sheet.
But those parameters are optional in IBIS. Therefore, you may or may not find
them in
IBIS files. In their absence, the buffer delay is assumed zero - sort of. I say
"sort
of" because the extracted V-t curves may already have a bit of buffer delay
even without
the specification of Vmeas, Rload, Cload parameters.
Moreover, the AC test load only provides a way to link your simulation results
with
other AC parameters provided in the device's data sheet. Suppose you measure
buffer
delay, D1, when you use the IBIS file with the specified AC test load, and you
measure
buffer delay, D2, when you use the same IBIS file with your load of interest.
D2-D1 is
your buffer delay correction when you do timing analysis along with other AC
parameters
provided in the device's data sheet. You may actually even end up with a
negative buffer
delay (probably to your advantage), for instance, if your actual load is less
capacitive
than the specified test load.
> * When simulating with IBIS model, does one has to "compensate" for
> anything (like load change). And if so, what would be the "correcting"
> test load, the one suggested in the components Data Sheet or the one
> defined inside the IBIS with C_ref, R_ref ...
See my answer above.
> * When one gets/provides an IBIS model what other information beside the
> file itself should he receive/supply
A well documented IBIS file is good enough.
Hassan.
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