RE: [IBIS-Users] Re: High frequency performance of IBIS model

Nirav,
        You need to examine input versus output capacitance if you are creating a
model for a I/O cell.
IBIS presently doesn't support unique capacitance for driving and recieving
of an I/O buffer.
If your cells have unique Input and Output models this shouldn't be an
issue.

regards,
Bob
-----Original Message-----
From: Nirav Patel [mailto:nirav@agere.com]
Sent: Wednesday, June 02, 2004 12:34 AM
To: Robert Haller
Cc: ibis-users@eda.org
Subject: Re: [IBIS-Users] Re: High frequency performance of IBIS model

Bob,

Thanks for your inputs. So far we are able to build IBIS models
which correlated well till 1GHz (most complex ones are LVDS
terminated). Now, SerDes buffers, which suppose to run at 2.5GHZ,
need to model. I am sure there will be special circuits, still
we like to give a try.

At first, we like to match buffer level behavior of hspice and
IBIS, so we are not worried about package model as of now.

Generally, we extract output capacitance at 100MHz, for all our
buffers, assuming that C_comp is almost constant at all frequencies.
I like to understand why we have to study input versus output
capacitance when it comes to high frequency?

Thanks,
Nirav

Robert Haller wrote:
> Nirav,
>
> A accurate IBIS model can be constructed that correlates to SPICE and
> bench at 2.5 Ghz. Yes there can be limitations in models depending on
> the I/O cell circuit design, and the simulator. Some of the potential
> issues;
>
> - Was the model accurately constructed ?
> - Accuracy of package model
> - Does the I/O cell use special circuit tricks that IBIS may have
> difficulty modeling (or the model creator doesn't capture)
> - Crossover current in the I/O cell
> - Input capacitance versus output capacitance (C_comp) on I/O cell
>
> regards,
> Bob
>
>
> Nirav Patel wrote:
>
>> Hi All,
>>
>> I need your help to get more clarification on the following issues:
>>
>> 1. Simulators are capable of handling IBIS model which needs to run at
>> 2.5 GHz.
>> 2. Is there any limitation in IBIS specification for characterizing
>> any buffer
>> which is operating at 2.5GHz.
>>
>> Thanks
>> Nirav
>>
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Received on Wed Jun 2 10:56:29 2004