RE: [IBIS-Users] C-Comp

Subject: RE: [IBIS-Users] C-Comp
From: Muranyi, Arpad (arpad.muranyi@intel.com)
Date: Wed Aug 06 2003 - 12:50:04 PDT

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Sorry for the late response.

The way this could be done is to simply repeat all C_comp
parameters twice, one set for drive mode, and another for
receive mode. One C_comp for receive mode would not
be enough.

However, there is more to this problem. The capacitance
is not only dependent on whether the buffer drives or
receives, but it is also voltage and frequency dependent.
(See BIRD 79 and related presentations). The question
in my mind is, BIRD 79 was voted down, because all those
features will be doable with the *-AMS extensions to IBIS.
The same is true for the C_comp drive/receive parameters.

Is it worth adding these parameters to the existing
style, or should we just go with the *-AMS style modeling
and be able to describe anything freely?

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

-----Original Message-----
From: Kim Helliwell [mailto:kimgh@apple.com]
Sent: Friday, July 18, 2003 1:31 PM
To: Robert Haller
Cc: Roy Leventhal; anshuli@ti.com; ibis-users@eda.org
Subject: Re: [IBIS-Users] C-Comp

I'm just curious how this would be folded in with the 4-part C_comp
(BIRD 76.1). Will we end up with 2 (or even 4) more C_comp
values? Or does just 1 value adequately characterize the
receiver?

Kim

On Friday, July 18, 2003, at 10:10 AM, Robert Haller wrote:

> IBIS users,
>
> At today's IBIS open forum call, the issue was raised concerning the
> limitations of Ccomp in the present IBIS spec. This issue is being
> added to the next ibis open forum agenda technical discussion.
>
> I would like to solicit feedback from Model developers and users for
> proposed changes, as well as voice my own opinion.
>
> Present syntax
>
> | typ min max
> |
> C_comp 3.90pF 3.10pF 4.80pF
>
> My personal experience has shown that I/O buffer often have different
> C_comp when driving and receiving. To keep things simple, I would
> suggest that a simple extension to the C_comp would be to specify a
> C_comp driving and C_comp receiving for Model_type = I/O
>
> regards,
> bob
> --
> Robert J. Haller (rhaller@sisoft.com)
> Principal Consultant
> Signal Integrity Software Inc.
> 6 Clock Tower Place, Suite 250
> Maynard, MA 01754
> Phone: (978) 461-0449, ext 15
>
>
>
> Roy Leventhal wrote:
>> Anshuli,
>> Be aware that capacitive behavior is included in the V-T behavioral
>> curves
>> and/or the slew rates based on them. Unsophisticated providers of
>> simulation
>> software (hopefully, few remain) can thus mistakenly "double count"
>> the
>> effects of Ccomp unless they adjust for its presence in the circuit.
>> So, why is Ccomp included? To account for the capacitive loading on
>> the
>> circuit, direct or reflected wave, and it is the total capacitive
>> loading
>> looking into the die pad.
>> Best Regards,
>> Roy
>
>
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Kim Helliwell
Apple Computer
kimgh@apple.com
408 974 9936

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