RE: [IBIS-Users] RE: [IBIS] RE: IBIS model behavior between Vinh and Vinl input

From: Akhilesh CHANDRA <akhilesh.chandra_at_.....>
Date: Sun Jan 06 2008 - 04:26:41 PST
Hello,

  I am agree with TOM comments. We will need to align IBIS community for
this unclear spec We can define X as 1, 0 or 0.5V but all will need to
follow it.

Regards
Akhilesh

-----Original Message-----
From: owner-ibis-users@server.eda.org
[mailto:owner-ibis-users@server.eda.org] On Behalf Of Tom Dagostino
Sent: Friday, January 04, 2008 11:32 PM
To: 'Muranyi, Arpad'; 'Akhilesh CHANDRA'; ibis@server.eda-stds.org;
owner-ibis-users@server.eda.org; ibis-users@server.eda.org
Subject: RE: [IBIS-Users] RE: [IBIS] RE: IBIS model behavior between Vinh
and Vinl input

Arpad

I think we are in agreement.  I took Akhilesh's comment:

IBIS specs don't define that how logic X represent in IBIS simulation, Due
to this different simulator give different behavior for X. In my view we
will need to define how logic X represent in IBIS model simulation. It will
help to align all the simulator results.

To mean that he wanted to define X as a 1 or 0.  

Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
503-430-1285 FAX
tom@teraspeed.com
www.teraspeed.com

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827 


-----Original Message-----
From: owner-ibis@server.eda.org [mailto:owner-ibis@server.eda.org] On Behalf
Of Muranyi, Arpad
Sent: Friday, January 04, 2008 9:41 AM
To: tom@teraspeed.com; Akhilesh CHANDRA; ibis@server.eda-stds.org;
owner-ibis-users@server.eda.org; ibis-users@server.eda.org
Subject: RE: [IBIS-Users] RE: [IBIS] RE: IBIS model behavior between Vinh
and Vinl input

Tom,

I may disagree with you on this one.  The 1 volt and 0 volt representation
of "true" and "false" is just as "unreal" as an "X".  None of these are
actual waveforms.  These are indicators which tells you whether the input
signal was below, above, or between Vinh and Vinl.  I think it is plain
wrong to have a "1" or a "0" on the output of the receiver when the signal
is between Vinh and Vinl and it misleads the user of these tools thinking
that they have good signal integrity while they have problems.

I fully agree that digital parts are not made to operate with waveforms
between Vinh and Vinl.  Ant that is exactly the reason we should have an
output value of "X" to find out when the waveforms are in that region.
And that fact that you described that the "actual output ... will change"
is exactly the reason for the "X", because we simply don't know what it will
be.  It is not guaranteed that it will be a "1" or a "0".  How do you
describe that if not with an "X"?

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

-----Original Message-----
From: Tom Dagostino [mailto:tom@teraspeed.com]
Sent: Friday, January 04, 2008 1:34 AM
To: 'Akhilesh CHANDRA'; Muranyi, Arpad; ibis@server.eda-stds.org;
owner-ibis-users@server.eda.org; ibis-users@server.eda.org
Subject: RE: [IBIS-Users] RE: [IBIS] RE: IBIS model behavior between Vinh
and Vinl input

...
...
...

But having all simulators default to some arbitrary state when the input is
between the reference levels is setting the user up for failure.  People
tend to assume if the simulator says X, X is real.  If they don't see X in
the real circuit then there is something wrong.  Not all parts will conform
to some arbitrarily designated state.

Digital parts are not made to operate with their inputs between Vinh and
Vinl.  Most parts have specifications that state the minimum slew rate
(input risetime/falltime) as the input to the part transitions between the
two reference levels.  The actual output of an input buffer for a given
input voltage between Vinl and Vinh will change depending on the internal
noise of the IC, the noise on the input, process, temperature, voltage,
phase of the moon, crosstalk, etc.

Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
503-430-1285 FAX
tom@teraspeed.com
www.teraspeed.com

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827

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