RE: [IBIS-Users] Correct use of [Temperature Range]

From: Muranyi, Arpad <Arpad_Muranyi_at_.....>
Date: Mon Mar 23 2009 - 07:48:27 PDT
The IBIS specification does not associate the numbers with
any meaning, i.e. a small number doesn't necessarily mean
slow/fast or best/worst.

This is because from a signal integrity or timing point if
view you can some times argue it both ways.  For example,
a small C_comp could result in a faster edge rate, but at
the same time it can also cause more overshoot and ringing.
If the timing is such that the ringing has to settle before
you have a valid signal, you got worse timing from a smaller
C_comp.  So in this case, is the smaller C_comp a best case
or a worst case scenario?

For this reason, the IBIS specification says that you put the
small numbers in the min place, and the big numbers in the
max case.  There is only one exception, as Radovan mentioned
it, which is the temperature.  Depending on whether you have
a bi-polar or CMOS device, you will either put the high temperature
(the weak condition) in the max or min place, respectively.
This was done so that a tool can apply different algorithms
to the model if they so desire, knowing what type the device
is.

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


-----Original Message-----
From: owner-ibis-users@server.eda.org
[mailto:owner-ibis-users@server.eda.org] On Behalf Of Vuletic Radovan
(QAG PX D PDE)
Sent: Monday, March 23, 2009 8:15 AM
To: Lars Snith; ibis-users@server.eda.org
Subject: RE: [IBIS-Users] Correct use of [Temperature Range]

Hi Lars,

usually in IBIS modeling I refer to the typ, min and max PVT cases as to
the nominal, slow and fast PVT cases.

In max (fast) PVT cases usually one should have the best transistor
device parameters ("fastest" transistors), highest voltage and - now
comes the trick (if there is one at all) - lowest temperature for CMOS
circuits (since CMOS transistors usually have negative temperature
coefficient - meaning lower temperature yields in higher current -->
faster switching) or highest temperature for bipolar transistors
(devices) since usually they have positive temperature coefficient and
therefore at higher temperatures they deliver higher current (in some
cases some smoke as well :-))

Similar (but opposite) in slow PVT case: put there slowest device
models, lowest voltage and highest temperature for CMOS or lowest
temperature for bipolar devices.

Of course,  I can imagine that in some very special cases some
deviations from above rules could happened.

So, if you are having IBIS models of some vendor that uses both CMOS and
bipolar technologies having different temperatures for the same PVT case
I would say that it makes sense - if that is not the case, I would than
directly clarify with the model provider if there is a bug in the model
or not.

I hope this helps.


Best regards / Mit freundlichen Gru?en / S postovanjem
Radovan Vuletic
Staff Engineer Product Development

Qimonda AG
QAG PX D PDE
MUC/10.2.236 AP 3
Am Campeon 1-12
D-85579 Neuebiberg
Germany

Phone:		+49 (0)89 60088 1233
Fax (PC):	+49 (0)89 60088 45 5305
Mobile:              +49 (0)160 7476262

E-mail: radovan.vuletic@qimonda.com
Web:  http://www.qimonda.com/


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Fischl
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J. Seifert
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-----Original Message-----
From: owner-ibis-users@server.eda.org
[mailto:owner-ibis-users@server.eda.org] On Behalf Of Lars Snith
Sent: Monday, March 23, 2009 1:27 PM
To: ibis-users@server.eda.org
Subject: [IBIS-Users] Correct use of [Temperature Range]

Hello Friends,

Let me once and for all try to nail down an issue that seem to be a
constant source of confusion.

The IBIS model syntax defines the triplet order [typ] [min] [max].
But this relates to the overall case, not the individual parameter,
right? So to make things match the real operational case the [min] of
[Temperature Range] would really need to be the maximum temperature,
right?

Looking at what others do is not much help here, I see examples of both
variants, frequently from the same vendor(!). So an authorative answer
would be appreciated.


Best regards,  Lars Snith
--
Those who can, Do
Those who can't, Simulate

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Received on Mon Mar 23 07:51:06 2009

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