[ibis-macro] Re: Question on seeting the EMD direction
- From: "Brad Brim" <bradb@xxxxxxxxxxx>
- To: "'IBIS-ATM'" <ibis-macro@xxxxxxxxxxxxx>
- Date: Thu, 26 Jun 2008 14:23:07 -0700
Is a decoupling capacitor on a board LTI? Most of us would answer "yes".
However, capacitors vary with temperature to imply time variance. Capacitors
also vary with DC bias voltage, which implies an underlying large signal
nonlinear behavior. Capacitors vary with age, again implying time variance.
Seems to me the issue was expressed quite well in the last meeting as one of
"time constant" and what we wish to consider in analyses. The time constant
of signals is picoseconds or nanoseconds. What time constant bounds do we
wish to consider in our analyses? If it's on the order of temperature
variations, then temperature certainly becomes a time varying parameter.
Do we believe it will be required in the foreseeable future to consider
passive interconnect as time varying or nonlinear in our
system/channel/component analyses with this time constant issue being fully
considered?
If not, then temperature, bias voltage and other such parameters become
higher level discrete state controls rather than low level continuous
parameters?
regards,
-Brad
Brad Brim
Sigrity, Inc.
4675 Stevens Creek Blvd, Suite 130
Santa Clara, CA 95051
408-260-9344 ext 147
503-628-6230 (alternate)
503-799-9917 (mobile)
bradb@xxxxxxxxxxx
_____
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Thursday, June 26, 2008 2:02 PM
To: IBIS-ATM
Subject: [ibis-macro] Re: Question on seeting the EMD direction
In our recent discussions on Interconnect-SPICE and our last
IBIS-ATM teleconference the question was raised whether we can
safely assume interconnects are LTI. Scott's message below
(from a different thread) seems to indicate that there are
situations when this may not be the case. This makes me
nervous about writing a specification that by its definition
would disallow those effects to be simulated... Any comments?
Arpad
===============================================================
_____
From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
Sent: Thursday, June 26, 2008 2:03 PM
To: Muranyi, Arpad
Cc: twesterh@xxxxxxxxxx; msteinb@xxxxxxxxxx; wkatz@xxxxxxxxxx;
huangchunxing@xxxxxxxxxx; IBIS-ATM; guantao@xxxxxxxxxx
Subject: Re: [ibis-macro] Re: IBIS-AMI
Arpad
I agree with you, and would add that even the analog network
characterization portion of a passive interconnect system is not a well
understood topic. Several issues come to mind:
* Time variance of the interconnect due to:
* Temperature
* Humidity
* Mechanical Vibration (think twin-ax cables in a vehicle)
* Equalizer training in the presence of crosstalk and noise spikes in
a hot-plug environment
But heck, I'd settle for an IBIS-AMI model that correlates with something
that can actually be measured.
Scott
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
http://www.teraspeed.com
TeraspeedR is the registered service mark of
Teraspeed Consulting Group LLC
Muranyi, Arpad wrote:
Sorry to everyone for arguing a little on what has
been stated so far. I tend to disagree with the
statement(s) that the analog corner modeling is
a well understood topic.
Just because it is common practice to use high/low
supply voltages with low/high temperatures, etc...
to achieve best/worst timings, it doesn't mean that
this practice actually gives the best/worst timings.
Having done large amounts of parameter sweeps while I
was working for my previous employer, I saw solution
space plots which had failing islands corresponding
to "in-between" parameter values, and not at the
extremes.
The answer then was that we do not know where the
system is failing unless we simulate all possible
combinations of parameter values. That's when the
frequency domain (resonance) analysis, sensitivity
analysis, design of experiments (DOE) and similar
techniques became popular. I tend to believe that
the application of statistical analysis techniques
is a natural continuation of this evolution, as
kind of an attempt to reduce the amount of time it
takes to go through all possible parameter combinations...
My $ 0.02 worth...
Arpad
===========================================================
-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Todd Westerhoff
Sent: Thursday, June 26, 2008 1:00 PM
To: msteinb@xxxxxxxxxx; scott@xxxxxxxxxxxxx
Cc: wkatz@xxxxxxxxxx; huangchunxing@xxxxxxxxxx; 'IBIS-ATM';
guantao@xxxxxxxxxx
Subject: [ibis-macro] Re: IBIS-AMI
It's worth pointing out an IBIS-AMI model actually has two models -
- the analog model in the .ibs file, and
- the algorithmic model pointed to by the .ibs file
IBIS-AMI analysis separates analysis of a link into two stages - network
characterization and link
analysis. The analog model is used for the former, while the
algorithmic model is used for the
latter.
When we talk about modeling PVT variation, it's worth considering how
PVT affects each type of model
separately. Modeling the effects of PVT on a transmitter's output stage
or a receiver's input stage
is well understood (it's what IBIS has been doing for years), while
modeling the effects of PVT on
equalization behavior is [relatively] new ground. I agree this is
something we should consider
standardizing, and I also agree that we need more experience in this
area before it makes sense to
try & put such standards in place.
Todd.
Todd Westerhoff
VP, Software Products
SiSoft
6 Clock Tower Place, Suite 250
Maynard, MA 01754
(978) 461-0449 x24
twesterh@xxxxxxxxxx
www.sisoft.com
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