[ibis-macro] Re: Question on seeting the EMD direction

  • From: Mike Steinberger <msteinb@xxxxxxxxxx>
  • To: Arpad_Muranyi@xxxxxxxxxx
  • Date: Thu, 26 Jun 2008 17:19:49 -0400

Arpad-
Taking either Scott's case of a vibrating vehicle or Richard Ward's even higher frequency case of a vibrating disk drive, how does the highest frequency of vibration compare to the data rate of the channel? I'm having a hard time imagining a significant harmonic component above about 100kHz. Maybe I don't have much imagination, so let's make it 1 MHz.
Still, with that many orders of magnitude difference between the mechanical frequencies and the electrical frequencies, any change in electrical wave shape due to mechanical movement is going to be insignificant, so the LTI approximation is still a good one.
What I think these examples do suggest is that the designer of a system that has mechanical vibration must analyze the channel performance for a representative sample of the mechanical configurations that will occur over the course of a cycle of vibration. Thankfully, most of us won't have to execute that procedure.
I'm reminded of an old saying about user interfaces: "If an interface is so easy to use that any fool could use it, only a fool would." I think a similar statement applies to engineering languages: "A language which is capable of expressing any engineering problem is too complex to be useful for any engineering problem." 

My 2c.
Mike S.

Muranyi, Arpad wrote:

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:
          o Temperature
          o Humidity
          o 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

Teraspeed® 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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