Re: [SI-LIST] : MECL System Design Handbook

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From: Steve Corey (steve@tdasystems.com)
Date: Fri May 18 2001 - 19:04:41 PDT


Mitch -- you may have lost the context under which this thread was
revived. The question that was brought up referred to a particular
figure in the MECL design handbook, specifically figure 7-17 on page 144
of the handbook (p. 155 in pdf-pages). It was hypothesized that the
figure might be in error, and furthermore that such results could not be
observed.

Unfortunately, the time scale in the figure isn't stated, nor is the
geometry of the layout given. (However, both can be estimated by
comparison with earlier examples in the handbook, in which this
information is provided). Regarding stackup, however, at the beginning
of the TDR section, on page 132 (143 in pdf-pages), the geometry for
example 1 states that the width of the 51-ohm line is 0.1 inches.
(Don't forget, the revision date on the hanbook, or at least on the PDF
I downloaded, is 1988.) It's probably a reasonable guess that all of
the microstrip examples in the TDR section used the same stackup. If
that's the case, 0.1 inch is probably the most meaningful trace width to
use in determining whether it's possible to see the effects of the bends
as described in the handbook. I personally appreciate Tom's taking the
time to do the measurements and report the results -- none of the rest
of us volunteered to do it.

The question to which I think you're alluding in your post is whether or
not such effects are important in someone's particular design, or
perhaps in a "typical" modern-day digital design. While it is related,
it is nevertheless a separate question from whether or not it's possible
to observe the TDR results implied in the MECL handbook. And although
it is an important question, it doesn't diminish the importance of the
question Tom is trying to answer.

  -- Steve

-------------------------------------------
Steven D. Corey, Ph.D.
Time Domain Analysis Systems, Inc.
"The Interconnect Modeling Company."
http://www.tdasystems.com

email: steve@tdasystems.com
phone: (503) 246-2272
fax: (503) 246-2282
-------------------------------------------

cadpro2k@dacafe.com wrote:

> ---------Included Message----------
> >From: "Dagostino, Tom" <tom_dagostino@mentorg.com>
> >Yes, these traces are quite wide, on the order of 0.100". There are
> several
> >right angel bends with square corners. The corners are quite
> visible.
> >
>
> "Oh Glory be to the wise..."
> Tom,
>
> Comeon, .1" traces on a test board, for this kind of test? Let's be
> reasonable for a moment. I'm sure at least a half dozen experts can
> show
> you results opposite to this, but they will probably use "more
> current
> board technology" to achieve this. I'm not saying you're wrong,
> you've
> generated YOUR data, but I honestly can't comprehend your experiment.
>
> Have a good weekend, I plan to have a beer and forget everything I
> learned today. :)
>
> Mitch
> _____________________________________________________________
> Tired of limited space on Yahoo and Hotmail?
> Free 100 Meg email account available at http://www.dacafe.com
>
>
>
> ----------------------------------------------------------------
>
> I have a board that demostrates this very nicely. As soon as I get my
> scope/extraction system working again I will publish some results.
> The board is two layers with ground on one side and 50 Ohm traces on
> the other. Yes, these traces are quite wide, on the order of 0.100".
> There are several right angel bends with square corners. The corners
> are quite visible.
>
> Tom Dagostino
> Modeling Manger
> Mentor Graphics Corp.
> SAE
> tom_dagostino@mentor.com
> 503-685-1613
>
> -----Original Message-----
> From: Dr. Edward P. Sayre [mailto:esayre@nesa.com]
> Sent: Thursday, May 17, 2001 6:47 PM
> To: Ritchey Lee; Rich Peyton
> Cc: Roehrner Wolfgang; si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : MECL System Design Handbook
>
> Lee and others:
>
> I don't know what kind of TDR or fixturing you might have used, but
> the
> excess capacitance is very real and can be seen. It is also
> illustrated in
> a number of microwave books. If your fixturing caused a significant
> loss (>
> 100 ps) of risetime of the step out of the TDR, then the capacitance
> effect
> will be washed out.
>
> Sincerely,
>
> ed sayre
> ==========================
> At 08:36 AM 5/10/01 -0700, Ritchey Lee wrote:
> >Any of you who want to know how the myth about right angle bends got
> >started, look
> >at figure 7.17 on page 155. This alleges that right angle bends can
> be
> >seen by a
> >TDR. I've done this measurement dozens of times and coiuld never see
> a right
> >angle bend.
> >
> >A few years ago, I called Mr. Blood the author of the book and asked
>
> >about the
> >diagram. His reply was that he knew the diagram was flawed, but
> there
> >wasn't time
> >to fix it before the book went to press.
> >
> >As a result, thousands of engineers have spend countless time
> worrying
> >about right
> >angle bends.
> >
> >When we publish technical information such as this, it is important
> to
> >insure it
> >is accurate.
> >This applies especially to applications notes, whic often contain
> entirely
> >false
> >data.
> >
> >Lee
> >
> >Rich Peyton wrote:
> >
> > > FYI,
> > >
> > > The hard copy can be ordered free of charge.
> > >
> > > Rich
> > >
> > > Roehrner Wolfgang wrote:
> > >
> > > > http://www.onsemi.com/home <http://www.onsemi.com/home>
> > > >
> > > > In the Menu-tree go to:
> > > >
> > > > Technical Documents
> > > > CD/Document Ordering
> > > > General Search
> > > >
> > > > search for document number: hb205
> > > > download it as pdf (or order!).
> > > >
> > > > regards,
> > > > Wolfgang
> > > >
> > > > -----Original Message-----
> > > > From: Ashok Babu K [mailto:k.ashokbabu@gdatech.co.in]
> > > > Sent: Tuesday, April 10, 2001 12:39 PM
> > > > To: si-list@silab.eng.sun.com
> > > > Subject: [SI-LIST] : MECL System Design Handbook
> > > >
> > > > Hi all,
> > > > I see that a good resource for general high speed termination
> design and
> > > > especially ECL/PECL termination is Motorola's MECL System Design
>
> > Handbook by
> > > > Blood Jr., and William R. Many articles and papers specify the
> same as a
> > > > good resource. Unfortunately I could not get the soft copy of
> the MECL
> > > > System Design Handbook. I could not get it from the ON
> Semiconductor
> > > > website. If any of you have the PDF file of the same or know
> where it
> > can be
> > > > obtained, please inform me. Any suggestions of other resources
> are highly
> > > > welcome.
> > > > Regards,
> > > > Ashok.
> > > >
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>
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+
> | NORTH EAST SYSTEMS ASSOCIATES, INC. |
> | ------------------------------------- |
> | "High Performance Engineering & Design" |
> +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~+
> | Dr. Ed Sayre e-mail: esayre@nesa.com |
> | NESA, Inc. http://www.nesa.com/ |
> | Primrose Park Tel +1.978.392-8787 |
> | 5 LAN Drive, Ste 200 Fax +1.978.392-8686 |
> | Westford, MA 01886 |
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