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

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From: Neeraj Pendse (cnepsc@ptg.nsc.com)
Date: Thu May 10 2001 - 14:32:10 PDT


Mike,

I think Dr. Johnson has a great article on his web page
www.signalintegrity.com that explains effects of bends.

- Neeraj

National Semiconductor Corp. (NYSE: NSM)
(408) 721-5226

>>>>>>>>>>>>>>>>>> Original Message <<<<<<<<<<<<<<<<<<

On 5/10/01, 9:07:56 AM, Michael Nudelman <mnudelman@tellium.com> wrote
regarding RE: [SI-LIST] : MECL System Design Handbook:

> In Johnson's book there is a chapter "Who's afraid of the big bad
bend?" (or
> is it in his course?)

> There is a capacitive property to a bend, but if you have 1-2-3 of
them at
> up to 10Gigs, the calculation showed that they don't really matter.
All
> those curved traces at these frequencies are more for designer's own
peace
> of mind, if he does not want to see dreams about the "Big Bad Bend"
for a
> couple of weeks before the final release.

> Mike

> -----Original Message-----
> From: Chris Padilla [mailto:cpad@cisco.com]
> Sent: Thursday, May 10, 2001 12:46 PM
> To: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : MECL System Design Handbook

> Lee,

> It is not a myth, there is "some kind of effect" from right angle
bends.

> The real question is, I believe, "Do I care, given the speed and/or
> frequency content of the signals I am dealing with?"

> For most of us right now, on this list, we probably *should not* care
as
> you point out.

> If one is designing a 50 GHz antenna, then it might make a world of
> difference!

> Out of curiosity, what kind of rise time were you pushing through that
> right angle bend? 100 ps? I am farily certain that I've seen some
small
> dips (aka capacitance) through right angle bends but I cannot honestly
say
> that it was directly attributed to the bend.

> Thanks----->Chris

> >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

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