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

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From: Ritchey Lee (leeritchey@earthlink.net)
Date: Tue May 15 2001 - 05:16:07 PDT


Chris,

IF you have seen dips at right angle bends, could you share you test
setup and measurements with us?

Lee

Dagostino, Tom wrote:

>
>
> If you look at the cross section of the trace at the bend it gets
> wider. A wider trace has more C per unit length. More C will look
> like a lower Zo. I've seen dips in impedance TDR'ing right angles.
>
> Tom Dagostino
> IBIS and Tau Modeling Manager
> SDD
> Mentor Graphics Corp.
> 503-685-1613
> tom_dagostino@mentor.com
>
> -----Original Message-----
> From: Chris Padilla [mailto:cpad@cisco.com]
> Sent: Thursday, May 10, 2001 9:46 AM
> 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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