RE: [SI-LIST] : What's your favourite Screwy SI Concept?

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From: cadpro2k@DACafe.com
Date: Thu Jan 13 2000 - 16:45:04 PST


Boys, you better read the latest from www.UltraCad.com Doug Brooks (with
the help of Lee Ritchey, or because of Lee) did some very well defined
test cases dealing with 90 degree bends, and you might be surprised with
the findings. I peronally don't do 90 degrees, since I let the
autorouter miter every trace, but I certainly don't do much clean up
either if something doesn't look "cosmetically" pretty. ;)

If this data had been done easlier (maybe in the 80's), we all might be
seeing boards with nothing but 90 degree traces! Enough said. Another
engineering "myth" disproved. :)

Mitch

---------Included Message----------
> Date: Thu, 13 Jan 2000 16:32:30 -0800
> From: "Jian Zheng" <jian@zeland.com>
> Reply-To: <si-list@silab.eng.sun.com>
> To: <si-list@silab.eng.sun.com>
> Subject: RE: [SI-LIST] : What's your favourite Screwy SI
Concept?
>
> Hi, Doug:
>
> Following are the comments I would like to make on right angle
corners:
>
> Normally, one bend should not create much radiation at relative
low
> frequency. The radiated power from a corner is normally very
small compared
> to the transmitted power when the trace to ground plane distance
is much
> smaller than one wavelength. Assuming your signal's frequency is
1 GHz and
> you are using silicon substrate, one wavelength in free space is
about 1
> foot at 1 GHz. One wavelength in the silicon substrate is about 4
inches.
> You do not need to worry about the radiation from the corners if
your
> substrate thickness is smaller than 0.2 inches (200 mils). The
radiation
> from a bend normall will be smaller than 1% of the transmitting
power.
>
> The problem is many bends. If one corner radiates 0.1% of the
power, then 10
> corners will radiate 1% of the power. 100 corners will radiate
10% of the
> power. Not only that, the biggest problem is the resonances
caused by the
> corners. When you have multiple corners, there might be some
reflection back
> and forth to create resonances. When a resonance happens, it is
possible
> much of the power will be radiated.
>
> Thanks!
>
> Best regards,
>
>
>
----------------------------------------------------------------------------
> ------------
> Jian-X. Zheng, Ph.D
> Zeland Software, Inc., 39676 Mission Blvd., Fremont, CA 94539,
U.S.A.
> Tel: 510-797-8109, Fax: 510-797-8241, Web: http://www.zeland.com
>
----------------------------------------------------------------------------
> ------------
>
> > -----Original Message-----
> > From: owner-si-list@silab.eng.sun.com
> > [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Doug
McKean
> > Sent: Thursday, January 13, 2000 3:34 PM
> > To: si-list@silab.eng.sun.com
> > Subject: Re: [SI-LIST] : What's your favourite Screwy SI
Concept?
> >
> >
> > Well, to continue, here's another one that has
> > me scratching my head frankly.
> >
> > SI Concept: Avoid Right Angle Corners in Traces
> >
> > Underlying Concept: Right Angle Corners in traces
> > decrease signal integrity/
> > increase emi ...
> >
> > Why It's Used: There may be some truth to it.
> >
> > Now, as far as Maxwell goes, we should see an
> > increase in radiation. But as far as I've read
> > and experimented, I just did a little mockup in
> > the chamber moments ago, the effect is minor.
> > It may in fact signify nothing.
> >
> > For instance, I take a six inch piece of wire,
> > stick it in one end of a barrel connector and
> > stick the other end of the barrel connector
> > to a coaxial cable which is connected to the
> > tracking generator of a Spectrum Analyzer.
> > This is my output.
> >
> > >From 0 to 1.3 GHz I see a particular maximized
> > profile on the SA at 3 meters. I then force a
> > sharp right angle in the wire and maximize again.
> > The profile at 3 meters has changed but slightly.
> > but, this is far field.
> >
> > I disconnect the antenna, disable the antenna
> > factors, connect directly to the SA a near
> > field probe and measure along the wire. At the
> > bend of the wire when compared to a straight
> > geometry, there is approx (very hard to tell)
> > a +3 dB increase. And there could be a host
> > of errors here. But I would expect some sort
> > of change.
> >
> > Now this might not say anything for emissions.
> > As far as a tdr in concerned, I doubt it would
> > show a significant change in impedance to worry.
> > BUT, the change in near field amplitude makes me
> > suspect a corresponding increase in crosstalk
> > (perhaps minor) say in a bus architecture. A
> > tight high speed bus architecture.
> >
> > The above experiment strictly an observation.
> >
> > Comments? - Doug McKean
> >
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> >
>
>
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