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

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From: Lee Ritchey (leeritchey@earthlink.net)
Date: Fri Jan 14 2000 - 08:55:41 PST


Mitch,

Good reply. Actually, tests of this nature were done in the 80s. They just got misplaced and we did it again.

cadpro2k@DACafe.com wrote:

> 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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