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

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From: Lee Ritchey (leeritchey@earthlink.net)
Date: Sat Jan 15 2000 - 12:13:46 PST


True. But is the added C significant? Answer, no!!!

Tom Dagostino wrote:

> Bending a wire keeps a uniform cross section. Putting a corner in a trace
> adds extra C at the corner from a larger area.
>
> Tom Dagostino
> ICX Modeling Group
> tom_dagostino@mentor.com
> 503-685-1613
>
> -----Original Message-----
> From: owner-si-list@silab.eng.sun.com
> [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Jian Zheng
> Sent: Thursday, January 13, 2000 4:33 PM
> 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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