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

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From: ajmani@us.ibm.com
Date: Thu Jan 13 2000 - 17:31:39 PST


I had run 3-D simulations using a certain length of trace, first running it
straight, and then giving it several 90 degree bends. I did not observe
any significant change in emissions up to a frequency of 2 GHz. In our
board designs, I freely allow use of 90 degree bends.

Regards, Ravinder
PCB Development and Design Department
IBM Corporation - Storage Systems Division
Email: ajmani@us.ibm.com
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Always do right. This will gratify some people and astonish the rest.
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Doug McKean <dmckean@corp.auspex.com>@silab.eng.sun.com on 01/13/2000
03:33:57 PM

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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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