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

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From: Chris Heard (chris_heard@cereva.com)
Date: Sun Jan 16 2000 - 17:37:22 PST


Scott,

What are the harmonics of the signal spectrum that need to be in the 5-10GHz
range in order for an additional C to take effec? When that question is
answered, the fundamental frequency and associated Tr may be implied as
well.

Chris
-----Original Message-----
From: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]On Behalf Of Scott McMorrow
Sent: Saturday, January 15, 2000 3:34 PM
To: si-list@silab.eng.sun.com
Subject: Re: [SI-LIST] : What's your favourite Screwy SI Concept?

At least not until about 5 to 10 GHz

regareds,

scott

Lee Ritchey wrote:

> 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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-- Scott McMorrow Principal Engineer SiQual, Signal Quality Engineering 18735 SW Boones Ferry Road Tualatin, OR 97062-3090 (503) 885-1231 http://www.siqual.com

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