Re: [SI-LIST] : May 9th Presentation: "Radiation from Edge Effects in Printe...

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From: Jim Freeman (freeman@broadcom.com)
Date: Tue May 09 2000 - 12:18:04 PDT


Hi,
    Would Innoveda be interested in funding such a project and providing lab
space for the effort.

Thanks
Jim Freeman

Chris Rokusek wrote:

> Mike,
>
> My interest in the 20H rule is to understand the mechanisms involved. I
> would like to quantify how well the 20H rule is able to reduce surface
> currents. I would like to quantify the magnitude of these surface currents
> with and without the 20H rule and compare. I would like to know what
> magnitude source is required to generate what magnitude surface currents. I
> would like understand the 20H rule's effects with and without other
> conductors on the board besides the planes. I would like to know whether
> the coupling to surface parts is capacitive or inductive or both. I would
> like to compare different stackups...
>
> Answers to these questions may allow better design techniques. Better
> decoupling can limit the source across the planes to safe level. Knowing
> the distribution of surface current can aid placement/routing. Knowing the
> coupling mechanisms can aid in placement/routiing. How can a board designer
> make tradeoffs among all the various design techniques (Timing/EMI/SI/etc.)
> without knowing the limits of each?
>
> Honestly I don't expect the answers to these tough questions to be posted on
> this list (great surprise if they would), but perhaps these SI-List threads
> will encourage a thesis or two and we can all catch the results at the next
> EMC Symposium.
>
> Knowledge is ultimate. Keep it coming!
>
> Chris Rokusek
> Innoveda
>
> > -----Original Message-----
> > From: owner-si-list@silab.eng.sun.com
> > [mailto:owner-si-list@silab.eng.sun.com]On Behalf Of MikonCons@aol.com
> > Sent: Monday, May 08, 2000 4:52 PM
> > To: si-list@silab.eng.sun.com
> > Subject: Re: [SI-LIST] : May 9th Presentation: "Radiation from Edge
> > Effects in Printe...
> >
> >
> > Chris R.:
> >
> > One exemplary case I recently came across had a series-terminated
> > clock line
> > that was immediately submerged to a stripline which went to a
> > connector on
> > the edge of a PCB. The optional card that would use the
> > connector was NOT
> > installed. The connector receptacle pin rose above the PCB about
> > 3/16 inch.
> > This small 3/16-inch stub coupled harmonic energy to the SURFACE
> > of the PCB
> > (a ground plane) at the SURFACE resonant frequency of the PCB. Surface
> > currents could be measured all over the surface ground plane
> > (with a small
> > Fischer Communications probe). NASTY radiation resulted.
> >
> > Simple removal of the series termination resistor at the clock driver end
> > reduced system radiation over 30 dB.
> >
> > The 20H rule had nothing to do with suppressing this radiation.
> > The moral?
> > Avoid inducing surface currents any way you can.
> >
> > Mike
> >
> > Michael L. Conn
> > Owner/Principal Consultant
> > Mikon Consulting
> >
> > *** Serving Your Needs with Technical Excellence ***
> >
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