RE: [SI-LIST] : Comments from your SI seminar (SendII)`

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From: Denomme, Paul S. (Paul.Denomme@viasystems.com)
Date: Wed Oct 27 1999 - 13:31:01 PDT


        Yes the high frequency content of the return current will couple
across the planes, the rising and falling edges is where the majority of the
expended energy can be found. In terms of delay and skew, it would be
minimal since the return current only needs to travel the distance from one
plane to another and back which in most cases would be less than 10 mils if
your planes are coupled properly. Remember that at high frequencys the
return current will travel the path of least impedance not resistance. With
closely coupled planes, the path of least impedance will be through the
power planes.

Paul Denomme

> -----Original Message-----
> From: Grasso, Charles (Chaz) [SMTP:GrassC@LOUISVILLE.STORTEK.COM]
> Sent: Wednesday, October 27, 1999 3:55 PM
> To: 'si-list@silab.eng.sun.com'
> Cc: 'EMC Group'
> Subject: RE: [SI-LIST] : Comments from your SI seminar (SendII)`
>
> Now hold on - in your answer you indicated a high frequency
> signalling environment.
>
> Remember - capacitance(& inductance) = delay = skew. Is this
> what we are really looking for in a high frequency signalling
> environment - Especially is skew is important?
>
> OK if the timing diagram is NOT critical and the signal
> is not "important" (eg reset) then maybe.
>
> Don't you mean that the high frequency content of the
> edges may couple across?
>
> -----Original Message-----
> From: Denomme, Paul S. [mailto:Paul.Denomme@viasystems.com]
> Sent: Wednesday, October 27, 1999 1:01 PM
> To: 'si-list@silab.eng.sun.com'
> Cc: 'EMC Group'
> Subject: RE: [SI-LIST] : Comments from your SI seminar (SendII)`
>
>
> In regards to comment 1. In a high frequency signalling environment, The
> return current will flow on the nearest plane whether it is power or
> ground.
> If you have two planes coupled closely togther you create a capacitor
> which
> the high frequency return current uses to traverse the planes and takes
> the
> path of least impedance.
> If there were not two planes coupled together, it would be an EMI
> catastrophe and you would not know where the return current is flowing.
>
> Regarding comment 2, he was stating that grounding in multiple locations
> is
> a bad idea. This can create some ground loops within the chassis. There
> will be some type of potential difference from one chassis connection
> point
> to another and this will create some current in the chassis. This is very
> bad from an EMI perspective.
> He believes one Solid connection to the ground plane is sufficient.
>
> I would like to hear a take from an EMI person.
>
> Regards,
>
> Paul S. Denomme
> Viasystems Inc.
> Richmond, VA
> paul.denomme@viasystems.com
>
>
> > -----Original Message-----
> > From: Grasso, Charles (Chaz) [SMTP:GrassC@LOUISVILLE.STORTEK.COM]
> > Sent: Wednesday, October 27, 1999 2:26 PM
> > To: 'leeritchey@earthlink.net'
> > Cc: 'EMC Group'; 'Signal Integrity'
> > Subject: [SI-LIST] : Comments from your SI seminar (SendII)`
> >
> > Sir,
> >
> > A collegue of mine has recently taken your SI seminar.
> > In discussing the class with him I came across two
> > statements from the semiar that I would like to discuss
> > with you and others in the EMC profession.
> >
> > Comment 1. On page 109 there is a slide that states:
> >
> > Traces crossing cuts in planes can function properly.
> >
> > Please explain your rationale.
> >
> > Comment 2: On page 110 there is a slide title:
> >
> > A bad grounding idea.
> >
> > The picture is of a board with multiple ground connections
> > and distances maked off as lambda/20
> >
> > Clearly this is a shot at the multiple stitching concept that
> > is prevalent in the EMC world.
> >
> > One of the problems in the EMC/SI world is that there is
> > contradictory information provided to the poor consumer.
> >
> > I look forward to a lively debate on these issues.
> >
> >
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