From: Grasso, Charles (Chaz) (GrassC@LOUISVILLE.STORTEK.COM)
Date: Wed Oct 27 1999 - 12:55:07 PDT
Now hold on - in your answer you indicated a high frequency
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?
From: Denomme, Paul S. [mailto:Paul.Denomme@viasystems.com]
Sent: Wednesday, October 27, 1999 1:01 PM
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.
Paul S. Denomme
> -----Original Message-----
> From: Grasso, Charles (Chaz) [SMTP:GrassC@LOUISVILLE.STORTEK.COM]
> Sent: Wednesday, October 27, 1999 2:26 PM
> To: 'firstname.lastname@example.org'
> Cc: 'EMC Group'; 'Signal Integrity'
> Subject: [SI-LIST] : Comments from your SI seminar (SendII)`
> 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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