[SI-LIST] Re: Is a copper plane not tied to any net a reference plane?
- From: Ege Engin <engin@xxxxxxxxxx>
- To: ericsilist@xxxxxxxxx
- Date: Wed, 05 May 2004 11:22:37 +0200
Eric,
I will assume a simpler case in that the medium is homogeneous (for
example all planes are embedded in FR4). The two planes and the signal
line can be considered as a 3-conductor transmission line. Consequently,
the two TEM modes of concern here are the stripline and parallel-plate
modes. For signal transmission, stimulation of the parallel-plate mode
is not desired, since it results in voltage fluctuations between the
planes.
Both modes are excited in this 3-conductor transmission structure
assuming that it is terminated in a way that the return current is
forced to flow on the GND at the driver and receiver. The parallel-plate
mode is excited with a mode current equal to I*H1/(H1+H2), where I is
the current on the signal line, H1=100mil, and H2=5mil. For wide planes,
the parallel-plate mode can be considered as a radial wave (Larry gives
a qualitative description of how this wave propagates). This current is
normally not compensated by the signal return current; therefore, there
is a current on both planes.
Ege
eric steimle schrieb:
>
> I?m trying to settle an argument without saying which
> side I?m on, and I was hoping someone could give a
> quick and easy example to prove this.
>
> You have a four layer board that looked like this
>
> SIG1
> GND
> VCC
> SIG2
>
> And the maximum rise time on the board was about 2ns
> (say a 100MHz clock), then if I ran a trace from one
> IC to another on SIG1 the return current would flow
> along the GND plane (assuming no splits in the plane
> etc.)
>
> What if I covered SIG1 with a plane of copper say
> hovering 5 mil above SIG1, and then made the distance
> between SIG1 and GND 100mil so..
>
> Plane sheet of Copper
> 5 mil of air
> SIG1
> 100 mil FR4
> GND
> VCC
> SIG2
>
> Now that plane sheet is not GND and it has no
> association to any net it is just a continuous sheet
> of copper about the size of the board. One of us
> argues that the return current will continue to flow
> along the GND plane as it did before. The other
> argues that the return current will instead flow
> mostly along that sheet of copper unitl it jumps back
> to the GND plane as it gets closer to the IC. Any
> help in this would be much appreciated.
>
> Thanks
>
>
>
> __________________________________
> Do you Yahoo!?
> Win a $20,000 Career Makeover at Yahoo! HotJobs
> http://hotjobs.sweepstakes.yahoo.com/careermakeover
> ------------------------------------------------------------------
> To unsubscribe from si-list:
> si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
>
> or to administer your membership from a web page, go to:
> //www.freelists.org/webpage/si-list
>
> For help:
> si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
>
> List FAQ wiki page is located at:
> http://si-list.org/wiki/wiki.pl?Si-List_FAQ
>
> List technical documents are available at:
> http://www.si-list.org
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
> or at our remote archives:
> http://groups.yahoo.com/group/si-list/messages
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
--
Diese E-Mail kann Betriebs- und Geschäftsgeheimnisse, dem
Anwaltsgeheimnis unterliegende oder sonstige vertrauliche
Informationen enthalten. Sollten Sie diese E-Mail irrtümlich
erhalten haben, ist Ihnen die Kenntnisnahme des Inhalts,
eine Vervielfältigung oder Weitergabe der E-Mail ausdrücklich
untersagt. Bitte benachrichtigen Sie den Absender der E-Mail
und vernichten die empfangene E-Mail. Vielen Dank.
Since this e-mail contains confidential information, it must
be treated with utmost confidentiality. Any person who may
get in contact with this information by mistake should not
take any notice of the topic and should not pass on or
duplicate any part of this information. The e-mail has to be
destroyed and the sender of the the e-mail has to be informed
immediately.
Thank you.
-- Binary/unsupported file stripped by Ecartis --
-- Type: text/x-vcard
-- File: engin.vcf
-- Desc: Visitenkarte für Ege Engin
------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field
or to administer your membership from a web page, go to:
//www.freelists.org/webpage/si-list
For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field
List FAQ wiki page is located at:
http://si-list.org/wiki/wiki.pl?Si-List_FAQ
List technical documents are available at:
http://www.si-list.org
List archives are viewable at:
//www.freelists.org/archives/si-list
or at our remote archives:
http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
