[SI-LIST] AW: Split in Reference Planes for XAUI

  • From: "Havermann, Gert" <Gert.Havermann@xxxxxxxxxxx>
  • To: "Subramanya_CK@xxxxxxxxxxx" <Subramanya_CK@xxxxxxxxxxx>, "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
  • Date: Mon, 25 Jun 2012 07:33:48 +0000

Subramanya,
the only way to keep reference over splited plane is to use stitching caps to 
provide a current return path from one plane to the other. This is not an ideal 
solution, as crosstalk will rise, but at least it helps to control EMC 
behavior. You can also use an non symmetrical impedance cell that keeps the 
signal lines closer to the non splitted GND-plane (i.e. thin dielectric between 
signal and gnd, and thicker dielectric between power and signal). This reduces 
the amount of return current that has to pass the split.

Regarding the copper thickness I recommend to use the SI-List archive 
//www.freelists.org/archives/si-list there have been many useful 
information, software tool recommendations and formulas that were discussed.

BR
Gert


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-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im 
Auftrag von Subramanya C.K
Gesendet: Montag, 25. Juni 2012 08:20
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Split in Reference Planes for XAUI

Dear Gurus,
This is an old topic on split planes, but just wanted to get an opinion from 
experts regarding reference plane for XAUI signals in my current assignment.
There is a possibility that some of these XAUI lines in my new PCB might cross 
the split planes in power layer that is beneath this signal layer where these 
XAUI lines are routed. These islands in the power layer are used for -48V and 
RTN power rails of the system. I am unable to accommodate these lines elsewhere 
on the PCB due to space constraints. Is there any way by which I don't end up 
losing ground reference for these lines?

Another question, is there a rule of thumb to determine the copper thickness / 
area of copper layers based on the power requirement?

Thank you all in advance for your help..

Best Regards,
Subramanya C K

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