[SI-LIST] Re: Split Ground Planes

Doug,

Well put.

Lee W. Ritchey
Speeding Edge
P. O. Box 2194
Glen Ellen, CA 95442
Phone- 707-568-3983
FAX-    707-568-3504

I just used the energy it took to be angry to write some blues.
Count Basie


> [Original Message]
> From: Doug Smith <doug@xxxxxxxxxx>
> To: <jose_moreira@xxxxxxxxxxx>
> Cc: <si-list@xxxxxxxxxxxxx>
> Date: 10/26/2004 3:04:16 PM
> Subject: [SI-LIST] Re: Split Ground Planes
>
> Hi Jose and the group,
>
> I normally reply personally to people to avoid the glut of 
> "out-of-office" messages, but feel I needed to add to this discussion.
>
> Signal propagation is an important but small part of the trouble you 
> can get into with split planes if not implemented properly. Even if 
> you manage to get the signal propagation right, system reliability can 
> be severely compromised as it is easy to turn every cable in the 
> system into a great receiving array to pick up impulses you can easily 
> miss in the lab, but your customers won't!
>
> I worry also about the common mode voltage that can result across the 
> board and drive enclosures, cables, etc. This voltage will cause 
> radiation that depends on a lot more that the board itself. Also 
> common mode voltages can be developed from outside sources as 
> mentioned above.
>
> There are probably thousands of modes to get in trouble with split 
> planes of which the referenced paper covers a subset. You can cover 
> many of the problems by not ever allowing a trace to cross the slit. 
> Even DC signals like LEDs are generally too noisy to allow to cross a 
> slit in many cases.
>
> Most of the examples of splitting up ground planes I have seen were 
> not necessary and just caused problems (remember that at high 
> frequencies everything is connected together whether you want them to 
> be or not, lots of articles on my website about this effect). There 
> are a few justified cases though. Video can be one example where the 
> signal can be degraded by just a small amount of powerline current 
> (hum bars in the video).
>
> In general, I would not recommend splitting planes unless you can 
> state and MEASURE (to confirm) why a split plane is needed.
>
> Doug
>
> jose_moreira@xxxxxxxxxxx wrote:
>
> > Nikhil,
> > 
> > you can find the article on the IEEE xplore site (if you have acess) or
=
> > in a library.
> > 
> > Details:
> > 
> > Signal propagation and radiation of single and differential microstrip =
> > traces over split image planes
> > Orhanovic, N.; Raghuram, R.; Matsui, N.;
> > Electromagnetic Compatibility, 2000. IEEE International Symposium on  =
> > ,Volume: 1 , 21-25 Aug. 2000=20
> > Pages:339 - 343 vol.1
> > 
> > Best Regards
> > Jose
> > 
> > -----Original Message-----
> > From: si-list-bounce@xxxxxxxxxxxxx
> > [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Nagel, Michael
> > Sent: Dienstag, 26. Oktober 2004 16:39
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Re: Split Ground Planes
> > 
> > 
> > Nikhil,
> > 
> > There is a quite instructive paper with the title:
> > 
> > Signal Propagation and Radiation of Single and Differential
> > Microstrip Traces Over Split Image Planes
> > 
> > written by:
> > N. Orhanovic, R. Raghuram, N. Matsui
> > from: Applied Simulation Technology
> > e-mail: { neven, raghu, matsui} @apsimtechcom
> > 
> > Unfortunately I have no direct link to the document.
> > 
> > Generally spoken - the split plane itself may not be
> > harmful in terms of EMI unless you start routing=20
> > traces across the gap!
> > 
> > Best regards,
> > Michael
> > 
> > 
> > -----Original Message-----
> > From: Nikhil Patel [mailto:npatel@xxxxxxxxxxxxxxxxxxx]
> > Sent: Dienstag, 26. Oktober 2004 15:40
> > To: si-list@xxxxxxxxxxxxx
> > Subject: [SI-LIST] Split Ground Planes
> > 
> > 
> > Hi all,
> > =20
> > 
> > I have been doing a lot of reading on Split ground planes and am a bit
> > confused now. Do most people use just one solid ground in the schematic
=
> > and
> > layout for EMI issues or do you prefer split ground planes? Any input is
> > greatly appreciated.=20
> > 
> > =20
> > 
> > Thanks
> > 
> > =20
> > 
> > Nikhil=20
> > 
> > =20
> > 
> > 
> > 
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>
> -- 
> -------------------------------------------------------
>      ___          _       Doug Smith
>       \          / )      P.O. Box 1457
>        =========          Los Gatos, CA 95031-1457
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