[SI-LIST] Re: slots in planes (once again)
- From: steve weir <weirsi@xxxxxxxxxx>
- To: Gene Glick <gglick@xxxxxxxxxxxx>
- Date: Thu, 22 Jul 2010 11:47:22 -0700
This is one of those: It depends.
Slots are a method. Like any method if one applies them inappropriately
they add no value. And if one ignores their consequences then bad
things can happen.
When can one cross a slot?
When the resulting radiation from the slot is not large enough to be
a problem.
When the impedance discontinuity is not large enough to be an SI
problem to the signal(s) crossing.
When the energy injected into other structures is not large enough
to be a problem: victim crosstalk, PDN noise injection.
There are various techniques to reduce all three effects: By far the
simplest and most fool-proof is simply to avoid coupling energy into the
slot. Others like stitching capacitors, or skinny cavities that have
solid polygons on the other side reduce the impedance discontinuity
presented by the slot, but have limitations and side effects of their own.
Let me put it to you this way: If I have a board that can route in
fewer layers by crossing a slot or slots with a few signals, I am going
to do the homework to see if I can make that work. The likelihood of
finding a viable solution goes down geometrically with the number of
fast lines that would cross the slot(s).
Steve.
Gene Glick wrote:
> Realizing that slots in a plane (ground, for example) are a bad idea, is
> it ever acceptable?
>
> Here's something some info from Henry Ott:
> http://www.hottconsultants.com/techtips/tips-slots.html
>
> He says "don't", but then says well, if you do so, don't allow any lines
> to cross them. OK, I'm good by that. But, don't slotted planes give
> rise to eddy currents around the aperture (even if nothing ever crosses
> the slots)?
>
>
> gene
> ------------------------------------------------------------------
> 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 technical documents are available at:
> http://www.si-list.net
>
> List archives are viewable at:
> //www.freelists.org/archives/si-list
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
>
--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
------------------------------------------------------------------
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 technical documents are available at:
http://www.si-list.net
List archives are viewable at:
//www.freelists.org/archives/si-list
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
