[SI-LIST] Re: [SPAM] Re: Question about split gnd planes
- From: esayre@xxxxxxxx
- To: joel@xxxxxxxxxx
- Date: Tue, 30 May 2006 10:19:10 -0700
All:
Please look into the patent apple claims to own for caps across split
planes. I haven't read anywhere that apple patent attorney's have said
its OK to violate their patent.
This is just another examp-le of poor review of patents and the abuse of
simp0le but effective fixes that should be available to all. I am sure
there is prior art which would make this patent unenforcable.
ed
==========
Dr. Edward P. Sayre, P. E.
North East Systems Associates, Inc.
1 South Avenue, 3rd Floor
Natick, MA 01760
[T] 508-652-0088
[F] 508-652-0083
> -------- Original Message --------
> Subject: [SPAM] [SI-LIST] Re: Question about split gnd planes
> From: Joel Brown <joel@xxxxxxxxxx>
> Date: Tue, May 30, 2006 9:26 am
> To: weirsi@xxxxxxxxxx
> Cc: manickavelu_m@xxxxxxxxxxxx, istvan.novak@xxxxxxxxxxx, Ed Troy
> <etroy@xxxxxxxxxxxxxxx>, si-list@xxxxxxxxxxxxx
>
> This is similar to a question I posted about an Intel app note for an
> Ethernet controller that recommended a plane split between the controller
> andEthernet connector with built in magnetics. Intel also suggested that
> capsof various values might be needed to bridge across the split which would
> seem to negate the purpose of the split. Our EMI consultant said do not use
> aplane split. Most responses I got back said the plane split was necessary
> toprevent common mode noise on the ground plane from coupling across the
> Ethernet magnetics which are designed to attenuate common mode noise. I also
> had a thought to eliminate ground planes around the Ethernet connector
> excepton the bottom layer of the board thinking there would be less coupling
> from the bottom of the board to the Ethernet connector. My understanding of
> plane splits is this: a plane split is a slot antenna, there is likely to be
> an RF potential with respect to the ground planes on either side of the
> splitwhich energizes the antenna and causes radiation. This can be mitigated
> by bridging across the plane split with capacitors at intervals which are
> small compared to the wavelength of the noise on the planes. This is more
> commonly done with plane splits where the DC voltages of the planes are at
> different potentials.
> Joel
>
>
> steve weir wrote: Manix, no. There are many misconceptions out there about
> the myth of ground and its relation to noise isolation. Those myths get
> propagated into misguided applications of moats and such. Think in fields
> andthe misconceptions go away. Steve. At 09:50 PM 5/25/2006, Manickavelu M.
> wrote: Istan, Is it not that the analog and digital grounds planes can not
> beconnected together anywhere but only under the chip that sources the
> analogsignals? Also that while coupling these two planes we should not use
> direct Cu plane connection but couple them via inductors? Manix, MindTree.
> -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx[1]
> [mailto:si-list-bounce@xxxxxxxxxxxxx[2]] On Behalf Of
> istvan.novak@xxxxxxxxxxx[3] Sent: Friday, May 26, 2006 6:26 AM To: Ed Troy;
> si-list@xxxxxxxxxxxxx[4] Subject: [SI-LIST] Re: Question about split gnd
> planes Ed, Splitting more than one ground plane in the stackup requires a
> lotof consideration, and mostly it is not necessary. Isolating a sensitive
> circuit (e.g., analog input, low-jitter oscillator) may be a good idea, but
> instead of cutting a large solid ground plane, you may want to try first to
> put the circuit to be isolated on a grounded patch on a 'non-ground' layer.
> You can make ground surface patches under and around your circuit to be
> isolated, or you can put the patch on a signal layer. Regards, Istvan Novak
> SUN Microsystems From: Ed Troy <etroy@xxxxxxxxxxxxxxx>[5] Date: Thu May 25
> 15:38:33 CDT 2006 To: si-list@xxxxxxxxxxxxx[6] Subject: [SI-LIST] Question
> about split gnd planes If you have a circuit board that requires a split gnd
> plane over a small section of the board, and you have several ground planes,
> should only one have the split (the one nearest the side containing the
> components that require analog ground) while the rest of the ground planes
> are continuous, or should the split section be on all ground layers? I would
> think that you should only have it on one layer. Also, if it should only be
> on one layer, I would imagine it would be best to connect it to the digital
> ground with one, and only one, via. Is that generally correct? What are some
> good references for layer stackups, etc? I know I saw one, once, but can't
> remember where. Ed
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