[SI-LIST] Re: [SPAM] Re: Question about split gnd planes
- From: "JaMi Smith" <jamismith@xxxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 1 Jun 2006 22:03:27 -0700
Apple clames to have patents on a lot of things, including much of the
things that were developed by Xerox at their Park Research Center, which
Apple outright stole (although there are those that would argue that someone
at Xerox gae it to them). Regardless whether it was stolen or given to them,
they certainly are not in fact the true inventor of many of the things that
they have patented
I find it rather amusing that after all of these years of hearing Apple
owners slam non Apple users for having inferior equipment, Apple itself is
installing an Intel Processor. What is real telling here, is that Apple
themselves is doing it, rather than waiting for someone else to do it.
Remember the Apple II, how it's users touted it above all other systems,
such as S-100 systems running CP/M
. If you ask those Apple II owners what kind of cards they had plugged in, 9
out of 10 times, actually 99 out of 100 times, the first card they would
mention was the Microsoft Z80 Soft Card (sp?), not realizing that they
themselves were relying on Intel Technology (as interpreted by Zilog) in
which the Z80 Soft Card was really turning their system into a CP/M system
that used the Apple II as simply as an I/O Device.
Back to the issue of the patent, does anyone have a link?
You will probably find that Apple would not want to try and defend many of
their patents, just on the grounds that they would not pass the "prior art"
test.
But looking into the real issue behind this conversation, that of split
gtound planes, the "problem" of how to connect different grounds has only
appeared since we abandoned hand taping, and took up these infernal PCB
Design Systems that run on a PC or something else, where the software was
never written by someone that actually understood PCB Design itself, and
invented this system of "Drafting Rules" that was going to be compared to
your Design, during DRC (Drafting Rules Check(er)), whereby this System
which was written by person who is experientially an idot, is going to turn
around and tell you that your Design iis no good because it flunked the DRC.
The point here is that many times in real life you actually do want to
isolate planes, and have them connect only at one point, with what many call
a tie point, but much of todays PCB Software simply can't cope with such a
sitution.
The whole point here is this: Don't let a piece of software tell you what
you can and can't do. If you have a legitimate reason for making the DRC
blow up on itself, then don't worry about the DRC, just go ahead and do it,
but, it is good practice to document somewhere just why you violated the
DRC, simply so that it will be understandable by the next guy to work on
that board somewhere down the line in a couple of years.
Actually, why would you want to couple two different planes by a capacitor,
unless they actually had different DC Voltage sources and returns. In cases
such as the GND and AGND situation, I would prefer a ferrite bead myself,
which would actually provide for a commen electrical ground, and yet provide
some.noise immunity.
----- Original Message -----
From: <esayre@xxxxxxxx>
To: <joel@xxxxxxxxxx>
Cc: <manickavelu_m@xxxxxxxxxxxx>; <istvan.novak@xxxxxxxxxxx>; "Ed Troy"
<etroy@xxxxxxxxxxxxxxx>; <si-list@xxxxxxxxxxxxx>; <weirsi@xxxxxxxxxx>
Sent: Tuesday, May 30, 2006 10:19 AM
Subject: [SI-LIST] Re: [SPAM] Re: Question about split gnd planes
> 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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