[SI-LIST] Re: Question about split gnd planes
- From: "Manickavelu M." <manickavelu_m@xxxxxxxxxxxx>
- To: <istvan.novak@xxxxxxxxxxx>, "Ed Troy" <etroy@xxxxxxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 26 May 2006 10:20:05 +0530
Istan,
Is it not that the analog and digital grounds planes can not be connected
together anywhere but only under the chip that sources the analog signals?
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 [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of istvan.novak@xxxxxxxxxxx
Sent: Friday, May 26, 2006 6:26 AM
To: Ed Troy; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Question about split gnd planes
Ed,
Splitting more than one ground plane in the stackup requires a lot of
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>
Date: Thu May 25 15:38:33 CDT 2006
To: si-list@xxxxxxxxxxxxx
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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