[SI-LIST] Re: Question about split gnd planes
- From: "Andrew W. Riley III" <drew3rdof3@xxxxxxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Fri, 26 May 2006 12:34:57 -0700
Just a note,
>> As per I know no tool will allow you
>> to connect the AGND and DGND directly
Allegro and the Altium package that I am now forced to deal with have this
capability. And I can't imagine that no others have the same capability.
Cheers!
Drew
----- Original Message -----
From: Ayan Bhattacharyya
To: weirsi@xxxxxxxxxx ; Manickavelu M. ; istvan.novak@xxxxxxxxxxx ; Ed Troy ;
si-list@xxxxxxxxxxxxx
Sent: Friday, May 26, 2006 4:32 AM
Subject: [SI-LIST] Re: Question about split gnd planes
Hi,
As per I know no tool will allow you to connect the AGND and DGND
directly....u can connect them through CAPs also...
Else in same ground plane u can maintain less noise interference by making
bottle-necks in the layout for the different noise sources.
"Istvan Novak"'s approach is a good one...ground guard signals also help a
lot ...specially for clock signals...around crystals.
Regards
Ayan Bhattacharyya.
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of steve weir
Sent: Friday, May 26, 2006 4:47 PM
To: Manickavelu M.; istvan.novak@xxxxxxxxxxx; Ed Troy; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Question about split gnd planes
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 and the 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 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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