[SI-LIST] Re: Question about split gnd planes

 Hi Troy,
If  u have several ground layers,Why can't you give a continous plane for
this particular one?

Anyway if you want to splitt GND plane, jus make sure that all the signal
routed  for that session refers  to the same GND.Do the placement
isolation accordingly . I don't think you  need to split the other
planes.

Sreekanth Nampoothiri

EDA Interoperability,

PTC.

  ----- Original Message -----
  From: "Ayan Bhattacharyya"
  To: weirsi@xxxxxxxxxx, "Manickavelu M." , istvan.novak@xxxxxxxxxxx,
  "Ed Troy" , si-list@xxxxxxxxxxxxx
  Subject: [SI-LIST] Re: Question about split gnd planes
  Date: Fri, 26 May 2006 17:02:49 +0530


  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
  > 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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