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 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ List technical documents are available at: http://www.si-list.org List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu