We use split planes all the time. When you have circuits of *vastl8 different noise floors co-existing on one board - it's the only way to go. Chas -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of steve weir Sent: Tuesday, April 07, 2009 10:11 AM To: Sol Tatlow Cc: si-list Subject: [SI-LIST] Re: Split gnd planes - for/against? Sol, unfortunately there is not a single answer. In most cases moating is a bad idea, particularly if one does not understand the caveats and how to deal with them. It's not just the moats: It's the placement, clearances, stitching, and routing that all need to be considered. Steve Sol Tatlow wrote: > I know this subject has been raised before, countless times in one > guise or another. I have also googled plenty. I'm not looking for > theoretical opinions, either, about whether or not, or when, they > should be used (specifically not, "it depends", unless you've got > REAL-LIFE examples, for and against!!!). > > This subject raised its head for me in this case due to using > 2 A/Ds as well as 2 D/As, both from Analog Devices, where one > specifies a split plane, the other specifies no split. Now, I am > all too wary of relying simply on evaluation boards, where, in > general, one layout is done, and if it works, that's how everyone > should do it (_without_ comparing 2 different approaches). > > I personally have 3 concrete cases where split gnds had no positive > effect on SI, but significantly worsened EMC results (despite > sticking to all the usual guidelines, like no tracks over the > splits, etc.), but I have no concrete case FOR split ground planes. > > So, what I'm interested in is: does anyone have CONCRETE examples > which they would like to share for/against split planes? The kind > of thing I mean would be like in one of the cases I had, where I > wanted to go against the suggested approach of using a split gnd, > and persuaded my customer to pay for 2 variants of the same board > on the same manufacturing panel, one with split ground, one with > solid ground. Both variants were assembled and tested, with regards > to both SI as well as EMC: both were functionally satisfactory; at > EMC testing, however, the split-plane bombed out big time, while > the non-split sailed through. I like to think that it wasn't due > to any screw-ups on my side, that the split ground failed - I am > not a newbie to PCB layouts, and, while for sure no professional > expert on all areas of SI, I believe I avoided the typical blunders > often present in split ground layouts. > > Anyway, my customer was more than happy, but not everyone has the > money/time/desire to do as I suggested. So, any 'war stories' to > support one or the other approach would be appreciated to help > expand my knowledge and understanding of this subject - obviously, > we all respect confidentiality, so I'm not looking for circuits, > layouts and so on, but I figure many of you must have stories that > can be related regarding this subject. Or perhaps some good links > to non-confidential 'real-life' examples/studies? > > Regards, > Sol > > -- Steve Weir Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 California office (866) 675-4630 Business (707) 780-1951 Fax Main office (401) 284-1827 Business (401) 284-1840 Fax Oregon office (503) 430-1065 Business (503) 430-1285 Fax http://www.teraspeed.com This e-mail contains proprietary and confidential intellectual property of Teraspeed Consulting Group LLC ------------------------------------------------------------------------ ------------------------------ Teraspeed(R) is the registered service mark of Teraspeed Consulting Group LLC ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.net 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 technical documents are available at: http://www.si-list.net 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