Hi Steve, I agree with you that to split GND plane is useful method for many situations in RF or analog circuit design. But in general, the price it paid in terms of routing difficulty and more noise introduced make it not practical for high-density high speed digital system on both package and PCB level. Thanks Tony -----Original Message----- From: steve weir [mailto:weirsi@xxxxxxxxxx] Sent: Thursday, April 09, 2009 6:23 PM To: Tony Luan Cc: Sol Tatlow; si-list@xxxxxxxxxxxxx Subject: Re: [SI-LIST] Re: Split gnd planes - for/against? - Thanks! Tony usually that is the right decision. However, there are cases when a package will not fit and still provide adequate isolation between circuits without implementing a split. These don't happen in digital designs running one signaling level. But suppose that you have a big digital bus switching 5A / ns that is 0.25" away from some analog circuit that is sensitive to 10uV noise. Do you think the 0.25" separation will be enough? If you cannot change the placement to put the analog circuitry further away, what will you do? Steve. Tony Luan wrote: > Hi Sol, > > I think to split GND plane is not a good idea. > For any high frequency noise, GND and power plane are playing completely > equivalent role. How can a high frequency noise tell which plane is GND? > Which plane is power? Why not split power plane instead and keep a solid > complete GND plane, because in package or PCB, we have tons of power > rails and power islands already. > The biggest disadvantage to split GND plane I saw is that it increases > routing difficulty when try to avoid high speed signal, clock, parallel > bus across those gaps on GND plane. > > Thanks > Tony > -----Original Message----- > From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] > On Behalf Of Sol Tatlow > Sent: Thursday, April 09, 2009 4:58 AM > To: si-list@xxxxxxxxxxxxx > Subject: [SI-LIST] Re: Split gnd planes - for/against? - Thanks! > > One last mail to put this thread 'to bed'... > > Thanks to everyone who took the time to reply, particularly to > those who actually gave me what I asked for, those reluctant beasts, > the real-life examples - it's great that you're willing to so fully > participate in such a discussion. After all, theory is great; > coupled with real-life examples it's even better. > > Of course, the specific examples can't be applied 1:1 to any other > design, as has been said 'x' times, but I, for one, am nevertheless > wiser for the experiences that have been shared... I believe I'm a > good engineer, but won't stop learning 'till the day I die. > > It was also good to see that I am not the only one suffering at the > hands of less-than-perfect datasheets and the implementation of > often contradictoray 'hints' :) - regardless of simulation results > and past experiences, it's not always easy when it comes to > persuading a customer, who is still convinced that app notes are > written by all-knowing beings, to 'do the right thing'. > > 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