Howdy, In response to one of the questions that I received off-line; >> do u think its good that the tool allows >> the merging of two nets without a DRC error No, I believe using a net short capability in any package is bad design practice and I strongly urge and suggest other ways to work around it. Though in the end, it is the customer or more senior design engineer at my current employer who makes the final decision because I want all of us to be pleased with the product. If I must short the nets, I will put a note in the readme file with the offending object's X:Y coordinates included with the manufacturing files. Thanks goes to the Cadence forum as well as this list that I did not have to learn this issue the hard way. Cheers! Drew ----- Original Message ----- From: Sol Tatlow To: drew3rdof3@xxxxxxxxxxxx ; si-list@xxxxxxxxxxxxx Sent: Sunday, May 28, 2006 2:58 PM Subject: Re: Question about split gnd planes/"tools to predict Radiated Emissions" As Drew states, there are possibilities with at least these 2 (and as per my experience at least 5 other tools) that allow this to be done in one way or another - certainly a specific CAD system need in no way be a reason for only realising one system or another, if the CAD operator even half-way knows his stuf ... As the significant amount of often contradictory evidence might suggest, I believe there is no one blanket solution for all cases. However, one can perhaps (underline 'perhaps') make the blanket statement that single-plane gnd systems are at least better for EMC (EMV) reasons, and in some cases (again, underline 'some', although here, in particular, I can support this with my own layout experiences in high quality analog audio system designs!) even for audio reasons. I also believe that this overlaps, to a large degree, the subject of "tools to predict Radiated Emissions" - here, I have to say, that, IMHO, software tools are way off resembling even simple real-life situations, where tolerances with regards to manufacturing and assembling 'simple' cable assemblies are not even close to being represented (although they must have a really significant effect with regards to phase related radiations). Would that the situation was different ... and, of course, it should all cost nothing!! On the upside, I guess we can only expect things to get better (at least with respects to the long term development of the quality of the actual results :)!!). ____________________________________ Sol Tatlow, M.Eng. (Oxon) Pro Design Electronic GmbH Product Developer Albert-Mayer-Str. 16 D-83052 Bruckmuehl Phone: +49 (0) 8062/808-302 Fax: +49 (0) 8062/808-333 Mailto:sol.tatlow@xxxxxxxxxxxxxxxxxxxx www.prodesign-europe.com ____________________________________ -----Ursprüngliche Nachricht----- Von: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] Im Auftrag von Andrew W. Riley III Gesendet: Freitag, 26. Mai 2006 21:35 An: si-list@xxxxxxxxxxxxx Betreff: [SI-LIST] Re: Question about split gnd planes 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 > > ------------------------------------------------------------------ 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