I would like you to answer a simple question : If tomorrow you are going into a client's office to consult on designing a 2.4GB/s differential signal system. Will you recommend them to "routed thousands of differential signal where each member of the pair is on a different layer". Do you think that is good engineering practice ? Do you think you can still keep your job as a consultant after making that statement ? We all cheat in some of our design, when spacing is tight we might change the minimum separation between trace from x mils to y mils. And most of the time we can get away with it because everything being worst case and fail your margin is very rare. But that doesn't mean it is good design practice or something you should brag about. This is a public discussion forum and people are welcome to share whatever ridiculous idea they have as long as they themselves believe in it and actually practicing it. I just want to make sure you "talk the talk and walk the walk". -----Original Message----- From: Lee Ritchey [mailto:leeritchey@xxxxxxxxxxxxx] Sent: Thursday, October 09, 2003 9:30 AM To: Doug Brooks; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Diff.Pairs ..........................This is a very common termination for 2.4 GB/S signal links. It is time to stop representing differential signals as needing to be tightly coupled to each other in order to operate properly. It is simply not so. I have routed thousands of differential signal where each member of the pair is on a different layer. If this were not possible, 1 mm pitch BGAs with differential signals would be un routable. There are tens of thousands of such parts being shipped every month on PCBs where they are routed apart from each other. This is all described in my recently published book, "Right the First Time, A Practical Handbook on High Speed PCB and System Design". It is also covered in Howard Johnson's new book whose title escapes me at the moment.. Lee ------------------------------------------------------------------ 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 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