Michael, What you are suggesting below is "tight coupling" of differential pair. Lee was bragging about not needing any coupling for differential pairs. If what he claims and what you mentioned below is the same, he will be contradicting himself. I am still waiting for him to answer my question : "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 ?" Like the famous quote, "I will be waiting until hell freeze over". -----Original Message----- From: Michael Chin [mailto:mchin@xxxxxxxxx] Sent: Sunday, October 12, 2003 10:40 AM To: scott@xxxxxxxxxxxxx Cc: bmgman@xxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Diff.Pairs Scott, I've followed your emails exchanges with Mike Brown closely. This subject is a very important item as we tackle high speed design using differential pairs. Today, we have differential pair in CMOS logic, LVDS, and differential HSTL (RLDRAM). Both of you have argued with very good points and I appreciated your thoughts. But in this case, I would side with what Lee has stated. He may not have explicitly stated the stackup in his assumption, but it is commonly referred as the the broad side coupled differential pair vs. edge coupled stripline differential pair. There is no question about the benefits and level of control from edge coupled differential where both tracks are routed on the same layer. But it is also very common to have a dual stripline layers between two Ground layers for broadside coupling. This is mostly used in the backplane side and have demonstrated success in many designs. An example of this stackup can be: ============= Ground plane for image return Core, thickness H ===== Diff Layer #1 Prepreg ===== Diff Layer #2 Core, thickness H ============= Ground plane for image return I have been to a lot of seminar where SI experts argued the Pro/Con of edge coupled vs. broadside coupled differential pair. I have seen good results from both styles on frequency under 3GHz. Just my two cents, Michael Chin ------------------------------------------------------------------ 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