Srikanth, A rough rule of thumb is greater than 3 times trace width separation between pairs. Using a 2D field solver will ultimately give you the crosstalk coupling factor for the exact geometry in your stackup, and dictate the routing rules you need to follow to satisfy your noise budget. Adding GND guarding will more often than not present more issues than it solves. You should stitch these guard traces at regular intervals approximately 1/10 of the wavelength of the highest frequency component of the aggressor signal to avoid it from resonating and coupling noise back onto other adjacent traces. This further reduces routing density of the board. By the time you factor in the additional space of one trace width between the guard trace and Diff pair, plus the additional via stitching, you will find you are already at 3 times separation between pairs and you would gain back more real estate. Regards, Bert Simonovich -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of chundi srikanth Sent: October-16-09 12:40 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Routing guidelines for 3.12Gbps LVDS pairs Hi Techies, We have a 12-layer board in which we have lot of differential LVDS pairs operating at several hundreds MHz. And we have SERDES signals (differential TX & RX pairs) operating at CPRI rate-4 i.e., 3Gbps. So can you just share me some inputs on exactly what are the guidelines to be followed while routing these signals. And is GND gaurding between the differential pairs improve the SI?Please share or refer me any documents in which i can get Good information on High-Speed design guidelines. Thanks With Best Regards Srikanth ------------------------------------------------------------------ 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