Without a ground plane you will not be able to achieve 50 Ohm impedance with an edge coupled diff pair. Even with a spacing (air gap) equal to line width, and assuming 50 Ohm line impedance, ~90% of the return current still flows in the ground plane. Removing ground plane here will result in a very high characteristic impedance. Examples without a ground plane would be twisted pair cables, but here the spacing is much smaller than the wire diameter. Wolfgang -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of krishna@xxxxxxxxxxxxxxxxxxx Sent: Friday, March 16, 2012 12:47 PM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Differential Traces and GND planes Hi Everyone, Differential traces perfectly cancel out the noise induced on the trace provided the length of the two lines are same and are closely tied up all along with the controlled impedance maintained throughout the routing. But what is not sure is 1. Whether a solid ground plane is needed for a differential pair for getting the full benefit of differential traces? 2. Are there any special considerations in making the choice - to consider providing solid GND plane or get away with it - for say, better EMI/EMC and crosstalk performance? 3. Is there any trade off involved? Would you please help me get things right here if my understanding is wrong? Thank you very much, With Thanks and Best Regards, Krishna. ------------------------------------------------------------------ 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list 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 forum is accessible at: http://tech.groups.yahoo.com/group/si-list List archives are viewable at: //www.freelists.org/archives/si-list Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu