Mike see below > > Scott, > how did the difference between the noise voltages get to be common > mode? Given identical noise voltages on both traces, the difference > is zero - and that is differential noise. The CM noise is the average > of the two noise voltages (sum/2) I am talking about a case where Lee has suggested that the differential pair can be split between two different routing layers. The stackup might be as follows: Ground diff layer 1 Power 1 Ground diff Layer 2 Power 2 The noise on each of these layers is totally different. Thus at any point along the differential pair there is a common mode voltage differential that occurs, causing a net current flow in one direction or the other. You are correct for signals that are referenced to the same layer. Oh, and your point is well taken. -1.5 dB of loss would be 1.5 dB of gain. Oops! regards, scott -- Scott McMorrow Teraspeed Consulting Group LLC 2926 SE Yamhill St. Portland, OR 97214 (503) 239-5536 http://www.teraspeed.com ------------------------------------------------------------------ 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