Hi Conrad, The rx jitter tolerance mask usually shows a diamond shape. So let's say a vertex of left extreme is X1, then X1=DJ/2+Q*Jrms, hence, the right extreme is 1-X1. This tells the width of the tolerance mask gets narrower as Q is increased. From your example, the width is 0.2UI and 0.12UI for BER of 1E-12 and 1E-15, respectively. In the case of 1E-15, RJ becomes 0.58UI(0.88-0.3), therefore Jrms didn't change. TK -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Conrad Herse Sent: Monday, June 21, 2010 12:40 PM To: si-list@xxxxxxxxxxxxx Cc: herse@xxxxxxxxxxxxxxxxxx Subject: [SI-LIST] Rx Eye Mask width, BER, and Jitter Hello experts, I've been working on trying to scale receiver eye mask widths to different bit error rates. There is something which is puzzling me which I'm hoping someone can clear up for me. I've been studying the dual-Dirac jitter model given by the formula: Tj = Dj + 2Q * Jrms where Q is a constant from the Complimentary Error function for a given BER (2Q*Jrms = Rj at a specific BER). So if I have a receiver with the following jitter tolerance spec: Tj = 0.8 UI Dj = 0.3 UI Rj = 0.5 UI BER = 1e-12 then, given 2Q = 14 for BER = 1e-12: Jrms = 0.5 / 14 = 0.036 UI The Rx eye mask width would be: 1 - 0.8 = 0.2 UI If I want to scale the Rx eye mask width to BER=1e-15 I would expect I need to *grow* the eye mask width by Jrms. Given that 2Q = 15.883 at BER = 1e-15, then my new eye mask width would be: 0.2 + (15.883 - 14) * 0.036 = 0.268 UI So far so good, assuming I did this correctly. Here's what puzzles me, if I adjust my Rx jitter tolerance to accommodate the new Rx eye mask: Tj = 1.0 - 0.268 = 0.732 UI Dj = 0.3 UI Rj = 0.732 - 0.3 = 0.432 UI BER = 1e-15 and recalculate Jrms: Jrms = 0.432 / 15.883 = 0.027 UI The Jrms number has changed, I wouldn't expect this to happen simply because I'm extrapolating to a different BER. Can someone please straighten me out? Thanks! -- Conrad Herse ------------------------------------------------------------------ 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 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 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu