The article to which Mr. Smolyansky refers, "Characteristic impedance of lossy line", appeared in my regular EDN column on 10/3/2002. The article is posted at http:\\sigcon.com, under "archives", see the alphabetical index , or go here: http://www.sigcon.com/Pubs/edn/LossyLine.htm Figure 1 in the article illustrates, for a hypothetical, 150-micron (6-mil), 50? FR-4 stripline, the relative influence of skin-effect and dielectric losses on the characteristic impedance of a lossy transmission line. The chart depicts the characteristic impedance of a trace with only skin-effect and dc-resistive losses (assuming a perfect dielectric), a trace with only dielectric losses (assuming zero resistance), and a combination of both. Figure 2 shows how line losses affect the shape of the TDR response. Similar figures appear on pp. 204-205 of my latest book, "High-Speed Signal Propagation", ISBN 0-13-084408-X, along with a great deal of additional explanatory text. Best regards, Dr. Howard Johnson, Signal Consulting Inc., tel +1 509-997-0505, howiej@xxxxxxxxxx http:\\sigcon.com -- High-Speed Digital Design articles, books, tools, and seminars -----Original Message----- From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Dima Smolyansky Sent: Friday, November 21, 2003 2:22 PM To: Suresh.Subramaniam@xxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: TDR and line losses Suresh, The upward slope of the TDR trace is indicative of losses. However, the losses will need to be quite substantial for the upward "creep" to be clearly visible. In other words; your transmission trace (TDT) will show even fairly small losses through rise time amplitude degradation; however, when you begin to see the "creep" in the reflection (TDR), that will show up as large rise time and amplitude degradation in TDT. Also, Howard Johnson did an article once, where he played with skin effect and dielectric loss, and showed how they affect different portion of the TDT waveform. You can do the same in IConnect's lossy line model by varying the skin effect and dielectric loss parameters independently, and evaluating their effect on the TDT (or TDR) waveform. Thanks, -Dima ----- Original Message ----- From: "Suresh Subramaniam" <Suresh.Subramaniam@xxxxxxxxxx> To: <si-list@xxxxxxxxxxxxx> Sent: Friday, November 21, 2003 2:00 PM Subject: [SI-LIST] TDR and line losses > > If I TDR (rise time 26ps) a long lossy transmission line, should I expect > the impedance profile to gradually creep up to a higher value (assuming I > start out with a 50 Ohm impedance?). In other words, how does the TDR > take into account the effect of losses? > > Thanks > Suresh > > > ------------------------------------------------------------------ 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.org 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