King, the line to line impedance ( odd mode ) is roughly twice the line to reference impedance of each line ( even mode ). Terminating the energy from both modes is desirable. Maybe you have special requirements, but I would normally terminate both modes at the receiver. Eric's book discusses both pi and T end terminations to do that. Steve King Da wrote: > Dear Steve, > Thanks for your answer, but I don't really know what your mean "you've > got your impedances backward" ? Could you explain more detail ? > > I use 100 Ohm for differential termination for diffrential signal > and also want use series termination for each line for common mode > signal termination. How to choose the series resistor value ? > > > On 12/5/08, *steve weir* <weirsi@xxxxxxxxxx > <mailto:weirsi@xxxxxxxxxx>> wrote: > > Parallel terminations absorb energy at the far end and is related > only to the channel, not the driver Z. Also, you've got your > impedances backward. > > Steve. > King Da wrote: > > Hi,Folks, > I have a differential pair which odd mode impedance is 48 Ohm > and even mode > impedance is 108 Ohm by TDR measurement. > I would like use 100 Ohm for differential termination at far > end, but how to > choose series termination resistor for each trace at near end? > > I refered Bogatin's "Signal Integrity:Simplified" book that > said parallel > termination R2 equal Zeven, So, I should use 108 Ohm subtract > 20 Ohm of my > driver's Ro is 88 Ohm for my series termination at near end, > am I right? > > The Rseries = 108 (Zeven) - 20 (Driver's Ro) = 88 Ohm, right ? > > Does the differential termination resistor is 100 Ohm better > than 91Ohm ? > > Thanks, > > Yardala > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx > <mailto: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 > <mailto:si-list-request@xxxxxxxxxxxxx> with 'help' in the > Subject field > > > List technical documents are available at: > http://www.si-list.net <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 > > > > > > > -- > Steve Weir > Teraspeed Consulting Group LLC 121 North River Drive Narragansett, > RI 02882 > California office > (866) 675-4630 Business > (707) 780-1951 Fax > > Main office > (401) 284-1827 Business (401) 284-1840 Fax > Oregon office > (503) 430-1065 Business > (503) 430-1285 Fax > > http://www.teraspeed.com <http://www.teraspeed.com/> > This e-mail contains proprietary and confidential intellectual > property of Teraspeed Consulting Group LLC > > ------------------------------------------------------------------------------------------------------ > Teraspeed(R) is the registered service mark of Teraspeed > Consulting Group LLC > > -- Steve Weir Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 California office (866) 675-4630 Business (707) 780-1951 Fax Main office (401) 284-1827 Business (401) 284-1840 Fax Oregon office (503) 430-1065 Business (503) 430-1285 Fax http://www.teraspeed.com This e-mail contains proprietary and confidential intellectual property of Teraspeed Consulting Group LLC ------------------------------------------------------------------------------------------------------ Teraspeed(R) is the registered service mark of Teraspeed Consulting Group LLC ------------------------------------------------------------------ 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