Steven The answer is: "Yes, you should be concerned." The primary reason for the parallel termination to Vdd/2 is to center the switching around Vref. At low speeds this is not critical. But at high speed, intersymbol interference (ISI) and pattern run lengths of all zeros and all ones will eat your timing margin alive. There are two reasons for series termination. The first reason is to provide a better impedance match for the drivers. The second reason to to provide resistive losses to de-Q resonances in the channel. DDR even with series and parallel termination is not a well damped system. At higher frequencies the channel resonances will kill you. best regards, scott Scott McMorrow Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 (401) 284-1827 Business (401) 284-1840 Fax http://www.teraspeed.com Teraspeed® is the registered service mark of Teraspeed Consulting Group LLC Santangelo, Steven wrote: >Hi, > >I'm looking at a DDR interface which consists of a controller and a = >single SODIMM module. In the past we've successfully simulated, built = >and tested this interface using only series terminations but have always = >run it fairly slow, 100MHz or 133MHz. As we crank up the clock on = >future designs I'm starting to wonder if we should switch to the more = >standard series+parallel termination scheme. Aside from the increased = >over and undershoot and any resulting EMI issues, I don't see a big = >difference between the 2 approaches. If anything, the series only = >approach appears to give me better noise margin due to the increased = >swing. Should I be concerned about using the series termination only = >approach when running at higher speeds, say 166MHz or 200MHz? What = >areas should I be concerned about? > >Thanks > >Steve > =20 >------------------------------------------------------------------ >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 FAQ wiki page is located at: > http://si-list.org/wiki/wiki.pl?Si-List_FAQ > >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 > > > > > ------------------------------------------------------------------ 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 FAQ wiki page is located at: http://si-list.org/wiki/wiki.pl?Si-List_FAQ 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