Hi Alex, I assume you're talking about end termination for the DQ and A/C lines, not Vref, which is the reference voltage for the VREF pins. Do not use resistor networks for Vtt. They will have one or maybe two connections to Vtt. The resulting high mounting inductance will cause the "terminated" lines to influence each other. If you have 50 Ohm from the terminated line to 1 shared Vtt pin, it also means you have 100 Ohm between each terminated line. The result will be that if all lines except one are driven with 0 and the remaining line with 1, it can be pulled to a value below Vih of the IO spec. It is sort of the same effect as ground bounce. We once had to debug a customer design where they used resistor packs but had long shared traces from the resistor pack to vias to the Vtt plane. The same effect as described above happened and the DDR memory system was not working. I would advise against resistor networks in general except for pullsomewheres in the kOhm range. Regards, Stefan Ludwig Alex Jose wrote: >Hi, > >I am curious about knowing the impact of using resistor networks instead >of resistor packs for the 50E pull ups to Vref on the DDR bus? >All the design guides I checked seem to use resistor packs. Any idea >whether using resistor networks instead of resistor packs will have any >impact on signal integrity? > > Thanks and Regards, >Alex Jose, > > >------------------------------------------------------------------ >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 > > > > > -- Ludwig Systems Engineering Consulting - Design - Implementation WWW: www.ludwigsystems.com System Architectures - FPGAs - PCBs Ph/Fx: +41-43-355-58-73/74 Hardware - Firmware - Software ------------------------------------------------------------------ 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