Jabori, the issue in each case will be the resonant frequency of the GND - GND cavity. Stitch the cavity with an adequate via density to get the resonance well above your signal energy and either topology can be made to work well. Steve. Jabori, Monji wrote: > Hi Experts, > > > I am looking at two designs for a 2-slot DDR2-800 memory system. One is > a butterfly design and the other has the slot on opposite sides of the > motherboard (top and bottom). > > I am looking at the GND reference for both designs and have the > following question knowing that I have to use GND referenced layers for > each DDR2 channel. > > > > For a butterfly design, my traces on an 8-layer design will flow from > the memory controller via 2 internal layers with 2 different GND layers, > i.e., one slot will have to change GND reference while the other will > not. > > > > In an opposite 2-slot design, however, we can make the traces that go to > each internal layer have the same GND reference as the DIMM that is > closer to it. For example, the Top DIMM will have the same GND reference > (L2) as its channel traces coming on L3 while the Bottom DIMM will have > its GND reference (L7) as its channel traces coming on L6. > > > > Having said the above, would you guys prefer one design over another > from an Signal Integrity point of view?? > > > > Thanks in advance. > > > > Monji > > > > > > > ------------------------------------------------------------------ > 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 > > > > > -- Steve Weir Teraspeed Consulting Group LLC 121 North River Drive Narragansett, RI 02882 California office (408) 884-3985 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