[SI-LIST] Re: DDR2 2-slot design preference...
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "Steve Weir" <weirsi@xxxxxxxxxx>, Monji.Jabori@xxxxxx
- Date: Mon, 29 Oct 2007 10:09:28 -0700
I have heard many times about cavity resonances between power and ground
planes being the source of problems. However, I have yet to see any clear
proof that such things happen and I have never seen a product fail from
this in the design of 3000+ PCBs. Could those who claim this happens
please supply some evidence of this? Not simulations, but actual measured
results and not a statement that the last place it happened was at a client
who has an NDA in place that prevents revealing the data.
Lee Ritchey
> [Original Message]
> From: steve weir <weirsi@xxxxxxxxxx>
> To: <Monji.Jabori@xxxxxx>
> Cc: <si-list@xxxxxxxxxxxxx>
> Date: 10/27/2007 2:09:16 PM
> Subject: [SI-LIST] Re: DDR2 2-slot design preference...
>
> 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
>
------------------------------------------------------------------
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
Other related posts:
