[SI-LIST] Re: PCB layer stackup
- From: "ChandraKanth Gajawada" <chandrakanth.gajawada@xxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Tue, 9 Jan 2007 22:09:38 +0530
Hi All,
One basic Doubt,(May not be related to this Subject)
Do LVDS signals needs to refer GND plane (A plane in Specific!)
As differential pair has the other trace as return current,I dont think
they need for a Continous plane underneath it for reference....
Am I true with this Idea,Please clear?
Regards
Chandra kanth
On 1/9/07, Curt McNamara <CurtM@xxxxxxxxxxx> wrote:
>
> I like stack-up 2 with the suggestion of turning one of the internal
> power planes to a ground plane. Here is why:
>
> Many times you will get lower emissions from a product by routing your
> clock traces on the outer layers (assuming they are over a ground
> plane). I first saw this in an IEEE EMC conference paper and experience
> bears it out.=20
>
> The second reason is that your devices (also sources of noise) are
> mounted on the outside of the board. In stack-up 2, this means they are
> directly over the ground layer, also increasing coupling to ground.
>
> So from an EMC perspective stack-up two (with an internal ground layer
> next to the power layer) is best.
>
> Curt=20
>
> Curt McNamara // senior electrical engineer=20
> Logic Product Development
> 411 Washington Ave. N. Suite 400=20
> Minneapolis, MN 55401
> T // 612.436.5178
> F // 612.672.9489=20
> www.logicpd.com
> / / / / / / / / / / / / / / / / / / / / / / / / /
> This message (including any attachments) contains confidential
> information intended for a specific individual and purpose, and is
> protected by law. If you are not the intended recipient, you should
> delete this message and are hereby notified that any disclosure,
> copying, or distribution of this message, or the taking of any action
> based on it, is strictly prohibited.
>
>
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of Kindt, Jan
> Sent: Tuesday, January 09, 2007 6:26 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] PCB layer stackup
>
>
> Hi,
> =20
> I need to specify a 8layer board. Fastest edges on the board are on the
> 600Mbit LVDS channels : about 500ps. I have two stackups in mind :
> =20
> stackup 1 stackup 2
> ---------------------------------------------------------
> L1 routing routing
> Substrate
> L2 power plane GND
> Substrate
> L3 power plane routing
> Substrate
> L4 GND power plane
> Substrate
> L5 routing power plane
> Substrate
> L6 routing routing
> Substrate
> L7 GND GND
> Substrate
> L8 routing routing
> =20
> Stackup 1 has the advantage that all routing on L5, L6 and L8 is
> referenced to GND. We need to push the LVDS channels over a board to
> board connector. On the board to board connector, there are GND's
> between separate pairs. So we keep the same reference to GND over the
> connector.
> =20
> Stackup 2 is the stackup I would normally use due to it's symmetry.
> Signals on L3 and L6 are referenced to both GND and a power plane. But I
> don't know why I would need to favour stackup 2 over stackup 1.
> =20
> Can you comment om which stackup is most preferred ? Or what are the
> drawbacks/advantages of one stackup to another.
> =20
> best regards,
> Jan
>
> DISCLAIMER:
> Unless indicated otherwise, the information contained in this message is
> privileged and confidential, and is intended only for the use of the
> addressee(s) named above and others who have been specifically
> authorized to receive it. If you are not the intended recipient, you are
> hereby notified that any dissemination, distribution or copying of this
> message and/or attachments is strictly prohibited. The company accepts
> no liability for any damage caused by any virus transmitted by this
> email. Furthermore, the company does not warrant a proper and complete
> transmission of this information, nor does it accept liability for any
> delays. If you have received this message in error, please contact the
> sender and delete the message. Thank you.
>
> ------------------------------------------------------------------
> 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: =20
> //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
> =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
Other related posts:
