[SI-LIST] Re: "Ground" strips between LVDS pairs
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Mon, 24 Oct 2011 03:19:44 -0700
Bad habits die hard. One bad habit you want to break for certain is
copying magical mystery folklore design techniques.
At audio frequencies shield traces work great. They are wonderful for
keeping junk out of high impedance Op-Amps. High speed digital
transmission lines are a different animal. As has been covered on this
reflector many times: Inserting guard traces is usually ineffective and
can actually create a tuned coupler.
The most effective way to isolate signals that run over a reflection
plane is to minimize the height over the plane and maximize the
separation between aggressors and victims. If you can't meet your cross
talk numbers that way, consider altering your stack-up, routing layer
assignments, etc. One option always is co-planar wave guides. If you
know how to design them, then you can pull out that option when it is
appropriate.
Steve
On 10/24/2011 2:56 AM, Jason Young wrote:
> Dear Experts,
> Often on boards with LVDS signals, for instance connecting an LVDS
> transmitter to a LCD panel, I see thin 'ground' strips running between the
> differential microstrips. These strips have a sprinkling of vias connecting
> them to the reference plane on layer 2. Either end generally has a via and
> they extend most of the way between the source and termination. I'm told the
> reason is to reduce crosstalk between the pairs. Can someone please explain
> this reasoning?
> Yours
> Jason
> Ps. Sorry for using the 'G' word.
>
> ------------------------------------------------------------------
> 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
>
> Old (prior to June 6, 2001) list archives are viewable at:
> http://www.qsl.net/wb6tpu
>
>
>
--
Steve Weir
IPBLOX, LLC
150 N. Center St. #211
Reno, NV 89501
www.ipblox.com
(775) 299-4236 Business
(866) 675-4630 Toll-free
(707) 780-1951 Fax
------------------------------------------------------------------
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
Old (prior to June 6, 2001) list archives are viewable at:
http://www.qsl.net/wb6tpu
Other related posts:
