[SI-LIST] Re: "Ground" strips between LVDS pairs
- From: "Lee Ritchey" <leeritchey@xxxxxxxxxxxxx>
- To: "steve weir" <weirsi@xxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
- Date: Mon, 24 Oct 2011 09:26:53 -0700
Well put!
--------------------------------------------------
From: "steve weir" <weirsi@xxxxxxxxxx>
Sent: Monday, October 24, 2011 3:19 AM
To: <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: "Ground" strips between LVDS pairs
> 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.
>>
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>
>
> --
> Steve Weir
> IPBLOX, LLC
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