RE: [SI-LIST] : Split Plane

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From: sweir (weirsp@atdial.net)
Date: Mon Apr 24 2000 - 16:13:41 PDT


Chung,

The signals are only better shielded if the ground that surrounds the
signals encloses the entire common-mode return path. Ie, does the ground
extend as a plane from the source to the destination of the signals? If the
ground plane stops or has a split, then the transitions on your LVDS may
radiate quite a bit.

Regards,

Steve.
At 05:03 PM 4/24/00 -0400, you wrote:
>Mike,
>
>I have 10 layers on my board, I just used the four layers as an example why
>I choose
>to split up the Ref. plane.
>
>What I tried to illustrate is that if the Ref. plane is split in two as
>shown, my signals would be better
>shielded. My signals are now shielded from above/below/and to the right with
>GND. And they are all high speed digital signals.
>
>
> > FOR EXAMPLE
> >
> > GND
> > signal
> > GND
> > signal
> >
> > can be broken up as
> >
> > GND
> > 1/2 signal 1/2 GND
> > 1/2 GND 1/2 signal
> > GND
>
>-----Original Message-----
>From: Degerstrom, Michael J. [mailto:degerstrom.michael@mayo.edu]
>Sent: Monday, April 24, 2000 4:15 PM
>To: si-list@silab.eng.sun.com
>Subject: RE: [SI-LIST] : Split Plane
>
>
>Sinh,
>
>I don't think you've provided us with enough information.
>Since you are using LVDS, which is differential, there
>shouldn't be any problem with splitting the plane as long
>as crosstalk between true/comp. pairs is kept in check.
>
>There are two other things to consider assuming that
>your board is only four layers as you defined below. First,
>and others on this list know this far better than I, is that
>your board (especially the first stack-up) may warp since your
>your metal loading is not well balanced. Secondly, how do
>bring in power? Depending on the rest of your circuitry,
>you may have an AC power delivery problem since you
>apparently have not provided a power plane.
>
>Mike
>
>_______________________________________________________________
>Mike Degerstrom Email: degerstrom.michael@mayo.edu
>Mayo Clinic
>200 1st Street SW
>Gugg. Bldg. RM 1042A Phone: (507) 284-3292
>Rochester, MN 55905 FAX: (507) 284-9171
>WWW: http://www.mayo.edu/sppdg/sppdg_home_page.html
>_______________________________________________________________
>
>
> > -----Original Message-----
> > From: Chung, Sinh [mailto:Sinh_Chung@littonas.com]
> > Sent: Thursday, April 20, 2000 5:54 PM
> > To: 'si-list@silab.eng.sun.com'
> > Subject: [SI-LIST] : Split Plane
> >
> >
> > To Layout Experts,
> >
> > I'm wondering if anyone can offer some advice/opinions.
> > I'm laying out a board where most of the critical LVDS signals
> > are near the connectors but I cannot route all of them on the
> > same layer.
> > So therefore multiple layer is required, but they don't take
> > up the entire
> > layer since I
> > want all the trace to be short, near the connector.
> >
> > I'm wondering if I split up the plane into two and make the
> > other half gnd
> > so that
> > I can have more gnd and more layer to route my signals optimal signal
> > integrity.
> >
> > FOR EXAMPLE
> >
> > GND
> > signal
> > GND
> > signal
> >
> > can be broken up as
> >
> > GND
> > 1/2 signal 1/2 GND
> > 1/2 GND 1/2 signal
> > GND
> >
> > My question is that by splitting up the layer, am I asking
> > for trouble.
> >
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>
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