FreeLists / si-list / [SI-LIST] Re: stripline return paths etc.

[steve weir <weirsp@xxxxxxxxxx>]

Leonard, what you have with all the plane breaks is much more like a buried 
microstrip.  The signal layer closer to the solid plane will exhibit higher 
impedance than a true stripline, and some modulation along the frequency 
axis.  The signal layer closer to the split planes could look like a mess 
depending on several factors.  You should avoid placing signals with high 
edge rates close to those splits.  If you must run signals across the 
splits then bypass the splits with capacitors.

It is all in the inductance.  If you have a high inductance loop, between 
the two grounds, then you are setting yourself up for a lot of 
trouble.  You really need to ask yourself, or whoever came up with this 
scheme what it is they are trying to do, and why those grounds need to be 
single pointed.  You really ought to consider getting some expert help.

Steve
At 07:55 AM 12/6/2004 -0800, Leonard Alexman wrote:
>Hi All,
>I am designing many pcb's with multiple power and ground planes and I was
>curious if some has an opinion or could point me to any articles on the
>following questions.
>
>
>1.      I know its best to have a sold ground plane (or solid power plane )
>on either side of the a stripline trace but is it acceptable to have a solid
>ground plane on one side and a power plane on the other side with many
>splits in the plane ?  The same question for a dual stripline configuration
>?
>
>2.      I have some high speed differential signals that have a separate
>ground (HSGND). HSGND is tied to digital ground thru a zero ohm resistor. I
>am routing these signals in a stripline configuration with HSGND planes on
>either side. Can I also route digital signals(that use the digital ground )
>on this layer ? I am concerned that the return path goes thru the zero ohm
>resistor to the digital ground plane. and it will be a very long return
>path. Is my assumption correct ?
>
>
>Thanks for any help
>
>Leonard Alexman / American Electronics Group Inc.
>PH: 951-354-6493
>Cell: 951-640-5469
>Fax: 208-247-33470
>
>
>
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