[SI-LIST] Re: Question about split gnd planes

Ed, if I have a transmission line with a noise source on one end and 
a victim circuit at the other, it sounds reasonable to put a break in 
that line to block the noise.  This is how moats get born.  What 
happens if I have multiple transmission lines?  It should stand to 
similar reason that if putting a break in one line is going to help, 
I will have to put a break in each line capable of delivering 
substantial unwanted noise energy to my victim circuit.  There can be 
some mighty sneaky transmission structures lurking around circuit 
boards.  Inserting moats in the wrong place at the wrong time can do 
bad bad things.  Often it is more effective to shunt noise somewhere 
else by placement and routing than to try and break all the possible 
transmission paths.  In other cases a combination of measures is 
appropriate.  I find it helpful to think in terms of what the fields 
are doing, or are likely to do.

Steve.

At 01:38 PM 5/25/2006, Ed Troy wrote:
>If you have a circuit board that requires a split gnd  plane over a
>small section of the board, and you have several ground planes,
>should only one have the split (the one nearest the side containing
>the components that require analog ground)  while the rest of the
>ground planes are continuous, or should the split section be on all
>ground layers? I would think that you should only have it on one
>layer. Also, if it should only be on one layer, I would imagine it
>would be best to connect it to the digital ground with one, and only
>one, via. Is that generally correct? What are some good references
>for layer stackups, etc? I know I saw one, once, but can't remember where.
>
>Ed
>
>
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