I'm wondering if anyone has any thoughts about the best place to tie
grounds in a design with high-speed data converters.

 

I am working on a software-defined radio that has high-speed ADC and
DAC, processor, FGPA, SDRAM, etc.  This is all on a 2.7 x 2.2 in, 12
layer board.  We are attempting to isolate the RF section, that is
everything on the analog side of the data converters, in an RF "can".
The "can" consists of a solid ground plane on layer 4, ground vias on
the sides, and a metal can on top of the (layer 1) RF components.  The
"can" region accounts for a third of one side of the board.  There are
digital components in all other areas of the board.  The data converters
are located on the opposite side of the board (layer 12) near the can:

 

Question: Where is the best place to tie the analog (RF) and digital
grounds?

 

We think it should be at the data converters because data converters
expect a single solid ground.  

 

BUT, most of the analog ground is located in the RF section on layers 1
through 4.  Tying them on layer 11 under the data converters means we'll
have a little patch of ground on layer 11 for the data converters tied
to the digital ground on one side and tied by vias to the "can".  This
intuitively doesn't sound like a good idea.  

 

Does anyone know of good articles or books on grounding high-speed data
converters in very tight designs?  This design is bound to take some
trial and error.  I'm just trying to get the most mileage out of each
spin.

 

Thanks,

 

CJ

 

 

 


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