Hi Charles,

Check out Henry Ott's web page at http://www.hottconsultants.com. Henry is widely considered the "father" of EMI understanding, but he speaks in very clear language... and is a great guy!

He has some books, seminars and articles there that may help you.... especially one called "Partitioning and Layout of a Mixed Signal PCB".

Good luck,
Susy


>
> From: Charles Gervasi <[log in to unmask]>
> Date: 2006/09/14 Thu AM 11:06:03 CDT
> To: [log in to unmask]
> Subject: [DC] High-speed data converter grounding
>
> 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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