I have recently tried a split groundplane board, it was horrible!
Changing to a continuous plane was far better.
There has I think been a recent discussion about this very thing in this group that also
pointed to websites that recommend a single unbroken plane, that the signals need a good
return path rather than being isolated etc.
You can read up about it at http://www.hottconsultants.com/tips.html
Matthew.
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]]On Behalf Of
Patrick Jabbaz
Sent: Friday, September 15, 2006 12:48 AM
To: [log in to unmask]
Subject: Re: [DC] High-speed data converter grounding
Hi Charles,
I have been involved in Circuit design and RF layouts for about a year now,
and all the products designed so far have continuous ground plane over RF
and Digital circuit, and never had any problems or encounter any issues of
having one solid ground plane.
In fact the only issue that could happen is the fact of splitting the ground
plane, I just don't see any reason for doing so.
My designs consists of Digital portion "processor, memory and PCI bus, the
rest RF 900MHz to 6GHz always works, however I do not have any digital
signals crossing the RF portion, I keep them isolated on purpose.
Regards,
Patrick Jabbaz
Ubiquiti Networks
495-499 Montague Expwy
Milpitas, CA 95035
T: (408) 942-3085
M: (408) 621-6533
www.ubnt.com
----- Original Message -----
From: "Charles Gervasi" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Thursday, September 14, 2006 9:06 AM
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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