Ground plane slit?

[[email protected]]

I have an analog circuit (A-D and filter) that has to get placed
relatively close to an FPGA (0.3" between the nearest points on the
FPGA to the closest component of the filter, generally about 1" for
most parts). I'm concerned about picking up any noise from the digital
stuff. My intuition tells me that (in the absence of a proper split
plane, which isn't doable in this case) it would be useful to put a
slit in the ground planes between the filter and the fpga.

Any opinions? Alternatives (can't move either block)?

Thanks,

Chris

 

[MooseFET]

I have an analog circuit (A-D and filter) that has to get placed
relatively close to an FPGA (0.3" between the nearest points on the
FPGA to the closest component of the filter, generally about 1" for
most parts). I'm concerned about picking up any noise from the digital
stuff. My intuition tells me that (in the absence of a proper split
plane, which isn't doable in this case) it would be useful to put a
slit in the ground planes between the filter and the fpga.

Any opinions? Alternatives (can't move either block)?

I you are doing an FPGA, it is likely that you have many layers in the
board. This can let you put an extra ground plane in the board under
the analog on the comp-side buried trace layer.

Something like this

Analog Digital

Comp copper Comp copper
Analog Ground Traces
Ground Ground
Analog power traces
Analog ground traces
Vcc Vcc
analog ground traces
solder copper solder copper

 

[[email protected]]

I you are doing an FPGA, it is likely that you have many layers in the
board.  This can let you put an extra ground plane in the board under
the analog on the comp-side buried trace layer.

Something like this

Analog                Digital

Comp copper           Comp copper
Analog Ground         Traces
Ground                Ground
Analog power          traces
Analog ground         traces
Vcc                   Vcc
analog ground         traces
solder copper         solder copper







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to the OP

read all of HJ's books on black magic...the answer is in there..

Mark