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Need help to design a PCB board

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Newbie level 1
May 1, 2011
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I would want to have your opinion about the design of my board. My design is a analog amp for a sensor which use a 300kHz bandwidth and two voices. I have to use a FR4 4 layers PCB. I have the TOp for routing signal, the inner1 for the GND (which is a plane), the inner2 for the VCC/VEE supply rails (planes too), and the bottom layer (plane or not...?)
My question is what is the best way to reduce crosstalk beetwen my two voices ? can I place a gound plane on the top ? and for the bottom layer what should you suggest me ? in fact what is the advantge of placing a ground plane on the TOP and the bottom layers ? Is there any drawbacks to do this ?


The best way to reduce crosstalk between your two voices is careful layout and positioning of the components. The stack up should be Top layer routing, inner one for ground plane, inner two for power plane and bottom layer for routing.
Do not be tempted to flood the top and bottom with ground copper, this will make things worse. Having two routing layers will help in optimum placement of components.
PCB design is 90% placement of components and 10% routing of tracks.

I agree with btbass, I would also add that you need to identify and carefully handle the specific traces that are likely to cause the most trouble, i.e. the lowest-level signals, before they are amplified. These have to be routed very carefully, and kept away from not only each other but especially from any high-level signals, even from the same channel. Make sure the traces are kept away from high-level areas, and don't run parallel close to any other signals. You can also put a grounded guard trace around it, but only ground it at one point so it doesn't carry any current. If the amplifier section draws more than a small amount of current, and the two voices are completely separate sections of the PCB, I'd consider putting a partial split in the ground and power planes between the 2 channels, connecting the the split portions in the area where power and ground enter the board. The power needs to be clean, so it has to be well filtered/decoupled, and in an extremely sensitive design you might need to separately filter the power to the 2 channels (i.e. separate LC filters on the power).

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