pcb layout, ground plane question

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seavote

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May 31, 2006
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im about to layout my first pcb. it seems to me that an easy way to deal with 0Vground would be to make a 2 layer board with ground connections all made on a single layerand all(or most) other connections made on the other . is this a wise lay out strategy?what problems could arise? what should i look out for?thanks for any comments
 
Unfortunately there isn't a cut and dry answer to this. For audio and low speed signals(less than a couple dozen Mhz..) you can do pretty much what you want as long as you make sure that the traces correspond to proper current densities and routing to avoid noise coupling and so forth.

For high speed signals, things change greatly. Too much to go over actually.

So if this is just an audio PCB you can simply do ground traces in a single layer no problem, easier to draw and etch. When you get to high speed that is when you'll need to move to multiple layers. Or you can do multiple layers if you simply need more room for traces.

Just do your ground traces in a star pattern and make sure that there are no high current devices on the same legs as sensitive audio devices like opamps.

I suggest reading books by Dr. Howard Johnson if you want some serious layout/decoupling theory.
 
[quote author="seavote"]what problems could arise?[/quote]
Capacitive coupling to ground. A board with a ground plane has capacitance between the traces on the top layer and the ground plane. While that's not always a problem (and often a good thing), it can create instabilities. Sensitive circuit nodes include the negative input of fast opamps (such as, say, the 990).

JDB.
 
I try to have all the lines on one side of the board moving in the same direction, horizontally or vertically, and the lines on the other side of the board running at right angles to the first. I try to run power buses on the top of the board. I don't usually use ground planes for audio work. Stray capacitive coupling of ground noise is probably the biggest reason. Ground planes are more effective in digital boards for distributing ground current over large board areas and suppressing transient noise in the power supplies, when used with lots of distributed decoupling.
 
While we're on the topic. I use Osmond Quartz, and know how to make a ground plane with the "copper flood" funtion. However, I can't figure out how to print the "copper flood" as dark as the traces, so that I can do a home etch proto with the copper flood...
 

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