[SI-LIST] Re: gridded ground/power for 2-layer designs
- From: Ken Wyatt <ken@xxxxxxxxxxxxxxxx>
- To: "Oglesbee, Robert A" <roglesbe@xxxxxxxxxx>, Colin D Bennett <colin@xxxxxxxxxxx>
- Date: Fri, 24 Feb 2012 14:37:57 -0700
Colin Besides the references you shared, Henry Ott also described this solution
in his first edition "reducing noise" book. I did some experiments and
resulting presentation back in the early 90s where I took an existing 2-layer
open-frame oscilloscope demo PC board and interconnected as many grounds as I
could (forming a rather haphazard grid) on the bottom side. Measuring the
before and after demonstrated up to 8 dB reduction in radiated emissions. This
is a great solution for low-cost electronic products.
Cheers, Ken
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On Feb 2, 2012, at 7:06 AM, Oglesbee, Robert A wrote:
> Colin,
> A signal crossing the power trace without being accompanied by a ground
> return would have a similar bad effect. However, when laying out two layer
> boards you have to pay attention to the loop area of all the traces, and make
> sure a ground return follows the signal. Some good rules of thumb on 2-layer
> boards are:
>
> - Route critical signals G-S-G (these are either noisy lines like clocks, or
> susceptible lines like resets)
> - Put a ground via next to every signal via (this is impossible, but make
> tradeoffs later rather than sooner)
> - Make sure there are no ground islands (every copper pour has at least two
> vias)
> - Keep connectors on as few edges as possible
>
> After that you can examine the layout for any areas where ground can't flow.
> By running traces East-West on one side and North-South on the other you
> minimize this possibility.
>
> Rob Oglesbee
>
> (765) 494-5234
> Senior Instrumentation Specialist
> Jonathan Amy Facility for Chemical Instrumentation
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