> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of Bob Axtell
> 
> In most commercial designs of almost any speed, a ground plane is a
> necessity.
> 

I am not so sure if this is true also for AC/DC and DC-DC converters 
especailly when line voltage are involved. Most likely it is not 
possible to have a "good ground plane" within the high voltage side.

But I will agree that ground plane is important for even not very
high speed analog circuits if I can afford to have a good ground
plane. 4-layer boards in general have much better performance for
our optic proximity sensors but 4-layer boards are much more
expensive than normal 2-layer boards.

Regards,
Xiaofan

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