[sdiy] PCB layout rules

[John Luciani]

On 12/23/06, Seb Francis <seb at burnit.co.uk> wrote:
> Joe Grisso wrote:
> > I have
> > yet to see a SDIY design operating at 25MHz with a bunch of 16-bit+
> > digital peripherals hanging off of a CPU.
>
> This is one with 2 dsPICs running at 120MHz with an SRAM each...
> http://burnit.co.uk/sdiy/index.php?page=4xd&subpage=layout
>
> As you can see from the bottom image I kept the digital and analog board
> sections completely separate with the ground planes being connected only
> back at the PSU (top middle).  The hybrid components (the CODEC ICs)
> straddle the moat between the digital and analog ground.

I think your excellent results are more due to keeping the digital and analog
board sections separate rather than keeping the ground plane separate.
By keeping the sections separate you prevent high frequency signals from
radiating noise onto your analog circuitry.

Also the *massive* planes you have help to prevent radiation and provide a low
impedance connection.

Your board is *all* copper ;-) Nice job!

(* jcl *)

-- 
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