From: "Bill Sloman"
Subject: Re: Ground pours on top and bottom layers?
Date: Sun, 5 Jan 2003 14:02:53 +0100
Organization: Planet Internet
NNTP-Posting-Date: 5 Jan 2003 13:02:52 GMT
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
"John Larkin" wrote in
> On Sun, 05 Jan 2003 02:21:59 GMT, Andy Peters
> >Hi, all,
> >I'm just wondering. What's the current thinking regarding grounded
> >copper pours on the top and bottom layers of boards that already have a
> >power and ground plane?
> >My application is a DSP board with an analog audio front-end, a CODEC
> >and a processor. My board has four layers: top and bottom are signal,
> >layer two is ground, layer three is power.
> >The ground layer has a split to separate the analog and digital grounds.
> >The power layer has splits to accomodate the different supply voltages.
> >Any pros/cons of the added ground pours on the signal layers are welcome.
> On a 4-layer, it probably won't make any difference.
> And why split the ground plane? (begin religious war now)
I believe that the orthodox answer is that you don't so much split them as
divide with long slots to make sure that the digital return currents through
the ground plane (and the corresponding voltage differences across the
ground plane) are confined to the digital parts of the board.
This makes sense to me, but I wouldn't fry a heretic in the microwave.
Bill Sloman, Nijmegen