Re: gEDA-user: pcb, howto partition power planes?

[Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx>]

I won't argue this point. I will refer every one to an Analog Device
publication "High Speed System Applications" copyright 2006 ISBN-10:
1-56619-909-3  or ISBN-13: 978-1-56619-909-4

In particular if you get a copy of this book (and they gave me mine)
look at pages 4.15 and 4.16

There AD recommends connecting both of the A/D grounds "digital" and
"analog" to the analog ground plane "this is because it causes less
problems for the relatively small amount of digital return current to be
returned through the analog ground than it would to connect the
converter to the much noisy digital ground.

There is a lot more talked about then just that one blurb.

Steve Meier



On Tue, 2008-10-28 at 11:22 -0700, Joerg wrote:
> Stefan Salewski wrote:
> > Sometimes it is necessary/recommended to partition (separate) power or
> > ground planes, i.e. for ADC or DC/DC-Converters, see page 16 and 17 in
> > 
> > http://focus.ti.com/lit/ug/slwu028c/slwu028c.pdf
> > 
> > We can do this in pcb program with (adjoining) polygons.
> > Disadvantage is, that if we change the size of one of the polygons we
> > have to manually adjust the other sizes. A other method may be so divide
> > a large polygon by copper clearing traces (with trace width zero). 
> > 
> > This is related to my question from
> > 
> > http://archives.seul.org/geda/user/Sep-2008/msg00387.html
> > 
> > but not identical.
> > 
> > What is the best way to handle this?
> > 
> 
> I can't speak to that but just one word of caution: In my 20+ years in 
> engineering I have yet to see one case where splitting a ground plane 
> under high-speed ADCs has worked. Regardless of what application notes 
> say. Usually it didn't work, lots of noise. Or it kind of worked but 
> fell apart the instant somebody whipped out a GSM cell phone or BlackBerry.
> 
> Myself, I never spilt a ground place. OTOH the industry practice of 
> splitting planes is providing part of my income :-)
> 
> The only time I split is where required for safety, for example patient 
> isolation per 60601 (ECG, ultrasound etc.).
> 



_______________________________________________
geda-user mailing list
geda-user@xxxxxxxxxxxxxx
http://www.seul.org/cgi-bin/mailman/listinfo/geda-user