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

[Steve Meier <smeier@xxxxxxxxxxxxxxxxxxx>]

I went looking to see if the Analog Device book was available
electronically. Here are the links.


Steve Meier


High Speed System Applications Table of Contents



High Speed System Applications Section 1: High Speed Data Conversion
Overview



High Speed System Applications Section 2: Optimizing Data Converter
Interfaces



High Speed System Applications Section 3: DAC, DDS, PLL's, and Clock
Distribution




High Speed System Applications Section 4: PC Board Layout and Design
Tools



On Tue, 2008-10-28 at 13:44 -0700, Steve Meier wrote:
> 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.).
> > 
> 
> 
> 
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