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

[Dave McGuire <mcguire@xxxxxxxxxxxxx>]

   I don't see any URLs in there..

          -Dave

On Oct 29, 2008, at 6:08 PM, Steve Meier wrote:
> 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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>
>
>
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-- 
Dave McGuire
Port Charlotte, FL




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