[hpsdr] Ground planes with multiple parts in both analog and digital domains

[mike]

Hi Richard,

I have had difficulties with doing that because there are situations 
where the grounds may be separated everywhere except at one point, 
however there are other signal interconnections that are not necessarily 
at that one point.

Put another way, by splitting planes you are allowing a potential 
difference to exist in the grounds everywhere except the common point, 
which can make things noisy on Vcc and the signal lines. In my 
experience split planes are just generally very difficult to get right 
for high frequencies.

Again, "your mileage may vary" as they say, but it has been a pain every 
time I've tried splitting planes, even where IC manufacturers recommend 
it. I've never had an issue due to using a single plane, except 
complaints about not enough thermal relief on certain ground connections.

As for multilayer, there is some improvement in noise caused by ground 
shifts but whether it's worth it depends on the design. If it will route 
ok on 2 layers, and your placement allows a good signal flow, stay with 
2 layers. It's easier to troubleshoot and cheaper. I only do multilayer 
when the component density is too high to support a clean design and a 
good placement from a signal perspective.

73,

Mike
WO1U

richardh at iinet.net.au wrote:
> In the first draft of Phoenix I have used a double sided board (would we gain much 
> by using multilayer boards? - would the cost be justifed?)
> I have attempted to split the digital + analogue sections and join them at one 
> point.
> So far have had no comments re the layout - I guess it is difficult for someone to 
> look at it.   
> I guess we will have to wait for the first build - should receive the first boards 
> any day now...
> 
> Richard VK6BRO
> 
> On Tue Feb 26  3:57 , <mj.hamel at verizon.net> sent:
> 
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>> Others may have a different take on this but I strongly recommend one big 
> continuous ground plane, and control current paths by component placement. Split 
> planes work OK for audio and LF but with mixed analog and digital and RF definitely 
> go with a full ground plane.
>> YMMV
>>
>> Mike 
>> WO1U
>>
>>
>>
>>> From: Howard Long hlong at btinternet.com>
>>> Date: 2008/02/25 Mon AM 09:02:11 CST
>>> To: hpsdr at lists.hpsdr.org
>>> Subject: [hpsdr] Ground planes with multiple parts in both analog and	digital 
> domains
>>> ***** High Performance Software Defined Radio Discussion List *****
>>>
>>> Folks
>>>
>>> Traditionally with a signle device such as a CODEC straddling the analog and
>>> digital domains, there seems to be a fairly uniform agreement to use a
>>> common ground plane with an insulating split between analog and digital
>>> sections of the board and a single connection under the CODEC.
>>>
>>> How do you deal with a situation where there are multiple devices in both
>>> the digital and analog domains?
>>>
>>> I have read this article
>>> http://www.google.com/search?hl=en&q=mixed+signal+pcb+layout that seems to
>>> suggest the use of a single unsplit ground while maintaining physical
>>> partitioning between the mixed signal/analog devices and their digital
>>> counterparts.
>>>
>>> I wonder if anyone has any views on this? In my particular case I have a
>>> CODEC, a DDS and a PLL/VCO to deal with using I2S/I2C/SPI interfaces to a
>>> DSP.
>>>
>>> 73, Howard G6LVB
>>>
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