[hpsdr] Ground planes/ Phoenix boards

[mj.hamel at verizon.net]

Hi Richard,

It was not my intent to critique your choices. Sorry if it sounded that way.

Sometimes you just can't use one big plane. 

I use Protel99 (kind of a dated tool) at home, but it has a 'copper pour over specified net' function, and I always cover the design with ground everywhere as a last routing step, then go back and tweak as necessary. So when I say I use one big plane I mean pour copper over the ground net for 2 layers. Typically on multilayer, I end up not using the automatic power and ground plane feature because they do not allow you to add signals to those layers, more like 'mostly ground' and 'mostly power' mid layers. Seems to work well for me anyway.

73,

Mike
WO1U



>From: "richardh at iinet.net.au" <richardh at iinet.net.au>
>Date: 2008/02/26 Tue PM 08:26:07 CST
>To: mike <mj.hamel at verizon.net>
>Subject: Re: [hpsdr] Ground planes/ Phoenix boards

>
>
>I have had to use the ground plane for some signals and power. Power is generally 
>around the edge of the board and the signal lines are for driving the DDS (low 
>traffic) and the mixer oscillator drive from the CPLD lines - these are probably 
>the most problematic, but I couldnt do it on one plane.
>I have just got the first PCBs in my hand today. One is going to Phil Harman and 
>one to Ramakrishnan VU3RDD. 
>
>I have two available for someone to build as a first cut - any 
>takers?
>
>Richard VK6BRO
>
>On Tue Feb 26 21:41 , mike mj.hamel at verizon.net> sent:
>
>>***** High Performance Software Defined Radio Discussion List *****
>>
>>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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