[hpsdr] Phoenix again

[richardh at iinet.net.au]

In fact doing a quick bit of reading it seems that I have made a number of
mistakes with the original design. (grr why didnt I do the reading before :))

Some of the mixer clock traces cross several sections of ground plane which are
digital and then analog. This is probably the source of the spurs that I have
had. It will probably be impossible to do this on a 2 layer board.

I think I also have to separate the quadrature generation from the FPGA = the
clock here should be treated as an "analog" signal = maybe the old Johnson
counter implemented in tinyLogic , with chip select for transmit and receive.
 
It seems more important (according to the articles = see
www.e2v.com/assets/media/files/documents/...data.../doc0999A.pdf and
www.einfochips.com/.../designers.../Grounding%20in%20Mixed%20Signal%20PCB.pdf) to
isolate both power and ground planes into digital and analog sections and run
traces that connect between them over a "bridge" between them than worry about a
connection at a single point.
 
I would be interested in comments 

Richard

On Sun Nov  1 14:10 , "richardh at iinet.net.au"  sent:

>***** High Performance Software Defined Radio Discussion List *****
>
>Anthony
>
>Thanks for the comments
>
>OK on the H mode mixer = this is somewhat more complex than the current
>arrangement = what performance gain am I likely to see?
>
>I cant quite see the connection on the pdf files 
>I presume you make a connection between the two at the GND point on the Atlas
>connector = close to the +5V pins = is that correct?
>
>I tried to separate the Analog and digital planes on the original Phoenix 
>I wonder if the problem lies with the fact that the DDS has an analog section =>
>FPGA for quadrature generator section (this has a digital ground plane)  => back
>to the analog plane fore the mixers. Maybe all these sections should be separated
>and tied together at one point.
>Alternatively, should I have a layer for digital and another layer for analog?
>
>Also = what is the name of the PCB manufacturer you are using?
>I dont want to go through a process of finding one who I can work with if you
>guys have already done so.
>I take it they would want all layers in Gerber format.
>
>What sort of cost am I looking for if I have say 
>
>Top
>Power Plane
>signal plane 
>Analog Ground plane 
>Bottom/Digital ground plane 
>
>for prototypes?
>
>Does the order matter?
>
>Thanks for any feedback = I am a novice at this stuff
>
>Richard VK6BRO
>
>
>On Wed Oct 28  7:53 , Anthony Taylor  sent:
>
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