Yes.


It's difficult to answer, because you have three mixed analog/digital chips on your board! I would try your old layout with a common solid ground plane first, because the AD9835 only contain 10bit DACs and you can always filter the outputs by suited low pass filters.
But you urgently need to filter all supply voltage pins (by state of the art pi-filters), especially those of the oscillator moduls (!!) and all digital outputs, means all digital outputs of DSP, oscillator modules, etc.! These recommended 47R resistors is only a first step. You can achieve much better results when using special chip emi line filters (see below).
You should separate the digital in-/outputs of DSP better from the AD9835 section. Strictly separating digital and analog lines by several centimeters in combination with a common solid ground plane is nearly as powerfull as the introduce of a splitted ground plane. So, be not surprised if you have to choose a larger PCB for your application.


Not neccesarily, if you use low pass filters at the analog inputs of DSP, too. I think the most critical part is the digital components, like oscilator modules and serial data transmission from DSP to AD9835.


It all depends on what precision you need! If precision is rather low, than put everything on the board and have one solid ground plane. But if you need higher precision, then splitting of ground plane is needed eventually. Or maybe it's enough to filter here and there.
Mahmood, there's no universal answer, you always need to develop, try things, change things up you are satisfied. It's always a stoney way, and results become the better the more time and energy you are willing to spend.

Finally, here comes a bonbon:

http://www.murata.com/emc/knowhow/noise.html

Please read all the pdf-files of this link, and do it very carefully!!! It's an eye opener and tells you how to filter and shield properly. This site is one of the most informative I have ever found!


Kai