On Thu, 28 Jul 2016 23:39:24 +0000 (UTC)
life speed via time-nuts <[email protected]> wrote:
> The DDS tunes over more than an octave, so obviously the single low pass
> filter isn't going to cut it. I am noticing up to 3 dB phase noise
> degradation at the output of the divider as the DDS frequency decreases and
> the 2nd harmonic is in-band to the LPF. I suspect this is disturbing the
> threshold crossing in the high speed digital logic divider, as described in
> "The Effect of Harmonic Distortion on Phase errors in Frequency Distribution
> and Synthesis" by F.L. Walls et al at NIST.
>
> What do you think? I should probably put in a switched filter to get my 3 dB
> back ;)
Without being an expert in DDS and knowing your circuit, this sounds
like the most likely cause and the easiest solution. All other harmonics
reduction systems I am aware of are much more complicated.
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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