I'm looking for a clock to drive the DDS. What are the most important parameters/features for a 'good' REF CLK source?
Probably the most important parameter is the phase noise of the REF CLK source.
Adequate DDS phase performance starts with the REF CLK source. Better phase noise performance at the input translates to better output jitter performance for the DDS.
Having good SFDR performance is just as important. Spurious on the REF CLK source can impact the DDS output as well. See AN-927 attached.
Another feature to look for in a REF CLK source is frequency drift. The DDS is a high resolution divider, it does not frequency drift with a static frequency tuning word. In that case, if the DDS output frequency drifts, it’s caused by the REF CLK source frequency drifting.
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