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AD9914 evaluation board - Unknown spurious

Question asked by PHM on Jun 21, 2013
Latest reply on Dec 28, 2015 by byrktr

Hi,

 

I test out the AD9914 evaluation board.

I use this DDS with direct low noise 2.5 GHz clock and I use output frequency ranges where the FTW are exact integer to the system clock and where these last produce no phase truncation spurs.

However I observe unknown spurious in output spectrum around the output frequency and around harmonics of the output frequency, and the narrow-band SFDR is greater than -70 dBc (Attached are examples of output spectrum plot).

 

How can I explain these spurs that are too close to output frequency? How can I reduce them?

 

PHM

 

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