I use AD9957 with my layout board and find some spurs in spectrum. The spurs level are around -80dBm, and they seem to be the harmonic of reference clock(24.576MHz).
I try 3 different way(from the datasheet) to generator reference clock, but the spur. level seems the same. The 3 ways are (1)use xtal driven (2)single ended input direct drive with an oscillator.
(3)single ended oscillator and differential input.
Is there other way I can try to reduce the harmonic of reference clock?
2 spectrum are in the attach:
(1)I make a band-width 1.536MHz DAB signal, center frequency is 174.928MHz. I mark clock harmonic 147.456MHz and 172.032MHz.
(2)When AD9957 Tx enable pin turns low, the spectrum still have reference clock frequency: 122.88MHz, 147.456MHz, 172.032MHz, 196.608MHz, 211.184MHz.