ad9913

Hi, on the AD9913, how much worse should the phase noise be when the PLL is engaged (2x multiplication) vs.

when it is direct fed? In this specific case:

Fref: 90 MHz  = sysclk

vs.

Fref: 90MHz using PLL=2x, 180 MHz = sysclk

For a FIXED output frequency, would there be a 20*log(2) degradation? That is not clear to me since the output frequency

is actually fixed.

The data sheet does not show this kind of comparison, only residual phase noise for direct fed and absolute

phase noise for PLL=4x.

Thanks, Jerry