Which is your lowest phase noise DDS?
For output phase noise performance, the highest performing DDS is the AD9912 (as of 4/17/2010)
Note, the DDS's contribution to output phase noise is dominated by the noise in the REF CLK path.
Most of the degradation occurs at the REF CLK front end (input). As a result, slew rate of the input REF CLK signal is important, especially if a sine wave. Decreasing the slew rate can degrade output phase noise performance.
How does the AD9910 compare to the AD9912 in terms of phase noise?
The easiest way is to compare the phase noise curves of figure 15 (in the AD9910 data sheet) to the appropriate phase noise curves of figure 21 in the AD9912 data sheet. Note, figure 15 is actually a residual phase noise plot. This type measurement cancels the REF CLK source's contribution, unlike the absolute phase noise plots in the AD9912 data sheet. However, notice the AD9912's phase noise curves still show a lower phase noise floor and better in close performance . This is why the AD9912 has better phase noise performance.
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