I am looking at the AD9958 and had 2 questions regarding the phase noise:
1. In the datasheet figures 16, 17, 18 which shows phase noise vs. frequency, what amplitude was the DAC output amplitude for these results?
2. In general is there any relationship between phase noise and DAC output amplitude?
Specifically I am looking for data at Fout=80MHz.
The residual phase noise plots and SFDR plots in the data sheet were generated using AD9958 evaluation boards. That said, the output power of the fundamental shown in the SFDR plots is approximately -4dBm. So, that corresponds to 399mVp-p for the phase noise measurement. Typically, the more output power, the better the phase noise performance. See attachments for specific cases. I have also attached an excel file to calculate the DAC output power when coupled to a transformer like the one used on the evaluation board.