What are the Jitter and phase noise considerations in a DDS system?

The output signal quality of a direct digital synthesizer is dependent upon the signal quality of the reference clock that is driving the DDS. Important quality aspects of the clock source, such as frequency stability (in PPM), edge jitter (in ps or ns), and phase noise (in dBc/Hz) will be reflected in the DDS output. One quality, phase noise, is actually reduced according to: 20 log (Fout/Fclk). This means that a 10 MHz output signal will have 20 dB less phase noise than the 100 MHz reference clock that “created” it.