Hello,

I would like to generate sine waves at 4 different frequencies around 200MHz, in order to synchroneously drive 4 AOMs. Would you recommand to use the AD9959 chip? Does the available frequency range depend on the external reference clock? (In my application I will use a 76MHz external reference clock).

Thanks in advance for your comprehensive answers (I've never used DDS before and I'm not an electrical engineer :-)

Exactly what output frequency range do you require?

The DDS output frequency is, indeed, dependent on its external clock rate. Because the DDS is a sampled device, the maximum normal operating range is up to 1/2 of the clock frequency (known as the Nyquist frequency).

Although the AD9959 would be the ideal choice for generating 4 simultaneous sine waves at different frequencies, your 76MHz external clock poses a problem. You can mitigate the problem to some extent by using the AD9959's internal reference clock multiplier PLL to boost the external clock frequency up by a factor of 6 to yield an internal clock frequency of 456MHz. This yields a Nyquist frequency of 228MHz allowing you to hit your output target frequencies around the 200MHz mark. However, you must filter (lowpass or bandpass) the DDS output to remove the sampling artifacts. With your desired output frequencies so close to the Nyquist frequency filtering will be a challenge.