How the AD9914 DDS can configured to preform continuous phase frequency hopping?
The easiest way to do frequency hopping is by using two profiles of the AD9914. Program each profile with the desired lower and upper frequency and toggle between these two profiles to generate the hop. Phase continuous is inherent to single channel DDS. The AD9914 is a single channel DDS but I have to verify in the lab if phase is continuous if toggling between profiles. In case that it is not continuous, you can still achieve continuous phase frequency hoping by first programming the lower frequency and toggle I/O update to have the output. Then program a new frequency, which is the upper frequency, and toggle I/O update to apply the change in frequency. The next phase will simply be incremental with respect to the last phase value in the phase accumulator, and therefore the output will be phase continuous.
As Mark points out, DDS is inherently phase continuous. Although I haven't checked this on the bench, I can assure you that the AD9914 frequency hops in phase continuous fashion when switching profiles. By the way, profile switching is via external pins (PS[2:0]). This provides access to up to 8 profiles, each can be programmed for a different frequency. The simplest way to do 2-frequency hopping is to program Profile 0 with one frequency and Profile 1 with the other frequency. Then, force PS2 and PS1 to Logic 0, and use PS0 to toggle between Profile 0 & 1 (PS0=0 and PS0=1, respectively).
Just to be clear, phase continuous is not the same as phase coherent. The AD9914 performs phase continuous frequency hops. Phase coherent hopping requires a specially designed architecture.