How to make DDS AD9854 output Phase-Coherent ?

Phase coherent with what?

-- John

Dear John,

In a chrip signal, the output goes from F1 to F2 and then back to F1 at each I/O UD pulse. I want the phase to remain the same (or zero) at every transition from F2 to F1. This is what I mean by phase- coherent.

Many Thanks.

So, the phase behavior should be the same on successive chirps? It sounds as if you would have to synchronize the pulse that starts the transition from F1 to F2 with the state of the device, or reset the device, and it would have to behave stably enough during the chirp to keep the phase from deviating at F2. If you also mean that the return from F2 to F1 must begin at zero absolute phase, then the length and rate of change of the chirp would have to be controlled as well. I'm not familiar with the device you mention, but logic would seem to require synchronization.

-- John

Thanks John for your help. Yes I think synchronization would be the answer.

But instead of reseting the device everytime wouldn't clearing the Phase Accumulator be a better option?

regards, Farrukh

As I mentioned, I'm not familiar with it. Would resetting the phase accumulator make an instantaneous discontinuity? Does it have to run all the time, even when it's not chirping? Maybe detecting a certain state of the device and synchronizing the external request to that would be better than resetting or changing it. Good luck.

-- John