AnsweredAssumed Answered

AD9954, change freq during zero cross or with new freq start in phase

Question asked by JordanG on Dec 5, 2011
Latest reply on Dec 5, 2011 by JordanG

Dear Analog Support,


I'm experimenting with AD9954s for a low frequency application (2Hz-5kHz), where I need to change frequences often. From several aspects it gives very good performance. In the other hand, I have a problem, for this application the chip behaviour, that at frequency changes when I issue I/O update it immediately starts with 0 phase - it is a problem. I need smooth transition. I can wait for zero cross, or it would be even better if at I/O update, the chip would continue with the new frequency, but with the same phase within the sinus circle. The sudden changes in amplitude is not tolerated well.


Do you have an idea how to achieve this ? If there would be a signal to indicate 0 phase for example, that would solve the problem, because than I wait with the controller for the zero cross before I issue the I/O update.


I have tried to solve it by using sweep mode, but when I change from single tone to sweep mode, it resets the phase also.

My plan was, for example to change from 200Hz to 500Hz and back to 100Hz to start in sweep mode, 200Hz into FTW0, 500Hz into FTW1, it sweeps up nice, but when I write 100Hz into FTW0 and issue I/O update it resets phase.


What do you suggest ? I hope I do not have to go to the analog circuit and monitor zero crossing.


Thanks a lot,

Gabor Jordan