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Generation of LFM waveform by using POW under RAM modulation mode in AD9910

Question asked by Rohan_Kale on Aug 17, 2014
Latest reply on Sep 15, 2014 by KennyG

Hi everyone,

 

We are planning to use RAM modulation mode to generate LFM waveform on AD9910. We wish to use a total of N RAM addresses (out of 1024) to store the phase offset words. The underlying phase equation for LFM is :

phase LFM.jpg

; f1 --> starting frequency of the LFM

I believe the second term in the above equation corresponds to the time varying phase offsets. If not, please explain how the phase offsets can be computed? We have already succeeded in generating LFM by writing N (N<1024) 32-bit FTW on to the RAM with a playback rate as dictated by the formula given in the datasheet. But what if I have to design a scheme where amplitude tapering is essential, in that case the use of polar modulation mode becomes imperative. The info on ASF is clearly mentioned in the datasheet. I need to know how I can generate the LFM with a knowledge of 16-bit POW? Do I have to initialize the phase accumulator register with FTW corresponding to f1 , if yes, then what would be the other mode running simultaneously along with RAM mode? Would there be a sync related issue with this scheme?

 

Suggestions/advice pertaining to my queries would be really appreciated.

A tone of regards in advance.

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