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Pulse mode with AD9951-9954

Question asked by Rice on Jul 20, 2011
Latest reply on Jul 26, 2011 by JLKeip

Hallo,

 

i am trying to generate a train of pulses from 0 amplitude to full sin signal amplitude. I see that I have two possibilities to do this with this family of DDSs:

 

- To use the automatic OSK and the external pin. Here I have the problem that the time it takes the minimum ramp to reach the maximum value (around 17 us) is too big for my needs, which would be a couple hundred nanoseconds at most.

 

- Using the external power-down pin, at fast-recovery mode. This leads to satisfactory results in output but I am not very sure if it will be very healthy to operate the DDS this way. I would generate pulses at a maximum frequeny of around 100 kHz. Is there anything I have to fear about working this pulse mode through setting on and off the power of the DDS?

 

Previously I used an AD9959 which could deal with these with its amplitude modulation capacities... but unfortunately 10 output bits were too few for my application.

 

I though also about opening and closing the DAC feedback pin with a transistor to vary its gain from 0 to full amplitude... but I guess it will be more complicated and I am also not sure of the behavior of the DDS functioning this way.

 

Thank you in advance.

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