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AD9959 Synchronizing multiple Devices

Question asked by PrakashBJ on Dec 17, 2013
Latest reply on Jan 6, 2014 by PrakashBJ

Hi,

I am using 8 AD9959 DDS chips.

I am trying to synchronize all the DDS outputs. I have connected Master DDS SYNC_OUT to SYNC_IN of other DDS chips via a clock buffer.I am getting 6Mhz at SYNC_OUT  of the Master DDS.

I am writing to all the DDS registers one after the other and doing IO_UPDATE simultaneously . The REF_CLK to all the DDS are in phase.

I am writing the DDS FR2[6] = 1 for Master and FR2[6] = 0 for the slaves.And writing the Auto_sync enable bit FR2[7] = 1 for all DDS.

But the outputs are synced initially but after few seconds there is a periodic distortion at the output of all DDS.

TEK0004.JPG

The above image is the output from the DDS initially after the Power ON.

TEK0005.JPG

The above image is after few seconds where there is a periodic distortion on the DDS outputs.

In both the images the Frequency is 100Hz and Amplitude is 500mV. But the distortion in second image.

Can anybody explain what is the cause for distortion ? How to get rid of it?

 

Thanks,

Prakash BJ

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