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putting out a tone on a AD9783

Question asked by GarEngLLC on May 21, 2012
Latest reply on May 23, 2012 by Tguy

I have an AD9783 in a design I am working on, and we are using the 16b differential inputs to drive the DAC.  I have a generated sine wave from an FPGA feeding both ends of the differential input, and I can see the output on a oscope fine (so everything is hooked up fine on the PCB).

 

My question is, when I tried to put just a tone out on the DAC, I cannot seem to get it to work.  I am trying to feed a constant, but all I see is 0V coming out.  Am I missing something about this part?

 

Thinking that there was something up with just putting out a steady value, I then incremented the value on every clock tick (which decrements in the N leg every clock tick), and let it roll over.  This causes a zero crossing on the rollover, which is the only time I see a slight change on my oscope.

 

Why is it I cannot just feed the inputs 0x7FBC (P input) and 0x8044 (N input) and see a positive tone come out of the DAC?

 

Thanks.

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