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AD9106 Phase Accumulator Errors?

Question asked by TheShadders on Apr 19, 2016
Latest reply on Apr 26, 2016 by larrywelchusa


Hello,

 

I am using the AD9106 to output two in-phase sine waves on output 1 and 2. I am using the same commands as I posted here: AD9106 Discontinuities

 

I am using a signal generator to provide the clock. With a clock frequency of 3MHz, everything is as I expect. Unfortunately, some weirdness happens as I turn the frequency knob on my sig gen. Going from 3 to 3.2MHz causes very strange behavior. Namely, the DAC output is clearly constant for 1/2 and 3/2 clock cycles--which indicates to me  a problem with the phase accumulator.

 

In addition to the screenshots below, I have posted a YouTube video: AD9106 DDS DRIFT WEIRDNESS - YouTube

 

Best Regards,

 

Shad

 

The first picture shows a 3 MHz clock, and the DAC is clearly stepping once per clock cycle.

 

The next screen grab is at 3.2 MHz clock frequency, with all other settings the same. As can be seen, the DAC steps in the middle of some clock cycles, and also last 1.5 cycles in some places. This same behavior seems to happen regardless of tuning word, or if I dynamically change the clock frequency (before or after power up and sending SPI settings).

 

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