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AD9220 problem. It shows random zero values.


We are currently using an AD9220 to sample an ultrasonic echo signal. The schematic for the AD9220 placement is the following:

The CLK source for ADC conversion is 10Mhz supplied by a TTL/CMOS clock generator. And the signal on "Dig_In" as seen on scope looks like this:

The problem is that when I read the outputs from ADC and convert to decimal using MCU. I get this set of data:

I already double checked and the value I read on pins of the MCU represent values near to zero but on the physical signal there's no such thing. What would cause this readout? 

Note: even though the ADC is sampling at 10MSPS, right now using the MCU I'm currently using, I'm just able to capture the digital outputs at 2.5MSPS.

Any hint about what would cause those "zero" values noise and how to mitigate them?

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