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Strange Output-Signals with AD9833

Question asked by DO9XE on Apr 14, 2015
Latest reply on Apr 15, 2015 by DO9XE

Hey Guys,

 

on Friday i ran into a problem with the AD9833 on my prototype-PCB of my final project.

After changing a part (not the AD9833) i discovered a direct connection between AGND and DGND. I started measuring my Schottky-diodes, which connect AGND and DGND, result: the work just fine. I measured all the Voltages, also all are fine. Then I changed the AD9833. I found out, that the connection between AGND and DGND came from the AD9833 and was through the IC. I never had this problem in any measurement before, every time I checked the connection between AGND and DGND i only was able to measure the Voltage over my diodes (as it should be).

 

After changing the AD9833 the Problem occurred again. So I started measuring the device  in operation.

The Master-Clock is just fine, not a perfect square, but hits 5V and 0V. (I know that it should be this way)

I also checked the Data I get from my microcontroller over SPI. It is correct and all states and the timing fits the specs.

 

The problem now is the output-signal. I programmed the AD9833 to 50kHz and triangle-output, but my Output is only this:

strange-signal-ad9833.PNG

 

I've checked my setup multiple times and made sure everything is correct. It worked in the previous Prototype. I also tried to connect the grounds together, but the signal stayed the same.

You can find the circuit diagram here:

https://raw.githubusercontent.com/LabConnect/Signalgenerator/2dd6c661a8eab4993288aab7a8e9112a2a5977f2/schematics/Release…

 

Any help is very appreciated.

 

Thanks for the Help,

kind Regards, Hendrik

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