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AD9914: crosstalk during initialization

Question asked by PrYSO on Jan 20, 2014
Latest reply on Feb 7, 2014 by sitti

Hello,

we want to use the AD9914 in parallel mode to control AMP and Freq.

But in first place we need to initialize the AD9914 Eval. And that's where the trouble is found.

 

Another guy of our group started to implement an experiment using the AD9914. Because of some timing problems it didn't work out that well. For my experiment this problem won't occur, so I can use his AD9914 Eval. So when I recieved it, there was the following problem:

 

Most of the time the AD9914 worked fine. I could initialize it without a problem and create whatever output I wanted using parallel mode. I monitored the output via an RFSA (Radiofrequency Spectrum Analyzer) and sometimes the output changed and instead of one output frequency, several frequencies (like about 100-200 peaks) occured. I could figure out that if this was the case, I also couldn't initialize the AD9914 correctly. That means I had some crosstalking between registers. For example, if I set parallel mode on true, the extern OSK enable pin was also set on true. By unplugging the power of the AD9914 and restarting it, most of the time the problem didn't occur for at least a few minutes. I also realized that the problem occured everytime (but not exclusivly) when I wanted to stop the output of the AD9914, sending "0" using parallel mode.

 

I figured out that our power source could be the reason for this behavior. So I changed it using a buck converter (step-down converter) instead of linear voltage regulators, which have been used before and produced a lot of heat, to down convert the voltage to 1.8 and 3.3 V, respectively. So when I did that, the problem wasn't solved but changed its behavior:

 

Now I can stop the output wihtout any problems. Also, the output is perfect all the time. No other frequencies, no noise. BUT: I've got problems during initializing all the time. For me it's not that big deal, because the initializing problems don't affect the important options and I can control the output and that's all I want. But something seems to be wrong and I'd like to know what it is.

I'm pretty sure that it isn't a software problem, because it changes when I change the power supply. Also, the crosstalking between several registers doesn't occur permanently, but somehow statistically. Also I don't think that some bitlines are connected somehow, because this should'nt change by changing the power supply also. So I'm a little bit afraid that the AD9914 is damaged somehow.

 

Has anyone of you an idea, what the problem could be?

 

PS: To test it the new power supply is also not perfect, I replaced it with a lab power supply unit. And the behavior was the same like when I used the buck-converter.

 

Best regards

PRYSO

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