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AD8237 chopping clock problem

Question asked by m3atwad on Mar 18, 2016
Latest reply on Apr 4, 2016 by m3atwad

I have the AD8237 amp in a design and I'm seeing the 27 kHz "chopping/ALS" clock on my output.  Page 21 of the data sheet mentions this clock and that it can possibly couple to the output.  I am using the amp in low bandwidth mode (BW pin tied to GND) and with very small signals I see the content of this 27 kHz clock.  I'm confident now that this is the issue because the signal I'm seeing riding on my output signal is very small, but right at 27 kHz.

 

This device is configured in low bandwidth mode and supporting a gain of 1-10.  My input signals can range from 0 to 20kHz.  The clock feed through section of the data sheet mentions that you may have to add an output filter to deal with this issue.  How do I add an output filter to deal with this 27kHz signal when my pass band is 0-20kHz.  The data sheet has no recommendations.  Could anyone give me some recommendations?

 

The overall problem here is that this 27kHz oscillation is getting gained up as it travels through my analog front end.

 

 

screen shot zoomed in on the output of the AD8237

ADS00001.jpg

 

 

Screenshot of the output after going through the rest of my analog front end.

 

ADS00002.jpg

 

 

Result of this and it's affect on my data:

1Khz Sine Gain20 Clock feed through AD8237 getting gained.jpg

 

 

Thanks,

Rob

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