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Poor output linearity when AD5293 digital pot is used with AD5791 DAC

Question asked by Anoop on Mar 28, 2013
Latest reply on Mar 28, 2013 by Anoop

Hi,

 

I had managed to get 19 bit level(ie around 38uV) INL with the precision source I had designed using the AD5791 DAC (verified by generating a slow moving ramp from -5V to +5V). Then I did an experiment, I gave the output to an AD5293BRUZ-20 digital pot. The wiper was programmed for a 1:2 divider ratio. Keeping the wiper in that position, I gave the same ramp input again, but when I checked the linearity for the output of the voltage divider,

the INL was MUCH worse, ie at 14 bit level or 610uV. Do we expect this kind of a linearity deterioration with the digital pot being used? I believe the resistors in the divider are well matched as far as temperature co-coefficients and VCR are concerned, so why would we still see this huge a degradation in linearity, even when the wiper position is maintained constant

 

Please find the INL, DNL plots for the both cases attached

 

 

Thanks,

Anoop

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