Question
We would appreciate your help about the following issue regarding a developmentwe are performing on a AD7621ASTZ LQFP48, 16-bit A/D Converter for one of ourusers .
We are experiencing severe problems for which we would appreciate so much yourtechnical support. The problems we found are in the part of linearity anddynamic parameters.
We get the following performance:
(End Point) INL and DNL approx. 8 LSB error (at least for the full range).SNR approx. 78dBcSFDR approx. 85dBcTHD approx. –93dBcSINAD approx. 78dBcThe DUT will have several missing codes.
Answer
Your results with the eval board look really bad and point to a fundamental error in your setup.
Looking at the setup of your signal source it looks like the output common mode voltage is set to 0V (DAC setting).
This should be 1.25V. Remember the differential inputs must swing 0V-2.5V differential antiphase.
You are currently swinging around ground if I look at your source setup.