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AD4020 operation with single ended input gives non-zero reading even when inputs are not present ?

I'm using AD4020 for DC input measurement by implementing Figure 36 of AD4020 datasheet. Implemented schematic is below

But i'm getting non-zero readings which gives 0.25V reading by considering only MSB 15 bits and converting same to voltage by multiplying reading with 7.63uV. ie i'm getting readings like "7FB8x" as MSB. W.r.t to the schematic shared, what could be the problem, does this IC have some offset ? Please confirm single-ended DC input support for this part.

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  • Hi

    1) Please confirm AD4020 part will support DC voltage measurement w.r.t the figure above.

    2) Also in the tool shared, AD4020 is not present. Which part in the tool will be the best match for AD4020 ?

    3) As you see in schematic the RC between U23 an U21 is not connected (U23 output is directly connected to U21), so how this may get affected ?

    4) What could be the resistor values in above figure for best DC measurement possible ?