How to make input impedance of EVAL-AD7982-PMDZ to be high?

Thanks for your query,

The purpose of the R1/R3 and R2/R4 resistor dividers on the amplifier inputs is to ensure the factory default EVAL-AD7982-PMDZ boards have a common mode input voltage of VREF/2 on the AD7982 inputs.

This is because the AD7982 has a common mode input voltage requirement/specification of VREF/2 (nominally). In other words, the average voltage on the IN+ and IN- pins needs to be VREF/2 for the AD7982 to function properly.

If that common mode voltage can be achieved in another way, then these resistor dividers aren't necessary and can be removed. But be sure to keep the common mode voltage requirement in mind when designing the capacitive amplifiers you mentioned.

The bypass capacitors are also optional, they are just there to reduce the noise from the amplifier generating the VCM signal (A1).

Thanks,

Tyler

Thank you very much for the explanation!

Thank you very much for the explanation!