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

Hi,

Termination resistor on the ADC driver force some error on the output.R347 and R121 gives the unbalance. These resistor should  be apply also to  other input of the ADC driver to make it balance. Here's  some  tool to help determine the value and configuration on the termination resistors.

https://www.analog.com/en/design-center/interactive-design-tools/adi-diffampcalc.html

regards,

Lloben

Hi Gnib

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 ?

Hi Gnib

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 ?

Hi,

Correct AD4020 is capable of measuring DC voltage input as well. The tool will show you on how to configure  ADC driver which ADA4940 in this case. To properly configure  the ADA4940 you can place 25ohms in series to R124 to gnd. I would also recommend to use the RC connected to your ADC input.

regards,

LLoben

Hi

You mentioned "Termination resistor on the ADC driver force some error on the output.R347 and R121 gives the unbalance. " so if i remove these resistors will it fix the balancing issue ?

Hi,

Confirmed removing this  will help balance the adc driver output.

regards,

LLoben