ADC measurement problems

[helen]

Hi suport team

                            1、My ADC sampling circuit is shown in the figure below.

                                 

                         2、The actual voltage at ADC sampling is 1.37v, but the voltage measured by ADC is only 1.29v.

                         3、The ADC is configured with a reference voltage of 0.6V and a gain of 1 / 6.

                         4、I don't know what caused the deviation.

[Karl Ylvisaker]

Hello,

The actual voltage at ADC sampling is 1.37v, but the voltage measured by ADC is only 1.29v.

Could you elaborate on how you measured this 1.37 V value? Are you consistently measuring 1.29 V, or is this an average over some time interval?

The ADC is configured with a reference voltage of 0.6V and a gain of 1 / 6.

What is the rest of your configuration? What Acquisition time are you using?
Could you try to increase the acquisition time to 40 µs, and see if the measurement gets closer to your expected value then? Since you are using 20 M Ohm resistors I expect it to take quite some time for the charge to accumulate.
How often are you sampling?

It might also be helpful to have a read through this thorough blogpost about how to measure lithium ion batteries with the nRF52.

Best regards,
Karl