There is a statement in EFM8LB1 spec that pin leakage current is in the range of [-1.1 4] uA . Does this leakage current affects ADC result of external signal?
Correct, the leakage mainly dominated by the ESD protection circuit for the port structure. It may flow in or out of the device. The leakage current is strongly sensitive to the temperature.
Let us assume 100nA leakage, and output impedance for source signal to be measured is 10k ohm. Then the measurement error caused by the leakage likes an offset error of ADC result. This example gets 100nA*10kOhm = 1mV voltage offset (measured) on the pin.
Under condition that ADC is configured as 2.5V VFS and 12-bit resolution. Then we have 1 LSB equals to be about 2.5V/4096 = 610uV
Then the 10k Ohm resistance of external source signal to be measured would see 1 LSB offset error as 1mV>610uV.
Related KBA: Comparator Input Leakage