An electrocardiogram (ECG) sensor includes an analog front end device configured to remove a DC offset in a first ECG signal received from a measuring electrode, and adjust a gain amplification value based on the first ECG signal. The analog front end device is configured to output an adjusted first ECG signal, the adjusted first ECG signal being based on the adjusted gain amplification value and the removed DC offset in the first ECG signal. The ECG sensor includes a digital signal processor configured to analyze and process the adjusted first ECG signal based on an algorithm and to output information. The analog front end device is configured to remove the DC offset in the first ECG signal during a first period, and remove a DC offset in a second ECG signal and simultaneously adjust a gain amplification value for the second ECG signal during a second period.