An analog to digital converter includes a first DAC unit configured to vary a level of a reference voltage output through a first node according to a first code, a second DAC unit coupled in parallel to the first DAC unit on the basis of the first node and configured to vary the level of the reference voltage according to a second code, a comparator configured to generate a comparison result signal by comparing an input voltage and the reference voltage, and at least one register array configured to store the first code and the second code with initial values and store the first code and the second code by varying values of the first code and the second code according to the comparison result signal.