Fuente: Wipo "digitalization" According to an embodiment, an analog-to-digital (AD) converter includes a first AD conversion unit, a selector and a second AD conversion unit. The first AD conversion unit performs AD conversion of an analog signal in a first period to generate an upper-bit digital signal. The selector selects not less than one reference voltage based on the upper-bit digital signal to obtain a selected reference voltage group in a voltage range narrower than a full scale. The second AD conversion unit performs AD conversion of the analog signal by using the selected reference voltage group. The first period starts before settling of the analog signal up to an accuracy corresponding to a total resolution of the first AD conversion unit and the second AD conversion unit.