Ad converter

An AD converter, comprising:

• a unit voltage check integration unit that uses an input voltage as an initial value and repeats an operation of integrating one or both of two types of unit voltages with the input voltage, thereby generating an integrated voltage and also generates a check voltage larger than a larger one of the unit voltages;
• a threshold voltage unit that includes a threshold voltage causing the operation of integrating to be terminated;
• a comparator that compares the integrated voltage with the threshold voltage;
• an integration determination unit that, before the operation of integrating is started, causes the comparator to compare a sum voltage with the threshold voltage, the sum voltage being a sum of the input voltage and the check voltage;
• a unit voltage switching control unit that, when the threshold voltage is larger than the check voltage, controls the unit voltage check integration unit to generate the integrated voltage by using the two types of unit voltages;
• and
• a single unit voltage control unit that, when the threshold voltage is smaller than the check voltage, controls the unit voltage check integration unit to generate the integrated voltage by using only a smaller one of the unit voltages.