Ad converter, sensor device, and voltage measuring device

An AD converter comprising:

• an amplifier including a first input end and a second input end connected to an application end of a reference voltage;
• a capacitor configured to connect the first input end of the amplifier and an output end of the amplifier;
• a comparator including a first input end connected to the output end of the amplifier and a second input end connected to the application end of the reference voltage;
• a first resistor connected between an application end of an input voltage and the first input end of the amplifier;
• a first switch connected between the application end of the input voltage and the first input end of the amplifier;
• a second resistor connected between the first input end of the amplifier and a first node;
• a second switch connected between the first node and an application end of a ground potential;
• and
• a controller configured to perform ON/OFF control of the first switch and the second switch,
• wherein the controller is further configured to start charging the capacitor by switching the first switch to an ON state, thereafter discharge the capacitor by setting the second switch to an ON state during an offset regulation period so as to cancel an increase in a charging amount of the capacitor due to an offset of the input voltage, and measure a discharging period from an end of the offset regulation period to switching of an output level of the comparator.