A/d converter and sensor apparatus

An A/D converter comprising:

• an integrating circuit including:
• an amplifier including a first input end and a second input end connected to an application end of a first reference voltage;
• a capacitor connecting the first input end of the amplifier and an output end of the amplifier;
• 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 an application end of a second reference voltage and the first input end of the amplifier;
• and
• a second switch connected between the application end of the second reference voltage and the first input end of the amplifier;
• a first 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 first reference voltage;
• and
• a switch controller configured to control the first switch and the second switch,
• wherein the switch controller is configured to switch the first switch to an off state and switch the second switch to an on state upon detecting that an output voltage of the amplifier has reached a third reference voltage until a predetermined period has elapsed after turning on the first switch and turning off the second switch or when the predetermined period has elapsed without the output voltage of the amplifier reaching the third reference voltage.