Read-out circuit for a capacitive sensor

A read-out circuit comprising:

• an operational amplifier configured to receive an input voltage through a positive input terminal;
• a feedback capacitor connected between an output terminal and a negative input terminal of the operational amplifier;
• a sensor charging and discharging circuit configured to charge or discharge a sensor during a first time;
• an offset cancelling circuit having an offset capacitor connected between a first node and a second node and configured to charge or discharge the offset capacitor during the first time;
• a first switching circuit configured to provide a power supply voltage or a ground voltage to the first node during the first time;
• a second switching circuit configured to connect the operational amplifier with the offset cancelling circuit and to connect the offset cancelling circuit with the sensor during a second time after the sensor is charged or discharged;
• and
• a duty control circuit configured to control a duty ratio of the first time and the second time according to capacitance of the sensor or capacitance of the offset capacitor.