A read-out circuit includes an operational amplifier configured to receive an input voltage through a positive input terminal; a feedback capacitor connected between an output terminal of the operational amplifier 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; a switching circuit connecting the sensor and the operational amplifier during a second time after the sensor is charged or discharged; and a duty control circuit configured to determine a duty ratio of the first time and the second time according to a capacitance of the sensor.