In an embodiment, a touch sensor may include a sensor part including a first electrode and a second electrode, a signal receiving part, an amplifier circuit part connected between the second electrode and the signal receiving part, an analog-to-digital converter part configured to output a digital signal corresponding to a voltage difference between input terminals, and a processor configured to detect a touch input from the sensor part in response to the digital signal when operating in a first mode, and to output a gain control signal for calibrating a gain value of the amplifier circuit part in response to the digital signal when operating in a second mode.