A method of driving a touch screen display apparatus comprising a touch detector for detecting a touch by an object, a panel comprising a photo sensor unit for capturing an image of the object and a light emitting unit for displaying an image, the method comprising: generating an input signal ((a)) in response to the touch by the object with the touch detector; converting the input signal ((a)) into an output signal ((c)) by combining the input signal ((a)) and a reference signal ((b)), - the reference signal ((b)) having a first signal level (H 2) during a plurality of enable periods (a) and a second signal level during a plurality of disable periods (b) and - the output signal ((c)) having a first signal level (H 3) during the plurality of enable periods and a second signal level during the plurality of disable periods, - the first signal level (H 2) of the reference signal ((b)) being greater than the second signal level of the reference signal ((b)) and - the first signal level (H 3) of the output signal ((c)) being greater than the second signal level of the output signal ((c)); updating, during at least one disable period of the output signal ((c)), a noise determination reference of a sensing signal provided from the photo sensor unit; removing, during an enable period of the plurality of enable periods of the output signal ((c)), noise from the sensing signal according to the updated noise determination reference; and calculating a touch location of the object based on the sensing signal from which noise is removed. generating an input signal ((a)) in response to the touch by the object with the touch detector; converting the input signal ((a)) into an output signal ((c)) by combining the input signal ((a)) and a reference signal ((b)), - the reference signal ((b)) having a first signal level (H 2) during a plurality of enable periods (a) and a second signal level during a plurality of disable periods (b) and - the output signal ((c)) having a first signal level (H 3) during the plurality of enable periods and a second signal level during the plurality of disable periods, - the first signal level (H 2) of the reference signal ((b)) being greater than the second signal level of the reference signal ((b)) and - the first signal level (H 3) of the output signal ((c)) being greater than the second signal level of the output signal ((c)); - the reference signal ((b)) having a first signal level (H 2) during a plurality of enable periods (a) and a second signal level during a plurality of disable periods (b) and - the output signal ((c)) having a first signal level (H 3) during the plurality of enable periods and a second signal level during the plurality of disable periods, - the first signal level (H 2) of the reference signal ((b)) being greater than the second signal level of the reference signal ((b)) and - the first signal level (H 3) of the output signal ((c)) being greater than the second signal level of the output signal ((c)); updating, during at least one disable period of the output signal ((c)), a noise determination reference of a sensing signal provided from the photo sensor unit; removing, during an enable period of the plurality of enable periods of the output signal ((c)), noise from the sensing signal according to the updated noise determination reference; and calculating a touch location of the object based on the sensing signal from which noise is removed.