A method is provided for detecting a transmitter approaching or touching a touch sensitive display. The transmitter transmits an electrical signal which is mixed from a plurality of signals having different frequencies. The display includes a liquid crystal layer between pixel electrodes and common electrodes and a plurality of second electrodes. The common electrodes include a plurality of first electrodes. A plurality of sensing points is located in the intersections of the plurality of first electrodes and the plurality of second electrodes. The method includes: calculating the total signal strength of a received signal with respect to each of the first electrodes; calculating the total signal strength of a received signal with respect to each of the second electrodes; calculating a relative position between the transmitter and the display according to the calculated total signal strengths of the received signals with respect to each of the first and second electrodes.