A sensing device placed in a touch sensing system of a display device includes a selector, a sensing module, and a detection module for determining touch signals generated by the touch sensing system. The selector selects two of the touch signals according to at least one selection control signal. The sensing module comprises a first differential amplifier for comparing the selected touch signals and producing a first differential signal according to first control signals. According to second control signals, the detection module receives the first differential signal, generates an averaged sensing value and a reference value, and compares the averaged sensing value with the reference value to produce a second differential signal. Thereby, the touch sensing system uses the second differential signal to generate the first control signals and the second control signals to control the operation of the touch sensing system.