Two sensing units are configured as an exciter and a sensor connected to two trace lines, respectively, for mutual capacitance sensing from the capacitance units including these two trace lines. The two sensing units connect the two trace lines together to balance them to a same voltage level first, and then disconnect them from each other. Thereafter, the exciter connects the first trace line to an excitation node to induce a charge change on the second trace line, and the sensor senses the charge change to detect the variation of the mutual capacitance between the two trace lines.