A driving unit for an STN-LCD receives input image data and generates column signal functions for selected row lines according to on/off states of pixels, and row signal functions for the selected row lines according to negative/positive states of row signals. The driving unit determines a dot product value of the column signal function and the row signal function to find a mismatch value between the column signal function and the row signal function, and determines the total number of mismatch values corresponding to the row and column signals to be applied sequentially to the liquid crystal panel. The driving unit generates column signal voltages in a first driving time period T1 determined according to the total number of mismatch values, and applies the column signal voltages in period T1 to the column lines when the row signals are applied respectively to four row lines during the period T1.