An embodiment of the present invention relate to a liquid crystal display driving apparatus and a driving method for the same.
Recently, liquid crystal displays (LCDs) have been the main kind of displays. When a pixel of a LCD displays colors, the bidirectional driving manner is commonly used. If a positive voltage is applied to a pixel for displaying a same gray-level during one frame image, the positive voltage is the voltage drop between a voltage applied on a pixel electrode of an array substrate and a voltage applied on a common electrode of an color filter substrate, such as, +2V, so that liquid crystal molecules between the array substrate and the color filter substrate are tilted at a certain angle; in the next frame when still the same gray-level is displayed, a negative voltage is applied, such as, −2V, so that the liquid crystal molecules are tilted at a same angle in an opposite direction. Aging of the liquid crystal material can be effectively prevented by alternatively applying positive and negative voltages to display images.
However, in practice, when the positive and negative voltages having a same absolute value are applied to the liquid crystal molecules, the liquid crystal molecules are not tilted at the same angle in the opposite directions, so the transmittances of the liquid crystal layer are different in the cases, and a flicker phenomenon may occur when images are displayed by alternatively applying the positive and negative voltages. Positive and negative voltages that are nearly symmetrical with each other are alternatively applied to eliminate the flicker phenomenon. However, in practice, it is difficult to control the degree of the near symmetry when the nearly symmetrical positive and negative voltages are alternatively applied, so the flicker phenomenon cannot be completely avoided.
Meanwhile, the positive and negative voltages are applied to the pixel electrode with respect to the common electrode, so it is required that a power supply can supply a voltage twice as the voltage of the common electrode, which increases the power consumption. In order to produce the positive and negative voltages, two sets of gamma resistors are needed on the printed circuit board (PCB) and the chip on film (COF) of a LCD to provide the pixel voltages applied to the pixel electrode. The two sets of gamma resistors take much space on the PCB and COF and increase the cost of the PCB and COF.
In addition, when the array substrate and the color filter substrate are assembled to form a cell, some impurities may exist in the injected liquid crystal material. The stay position of the impurity ions may migrate under the voltages driving the liquid crystal molecules to tilt. When the LCD displays one image for a long time period, the impurity ions may migrate to a certain location. When the displayed image is changed, the impurity ions staying in a given location cannot move away rapidly, so image sticking may occur. Although image sticking can be prevented by reducing the amount of the impurities while applying a nearly symmetrical driving voltage on the pixel, the impurities cannot be removed completely. Further, the residence of the impurity ions is influenced to different degrees by the voltages in different directions, thus the migration of the impurity ions also are not uniform when the different nearly symmetrical voltages are applied on different pixels for a long time period, and finally image sticking will be formed.