1. Field of the Invention
The present invention relates to a control circuit of a liquid crystal display device, and more particularly to a control circuit of a liquid crystal display device which allows high-speed response by adding a compensation value to the driving voltage of a cell so as to compensate driving, and which allows a more accurate driving compensation by changing the compensation value conversion table depending on the status of the previous frame.
2. Description of the Related Art
Liquid crystal display devices are widely used as energy saving and space saving display devices. Recently, liquid crystal displays are also receiving attention as display devices for TVs, which displays moving pictures. A liquid crystal display panel is comprised of source electrodes to which a display driving voltage corresponding to the image data of the current frame is applied, gate electrodes which are driven at the scanning timing, and cell transistors and pixel electrodes which are disposed at positions where the source electrodes and the gate electrodes cross each other, wherein desired images are displayed by applying the display driving voltage to the liquid crystal layer between the pixel electrodes via the cell transistors, changing the transmittance of the liquid crystal layer.
Generally speaking, liquid crystal materials have poor response characteristics, and in some cases it is difficult to change to a status corresponding to the input gray scale data within one frame period, and these poor response characteristics cause a drop in the image quality of a moving picture display. To solve these slow response characteristics, a driving compensation method has been proposed (e.g. Japanese Patent Application Laid-Open No. 2002-297104 (corresponding to the U.S. published Unexamined Patent Application US-2002-0140652-A1), Japanese Patent Application Laid-Open No. 2002-6285 and Japanese Patent Application Laid-Open No. 2002-202763).
Japanese Patent Application Laid-Open No. 2002-297104 discloses that the display driving data for the image data of the current frame is determined by adding or subtracting (hereafter referred to as “adding”) the compensation value according to the combination of the post driving status data of the previous frame and the image data of the current frame to/from the image data of the current frame. Even if the liquid crystal layer is driven with the display driving voltage corresponding to the display driving data, the liquid crystal layer does not always become the status of the display driving data within a flame period, so the differential value corresponding to the combination of the post driving status data of the previous frame and the input gray scale data in the current frame is added to or subtracted from (hereafter referred to as “added”) the image data of the current frame, to determine the post driving status data, which is stored in the frame memory.
Japanese Patent Application Laid-Open No. 2002-297104 also discloses that in order to decrease the data capacity of the conversion table for determining the compensation values and the differential values, compensation values and differential values are stored for the combination of significant bits of the post driving status data of the previous frame and the image data of the current frame, and an interpolation operation is performed by insignificant bits.