Patent ID: 8581820

Claim:
A signal driving circuit of a liquid crystal display device, the signal driving circuit comprising: a column driver configured to: convert a plurality of signal voltages based on video data into analog gray-scale voltages; and apply the analog gray-scale voltages to pixels of a liquid crystal panel; a gamma voltage circuit configured to apply the plurality of signal voltages to the column driver, the signal voltages being used as the analog gray-scale voltages; an external voltage supplying unit configured to: generate both the plurality of signal voltages and a common voltage, the common voltage being an analog voltage applied to a common electrode of the liquid crystal panel; and adjust the plurality of signal voltages and the common voltage before being applied to the gamma voltage circuit and the common electrode of the liquid crystal panel, respectively, wherein the external voltage supplying unit comprises: a data storing part configured to store a plurality of signal data; a digital to analog converting part coupled to the gamma voltage circuit and the common electrode of the liquid crystal panel; and a controlling part configured to: select a signal data that represents a modification of one of a gray-scale voltage and a common voltage in response to user's command; and apply the selected signal data to the digital to analog converting part; wherein the digital to analog converting part comprises: a reference voltage generator configured to generate a reference voltage, and a plurality of digital to analog converters coupled to the reference voltage generator and the data storing part, wherein if the signal data represents the modification of the gray-scale voltage, the plurality of digital to analog converters generate a plurality of modified signal voltages, wherein if the signal data represents the modification of the common voltage, only one of the plurality of digital to analog converters generate a modified common voltage, the modified common voltage applied to the common electrode of the of the liquid crystal panel, and the absolute values of a normal (+) gray-scale voltage and an inverse (−) gray-scale voltage have the same voltage difference with respect to the modified common voltage, and wherein the digital to analog converting part is coupled directly to the common electrode of the liquid crystal panel.