1. Field of the Invention
The present invention relates to a gamma voltage generation circuit. More particularly, the present invention relates to a gamma voltage generation circuit capable of shifting gamma voltages by a common voltage level.
2. Description of Related Art
In a present information society, as information communication media and various electronic display devices are widely used in industrial apparatus or home appliances, the electronic display devices become indispensable, and the electronic display devices are continually updated to meet various demands of the information society.
Generally, the electronic display devices display and transmit various information to users. Namely, the electronic device can convert electronic information signals into optical information signals that can be visually recognized by the users.
In a present display device or a system, for example, a cathode-ray tube (CRT) or a liquid crystal display (LCD), a relationship between an input voltage and a display output thereof is not linear, and the relationship between the input voltage and the display output can be described by a gamma curve. Regarding the LCD, an output voltage (i.e. a gamma voltage) corresponding to each of gray levels can be found according to the gamma curve. A LCD panel can display a correct gray level according to the corresponding gamma voltage, so that the LCD can correctly display images.
To improve a display effect of the LCD, some of the LCD panels can divide a single pixel into two sub-pixels. Common voltage levels of the two sub-pixels are probably different due to a circuit structure design. In this case, when a same gamma voltage is output to the LCD panel, display effects of the two sub-pixels can be different, so that a display quality thereof is influenced. Referring to FIG. 1, a pixel is composed of two sub-pixels A and B. The common voltage level of the sub-pixel A is VCOMA, and the common voltage level of the sub-pixel B is VCOMB. A difference ΔV between the common voltage levels VCOMA and VCOMB causes a phenomenon of color shift of the LCD panel, such that the display quality of the LCD would be reduced.