A liquid crystal display (LCD) is a flat panel display widely used at present, which has the advantages of thin and light appearance, electricity economization and no radiation. The operating principle of LCD is that the voltage difference at the two ends of a liquid crystal layer is utilized to change the arrangement state of liquid crystal molecules in the liquid crystal layer, so as to change the light transmission of the liquid crystal layer, and display the image by cooperating the light source provided by a backlight module.
FIG. 1 is the schematic diagram for the circuit structure of an existing LCD. The LCD includes an LCD panel 110, a common voltage generator 15, a scanning driver 17 and a data driver 16, wherein the LCD panel 110 includes a plurality of scanning lines 9 and a plurality of data lines 14, the scanning lines 9 and the data lines 14 are crosswise arranged by way of insulation, thereby defining a plurality of pixel units 100 arranged in the way of a matrix.
Each pixel unit 100 is provided with a thin film transistor 10, a liquid crystal capacitor 12 and a storage capacitor 13. The liquid crystal capacitor 12 includes a pixel electrode 121 and a common electrode 122 oppositely arranged and a liquid crystal layer (not shown in the figure) sandwiched between the both. The storage capacitor 13 includes the pixel electrode 121 and a storage electrode 132 oppositely arranged and the insulating material (not shown in the figure) sandwiched between the both. Besides, the data lines 14, the common electrode 122 and the liquid crystal layer between the both generally form a parasitic capacitor 11.
The thin film transistor 10 includes a gate electrode, a source electrode and a drain electrode, wherein the gate electrode is connected with one of the scanning lines 9, the source electrode is connected with one of the data lines 14, and the drain electrode is connected with the pixel electrode 121.
The scanning driver 17 is used for outputting a plurality of scanning signals in sequence to each of scanning lines 9, when the scanning driver 17 outputs scanning signals to one line of scanning lines 9, the thin film transistor 10 connected with the line of scanning lines 9 is conducted, and meanwhile, the data driver 16 provides a plurality of gray-scale voltages to the plurality of data lines 14, thereby causing the gray-scale voltages to be loaded to the pixel electrode 121 through the source electrode and the drain electrode of the conducted thin film transistor 10.
The common voltage generator 15 is used for providing the common voltage Vcom to the common electrode 122 and the storage electrode 132. Therefore, after the gray-scale voltages are loaded to the pixel electrode 121 through the source electrode and the drain electrode of the conducted thin film transistor 10, the liquid crystal in the liquid crystal capacitor 12 deflects due to a voltage difference between the common voltage and the gray-scale voltages on the liquid crystal capacitor 12, thereby displaying the required gray scale according to the deflection angle of the liquid crystal. The function of the storage capacitor 13 is to maintain the gray-scale voltage on the pixel electrode 121, so as to keep the gray-scale voltage on the pixel electrode 121 lasting until the arrival of the next gray-scale voltage.
Please also refer to FIG. 2. FIG. 2 shows the arrangement diagram for pixel units 100 of a certain exemplary region of the LCD. The region is a pixel region in the size of 3*3, the middle pixel units 100 are represented by A, and the surrounding pixel units 100 are represented by B.
For a certain pixel unit A, the gray-scale voltages provided on the data lines 14 of the pixel units B certainly change when the image gray scale required to be displayed on the pixel units B surrounding the certain pixel unit A changes. At this moment, due to the fact that the voltage of the parasitic capacitor 11 of the pixel units B can not instantly change, the voltage of the common electrode 122 of the pixel units B fluctuates. Whereas, the common electrode 122 of each pixel unit is communicated, so the voltage of the common electrode 122 of the pixel unit A fluctuates as well. For example, for an ever-light type LCD, the gray-scale voltages on the data lines 14 of the pixel units B increase B when the pixel units B surrounding the pixel unit A displaying the bright state change from bright to dark; due to the fact that the voltage of the parasitic capacitor 11 of the pixel units B can not instantly change, the voltage of the common electrode 122 of the pixel units B fluctuates upwards, therefore, the voltage of the common electrode 122 of the pixel unit A displaying the bright state also fluctuates upwards. On the contrary, the voltage of the common electrode 122 of the pixel unit A fluctuates downwards when the pixel units B surrounding the pixel unit A displaying the bright state change from dark to bright.
Likewise, the problem that the voltage of the common electrode 122 fluctuates upwards or downwards exists in a plurality of single pixel units 100 of the LCD, and the common electrodes 122 of the pixel units 100 are communicated, therefore, the problem that the whole voltage of the common electrode 122 of the LCD fluctuates upwards or downwards easily generates the phenomenon of cross noise, thereby greatly influencing the display quality of the LCD.