CN101387773B - Common voltage generating circuit of liquid crystal display element and method thereof - Google Patents

Abstract

A common voltage generating circuit of liquid crystal display element includes an initial voltage source, an inverter and a panel actual common voltage input terminal. The initial voltage source generates an initial voltage. The voltage of the panel actual common voltage input end becomes compensation voltage through the inverter, the compensation voltage compensates the initial voltage to generate common voltage, and the common voltage is supplied to the panel of the liquid crystal display element.

Description

Common voltage generating circuit and method for liquid crystal display elements

technical field

The present invention relates to a common voltage generation circuit and its method for a liquid crystal display element, in particular to a common voltage generation circuit capable of stabilizing the actual common voltage of a panel and its method.

Background technique

A conventional liquid crystal display device includes an array substrate with a plurality of pixel electrodes, a color filter substrate with a common electrode, and a liquid crystal material between the two substrates. When a voltage is applied to the pixel electrode and the common electrode, the molecules of the liquid crystal material change directions due to a potential difference between the pixel electrode and the common electrode. The pixel electrodes are respectively arranged in the pixel matrix and connected with the thin film transistor elements. The thin film transistor element responds to a gate signal from a gate line, and selectively transmits a data voltage from a data line.

In the liquid crystal display element, a voltage is applied to the pixel electrode and the common electrode simultaneously to generate an electric field in the liquid crystal layer. And by controlling the intensity of the electric field to adjust the light transmittance passing through the liquid crystal layer, so as to obtain the desired image. In order to prevent image degradation caused by applying a unidirectional electric field for a long time, the polarity inversion of the data voltage and the common voltage can be made between each frame, each pixel column, each pixel row or each point.

However, as the resolution of liquid crystal display elements continues to increase (for example: from SXGA to WUXGA+, etc.), the capacitive coupling effect in the pixel area will become more obvious, so more consideration should be given to this when designing the panel. Generally speaking, when the capacitive coupling effect increases, the influence on the voltage of the pixel electrode is stronger, thus resulting in a partial voltage imbalance across the panel, and even greenish, reddish or bluish images.

FIGS. 1( a ) to 1 ( b ) are explanatory views of the greenish screen caused by the voltage drift of the common electrode in the conventional liquid crystal display element. As shown in FIG. 1( a ), the actual voltage Vcom′ of the common electrode will be higher than the ideal voltage Vcom due to the capacitive coupling effect. Since the green (R) sub-pixels are placed in the red and blue sub-pixels, there will be too much green color to form a greenish image. As shown in FIG. 1(b), when the polarity is reversed, the actual voltage Vcom' of the common electrode will be lower than the ideal voltage Vcom due to the capacitive coupling effect, and the proportion of green is too large to form a greenish screen.

Generally, it can be roughly divided into two methods to solve the aforementioned problems. One is to reduce the impedance value of the common electrode (transparent electrode made of ITO) on the color filter substrate, thereby increasing the actual voltage Vcom' Balance recovery ability; the other is to increase the contact area of the Au transfer point of the common electrode, thereby improving the stability of the actual voltage Vcom'. However, these two methods cannot effectively solve the aforementioned problems for large-sized liquid crystal display elements. Due to the limitation of the characteristics of the ITO material itself, it is impossible to reduce the resistance value without limit. On the other hand, increasing the gold-gel conversion point will increase the output time of the machine and reduce the output per unit time, and for large-sized liquid crystal display elements, the number of gold-gel conversion points cannot be increased without limit, in order to expect The actual voltage Vcom' is stabilized across the substrate.

Contents of the invention

The main purpose of the present invention is to provide a common voltage generation circuit and method for liquid crystal display elements, which reverses the actual common voltage on the panel and uses it as a compensation voltage to feed back to the common electrode of the panel. This is to use a dynamic compensation method to supply the compensation voltage to the common electrode in real time, so that the linkage relationship between the compensation voltage and the capacitive coupling effect makes the voltage supplied to the common electrode also change accordingly. Therefore, the cross-voltage of each area of the panel can maintain a stable value to avoid the generation of color shift images.

To achieve the above object, the present invention discloses a common voltage generating circuit for liquid crystal display elements, which includes an initial voltage source, an inverter, and an actual common voltage input terminal of the panel. The initial voltage source generates an initial voltage. The voltage at the actual common voltage input terminal of the panel becomes a compensation voltage through the inverter, and the compensation voltage compensates the initial voltage to generate a common voltage, and supplies the common voltage to the panel of the liquid crystal display element.

The invention also discloses a common voltage generating method of the liquid crystal display element. Generate the initial voltage and extract the actual common voltage on the panel from the liquid crystal display element. The actual common voltage is reversed to compensate the initial voltage, and then the compensated voltage is supplied to the panel.

Description of drawings

Figures 1(a) to 1(b) are explanatory diagrams of the greenish screen caused by the voltage drift of the common electrode of the existing liquid crystal display element;

FIG. 2 is a schematic diagram of a common voltage generation circuit according to the first embodiment of the present invention;

3 is a schematic diagram of a common voltage generating circuit according to a second embodiment of the present invention; and

4( a ) and FIG. 4( b ) are schematic diagrams of a common voltage generating circuit according to a third embodiment of the present invention.

Detailed ways

In the liquid crystal display element, a common electrode is provided on the color filter substrate to generate an electric field with the pixel electrodes on the array substrate to control the rotation direction of the liquid crystal molecules, and the actual common voltage of the common electrode is V _com ^CF . In addition, the common electrode is also provided on the array substrate to provide the basic voltage of the storage capacitor on the array substrate, and the actual common voltage of the common electrode is V _com ^AA .

FIG. 2 is a schematic diagram of a common voltage generating circuit according to the first embodiment of the present invention. In this embodiment, the common electrode of the color filter substrate and the common electrode of the array substrate are short-circuited, and generally the two common electrodes are both disposed on the array substrate. The common voltage generating circuit 20 includes an initial voltage source 21 , an inverter 22 and an actual common voltage input terminal 23 of the panel. The initial voltage source 21 generates an initial voltage Vi, which is supplied to the common electrode of the color filter substrate and the common electrode of the array substrate (not shown) through the first driving element 81 to the eighth driving element 88 . After the initial voltage Vi is input, the common electrode of the color filter substrate is subjected to the capacitive coupling effect of the panel to obtain an actual common voltage V _com ^CF . The actual common voltage V _com ^CF becomes the compensation voltage -V _com ^CF after passing through the inverter 22 . The compensation voltage -V _com ^CF compensates the initial voltage to generate a dynamic common voltage V _com , and supplies the common voltage V _com to the common electrode of the color filter substrate and the common electrode of the array substrate. In addition, R ₁ , R ₂ and R ₃ in FIG. 2 represent resistors.

In the embodiment shown in FIG. 2 , the common electrode of the color filter substrate and the common electrode of the array substrate are short-circuited. However, in order to prevent the voltages of the two common electrodes from interfering with each other, the embodiment in FIG. 3 further forms an open circuit for the two common electrodes, and supplies the same common voltage V _com respectively.

FIG. 3 is a schematic diagram of a common voltage generating circuit according to a second embodiment of the present invention. The common voltage generating circuit 30 also includes an initial voltage source 31 , an inverter 32 and an actual common voltage input terminal 33 of the panel. The initial voltage source 31 generates an initial voltage Vi, which is supplied to the common electrode of the color filter substrate via the first driving element 81 to the eighth driving element 88 . After the initial voltage Vi is input, the common electrode of the color filter substrate is subjected to the capacitive coupling effect of the panel to obtain an actual common voltage V _com ^CF . The actual common voltage V _com ^CF becomes the compensation voltage -V _com ^CF after passing through the inverter 32 . The compensation voltage -V _com ^CF compensates the initial voltage to generate a dynamic common voltage V _com , and supplies the common voltage V _com to the two common electrodes on the panel respectively.

With respect to the second embodiment of Fig. 3, Fig. 4 (a) and Fig. 4 (b) generate a common voltage respectively by different common voltage generating circuits 40a and 40b, to supply the common electrode and the array of the color filter substrate respectively The common electrode of the substrate.

4( a ) and FIG. 4( b ) are schematic diagrams of a common voltage generating circuit according to a third embodiment of the present invention. As shown in FIG. 4(a), the common voltage generating circuit 40a for supplying the common electrode of the array substrate also includes an initial voltage source 41a, an inverter 42a and an actual common voltage input terminal 43a for the common electrode of the array substrate. The ^{initial voltage source 41 a generates an initial voltage V iAA , and the initial voltage V iAA} _is ^supplied to the common electrode on _the array substrate via the first driving element 81 to the eighth driving element 88 . After the initial voltage V _i ^AA is input, the common electrode on the array substrate is subjected to the capacitive coupling effect of the panel to obtain an actual common voltage V _com ^AA . The actual common voltage V _com ^AA becomes the compensation voltage -V _com ^AA after passing through the inverter 42 a. The compensation voltage -V _com ^AA compensates the initial voltage to generate a dynamic common voltage V _com1 , and supplies the common voltage V _com1 to the common electrode on the array substrate. In addition, R ₄ and R ₅ in Fig. 4(a) represent resistors.

As shown in Figure 4(b), the common voltage generating circuit 40b that supplies the common electrodes of the color filter substrate also includes an initial voltage source 41b, an inverter 42a (shared with the common voltage generating circuit 40a) and the color filter substrate The actual common voltage input terminal 43b of the upper common electrode. The initial voltage source 41 b generates an initial voltage V _i ^CF , and the initial voltage V _i ^CF is supplied to the common electrode of the color filter substrate via the first driving element 81 to the eighth driving element 88 . After the initial voltage V _i ^CF is input, the actual common voltage V _com ^AA on the array substrate is still used as a feedback signal because the common electrode on the array substrate is greatly affected by the capacitive coupling effect of the panel. The actual common voltage V _com ^AA becomes the compensation voltage V _com ^AA after passing through the inverter 42 a. The compensation voltage -V _com ^AA compensates the initial voltage to generate a dynamic common voltage V _com2 , and supplies the common voltage V _com2 to the common electrode of the color filter substrate. In addition, R ₅ and R ₆ in Fig. 4(b) represent resistors.

The technical content and technical features of the present invention have been disclosed above, but those skilled in the art may still make various replacements and modifications based on the teaching and disclosure of the present invention without departing from the spirit of the present invention. Therefore, the protection scope of the present invention should not be limited to the contents disclosed in the embodiments, but should include various replacements and modifications that do not depart from the present invention, and are covered by the following claims.

Claims (17)

1. A common voltage generating circuit of a liquid crystal display element, comprising: an initial voltage source to generate an initial voltage; The panel actual common voltage input end receives the actual common voltage detected from the common electrode of the panel; and an inverter for inverting the actual common voltage into a compensation voltage; Wherein the compensation voltage compensates the initial voltage to generate a compensated common voltage for supplying to the panel. 2. The common voltage generating circuit of a liquid crystal display device as claimed in claim 1, wherein the compensated common voltage is used to supply a common electrode of the color filter substrate. 3. The common voltage generating circuit of the liquid crystal display element as claimed in claim 2, wherein the compensated common voltage is also used to supply the common electrode of the array substrate. 4. The common voltage generating circuit of the liquid crystal display element as claimed in claim 3, wherein the common electrode of the color filter substrate and the common electrode of the array substrate belong to two different circuits, and are all located at the on the array substrate. 5. The common voltage generating circuit of a liquid crystal display device as claimed in claim 1, wherein the compensated common voltage is supplied to the common electrodes of the color filter substrate and the common electrodes of the array substrate. 6. The common voltage generating circuit of the liquid crystal display element as claimed in claim 5, wherein the common electrode of the color filter substrate and the common electrode of the array substrate are short-circuited with each other. 7. A common voltage generation circuit for liquid crystal display elements, comprising: a first initial voltage source, generating a first initial voltage; a second initial voltage source for generating a second initial voltage; The first actual common voltage input terminal receives the first actual common voltage detected from the common electrode of the array substrate; The second actual common voltage input terminal receives the second actual common voltage detected from the common electrode of the array substrate; and an inverter, for inverting the first actual common voltage into a first compensation voltage, and inverting the second actual common voltage into a second compensation voltage; Wherein the first compensation voltage compensates the first initial voltage to generate a first compensated common voltage, and the second compensation voltage compensates the second initial voltage to generate a second compensated common voltage. 8. The common voltage generating circuit of the liquid crystal display element as claimed in claim 7, wherein the first compensated common voltage is used to supply the common electrode of the array substrate. 9. The common voltage generating circuit of the liquid crystal display element as claimed in claim 7, wherein the second compensated common voltage is used to supply the common electrode of the color filter substrate. 10. The common voltage generating circuit of the liquid crystal display element as claimed in claim 7, wherein the common electrode of the color filter substrate and the common electrode of the array substrate belong to two different circuits, and are all located at the on the array substrate. 11. A method for generating a common voltage of a liquid crystal display element, comprising the following steps: generate an initial voltage; Extract the actual common voltage on the panel from the liquid crystal display element; inverting the actual common voltage to compensate for the initial voltage, thereby generating a common voltage; and The common voltage is supplied to the panel. 12. The method for generating a common voltage of a liquid crystal display element as claimed in claim 11, wherein the actual common voltage is a voltage detected by a common electrode of a color filter substrate of the panel. 13. The method for generating a common voltage of a liquid crystal display element as claimed in claim 11, wherein the actual common voltage is a voltage detected by a common electrode of an array substrate of the panel. 14. The method for generating a common voltage of a liquid crystal display device as claimed in claim 12, wherein the common voltage is used to supply a common electrode of a color filter substrate. 15. The method for generating a common voltage of a liquid crystal display element as claimed in claim 13, wherein the common voltage is used to supply a common electrode of an array substrate. 16 . The method for generating a common voltage of a liquid crystal display element as claimed in claim 12 , wherein the common voltage is supplied to a common electrode of the color filter substrate and a common electrode of an array substrate of the panel. 17. The method for generating a common voltage of a liquid crystal display element according to claim 16, wherein the common electrode of the color filter substrate and the common electrode of the array substrate are short-circuited with each other.

Images