CN102568400A - Driving method of liquid crystal display - Google Patents

Abstract

The invention discloses a driving method of a liquid crystal display. In one embodiment, the driving voltage of the liquid crystal molecules is increased by using the capacitive coupling effect during the black frame insertion period of each frame, thereby reducing the power consumption of the display and improving the brightness, reliability and stability of the display.

Description

Driving method of liquid crystal display

technical field

The invention relates to a driving method of a liquid crystal display, in particular to a driving method of a field sequential liquid crystal display.

Background technique

Generally, there are two driving methods for liquid crystal displays: color filter (color filter) driving method and field sequential color (Field Sequential Color) driving method.

The driving method of the color filter is to divide the pixel into three sub-pixels corresponding to the red, green and blue color resistances of the color filter to generate three primary colors to form the color. The driving method of the field sequential liquid crystal display does not need a color filter. A single type of pixel cooperates with red, green, and blue backlight sources to display red, blue, and green sub-pictures in time sequence, and displays the color of the screen through the persistence of human vision.

Figure 1 shows a field color sequential driving method. Taking a frame frequency of 60 Hz as an example, the field color sequential driving method divides one frame into four sub-frames, namely red (R), green (G), blue (B), and black (K) sub-frames. Except for the black sub-frame (K) which only has a black picture writing period 101 , each sub-frame is divided into three parts: a data writing period 102 , a liquid crystal reaction period 103 , and a backlight-on period 104 . In another field color sequential driving method, the black picture writing interval 101 exists before (or after) each sub-frame or each frame, so there are three or one black picture writing interval 101 in total in one frame.

One of the purposes of writing the black picture is to reset the liquid crystal molecules so that the liquid crystal molecules deflect from a fixed starting angle each time they are driven. In addition, for different types of liquid crystal displays, writing a black screen may have different effects.

2A and 2B show an optically compensated bend liquid crystal display 10 (optically compensated bend liquid crystal display, OCB LCD), before entering the normal display state, it is necessary to apply an operating voltage difference between the upper substrate 12 and the lower substrate 13, so that The liquid crystal molecules 11 between the two substrates are converted from a stretched state (splay state, as shown in Figure 2A) to a bent state (bend state, as shown in Figure 2B); and, when the display is operating, the operating voltage must be kept greater than the critical voltage Vcr, The liquid crystal molecules 11 are kept in a bent state.

It has been pointed out in literature that if an optically compensated curved liquid crystal display uses a field color sequential driving method including inserting a black frame, the required threshold voltage Vcr can be reduced and the brightness of the panel can be increased. However, for some types of LCDs, such as optically compensated curved LCDs, the voltage inserted into the black screen cannot be increased infinitely. Fig. 3 is a graph showing the relationship between the brightness of an optically compensated curved liquid crystal display and the voltage applied to the liquid crystal molecules. When the voltage applied to the liquid crystal molecules is about 5 volts at point P1, all the liquid crystal molecules are deflected to a specific angle to block the backlight, so that the liquid crystal display displays a black screen. That is, the voltage at point P1 is the voltage applied to the liquid crystal molecules when inserting into the black frame interval 101 (as shown in FIG. 1 ) conventionally. When the voltage applied to the liquid crystal molecules is about 6 volts at the P2 point, the deflection speed of the liquid crystal increases, which can reduce the insertion of the black frame interval 101 . When the voltage applied to the liquid crystal molecules is increased to more than 8 volts, the liquid crystal molecules may be excessively deflected, resulting in light leakage. In addition, if the writing time for inserting black images is increased, although the effect of inserting black images can be increased, the display time of RGB images will also be sacrificed.

Therefore, there is an urgent need to provide a new structure and driving method for liquid crystal displays. Properly increasing the driving voltage for inserting black screen intervals can reduce the time for inserting black screens, improve the brightness of the display, and reduce the criticality of optical compensation for curved liquid crystal displays. Voltage, reduce power consumption, increase reliability and stability.

Contents of the invention

The purpose of the present invention is to provide a new driving method. Properly increasing the driving voltage for inserting black screen intervals can reduce the time for inserting black screens, improve the brightness of the display, and reduce the critical voltage of optically compensated curved liquid crystal displays. Power consumption, increased reliability and stability.

According to the above purpose, an embodiment of the present invention provides a driving method for a liquid crystal display, which is applied to a liquid crystal display. The liquid crystal display includes a plurality of data lines and a plurality of gate lines, thereby defining a plurality of pixels, each of which is Including a liquid crystal capacitor formed by a pixel electrode and a common electrode and a storage capacitor formed by the pixel electrode and a corresponding bias line, wherein the bias line is located below the pixel electrode, the method includes: respectively giving the common Different voltage sources for the electrode and the bias line; write red, green and blue frames and at least one black frame in each display frame, and write the first data to the pixel electrode of the first pixel during the black frame insertion period signal, and write the first bias line voltage to the first bias line corresponding to the first pixel, and write the common electrode voltage to the common electrode; wherein, the first data signal and the first bias line The voltages have the same first polarity, and the bias line voltage causes a coupling effect such that the voltage difference between the common electrode of the first pixel and the pixel electrode reaches a first voltage difference greater than that causing the first pixel The voltage difference required for deflecting the liquid crystal molecules of the liquid crystal molecule layer in the liquid crystal capacitor of a pixel to a specific angle for blocking the backlight source.

Description of drawings

Figure 1 shows an existing field color sequential driving method;

2A and 2B show a conventional optically compensated curved liquid crystal display;

Fig. 3 shows the relationship between the brightness of a conventional optically compensated curved liquid crystal display and the voltage applied to the liquid crystal molecules;

4A to 4D show four methods of polarity inversion according to an embodiment of the present invention;

FIG. 5 shows a method for driving a field color sequential liquid crystal display according to an embodiment of the present invention;

FIG. 6A shows an embodiment of a pixel structure matched with the driving method shown in FIG. 5;

FIG. 6B shows an equivalent circuit diagram of the pixel structure in FIG. 6A;

FIG. 7 shows a method for driving a field color sequential liquid crystal display according to another embodiment of the present invention; and

FIG. 8 shows an equivalent circuit diagram of the pixel structure matched with the driving method shown in FIG. 7 .

Detailed ways

Various embodiments of the present application will be described in detail below, combined with the accompanying drawings as examples. In addition to these detailed descriptions, the present invention can also be widely practiced in other embodiments, and any easy substitution, modification, and equivalent change of any of the described embodiments are included in the scope of the present case, and the following claims are allow. In the description of the specification, many specific details are provided in order to enable readers to have a more complete understanding of the present invention; however, the present invention may still be practiced under the premise of omitting some or all of these specific details. Furthermore, well known procedural steps or components have not been described in detail in order to avoid unnecessarily limiting the invention.

The invention discloses a structure and a driving method of a liquid crystal display, which can be applied to various types of liquid crystal displays, such as optically compensated curved liquid crystal displays and the like. Generally, a liquid crystal display includes an upper substrate, a lower substrate (such as a TFT array substrate), and a liquid crystal layer disposed between the two substrates. The common electrode is disposed on the upper substrate. A plurality of data lines and a plurality of gate lines are arranged on the lower substrate to define a plurality of pixels, each pixel has a pixel electrode, and the liquid crystal layer is located between the common electrode and the pixel electrode.

The driving method of the liquid crystal display of the present invention is a Field Sequential Color (Field SequentialColor) driving method, so the display does not need a color filter, and only uses a single pixel to cooperate with red, green, and blue backlight sources to display red color in time sequence. , blue, green and other sub-pictures, through the persistence of human vision, display the color of the picture. In the field color sequential driving method of the present invention, each frame has four sub-frames of red, green, blue and black, wherein the black sub-frame includes at least one black picture writing interval 101, as shown in FIG. 1 .

The driving method of the liquid crystal display of the present invention is mainly characterized in that the driving voltage of the liquid crystal molecules is increased each time the black screen is written into the interval 101, that is, the voltage difference between the pixel electrode and its common electrode is increased; usually, this The purpose can be achieved by modulating the voltage of the pixel electrode, modulating the voltage of the common electrode, or simultaneously modulating the voltage of the pixel electrode and the common electrode.

The voltage value of the common electrode is traditionally fixed. At this time, if you want to increase the driving voltage inserted into the black screen interval, you can increase the output data signal voltage of the source driver, and achieve this by transmitting a larger data signal (Data) voltage to the pixel electrode. , that is, modulating the voltage of the pixel electrode is controlled by the source driver. However, this method has a high manufacturing cost and is not an optimal solution.

In order to avoid phenomena such as flicker caused by the polarization of liquid crystal molecules, the liquid crystal display switches the polarity of the pixel driving voltage, positive polarity and negative polarity, to avoid the accumulation of charges. Figures 4A to 4D show four polarity inversion methods, including: Figure 4A is frame inversion (frame inversion); Figure 4 B is column inversion (column inversion); Figure 4 C is row inversion ( row inversion); and FIG. 4D is dot inversion, wherein each grid represents a pixel and indicates the polarity of its driving voltage.

The driving method of the liquid crystal display of the present invention is slightly different according to different polarity inversion methods. FIG. 5 shows a method for driving a field color sequential liquid crystal display according to an embodiment of the present invention. This embodiment can be applied to the frame inversion in FIG. 4A and the row inversion in the fourth figure C, but is not limited thereto. The driving method of this embodiment can be used with the pixel structure shown in FIG. 6A, wherein the scan lines Gn-1, Gn and the data lines Dn-1, Dn form a pixel Px, which includes a switch SW for controlling the data signal voltage (Data) input to the pixel electrode, and the bias line Bias1 is disposed under the pixel electrode PE. 6B shows the equivalent circuit diagram of FIG. 6A , the common electrode and the pixel electrode form the liquid crystal capacitor Clc, the pixel electrode PE and the bias line Bias1 form the storage capacitor Cst, and the common electrode and the bias line Bias1 are respectively connected to different voltage sources.

Returning to FIG. 5 , taking the row-inverted pixel Px1 as an example, the driving method of the embodiment of the present invention is described, wherein frame N is a positive polarity period, and frame N+1 is a negative polarity period. In the black sub-frame (K) interval of frame N, that is, the black image insertion interval 101, the source driver inputs the positive polarity black data signal voltage (Data) 501 to the pixel electrode, and then according to the screen requirements, respectively in the blue (B ), green (G), red (R) sub-frame data writing interval 102, write data signal voltages 502, 503, 504 to the pixel electrodes. It is worth mentioning that in this embodiment, only one black frame is inserted into each frame, and the black frame is inserted between the red (R) and blue (B) frames, but in other embodiments, each frame is not It is not limited to inserting a black frame, and the black frame is not limited to being inserted between the red (R) and blue (B) frames.

Referring to FIG. 5 again, at the time of the black sub-frame (K), the bias line voltage Vbias1 changes from the potential 505 to the potential 506, that is, the direction or polarity of the potential change is the same as that of the data signal voltage 501, and also That is, it belongs to positive polarity or positive voltage difference (Vbias1>0). Thus, the voltage difference ΔVbias1 (the voltage difference between the potential 506 and the original potential 505) will cause a capacitive coupling effect. Due to the principle of charge conservation, the voltage of the pixel electrode can be increased, thereby increasing the voltage difference between the pixel electrode and the common electrode (Vcom). , to increase the driving voltage of the liquid crystal molecules. If ΔV _pixel represents the change in voltage difference between the common electrode and the pixel electrode after capacitive coupling, that is, ΔV _pixel is approximately equal to:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; pixel</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&Delta;\; <figure-callout\; id="1"\; label="Vbias"\; filenames="HSA00000392567800041.png,HSA00000392567800042.png"\; state="\{\{state\}\}">Vbias</figure-callout></span>}\mathrm{<span\; class="notranslate">\; 1</span>}\frac{\mathrm{<span\; class="notranslate">\; Cst</span>}}{\mathrm{<span\; class="notranslate">\; Cst</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Clc</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Cgs</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Cx</span>}}$

Wherein, Cgs is the parasitic capacitance of the switch SW, and Cx is the stray capacitance. It can be seen from the above formula that the variation of the voltage difference between the common electrode and the pixel electrode increases as ΔVbias1 increases.

In addition, in the black sub-frame interval (K), the common electrode voltage (Vcom) changes from the potential 507 to the potential 508, that is, at this time, the common electrode voltage and the bias line voltage change in the opposite direction, and the common electrode voltage 508 The polarity is opposite to that of the data signal voltage 501, whereby the driving voltage of the liquid crystal molecules can be further increased. It is worth noting that, in another embodiment of the present invention, the voltage value and polarity of the common electrode voltage Vcom can always be kept constant (constant value) instead of doing positive and negative changes as shown in FIG. 5; in other words, increasing the liquid crystal The means of molecular driving voltage is mainly produced by the coupling effect of the voltage difference change of the bias line voltage. In addition, frame N+1 is a period of negative polarity, and its driving principle is the same as that of the period of positive polarity, except that the polarity is reversed, which will not be repeated here. In addition, the driving method of this embodiment can also be analogized to frame inversion.

FIG. 7 shows a method for driving a field color sequential liquid crystal display according to another embodiment of the present invention. This embodiment can be applied to the column inversion in FIG. 4B and the dot inversion in FIG. 4D , but is not limited thereto. The driving method of this embodiment can be combined with the pixel structure shown in FIG. 6A , but the difference is that two adjacent pixels in the same row are respectively connected to different bias lines, and the bias line Bias1 and the bias line Bias2 receive different voltages respectively. Bias line voltage signal; FIG. 8 shows its equivalent circuit diagram. In two adjacent pixels Px1 and Px2 in the same row, the common electrode and pixel electrode form liquid crystal capacitors Clc1 and Clc2, and the pixel electrode PE and bias line Bias1 form storage capacitor Cst1, The pixel electrode PE and the bias line Bias2 form a storage capacitor Cst2, and the common electrode and the bias lines Bias1 and Bias2 are respectively connected to different voltage sources.

Returning to FIG. 7 , taking the dot-inverted pixels Px1 and Px2 as an example, the driving method of the embodiment of the present invention is described, wherein the pixel Px1 is in the positive polarity period in frame N, and the negative polarity period in frame N+1; the pixel Px2 is in the Frame N is a negative polarity period, and frame N+1 is a positive polarity period. For the pixel Px1, in the black sub-frame (K) interval of the frame N, that is, the black screen insertion interval 101, the source driver inputs the positive data signal voltage (Data) 701 to the pixel electrode, and then according to the screen requirements, respectively in the blue In the data writing interval 102 of the color (B), green (G) and red (R) sub-frames, positive data signal voltages 702 , 703 , 704 are written into the pixel electrodes.

At the same time of the black sub-frame (K), the bias line voltage Vbias1 changes from the potential 705 to the potential 706, and the voltage change direction or polarity of the bias line voltage Vbias1 is the same as the data signal voltage 701, that is, positive polarity or positive polarity. Pressure difference (Vbias1 > 0). Thus, the voltage difference ΔVbias1 (the voltage difference between the potential 706 and the potential 705 ) will cause a capacitive coupling effect, which can increase the voltage difference between the pixel electrode and the common electrode. The principle is as described above.

For pixel Px2, in the black sub-frame (K) period of frame N, the source driver inputs the negative polarity data signal voltage (Data) 707 to the pixel electrode, and then according to the requirements of the screen, respectively in blue (B), green (G ), the data writing interval 102 of the red (R) sub-frame, writing negative data signal voltages 708, 709, 710 to the pixel electrodes. At the same time as this black sub-frame (K), the bias line voltage Vbias2 changes from the potential 705 to the potential 711, and the change direction or polarity of the bias line voltage Vbias2 is the same as the data signal voltage 707, that is, negative polarity or negative polarity. Pressure difference (Vbias1 > 0). Thus, the voltage difference ΔVbias2 (the voltage difference between the potential 711 and the potential 705 ) will cause a capacitive coupling effect, which can increase the voltage difference between the pixel electrode and the common electrode. The principle is as described above.

It is worth noting that in this embodiment, the voltage value and polarity of the common electrode voltage Vcom are kept fixed, that is, the means of increasing the driving voltage of the liquid crystal molecules is mainly through biasing with the same polarity as the corresponding data signal. The voltage difference between the voltage lines increases due to the capacitive coupling effect. In addition, the driving principle of the frame N+1 is the same as that of the frame N, and will not be repeated here. In addition, the driving method of this embodiment can also be analogized to column inversion.

It should be noted that in the embodiment of the present invention, the capacitive coupling effect is caused by the increase of the storage capacitance, thereby increasing the driving voltage of the liquid crystal molecules. The reference electrode of the storage capacitor is not limited. For example, another reference electrode of the storage capacitor can be a scan line, or the storage capacitor is formed by a bias line and a capacitor electrode, and the capacitor electrode and the data line can be formed in the same process. In addition, the same principle can be applied to other capacitances of the pixel structure.

As mentioned above, the embodiment of the present invention adds a bias line and controls the corresponding bias line electrode to generate the capacitive coupling effect of the storage capacitor, thereby increasing the voltage difference between the common electrode and the pixel electrode, and the voltage difference will be Greater than the voltage (P1) required to deflect the liquid crystal molecules to a specific angle for blocking the backlight, for example, the voltage difference can be P2 or a voltage greater than P2. According to this embodiment, in the interval 101 where the black screen is inserted, because the driving voltage of the liquid crystal molecules increases, the rotation speed of the liquid crystal molecules increases, and the interval 101 for inserting a black screen can be shortened. For a general liquid crystal display, the interval 104 for turning on the backlight can be increased. And improve display brightness; for optically compensated curved liquid crystal displays, it can also reduce its critical voltage, reduce power consumption and save costs, make liquid crystal molecules not easily affected by ambient temperature or external factors, return to the stretched state, and improve the stability of the display degree and reliability. In addition, since the method adopted in the present invention does not modulate the data signal voltage and the common electrode voltage, the voltage output range of the source driver does not need to be increased, thereby saving manufacturing cost.

The above-mentioned embodiments are only to illustrate the technical ideas and characteristics of the present invention, and its purpose is to enable those familiar with the art to understand the content of the present invention and implement it accordingly, and should not limit the patent scope of the present invention with it, that is, all other unidentified All equivalent changes or modifications deviated from the spirit disclosed in the present invention fall within the scope of the present invention and shall be included in the scope of the following claims.

Claims (10)

1. A driving method of a liquid crystal display, applied to a liquid crystal display, the liquid crystal display comprises a plurality of data lines and a plurality of gate lines, and thereby defines a plurality of pixels, each of which comprises a pixel electrode and a plurality of gate lines The liquid crystal capacitor formed by the common electrode and the storage capacitor formed by the pixel electrode and the corresponding bias line, wherein the bias line is located below the pixel electrode, and the method includes: providing different voltage sources to the common electrode and the bias line; Writing red, green and blue pictures and at least one black picture in each display frame, during the insertion period of the black picture, writing the first data signal to the pixel electrode of the first pixel, and writing the first data signal to the pixel electrode of the first pixel writing a first bias line voltage to the corresponding first bias line, and writing a common electrode voltage to the common electrode; Wherein, the first data signal and the first bias line voltage have the same first polarity, and the bias line voltage causes a coupling effect, so that the common electrode of the first pixel and the pixel electrode The voltage difference between them reaches a first voltage difference greater than the voltage difference required to deflect the liquid crystal molecules of the liquid crystal molecule layer in the liquid crystal capacitor of the first pixel to a specific angle for blocking the backlight source. 2. The driving method according to claim 1, wherein the common electrode voltage has a second polarity, and the second polarity is opposite to the first polarity. 3. The driving method according to claim 1, wherein the common electrode voltage is a fixed voltage. 4. The driving method according to claim 1, further comprising writing the second data signal to the pixel electrode of the second pixel, and writing the second bias line to the second bias line corresponding to the second pixel voltage, wherein the first bias line and the second bias line are independent from each other and connected to different voltage sources, and the second data signal and the second bias line voltage have the same second polarity , the second polarity is opposite to the first polarity. 5. The driving method according to claim 4, wherein the common electrode voltage is a fixed voltage. 6. The driving method according to claim 4, wherein the second pixel is adjacent to the first pixel, and the first bias line and the second bias line are respectively parallel to the plurality of scan lines . 7. The driving method as claimed in claim 1, wherein in the same display frame, the polarities of the red, green and blue frames displayed in the first pixel and the black frame are the same as each other. 8. The driving method according to claim 4, wherein in the same display frame, the red, green and blue pictures and the black picture displayed in the first pixel have the same first polarity; and the red, green and blue pictures and the black picture displayed in the second pixel have the same second polarity as each other. 9. The driving method according to claim 4, wherein the polarity distribution of the black picture is selected from one of frame inversion, row inversion, column inversion, and dot inversion. 10. The driving method according to claim 1, wherein the liquid crystal display is an optically compensated curved liquid crystal display.

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