KR20070073118A - Driving voltage producing module and liquid crystal display having the same - Google Patents

Abstract

A module for generating a driving voltage and an LCD device having the same are provided to improve degradation of image quality by minimizing a kick-back voltage of a liquid crystal capacitor using a compensated common voltage. An LCD(Liquid Crystal Display) device includes plural pixels having a liquid crystal capacitor connected to a TFT(Thin Film Transistor). A module for generating a driving voltage for driving the pixels includes a common voltage generating unit(420) for generating a common voltage(Vcom) supplied to the liquid crystal capacitor using a predetermined clock signal and a predetermined reference voltage. The common voltage generating unit varies the common voltage value, which is output according to an average grayscale value of grayscale data corresponding to the pixels.

Description

Driving voltage generating module and liquid crystal display including the same {Driving Voltage Producing Module and Liquid Crystal Display Having the Same}

1 is an equivalent circuit diagram of a unit pixel in a general liquid crystal display device.

2 is a schematic diagram of a liquid crystal display according to an exemplary embodiment of the present invention.

3 is a schematic block diagram of a control unit according to an embodiment of the present invention.

4 is a schematic block diagram of a driving voltage generator according to an exemplary embodiment of the present invention.

5 is a graph showing a change in kickback voltage according to a change in gray level.

6 is a partial circuit diagram of a common voltage generator according to an exemplary embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

100: liquid crystal display panel 200: gate driver

300: source driver 400: driving voltage generator

410: liquid crystal driving voltage generator 420: common voltage generator

423: line resistance 426: demultiplexer

430: gate on voltage generator 440: gate off voltage generator

500: control unit 510: data generation unit

520: Average gray value calculator

The present invention relates to a driving voltage generating module and a liquid crystal display including the same, and more particularly, to a driving voltage generating module for compensating a kickback voltage according to an average gray voltage of predetermined data and a liquid crystal display including the same.

Liquid crystal displays (LCDs) display a desired image by applying an electric field to a liquid crystal material having an anisotropic dielectric constant injected between two substrates, and controlling the amount of light transmitted through the substrate by adjusting the intensity of the electric field. Device.

1 is an equivalent circuit diagram of a unit pixel in a general liquid crystal display device. As shown in FIG. 1, the gate electrode g, the source electrode s, and the drain electrode d of the TFT are connected to the gate line Gn, the data line Dm, and the liquid crystal capacitor Clc, respectively. That is, a liquid crystal material is formed between the pixel electrode connected to the drain electrode of the TFT and the common electrode, thereby forming the liquid crystal capacitor Clc. An accumulation capacitor Cst is formed between the pixel electrode and the front gate line Gn-1, and a parasitic capacitor Cgd due to misalignment is formed between the gate electrode g and the drain electrode d. Is formed.

Such a liquid crystal display device is a gate signal for driving a gate electrode g connected to a gate line Gn to display an image. After the TFT is turned on by applying a gate-on voltage Von, the image signal is converted into a gate signal. A gray voltage for display is applied to the pixel electrode. Then, the gray voltage is applied to the liquid crystal capacitor Clc and the storage capacitor Cst through the pixel electrode, respectively, and an electric field is formed by the potential difference between the pixel electrode and the common electrode. As such, when an electric field is formed between the pixel electrode and the common electrode, the liquid crystal material is aligned to adjust the amount of light passing through the liquid crystal material.

On the other hand, the gray scale voltage applied to the liquid crystal capacitor Clc and the storage capacitor Cst when the TFT is on should not change even after the TFT is turned off, but the gate-off voltage Voff is applied to the gate electrode g of the TFT. When this is applied, due to the parasitic capacitor Cgd between the gate electrode g and the drain electrode d, the voltage applied to the gate electrode g of the TFT is lowered and the absolute value of the gradation voltage applied to the pixel electrode is reduced. Will be lowered together.

The voltage lowered in the gray voltage of the pixel electrode is called kick-back voltage, and the kick-back voltage Vk is obtained by the following equation.

When the kickback voltage Vk becomes large, the voltage applied to the liquid crystal capacitor Clc of the pixel changes, thereby changing the displayed image, thereby causing problems such as flickering and image sticking of the image. .

As a method for compensating the kickback voltage Vk, a method of reducing the kickback voltage Vk by applying the gate-on voltage Von and then gradually lowering it, together with the common voltage applied to the common electrode of the liquid crystal capacitor Clc Increasing the absolute value of the voltage (Vcom) is used to reduce the effect of the kickback voltage (Vk).

However, the dielectric constant in the liquid crystal capacitor Clc varies depending on the magnitude of the gray voltage applied, and the kickback voltage Vk also varies according to the dielectric constant of the liquid crystal. For example, in a liquid crystal display having 64 gray levels, the kickback voltage is high at high gray levels (0, white), but the kickback voltage is low at low gray levels (64, black). Therefore, when using the method of reducing the influence of the kickback voltage Vk by increasing the absolute value of the common voltage Vcom, the kickback voltage cannot be compensated correctly according to the grayscale, so that the image is clear because of the image shaking. There is a problem that cannot be displayed.

The present invention has been made to solve the above problems, and an object thereof is to provide a driving voltage generation module for compensating a kickback voltage according to an average gray voltage of predetermined data and a liquid crystal display including the same.

According to an aspect of the present invention for achieving the object of the present invention, in the liquid crystal display device including a plurality of pixels comprising a thin film transistor and a liquid crystal capacitor connected to the thin film transistor, driving the plurality of pixels A driving voltage generation module for generating a voltage for

And a common voltage generator configured to output a common voltage applied to one side of the liquid crystal capacitor using the predetermined reference voltage and a predetermined clock signal, wherein the common voltage generator is configured to the average gray value of the gray scale data corresponding to the pixel. A driving voltage generating module is provided, characterized in that for changing the value of the common voltage output accordingly.

The common voltage generator is further configured to add a kickback voltage corresponding to the average gray value to the common voltage and output the same in accordance with the average gray value of the gray scale data corresponding to the pixel.

The common voltage generator may calculate the kickback voltage from the permittivity of the liquid crystal having a corresponding gray value.

The pixel is a line of pixels.

The pixel is characterized in that all pixels.

According to another aspect of the present invention for achieving the object of the present invention, a liquid crystal display panel in which a pixel including a thin film transistor and a liquid crystal capacitor is formed corresponding to a plurality of gate lines, a plurality of data lines and the intersection of the gate line and the data line ; A controller configured to sequentially generate grayscale data of the pixel corresponding to an image signal, and calculate and output an average grayscale value of the grayscale data corresponding to the pixel; And a driving voltage generator configured to change and output the common voltage applied to one side of the liquid crystal capacitor according to the average gray scale value output from the controller.

The common voltage generator is further configured to add a kickback voltage corresponding to the average gray value to the common voltage and output the same in accordance with the average gray value of the gray scale data corresponding to the pixel.

The common voltage generator may calculate the kickback voltage from the permittivity of the liquid crystal having a corresponding gray value.

The pixel is a line of pixels.

The pixel is characterized in that all pixels.

EMBODIMENT OF THE INVENTION Hereinafter, with reference to an accompanying drawing, embodiment of this invention is described in detail.

2 is a schematic diagram of a liquid crystal display according to an exemplary embodiment of the present invention.

The liquid crystal display according to the exemplary embodiment of the present invention illustrated in FIG. 2 includes a liquid crystal display panel 100, a gate driver 200, a source driver 300, a driving voltage generator 400, and a controller 500. .

The liquid crystal display panel 100 includes a plurality of gate lines G1 to Gn formed in a column direction and a plurality of data lines D1 to Dm formed in a row direction, and pixels formed to correspond to intersections of the gate lines and the data lines. 110. The pixel 110 includes a thin film transistor TFT, a storage capacitor Cst, and a liquid crystal capacitor Clc, respectively. A liquid crystal material is formed between the pixel electrode connected to the drain electrode of the TFT and the common electrode, thereby forming a liquid crystal capacitor Clc.

In the liquid crystal display panel 100, when the gate driver 200 applies a gate-on voltage Von to the gate line, the data line and the pixel electrode connected to both ends of the thin film transistor are electrically connected to each other. Is driven by applying a predetermined gray scale voltage to the pixel electrode through the data line and applying a common voltage Vcom to the common electrode.

The control unit 500 receives an image signal from an external source, and provides gray level data of red (R), green (G), and blue (B), a vertical sync signal (Vsync), a horizontal sync signal (Hsync), and a main signal for distinguishing a frame. The clock signal CLK may be generated and output to the gate driver 200 and the source driver 300.

The timing signal output from the controller 500 to the gate driver 200 includes a vertical start signal (hereinafter referred to as a 'Vstart signal') for instructing the gate line to start applying the gate-on voltage Von, and the gate-on voltage ( A gate clock signal (hereinafter referred to as a 'CPV signal') for sequentially applying Von to each gate line, and a gate on enable signal (hereinafter referred to as 'OE') that enable an output of the gate driver 200. Signal ').

In the timing signal output from the controller 500 to the source driver 300, a horizontal start signal Hstart for instructing the gray line data to start driving is applied, and a gray voltage converted into analog in the source driver 300. There is a control signal such as a signal LOAD for commanding and a horizontal clock signal HCLK for data shift in the source driver 300.

The controller 500 according to an exemplary embodiment of the present invention calculates an average gray value of a predetermined number of gray data among the gray data and transmits the average gray value to the driving voltage generator 400.

For example, the controller 500 may calculate an average gray value of gray data corresponding to one line of pixels among the gray data. The controller 500 may calculate an average gray value of gray data corresponding to all pixels of one frame among the gray data.

The driving voltage generator 400 outputs the gate-on voltage Von and the gate-off voltage Voff used as the gate signal to the gate driver 200, and generates a gray voltage applied to the pixel electrode of the liquid crystal capacitor. The liquid crystal driving voltage AVDD and the common voltage Vcom applied to the common electrode of the liquid crystal capacitor are output to the source driver 300.

The driving voltage generator 400 according to an exemplary embodiment of the present invention receives an average grayscale value of a predetermined number of grayscale data from the control unit 500, thereby generating a common voltage Vcom in which the kickback voltage is compensated. Output to the source driver 300.

That is, since the dielectric constant of the liquid crystal capacitor Clc is changed depending on the magnitude of the gray voltage applied, the kickback voltage Vk to be compensated also varies according to the dielectric constant of the liquid crystal.

The gate driver 200 receives the CPV signal and the Vstart signal from the controller 500, receives the gate driving voltages Von and Voff from the driving voltage generator 400, and supplies the pixels to the pixels on the liquid crystal display panel 100. The TFT is controlled so that the gray voltage to be applied is transferred to the pixel.

The gate driver 200 sequentially turns on the TFT by applying the gate-on voltage Von to the gate lines G1 to Gn.

The source driver 300 uses the liquid crystal driving voltage AVDD received from the driving voltage generator 400 according to the grayscale data output from the controller 500 in synchronization with the TFT driving of the gate driver 200. A gray voltage is generated and applied to each data line D1 to Dm.

In addition, the source driver 300 applies the common voltage Vcom received from the driving voltage generator 400 to the common electrode of the liquid crystal capacitor.

Next, the controller and the driving voltage generator according to the exemplary embodiment of the present invention will be described in detail with reference to FIGS. 3 and 4.

3 is a schematic block diagram of a controller according to an exemplary embodiment of the present invention, and FIG. 4 is a schematic block diagram of a driving voltage generator according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the controller 500 according to an exemplary embodiment of the present invention includes a data generator 510 and an average gray value calculator 520.

The data generator 510 receives an image signal from the outside and generates grayscale data for each pixel. In this case, the data generation unit 510 sequentially generates one gray level data for pixels arranged in a matrix form.

The average gray value calculator 520 calculates an average gray value of a predetermined number of gray data displayed on the liquid crystal display panel 100 and transmits the average gray value to the driving voltage generator 400.

For example, the average gray value calculator 520 may calculate an average gray value of gray data corresponding to one line of pixels among the gray data, and calculate an average gray value of gray data corresponding to all pixels of one frame. You can also calculate

Referring to FIG. 4, the driving voltage generator 400 according to an exemplary embodiment of the present invention may include a liquid crystal driving voltage generator 410, a common voltage generator 420, a gate on voltage generator 430, and a gate off voltage. It includes a generator 440.

The liquid crystal driving voltage generator 410 receives the predetermined voltage Vin to generate the liquid crystal driving voltage AVDD obtained by rectifying the predetermined switching voltage PWM_SW and the switching voltage PWM_SW.

The common voltage generator 420 generates the common voltage Vcom using the liquid crystal driving voltage AVDD and the switching voltage PWM_SW.

The common voltage generator 420 according to the exemplary embodiment of the present invention receives the average grayscale value from the average grayscale value calculator 520 of the controller 500, and accordingly the common voltage Vcom in which the kickback voltage is compensated. It generates and outputs to the source driver 300.

Here, when the gray scale that can be displayed on the liquid crystal display is 64 gray scales, the kickback voltage compensated by the common voltage Vcom may be calculated by the following Equation 2.

In Equation 2, Vk average is an average kickback voltage value corresponding to the calculated average gray value, Vk32 is a kickback voltage value of 32 gray levels, which is an intermediate gray level that can be displayed on the liquid crystal display, and Vk0 and Vk63 are respectively. Kickback voltage values of the lightest and darkest grayscales, and the average grayscale value indicate the average grayscale value calculated by the average grayscale value calculator 520. The compensation kickback voltage calculated in Equation 2 is linearly represented as shown in FIG. 5.

The Vk0 and Vk63 can be calculated from the permittivity of the liquid crystal when displaying the brightest grayscale and the permittivity of the liquid crystal when displaying the darkest grayscale, respectively. That is, the common voltage generator 420 receives the dielectric constant of the liquid crystal when displaying the brightest grayscale and the dielectric constant of the liquid crystal when displaying the darkest grayscale, calculates Vk0 and Vk63, and calculates an average grayscale value accordingly. An average kickback voltage (Vk average) compensated for the common voltage may be obtained by substituting the average gray value received from the unit 520 into Equation 2 above.

A method of compensating the average kickback voltage to the common voltage will be described in detail with reference to FIG. 6. 6 is a partial circuit diagram of a common voltage generator 420 according to an embodiment of the present invention.

The common voltage generator 420 according to an embodiment of the present invention includes a first power supply for supplying a maximum voltage Vcom + Vk0 plus a kickback voltage Vk0 when displaying the common voltage Vcom and the brightest gray level. And a second power supply for supplying a minimum voltage Vcom + Vk63 plus a common voltage Vcom and a kickback voltage Vk63 when displaying the darkest gray level, and a line positioned between the first power supply and the second power supply. A resistor 423 and a demultiplexer (DMUX) 426 for selecting and outputting one of a plurality of voltages output from the line resistor 423.

The common voltage generator 420 generates a maximum voltage Vcom + Vk0 and a minimum voltage Vcom + Vk63 using a predetermined reference voltage and a predetermined clock signal. The generation of the maximum voltage Vcom + Vk0 and the minimum voltage Vcom + Vk63 using the predetermined reference voltage and the predetermined clock signal may be generated using a predetermined charging pumping circuit. Since the charging pumping circuit is a known technique, a detailed description thereof is omitted here.

The maximum voltage (Vcom + Vk0) and the minimum voltage (Vcom + Vk63) can be generated by using the dielectric constant of the liquid crystal when displaying the brightest gray scale input in advance and the dielectric constant of the liquid crystal when displaying the darkest gray scale. have. Here, it is preferable that the predetermined reference voltage uses the liquid crystal drive voltage AVDD.

Next, the line resistor 423 located between the maximum voltage (Vcom + Vk0) and the output terminal for outputting the minimum voltage (Vcom + Vk63) sets the maximum voltage (Vcom + Vk0) and the minimum voltage (Vcom + Vk63). A plurality of voltages equally divided at equal intervals are output. That is, the line resistor 423 outputs the common voltage Vcom and the kickback voltages Vk0 to Vk63 at the respective gray levels.

The demultiplexer 426 outputs one voltage among a plurality of voltages output from the line resistor 423 using a selection signal. That is, the demultiplexer 426 may output a voltage (Vcom + Vk average) corresponding to the average gray value by using the average gray value calculated by the average gray value calculator 520 as a selection signal.

The gate-on voltage generator 430 generates the gate-on voltage Von by pumping the switching voltage PWM_SW based on the liquid crystal driving voltage AVDD as a reference voltage.

The gate-off voltage generator 440 generates the gate-off voltage Voff by pumping the switching voltage PWM_SW with the ground voltage as the reference voltage.

Since the liquid crystal display according to the exemplary embodiment of the present invention uses the common voltage Vcom that compensates the kickback voltage according to the average gray value of the image to be displayed, the liquid crystal display device may correspond to the change in the dielectric constant of the liquid crystal according to the gray level. In addition, the kickback voltage of the liquid crystal capacitor can be minimized, and the kickback voltage can be compensated more accurately to improve image quality such as flickering, thereby displaying the image clearly.

The scope of the present invention is not limited to each embodiment described above, but all changes and improvements made by those skilled in the art using the basic concept of the present invention defined in the claims also belong to the scope of the present invention.

As described above, the liquid crystal display according to the present invention uses the common voltage Vcom that compensates the kickback voltage according to the average gray value of the image to be displayed, so that even if the dielectric constant of the liquid crystal varies depending on the gray scale, In addition, the kickback voltage of the liquid crystal capacitor can be minimized, and the kickback voltage can be compensated more accurately to improve image degradation such as flickering so that the image can be displayed clearly.

Claims (10)

A liquid crystal display including a plurality of pixels including a thin film transistor and a liquid crystal capacitor connected to the thin film transistor, wherein the driving voltage generation module generates a voltage for driving the plurality of pixels. A common voltage generator configured to output a common voltage applied to one side of the liquid crystal capacitor by using the predetermined reference voltage and a predetermined clock signal, And the common voltage generator is configured to change a value of the common voltage to be output according to an average gray value of gray data corresponding to a pixel. The method according to claim 1, And the common voltage generator is configured to add a kickback voltage corresponding to an average grayscale value to the common voltage and output the same in accordance with an average grayscale value of grayscale data corresponding to a pixel. The method according to claim 2, And wherein the common voltage generator obtains the kickback voltage from the permittivity of the liquid crystal having a corresponding gray value. The method according to any one of claims 1 to 3, And the pixel is a line of pixels. The method according to any one of claims 1 to 3, And the pixels are all pixels. A liquid crystal display panel in which pixels including a thin film transistor and a liquid crystal capacitor are formed corresponding to a plurality of gate lines, a plurality of data lines, and intersections of the gate lines and the data lines; A controller configured to sequentially generate grayscale data of the pixel corresponding to an image signal, and calculate and output an average grayscale value of the grayscale data corresponding to the pixel; And And a driving voltage generator configured to change and output the common voltage applied to one side of the liquid crystal capacitor according to the average gray scale value output from the controller. The method according to claim 6, And the kickback voltage corresponding to the average grayscale value is added to the common voltage according to the average grayscale value of the grayscale data corresponding to the pixel. The method according to claim 7, And the common voltage generator is configured to obtain the kickback voltage from the dielectric constant of the liquid crystal having a corresponding gray value. The method according to any one of claims 6 to 8, And the pixel is a line of pixels. The method according to any one of claims 6 to 8, And the pixels are all pixels.

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