KR20070052084A - Display device - Google Patents

Abstract

The present invention relates to a liquid crystal display device, comprising: a display panel having a plurality of pixels for displaying an image, a gamma correction unit for receiving input image data and correcting the value to a value smaller than the input image data at a temperature lower than a reference temperature; And a data driver converting the corrected image data into a data voltage and supplying the pixel. Therefore, the output image data may be corrected to have a gray level lower than that of the input image data at a temperature lower than the reference temperature, thereby preventing a change in luminance according to the temperature.

Liquid crystal display, gamma correction unit, temperature correction unit, gamma curve

Description

Display device {DISPLAY DEVICE}

1 is a graph showing a change in a gamma curve with temperature.

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

3 is an equivalent circuit diagram of one pixel of a liquid crystal display according to an exemplary embodiment of the present invention.

4 is a block diagram of a gamma correction unit according to an exemplary embodiment of the present invention.

5A and 5B are graphs showing a lookup table of a reference temperature and a function of a lookup table according to one embodiment of the invention.

6A and 6B are graphs illustrating a function of a lookup table and a lookup table at low temperature in accordance with one embodiment of the present invention.

The present invention relates to a liquid crystal display device.

In recent years, with the reduction in weight and thickness of personal computers and televisions, display devices are also required to be lighter and thinner, and cathode ray tubes (CRTs) are being replaced by flat panel displays.

Such flat panel displays include liquid crystal displays (LCDs), field emission displays (FEDs), organic light emitting displays, plasma display panels (PDPs), and the like. There is this.

In general, in an active matrix flat panel display, a plurality of pixels are arranged in a matrix form, and an image is displayed by controlling the light intensity of each pixel according to given luminance information. Among them, the liquid crystal display includes two display panels including a pixel electrode and a common electrode, and a liquid crystal layer having dielectric anisotropy interposed therebetween. The liquid crystal display device applies an electric field to the liquid crystal layer, and adjusts the intensity of the electric field to adjust the transmittance of light passing through the liquid crystal layer to obtain a desired image. In this case, the liquid crystal display is set to determine the luminance value according to the gray level according to a constant gamma curve.

1 is a graph showing a change in a gamma curve with temperature.

Referring to FIG. 1, the liquid crystal display at 25 degrees to 40 degrees Celsius forms a stable gamma curve having a constant gamma value. However, the gamma curve of the liquid crystal display changes rapidly at 10 degrees Celsius or less. This is because the viscosity of the liquid crystal of the liquid crystal display varies with temperature. The liquid crystal has a high rotational viscosity at low temperatures, and does not rotate well. Therefore, light of greater luminance is transmitted to the gray level at a temperature lower than room temperature, so that the image looks brighter.

Accordingly, an object of the present invention is to provide a liquid crystal display device capable of displaying a uniform image regardless of temperature.

According to an exemplary embodiment of the present invention, a display device having a plurality of pixels and a display panel for displaying an image and input image data are supplied to a display device having a smaller value than the input image data at a temperature lower than a reference temperature. And a gamma correction unit to correct and convert the corrected image data into a data voltage to supply the pixel to the pixel.

The gamma correction unit may not correct the input image data at the reference temperature.

The gamma correction unit measures a current temperature and outputs a control signal corresponding to the current temperature, and

And a temperature correction unit receiving the input image data and outputting the corrected image data according to the control signal.

The temperature corrector may include at least one lookup table that stores the input image data and the corrected image data corresponding to the input image data according to a temperature.

The gamma correction unit may output the same corrected image data with respect to one input image data in a predetermined temperature range.

The corrected image data at a temperature lower than the reference temperature may have a magnitude of a product of the positive number less than one.

The reference temperature may be 25 degrees to 40 degrees Celsius.

DETAILED DESCRIPTION Embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like parts are designated by like reference numerals throughout the specification. When a part of a layer, film, region, plate, etc. is said to be "on" another part, this includes not only the other part being "right over" but also another part in the middle. On the contrary, when a part is "just above" another part, there is no other part in the middle. Also, when a part is connected to another part, this includes not only a "direct" connection to another part but also a "through" another part.

A display device according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

First, a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to FIGS. 2 and 3.

2 is a block diagram of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 3 is an equivalent circuit diagram of one pixel of the liquid crystal display according to an exemplary embodiment of the present invention.

As shown in FIG. 2, the liquid crystal display according to the exemplary embodiment of the present invention includes a liquid crystal panel assembly 300, a gate driver 400, a data driver 500, and a data driver 500 connected thereto. And a gray voltage generator 700 connected to the signal 500, and a signal controller 600 for controlling the gray voltage generator 700.

The liquid crystal panel assembly 300 may include a plurality of signal lines G ₁ -G _n , D ₁ -D _m and a plurality of pixels PX connected to the plurality of signal lines G ₁ -G _n , D ₁ -D _m , and arranged in a substantially matrix form. Include. In contrast, in the structure shown in FIG. 3, the liquid crystal panel assembly 300 includes lower and upper panels 100 and 200 facing each other and a liquid crystal layer 3 interposed therebetween.

The signal lines G ₁ -G _n and D ₁ -D _m are a plurality of gate lines G ₁ -G _n for transmitting a gate signal (also called a “scan signal”) and a plurality of data lines for transmitting a data signal ( D ₁ -D _m ). The gate lines G ₁ -G _n extend substantially in the row direction and are substantially parallel to each other, and the data lines D ₁ -D _m extend substantially in the column direction and are substantially parallel to each other.

Each pixel PX, for example, a pixel connected to an i-th (i = 1, 2, ..., n) gate line G _i and a j-th (j = 1, 2, ..., m) data line Dj The PX includes a switching element Q connected to the signal line G _i -D _j , a liquid crystal capacitor C _LC , and a storage capacitor C _ST connected thereto. The holding capacitor C _ST can be omitted as necessary.

The switching element Q is a three-terminal element of a thin film transistor or the like provided in the lower panel 100, the control terminal of which is connected to the gate line G _i , and the input terminal of which is connected to the data line D _j . The output terminal is connected to the liquid crystal capacitor C _LC and the storage capacitor C _ST .

The liquid crystal capacitor C _LC has two terminals, a pixel electrode 191 of the lower panel 100 and a common electrode 270 of the upper panel 200, and a liquid crystal layer 3 between the two electrodes 191 and 270. It functions as a dielectric. The pixel electrode 191 is connected to the switching element Q, and the common electrode 270 is formed on the front surface of the upper panel 200 and receives the common voltage Vcom. Unlike in FIG. 3, the common electrode 270 may be provided in the lower panel 100. In this case, at least one of the two electrodes 191 and 270 may be formed in a linear or bar shape.

The storage capacitor C _ST , which serves as an auxiliary part of the liquid crystal capacitor C _LC , is formed by overlapping a separate signal line (not shown) and the pixel electrode 191 provided on the lower panel 100 with an insulator interposed therebetween. A predetermined voltage such as the common voltage Vcom is applied to this separate signal line. However, the storage capacitor C _ST may be formed such that the pixel electrode 191 overlaps the front gate line directly above the insulator.

On the other hand, in order to implement color display, each pixel PX uniquely displays one of the primary colors (spatial division) or each pixel PX alternately displays the primary colors over time (time division). The desired color is recognized by the spatial and temporal sum of these primary colors. Examples of the primary colors include three primary colors such as red, green, and blue. FIG. 3 illustrates that each pixel PX includes a color filter 230 representing one of the primary colors in an area of the upper panel 200 corresponding to the pixel electrode 191 as an example of spatial division. Unlike in FIG. 3, the color filter 230 may be formed above or below the pixel electrode 191 of the lower panel 100.

At least one polarizer (not shown) for polarizing light is attached to an outer surface of the liquid crystal panel assembly 300.

Referring back to FIG. 2, the gray voltage generator 700 generates two sets of gray voltage sets (or reference gray voltage sets) related to the transmittance of the pixel PX. One of the two sets has a positive value for the common voltage Vcom and the other set has a negative value.

A gate driver 400, a gate line (G ₁ -G _n) and is connected to the gate turn-on voltage (Von), and a gate signal consisting of a combination of a gate-off voltage (Voff), a gate line (G ₁ of the liquid crystal panel assembly 300 -G _n ).

The data driver 500 is connected to the data lines D ₁ -D _m of the liquid crystal panel assembly 300, and selects a gray voltage from the gray voltage generator 700 and uses the data line D ₁ as a data signal. -D _m ). However, when the gray voltage generator 700 provides only a predetermined number of reference gray voltages instead of providing all of the voltages for all grays, the data driver 500 divides the reference gray voltages and thus the gray voltages for all grays. Generate and select the data signal from it.

The signal controller 600 controls the operations of the gate driver 400 and the data driver 500, and includes a gamma correction unit 650 that receives input image data R, G, and B from the outside and corrects them. do.

Each of the driving devices 400, 500, 600, and 700 may be mounted directly on the liquid crystal panel assembly 300 in the form of at least one integrated circuit chip, or may be a flexible printed circuit film (not shown). It may be mounted on the liquid crystal panel assembly 300 in the form of a tape carrier package (TCP) or mounted on a separate printed circuit board (not shown). Alternatively, these driving devices 400, 500, 600, and 700 are integrated in the liquid crystal panel assembly 300 together with the signal lines G ₁ -G _n , D ₁ -D _m and the thin film transistor switching element Q. A system on panel (SOP) can also be implemented. In addition, the driving devices 400, 500, 600, and 700 may be integrated into a single chip, in which case at least one of them or at least one circuit element constituting them may be outside the single chip.

Next, the operation of the liquid crystal display will be described in detail.

The signal controller 600 receives input image data R, G, and B and an input control signal for controlling the display thereof from an external graphic controller (not shown). Examples of the input control signal include a vertical sync signal Vsync, a horizontal sync signal Hsync, a main clock MCLK, and a data enable signal DE.

The signal controller 600 properly processes the input image data R, G, and B based on the input image data R, G, and B and the input control signal according to the operating conditions of the liquid crystal panel assembly 300, and performs a gate. After generating the control signal CONT1 and the data control signal CONT2, the gate control signal CONT1 is sent to the gate driver 400, and the data control signal CONT2 and the processed output image data R ′ and G are processed. ', B') is sent to the data driver 500. In particular, the gamma correction unit 650 of the signal controller 600 performs gamma correction on the input image data R, G, and B, which will be described in detail later.

The gate control signal CONT1 includes a scan start signal STV indicating a scan start and at least one clock signal controlling an output period of the gate-on voltage Von. The gate control signal CONT1 may also further include an output enable signal OE that defines the duration of the gate-on voltage Von.

The data control signal CONT2 is a horizontal synchronizing start signal STH indicating the start of image data transfer for one row of pixels PX and a load signal LOAD for applying a data signal to the data lines D ₁ -D _m . ) And a data clock signal HCLK. The data control signal CONT2 is also an inverted signal that inverts the voltage polarity of the data signal relative to the common voltage Vcom (hereinafter referred to as " polarity of the data signal " by reducing the " voltage polarity of the data signal for the common voltage ") RVS) may be further included.

According to the data control signal CONT2 from the signal controller 600, the data driver 500 receives output image data R ′, G ′, and B ′ for one row of pixels PX, and outputs each of the outputs. By selecting the gray scale voltage corresponding to the image data R ', G', B ', the output image data R', G ', B' is converted into an analog data signal, and then the corresponding data line D ₁ -D _m ).

The gate driver 400 applies the gate-on voltage Von to the gate lines G ₁ -G _n in response to the gate control signal CONT1 from the signal controller 600, thereby applying the gate lines G ₁ -G _n . Turn on the switching element (Q) connected to. Then, the data signal applied to the data lines D ₁ -D _m is applied to the corresponding pixel PX through the switching element Q turned on.

The difference between the voltage of the data signal applied to the pixel PX and the common voltage Vcom is represented as the charging voltage of the liquid crystal capacitor C _LC , that is, the pixel voltage. The arrangement of the liquid crystal molecules varies depending on the magnitude of the pixel voltage, thereby changing the polarization of light passing through the liquid crystal layer 3. The change in polarization is represented by a change in transmittance of light by a polarizer attached to the display panel assembly 300.

This process is repeated in units of one horizontal period (also referred to as "1H" and equal to one period of the horizontal sync signal Hsync and the data enable signal DE), thereby all the gate lines G ₁ -G _n. ), The gate-on voltage Von is sequentially applied to the data signal to all the pixels PX, thereby displaying an image of one frame.

When one frame ends, the state of the inversion signal RVS applied to the data driver 500 is controlled so that the next frame starts and the polarity of the data signal applied to each pixel PX is opposite to the polarity of the previous frame. "Invert frame"). In this case, the polarities of the data signals flowing through one data line are changed (eg, row inversion and point inversion) according to the characteristics of the inversion signal RVS within one frame, or the polarities of data signals applied to one pixel row are also different from each other. Can be different (eg invert columns, invert points).

The gamma correction of the gamma correction unit 650 of the signal controller 600 will be described in detail with reference to FIGS. 4 to 6B.

4 is a block diagram of a gamma correction unit according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the gamma corrector 650 according to an embodiment of the present invention includes a temperature sensor 657 and a temperature corrector 653.

The temperature sensor 657 detects an external current temperature and outputs a control signal corresponding to the current temperature.

The temperature correction unit 653 includes a plurality of look up tables LUT1, LUT2,..., LUTk, and receives the input image data R, G, and B from the outside, and the temperature detection unit 657. The control signal is supplied to generate the output image data R ', G', and B 'corrected according to the current temperature.

Correction of the input image data R, G, and B is performed based on the built-in lookup tables (LUT1, LUT2, ..., LUTk), as shown in FIG. 4 (LUT1, LUT2, ..., ...). LUTk) may be formed for each temperature, or may be formed for each predetermined temperature range in consideration of the area occupied by the memory. Also, the lookup table (LUT1, LUT2, ..., LUTk) may be formed for each color.

5A and 5B are graphs showing a function of a lookup table and a lookup table of a reference temperature according to an embodiment of the present invention.

5A shows a lookup table at a reference temperature, ie, 25 degrees to 40 degrees Celsius.

When the input image data R, G, and B represent 256 gradations, the 256 gradations are divided into predetermined steps to set the corrected output image data R ', G', and B 'according to the divided steps. .

For example, when dividing 256 gray levels into 33 levels, the size of each level is set to 8 gray levels except for the 0 level. At the reference temperature, the input image data R, G, and B and the corrected output image data R ', G', and B 'have the same value at each step. Therefore, as shown in FIG. 5B, the graph of the corrected output image data R ′, G ′, and B ′ according to the step represents a linear function having an index of 1. In this case, the corrected output image data R ', G', and B 'in step 33 may be stored in the lookup table, and the output image data R', G ', and B' for other gray levels are interpolated. Can be obtained using the interpolation method.

6A and 6B are graphs illustrating a function of a lookup table and a lookup table at low temperature in accordance with one embodiment of the present invention.

FIG. 6A is a lookup table at a temperature lower than the reference temperature. As shown in FIG. 5A, 256 gray levels are divided into 33 levels, and the size of each step is set to 8 gray levels except for 0 level. In this case, the corrected output image data R ', G', and B 'are set to have a magnitude of a positive product smaller than 1 with the input image data R, G, and B. The corrected output image data R ', G', and B 'that are set are optimal values obtained through experiments.

In addition, since the gamma curve has a higher luminance with respect to a predetermined gray level at a lower temperature, the gamma curve has a larger amount of correction at a lower temperature. That is, as the temperature is lowered, the output image data R ', G', B 'corrected for the predetermined input image data R, G, B has a smaller value.

Therefore, as illustrated in FIG. 6B, the graph of the corrected output image data R ′, G ′, and B ′ according to the step represents a function having an exponent greater than one.

For example, when the input image data R, G, and B represent the 96th gray scale, when the current temperature is 25 degrees Celsius, the temperature correction unit 653 receives a control signal according to the reference temperature from the temperature sensor 657. The output image data R ', G', and B 'stored in the lookup table of the reference temperature are output. At this time, the stored output image data (R ', G', B ') shows the 96th gray level like the input image data (R, G, B).

When the current temperature is the temperature of FIG. 6A lower than the reference temperature, the temperature corrector 653 receives a control signal according to the temperature of FIG. 6A from the temperature sensor 657 and outputs the stored signal to the lookup table of the temperature of FIG. 6A. Image data R ', G', and B 'are output. At this time, the corrected output image data R ', G', and B 'represent a 24th gray level lower than the 96th gray level.

Therefore, by outputting the corrected output image data (R ', G', B ') having a gray level lower than the input image data (R, G, B) at the temperature of Figure 6a lower than the reference temperature to the data driver 500 In addition, it is possible to prevent the light having a luminance higher than the 96th gradation from being transmitted by the changed gamma curve.

As described above, according to the present invention, the output image data is corrected to have a gray level lower than that of the input image data at a temperature lower than the reference temperature, thereby preventing a change in luminance according to the temperature.

 Although the preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concepts of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (7)

A display panel having a plurality of pixels and displaying an image, A gamma correction unit receiving input image data and correcting the input image data to a value smaller than the input image data at a temperature lower than a reference temperature; and A data driver converting the corrected image data into a data voltage and supplying the pixel to the pixel. Liquid crystal display comprising a. In claim 1, And the gamma correction unit does not correct the input image data at the reference temperature. In claim 2, The gamma correction unit measures a current temperature and outputs a control signal corresponding to the current temperature, and And a temperature corrector configured to receive the input image data and output the corrected image data according to the control signal. In claim 3, And the temperature corrector comprises at least one lookup table that stores the input image data and the corrected image data corresponding to the input image data according to a temperature. In claim 4, And the gamma correction unit outputs the same corrected image data with respect to one input image data in a predetermined temperature range. In claim 5, And the corrected image data at a temperature lower than the reference temperature has a magnitude of a product of the input image data and a positive number less than one. In claim 6, The reference temperature is a liquid crystal display device of 25 degrees to 40 degrees Celsius.

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