KR100945584B1 - Driving device of liquid crystal display - Google Patents

Abstract

The present invention relates to a driving device of a liquid crystal display device capable of compensating a reference voltage in order to provide an accurate reference voltage.

According to an embodiment of the present invention, a driving apparatus of a liquid crystal display including a plurality of pixels generates a reference voltage generator, and converts the reference voltage from the reference voltage generator into digital. An analog-to-digital converter, a memory that stores a digital signal corresponding to the reference voltage, a comparator that compares the signals from the analog-to-digital converter and the memory and feeds the result back to its own input, from the comparator A digital analog converter for converting an output into an analog signal, and a plurality of gray voltages are generated based on the output from the digital analog converter, and a gray voltage corresponding to an image signal among the gray voltages is applied to the pixel as a data voltage. It includes a data driver. In this way, the desired color can be expressed by compensating before applying the reference voltage.

LCD, reference voltage, gradation voltage, ADC, comparator, memory, gamma curve, gamma constant

Description

Driving device of liquid crystal display {APPARATUS OF DRIVING LIQUID CRYSTAL DISPLAY}

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

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

3 is a block diagram of a reference voltage compensator according to an exemplary embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a driving device of a liquid crystal display device, and more particularly to a driving device of a liquid crystal display device capable of compensating a reference voltage.

A general liquid crystal display (LCD) includes two display panels and a liquid crystal layer having dielectric anisotropy interposed therebetween. An electric field is applied to the liquid crystal layer, and the intensity of the electric field is adjusted to adjust the transmittance of light passing through the liquid crystal layer to obtain a desired image. Such liquid crystal displays are typical of portable flat panel displays (FPDs), and among them, TFT-LCDs using thin film transistors (TFTs) as switching elements are mainly used.

The LCD includes a pixel including a switching element, a data driver for applying a corresponding data voltage to the pixel, and a reference voltage generator for generating a reference voltage and supplying the reference voltage to the pixel.

The reference voltage generator generates a gray voltage of positive and negative polarity for inversion driving, and the data driver selects a gray voltage corresponding to an image signal among a plurality of gray voltages and applies it to the pixel as a data voltage.

At this time, there are a method of supplying a gray scale voltage, a method of generating all necessary gray voltages in advance and supplying them to a data driver, and a method of supplying some gray scale voltages as reference, and dividing the rest within the data driving IC. . Recently, as the number of bits of data increases, the number of gradation voltages to be expressed also increases, and usually the latter method is employed.

For example, in the latter method, in case of 6-bit data, all of the gray scale voltages required are 64 gray scale voltages, of which eight are referred to as reference voltages (hereinafter referred to as "reference voltages"). The values in between are generated by a certain rule in the IC of the data driver.

What is needed to obtain such a constant rule is gamma correction, which is to correct the light transmittance of the liquid crystal so that it is intended to obtain uniform light transmission characteristics. In addition, a kind of curve used for gamma correction is called a gamma curve. On the LCD, the gamma constant is adjusted to have a gamma curve with 2.2.

On the other hand, a constant power generated by the DC / DC IC of the liquid crystal display device is applied to one stage of the resistor string, and the ratio of the resistance value is adjusted to generate a reference voltage. The resistor string includes a front end portion for generating a positive voltage and a rear end portion for generating a negative voltage with respect to a common voltage, and prevents deterioration of the liquid crystal by applying a positive and negative voltage.

However, the resistance value of the resistance string has an error of about 1%, and the resistance value corresponding to the same gray level of the front end portion and the rear end portion also has a slight error. In addition, there is an error in the power source applied to the resistance column, and the reference voltage changes as a whole. In this case, since the correct voltage for each gray level cannot be applied, the set gamma curve moves up or down. As a result, a case where a desired video cannot be obtained.

Accordingly, an object of the present invention is to provide a driving device of a liquid crystal display device capable of applying an accurate reference voltage.

According to an exemplary embodiment of the present invention, a driving device of a liquid crystal display including a plurality of pixels includes a reference voltage generator, a digital analog converter, a memory, a comparator, and a digital analog converter. The reference voltage generator generates two sets of multiple reference voltages, the analog-to-digital converter converts the reference voltage from the reference voltage generator into digital, and the memory stores a digital signal corresponding to the reference voltage. . The comparator compares the signals from the analog-to-digital converter and the memory with each other and feeds the results back to their inputs, which convert the output from the comparator into an analog signal.

At this time, the information of the memory is preferably stored on the basis of a gamma curve indicating the relationship between the transmittance of the liquid crystal and the gray scale.

The driving device of the liquid crystal display may further include a signal controller configured to receive the image signal and a control input signal for controlling the display of the image signal, and to control the data driver. The signal controller may include the analog to digital converter; It is preferable to include the memory, the comparator and the digital to analog converter.

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 portion of a layer, film, region, plate, etc. is said to be "on top" of another part, this includes not only when the other part is "right on" 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.

Now, a driving device of a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a block diagram of a liquid crystal display according to an exemplary embodiment of the present invention, and FIG. 2 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. 1, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal panel assembly 300, a gate driver 400 and a data driver 500 connected thereto. The signal controller 600 and a reference voltage generator 800 connected thereto are included.

The liquid crystal panel assembly 300 includes a plurality of display signal lines G ₁ -G _n , D ₁ -D _m and a plurality of pixels connected to the plurality of display signal lines G ₁ -G _n , D ₁ -D _m , and arranged in a substantially matrix form. .

The display 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 data signal line or data for transmitting a data signal. Line 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 includes a switching element Q connected to a display signal line G ₁ -G _n , D ₁ -D _m , and a liquid crystal capacitor C _LC and a storage capacitor C _ST connected thereto. It includes. The holding capacitor C _ST can be omitted as necessary.

The switching element Q is provided on the lower panel 100, and the control terminal and the input terminal are connected to the gate line G ₁ -G _n and the data line D ₁ -D _m, respectively. 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, the pixel electrode 190 of the lower panel 100 and the common electrode 270 of the upper panel 200, and the liquid crystal layer 3 between the two electrodes 190 and 270. It functions as a dielectric. The pixel electrode 190 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 a common voltage V _com . Unlike in FIG. 2, the common electrode 270 may be provided in the lower panel 100. In this case, both electrodes 190 and 270 may be linear or rod-shaped.

The storage capacitor C _ST is formed by overlapping a separate signal line (not shown) and the pixel electrode 190 provided on the lower panel 100, and a predetermined voltage such as a common voltage V _com is applied to the separate signal line. Is approved. However, the storage capacitor C _ST may be formed such that the pixel electrode 190 overlaps the front end gate line directly above the insulator.

Meanwhile, in order to implement color display, each pixel must display color, which is possible by providing a red, green, or blue color filter 230 in a region corresponding to the pixel electrode 190. In FIG. 2, the color filter 230 is formed in a corresponding region of the upper panel 200. Alternatively, the color filter 230 may be formed above or below the pixel electrode 190 of the lower panel 100.

A polarizer (not shown) for polarizing light is attached to an outer surface of at least one of the two display panels 100 and 200 of the liquid crystal panel assembly 300.

The reference voltage generator 800 generates two sets of gradation voltages related to the transmittance of the pixel. One of the two sets has a positive value for the common voltage (V _com ) and the other set has a negative value.

The gate driver 400 is connected to the gate lines G ₁ -G _n of the liquid crystal panel assembly 300 to receive a gate signal formed by a combination of a gate on voltage V _on and a gate off voltage V _off from the outside. It is applied to the gate lines G ₁ -G _n .

The data driver 500 is connected to the data lines D ₁ -D _m of the liquid crystal panel assembly 300 to select the gray voltage from the gray voltage generator 800 and apply the gray voltage to the pixel as a data signal. It consists of a circuit.

The signal controller 600 generates control signals for controlling operations of the gate driver 400 and the data driver 500, and provides the corresponding control signals to the gate driver 400 and the data driver 500.

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

The signal controller 600 inputs an input control signal for controlling the RGB image signals R, G, and B and their display from an external graphic controller (not shown), for example, a vertical sync signal V _sync and a horizontal sync signal. (H _sync ), a main clock (MCLK), a data enable signal (DE) is provided. The signal controller 600 generates a gate control signal CONT1 and a data control signal CONT2 based on the input control signal, and adjusts the image signals R, G, and B to match the operating conditions of the liquid crystal panel assembly 300. After appropriately processing, the gate control signal CONT1 is sent to the gate driver 400, and the data control signal CONT2 and the processed image signals R ', G', and B 'are sent to the data driver 500. In addition, the reference voltage compensator 650 included in the signal controller 600 compares and outputs the reference voltage V _ref from the reference voltage generator 800, which will be described in detail later.

The gate control signal CONT1 includes a vertical synchronization start signal STV indicating the start of output of the gate on pulse (gate on voltage section), a gate clock signal CPV for controlling the output timing of the gate on pulse, and a gate on pulse. An output enable signal OE or the like that defines a width.

The data control signal CONT2 is a load for applying a corresponding data voltage to the horizontal synchronization start signal STH indicating the start of input of the image data R ', G', and B 'and the data lines D ₁ -D _m . Signal LOAD, inverted signal RVS and data that inverts the polarity of the data voltage with respect to common voltage V _com (hereinafter referred to as " polarity of data voltage " by reducing " polarity of data voltage with respect to common voltage "). Clock signal HCLK and the like.

The data driver 500 sequentially receives image data R ′, G ′, and B ′ corresponding to one row of pixels according to the data control signal CONT2 from the signal controller 600, and generates a gray voltage generator ( The image data R ', G', B 'is converted into the corresponding data voltage by selecting the gray voltage corresponding to each of the image data R', G ', and B' among the gray voltages from the 800.

The gate driver 400 applies the gate-on voltage V _on 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.

The gate-on voltage V _on is applied to one gate line G ₁ -G _n so that a row of switching elements Q connected thereto is turned on (this period is "1H" or "1 horizontal period). (horizontal period) "and the same as one period of the horizontal sync signal (H _sync ), the data enable signal (DE), and the gate clock (CPV)]. D ₁ -D _m ). The data voltage supplied to the data lines D ₁ -D _m is applied to the corresponding pixel through the turned-on switching element Q.

The liquid crystal molecules change their arrangement according to the electric field generated by the pixel electrode 190 and the common electrode 270, and thus the polarization of light passing through the liquid crystal layer 3 changes. The change in polarization is represented by a change in transmittance of light by a polarizer (not shown) attached to the display panels 100 and 200.                     

In this manner, the gate-on voltages V _{on are} sequentially applied to all the gate lines G ₁ -G _n during one frame to apply data voltages to all the pixels. At the end of one frame, the next frame starts and the state of the inversion signal RVS applied to the data driver 500 is controlled so that the polarity of the data voltage applied to each pixel is opposite to that of the previous frame ("frame inversion). "). In this case, the polarity of the data voltage flowing through one data line may be changed (“line inversion”) within one frame or the polarity of the data voltage applied to one pixel row may be different according to the characteristics of the inversion signal RVS ( "Dot reversal").

Meanwhile, the signal controller 600 compares and outputs the reference voltage Vref from the reference voltage generator 800 and the reference voltage stored in the memory, which will be described with reference to FIG. 3.

3 is a block diagram of a reference voltage compensator 650 according to an embodiment of the present invention.

As shown in FIG. 3, the reference voltage compensator 650 includes an ADC 651, a comparator 652, a memory 654 connected thereto, and a DAC 653.

The ADC 651 receives a plurality of reference voltages, which are analog signals from the reference voltage generator 800, and converts the plurality of reference voltages into digital signals.

The reference voltage V _ref is generated as necessary according to the data of the corresponding bit. For example, if the video signal is 6-bit data and 64 gray levels, a voltage corresponding to 64 gray levels for each of the positive and negative polarities is required, so that 128 gray levels are required. Then, the reference voltages V _ref generated by the reference voltage generator 800 are sixteen in each of eight positive and negative polarities, and the voltage therebetween is generated using the resistor string in the data driver 500.

On the other hand, according to the specification of the liquid crystal display, positive and negative white gray voltages or black gray voltages including the common voltage may be generated in advance as reference voltages, and in this case, 19 reference voltages are generated.

In the case of 64 gray levels, a voltage corresponding to eight gray levels is generally generated as a reference voltage (V _ref ). For example, voltages corresponding to 8, 16, 24, 32, 48, and 64 gray levels are used as reference voltages. Create

The memory 654 stores, as a digital signal, information of voltages corresponding to the gray scales in the gamma curve having a gamma constant of 2.2. For example, when the voltage corresponding to 8 grays is 0.625V and the voltage 1.25V corresponding to 16 grays, the digital signal corresponding thereto is stored and provided to the comparator 652. Of course, it is also possible for the gamma constant to store information of voltages different from those described above.

Comparator 652 sequentially compares the signal from ADC 651 with the signal from memory 654. That is, when the number of reference voltages V _ref is 16, all 16 are sequentially compared and the result is output. At this time, if there is an error between the input value and the value stored in the memory 652, the result is fed back to the output of the ADC 651 to compensate for this difference.

The DAC 653 converts a digital signal into an analog signal. The compensated digital signal is converted into an analog signal and supplied to the data driver 500. The data driver 500 generates a gray scale voltage therebetween based on the reference voltage V ' _ref , and generates the gray scale voltage therebetween. The gradation voltage corresponding to the video signal among the voltages is selected and applied as the data voltage to the image signal.

In this way, a desired image can be obtained by correcting as close as possible to the set gamma curve.

Meanwhile, the above-described reference signal compensator 650 is located in the signal controller 600, which may be implemented as a separate chip to prevent an increase in component elements.

As described above, the voltage generated by the reference voltage generator 800 may be compared and compensated in advance, and then applied to the data driver 500 to express a desired image by applying an accurate reference voltage.

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 (3)

A driving device of a liquid crystal display device including a plurality of pixels, A reference voltage generator for generating two sets of reference voltages; An analog to digital converter for converting the reference voltage from the reference voltage generator into digital; A memory for storing a digital signal corresponding to the reference voltage; A comparator that compares the signals from the analog-to-digital converter and the memory with each other and feeds the results back to their inputs, A digital analog converter for converting the output from the comparator into an analog signal, and A data driver which generates a plurality of gray voltages based on an output from the digital-to-analog converter, and applies a gray voltage corresponding to an image signal among the gray voltages as a data voltage to the pixel; Containing Driving device for liquid crystal display device. In claim 1, And the information of the memory is stored based on a gamma curve representing the relationship between the transmittance of the liquid crystal and the gray scale. In claim 1, The driving device of the liquid crystal display device further includes a signal controller which receives the image signal and a control input signal for controlling the display of the image signal and controls the data driver. The signal controller includes the analog to digital converter, the memory, the comparator and the digital analog converter.

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