KR20070043360A - Liquid crystal display device for eliminating block dim - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device that eliminates the block dim phenomenon. More particularly, the present invention relates to a two-point gamma voltage applied to a data driver integrated circuit, and to forming a large resistance value of the entire string of the data driver integrated circuit. A liquid crystal display device for removing the phenomenon.

The present invention provides a gamma voltage for supplying a gamma reference voltage to a liquid crystal panel having a plurality of liquid crystal cells arranged in a matrix, a gate driver driving a gate line of the liquid crystal panel, a data driver driving a data line of the liquid crystal panel, and a data driver. A liquid crystal display comprising a portion, wherein the gamma voltage generator outputs a first gamma reference voltage divided by a first resistor, a second resistor, and a first resistor connected in series between a first reference voltage and a second reference voltage. And a second output buffer configured to output a first gamma reference voltage divided by the second resistor and a second output buffer applied to the data driver.

Gamma Voltage, Block Dim, R-String, Data Driver IC, Chip On Film (COG)

Description

Liquid crystal display device for eliminating block dim

1 is a circuit diagram of a gamma voltage generator of a conventional liquid crystal display;

2 is a diagram illustrating an egg string inside a data driver IC of a conventional liquid crystal display device;

3 is a circuit diagram of a gamma voltage generator of a liquid crystal display according to an exemplary embodiment of the present invention;

4 is a diagram illustrating an egg string inside a data driver IC of a liquid crystal display according to an exemplary embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device that eliminates the block dim phenomenon. More particularly, the present invention relates to a two-point gamma voltage applied to a data driver integrated circuit, and to forming a large resistance value of the entire string of the data driver integrated circuit. A liquid crystal display device for removing the phenomenon.

In general, a liquid crystal display device displays an image by adjusting the light transmittance of a liquid crystal according to an image signal. The liquid crystal display device is composed of an LCD panel, a driving circuit unit, and a backlight to perform an information display function in a notebook computer, a computer monitor, and an LCD TV. It is mounted and utilized as a part.

The LCD panel has a structure in which a thin film transistor array and a color filter substrate are maintained at regular cell gaps, liquid crystal is injected therebetween, and polarizers are attached to both sides of the panel. The signal wiring of the LCD panel is connected to grouping bonding pads to facilitate signal supply using a multi-channel output LCD Driver IC (LDI).

The driving circuit unit is a printed circuit board (PCB) with circuit elements such as an LDI for operating a liquid crystal panel, a timing controller for inputting source data and control signals to the LDI, and a gamma voltage generator for supplying a gamma reference voltage to the LDI. It is composed. The LDI includes a gate driver IC for driving the gate line of the LCD panel and a data driver IC for driving the data line of the LCD panel.

A backlight is a flat light device that emits uniform brightness in the direction of the LCD.It is used as a cold cathode tube (CCFL), a reflector, a light guide panel (LGP), or a diffuser plate. It is composed.

As a method of connecting a driver IC to a bonding pad, a method of mounting a tape carrier package (TCP) using a tape automated bonding (TAB) technology, a mounting method using a chip on film (COF) technology, which is more flexible than a TCP mounting method, and an LDI There is a chip on glass (COG) mounting method in which a chip is directly connected to a bonding pad.

Unlike the TCP / COF structure in which the LDI is mounted on the film, the COG mounting method uses the bump technology on the glass substrate of the LCD panel to directly mount the LDI. Therefore, the film used in the TCP / COF structure is removed to remove the LCD panel. The area connecting the PCB with the PCB is minimized and the signal lines applied from the PCB to the LDI are placed on the LCD panel.

The conventional COG mounting method reduces the cost by eliminating the film used in the TCP / COF structure, while increasing the metal resistance of the signal lines located on the LCD panel, and increasing the metal resistance. Due to the voltage drop, gamma reference voltages and Vcom voltages applied to a plurality of LCD driver ICs mounted on the LCD panel are changed for each LCD driver IC.

When the gamma reference voltage, Vcom voltage, etc. applied to the LCD driver IC mounted on the LCD panel is changed for each LCD driver IC, a block dim that causes a luminance difference on the LCD screen for each data line unit driven by the data driver IC ) Phenomenon occurs.

In order to solve this problem, an op amp (Operational Amplifier) is embedded in the gamma line inside the data driver IC to reduce the voltage difference between adjacent driver ICs.The same resistance is formed in the data driver IC in advance as the resistance formed in the LCD panel. A method of reducing the voltage difference between data driver ICs is used.

However, in the case of the method in which the OP amplifier is embedded, there is a problem in that the driving circuit becomes complicated due to the OP amplifier, the current consumption increases, the voltage drop of the power line increases, and the offset of the OP amplifier has a difference.

In addition, the method of forming the same resistance forms a compensation resistor only at both ends of the positive voltage and the negative voltage of the gamma voltage, so that the difference between the intermediate voltages cannot be compensated. However, since the intermediate voltage is a section in which the voltage difference between gray levels is the smallest, a block dim phenomenon occurs on the screen even if a small voltage difference occurs.

The problem of the conventional liquid crystal display will be described in more detail through an al string structure inside the gamma voltage generator and the LCD driver IC.

1 is a circuit diagram of a gamma voltage generator of a conventional liquid crystal display. Referring to FIG. 1, a gamma voltage generator of a conventional liquid crystal display includes first to fifth resistors r1 to r5 connected in series between a first reference voltage and a second reference voltage, and first to fifth resistors. An output buffer is connected to each of the first to fifth divided points n1 to n5 which are the contacts between the resistors r1 to r5.

The gamma voltage generator of the conventional liquid crystal display shown in FIG. 1 simultaneously shows a positive gamma reference voltage generator and a negative gamma reference voltage generator. For example, GMA 1/6 represents a positive gamma reference voltage GMA1 and a negative gamma reference voltage. Means GMA6.

The conventional gamma voltage generator inputs the positive / negative gamma reference voltages (GMA1 to GMA5 / GMA6 to GMA10) 5 points each to the data driver IC, so the circuit configuration is complicated, especially when the COG mounting method is used. The number of wirings to be formed is increased, but when the number of wirings is increased in a predetermined space, the wiring width is reduced and the resistance is increased.

As the wiring resistance formed on the LCD panel increases, the voltage drop caused by the resistance of the gamma voltage wiring increases, so the gamma reference voltage applied to the data driver IC mounted on the LCD panel varies for each LCD driver IC, resulting in a block dim phenomenon. Will be generated.

2 is a diagram illustrating an egg string inside a data driver IC of a conventional liquid crystal display. Referring to FIG. 2, an r-string inside a data driver IC of a conventional liquid crystal display is serially connected for negative gamma voltages with first to fourth resistors r11 to r14 connected in series for positive gamma voltages. It consists of the fifth to eighth resistor (r15 ~ r18) connected.

Here, the divided points n11 to n15 formed as the contacts between the first to fourth resistors r11 to r14 are matched to the positive gamma reference voltages GMA1 to GMA5 applied from the gamma voltage generator of FIG. The divided points n16 to n20 formed as the contacts between the eighth resistors r15 to r18 match the negative gamma voltages GMA6 to GMA10 applied from the gamma voltage generator of FIG. 1.

If the digital input data is 6 bits, the gamma voltage is divided into 64 steps, wherein each of the first to eighth resistors r11 to r18 has 15 or 16 connected in series to generate 16 gamma voltages. It consists of a resistor.

The sum of the positive gamma resistors (r11 + r12 + r13 + r14) and the negative gamma resistors (r15 + r16 + r17 + r18) in the al string inside the conventional data driver IC usually use a resistor of 10 KΩ to 20 KΩ. have.

If the voltage applied to the positive / negative gamma resistors r11 to r14 / r15 to r18 is 4 V, the current flowing in the gamma line is 0.2 mA to 0.4 mA, which is caused by the resistance formed on the LCD panel. The amount of voltage drop is determined. Therefore, when the resistance formed on the LCD panel is 60Ω, the voltage drop is 12mV to 24mV.

When the voltage drop is combined with an offset between output channels of the data driver IC itself or an offset difference existing between the data driver ICs, the voltage drop may be about 22 mV to 34 mV. The offset specification of most driver ICs allows ± 10mV between channel to channel and IC to IC, which indicates that the block dim phenomenon that can be perceived by the user is very likely to occur.

In the case of the intermediate gamma voltage, the amount of the voltage drop is small because the current flowing in the line is smaller than the voltage at both ends of the gamma, but the intermediate gamma voltage is recognized by the user even if the voltage difference between adjacent driver ICs is small because the voltage difference between grayscales is small. A block dim phenomenon may occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object thereof is to provide a liquid crystal display device which removes a block dim phenomenon by applying a 2-point gamma voltage to a data driver integrated circuit.

In addition, another object of the present invention is to provide a liquid crystal display device in which the entire resistance value of an Al string of a data driver integrated circuit is formed to remove a block dim phenomenon.

In order to achieve the above object, the present invention provides a gamma reference to a liquid crystal panel in which a plurality of liquid crystal cells are arranged in a matrix form, a gate driver driving a gate line of the liquid crystal panel, a data driver driving a data line of the liquid crystal panel, and a data driver. A liquid crystal display comprising a gamma voltage generator for supplying a voltage, wherein the gamma voltage generator comprises: a first resistor and a second resistor connected in series between a first reference voltage and a second reference voltage; A first output buffer configured to output a first gamma reference voltage divided by the first resistor and apply the first gamma reference voltage to the data driver; And a second output buffer configured to output a second gamma reference voltage divided by the second resistor and apply the second gamma reference voltage to the data driver.

The gamma voltage generator may be a positive gamma reference voltage generator in which the first reference voltage is a power supply voltage.

In addition, the gamma voltage generator is preferably a negative gamma reference voltage generator in which the second reference voltage is a ground voltage.

In addition, the data driver includes an AL string in which a plurality of resistors are connected in series, and receives the first gamma reference voltage and the second gamma reference voltage and divides them according to a resistance ratio to generate a plurality of positive gamma voltages.

In addition, the data driver includes an al string having a plurality of resistors connected in series and receiving the first gamma reference voltage and the second gamma reference voltage and dividing them according to a resistance ratio to generate a plurality of negative gamma voltages. .

In addition, the total resistance value of the string is preferably 50KΩ or more.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 is a circuit diagram of a gamma voltage generator of a liquid crystal display according to an exemplary embodiment of the present invention. As shown in FIG. 3, the gamma voltage generation unit of the liquid crystal display according to the exemplary embodiment of the present invention may include a first resistor R1 and a second resistor, which are connected in series between the first reference voltage and the second reference voltage. R2) and an output buffer connected to the first voltage dividing point N1 and the second voltage dividing point N2, respectively, to output voltage divided by the first resistor R1 and the second resistor R2.

The gamma voltage generator of the present embodiment shown in FIG. 3 shows the positive gamma reference voltage generator and the negative gamma reference voltage generator at the same time. For example, GMA 1/6 represents the positive gamma reference voltage GMA1 and the negative gamma reference voltage GMA6. it means.

First, a process of generating the positive gamma reference voltage in which the first reference voltage is the power supply voltage VDD will be described. The first resistor R1 and the second resistor R2 divide the voltage applied to both ends according to the resistance ratio, A gamma reference voltage GMA1 and a gamma reference voltage GMA5 are generated at each of the first divided point N1 and the second divided point N2. The output buffer comprises a voltage follwer to buffer and output the gamma reference voltage GMA1 from the first voltage dividing point N1 and the gamma reference voltage GMA5 from the second voltage dividing point N2.

Next, when a negative gamma reference voltage is generated in which the second reference voltage is the ground voltage VSS, the first resistor R1 and the second resistor R2 divide the voltage applied to both ends according to the resistance ratio. A gamma reference voltage GMA6 and a gamma reference voltage GMA10 are generated at each of the first divided point N1 and the second divided point N2. The output buffer includes a voltage follwer to buffer and output the gamma reference voltage GMA6 from the first voltage dividing point N1 and the gamma reference voltage GMA10 from the second voltage dividing point N2.

Unlike the gamma voltage generator that generates the positive / negative gamma reference voltage of the conventional five points, the gamma voltage generator of the present embodiment generates two points of the positive / negative gamma reference voltages GMA1, GMA5 / GMA6, and GMA10. Apply to the data driver IC. Therefore, the liquid crystal display of the present embodiment can reduce the number of wirings formed on the LCD panel compared to the conventional liquid crystal display device, thereby reducing the resistance of the wirings formed on the LCD panel.

When the resistance of the wiring formed on the LCD panel decreases, the voltage drop caused by the resistance of the voltage wiring decreases, thus eliminating the block dim phenomenon in which the applied gamma reference voltage varies for each data driver IC mounted on the LCD panel. Will be.

4 is a diagram illustrating an egg string inside a data driver IC of a liquid crystal display according to an exemplary embodiment of the present invention. As shown in FIG. 4, the AL string inside the IC of the liquid crystal display according to the exemplary embodiment of the present invention includes a first resistor R11 for the positive gamma voltage and a second resistor R12 for the negative gamma voltage. . In this case, it is preferable that the AL string inside the data driver IC of the present embodiment exactly matches the V-T (Voltage vs. Transmittance) characteristics of the LCD panel to obtain optical characteristics desired by a user.

The first resistor R11 may be configured by dividing an external input power applied to both ends according to a resistance ratio to connect a plurality of resistors (not shown) in series to generate a plurality of positive gamma voltages. The total resistance of the first resistor R11 configured by connecting a plurality of resistors in series is preferably 50 KΩ or more.

The external input power is preferably gamma reference voltages GMA1 and GMA5 applied from the gamma voltage generator of FIG. 3. For example, if the digital input data is 6 bits, the first resistor R11 may include 63 resistors connected in series to generate a positive gamma voltage of 64 steps.

Similarly, the second resistor R2 may be configured by dividing an external input power applied at both ends according to a resistance ratio to connect a plurality of resistors (not shown) in series to generate a plurality of negative gamma voltages. The total resistance of the second resistor R12 configured by connecting a plurality of resistors in series is preferably 50 KΩ or more.

The external input power is preferably gamma reference voltages GMA6 and GMA10 applied from the gamma voltage generator of FIG. 3. For example, if the digital input data is 6 bits, the second resistor R12 may be configured by connecting 63 resistors in series to generate a negative gamma voltage of 64 steps.

Unlike the conventional AL strings in the data driver ICs, the AL strings of the present exemplary embodiment have a structure in which the AL strings are applied by receiving only positive / negative both voltages without receiving an intermediate gamma reference voltage from the gamma voltage generator. The voltage is divided and output by using. Therefore, the voltage difference of the halftone generated between the data driver ICs adjacent to each other on the LCD panel does not occur.

In addition, the AL string inside the data driver IC of this embodiment has a sum of resistances for the positive / negative gamma voltage which is 2.5 to 5 times larger than the AL string inside the conventional data driver IC.

If the voltage applied across the positive / negative gamma resistor is 4V, the current flowing in the gamma line is less than 0.08mA, and if the resistance formed on the LCD panel is 60Ω, the voltage drop is only 4.8mV. Given that the voltage difference between the high and low gray areas is more than a few tens of mV, the block dim phenomenon is eliminated even if combined with the offset of the data driver IC.

As described above, the liquid crystal display of the present invention reduces the number of wires to which the gamma reference voltage is applied by applying a 2-point gamma voltage to the data driver integrated circuit, thereby eliminating the block dim phenomenon and simplifying the circuit. .

In addition, by reducing the current of the gamma line by increasing the entire resistance value of the whole string of the data driver integrated circuit, the block dim phenomenon caused by the voltage drop is eliminated.

In addition, preferred embodiments of the present invention are disclosed for the purpose of illustration, those skilled in the art will be able to various modifications, changes, additions, etc. within the spirit and scope of the present invention, these modifications and changes should be seen as belonging to the following claims. something to do.

Claims (6)

A liquid crystal panel comprising a plurality of liquid crystal cells arranged in a matrix form, a gate driver driving a gate line of the liquid crystal panel, a data driver driving a data line of the liquid crystal panel, and a gamma voltage generator for supplying a gamma reference voltage to the data driver. As a liquid crystal display device, The gamma voltage generator A first resistor and a second resistor connected in series between the first reference voltage and the second reference voltage; A first output buffer configured to output a first gamma reference voltage divided by the first resistor and apply the first gamma reference voltage to the data driver; And And a second output buffer configured to output a second gamma reference voltage divided by the second resistor and apply the second gamma reference voltage to the data driver. Liquid crystal display to remove the block dim phenomenon. The method of claim 1, The gamma voltage generator is a positive gamma reference voltage generator in which the first reference voltage is a power supply voltage. Liquid crystal display to remove the block dim phenomenon. The method of claim 1, The gamma voltage generator is a negative gamma reference voltage generator in which the second reference voltage is a ground voltage. Liquid crystal display to remove the block dim phenomenon. The method of claim 2, The data driver includes an al string having a plurality of resistors connected in series, and receiving the first gamma reference voltage and the second gamma reference voltage and dividing them according to a resistance ratio to generate a plurality of positive gamma voltages. Liquid crystal display to remove the block dim phenomenon. The method of claim 3, wherein The data driver includes an al string in which a plurality of resistors are connected in series, and receives the first gamma reference voltage and the second gamma reference voltage and divides them according to a resistance ratio to generate a plurality of negative gamma voltages. Liquid crystal display to remove the block dim phenomenon. The method according to claim 4 or 5, The total resistance value of the string is 50KΩ or more Liquid crystal display to remove the block dim phenomenon.

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