KR100806908B1 - device for driving liquid crystal device - Google Patents

Abstract

The present invention relates to a drive device for a liquid crystal display device.

A plurality of gate lines and data lines are formed in the row and column directions, respectively, and a plurality of pixels having switching elements connected to the gate line and the data line are formed in an area defined by the intersection of the gate line and the data line, respectively. A drive device for a liquid crystal display device comprising a liquid crystal panel, comprising: a scan driver for supplying a gate voltage to the gate line; A data driver supplying a corresponding gray voltage to the data line according to an applied data signal; A timing controller which generates a digital signal for driving the data driver and scan driver; And a gray voltage generator for generating a plurality of gray voltages and supplying the gray voltages to the data driver, wherein the gray voltage levels vary according to the ambient luminance.

According to the present invention, gamma correction is performed according to the luminance of the surrounding environment, thereby further improving visibility of the liquid crystal display.

LCD, gradation voltage correction, gamma correction, luminance measurement

Description

Device for driving liquid crystal device

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

2 is an exemplary view illustrating a mounting state of the luminance measuring unit of FIG. 1.

3 is a diagram illustrating in detail a gray voltage generator of FIG. 1.

4 is a graph illustrating a relationship between ambient luminance and gray voltage according to an exemplary embodiment of the present invention.

5 is an exemplary diagram illustrating luminance characteristics of an image according to gamma correction 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 (hereinafter, referred to as an LCD), and more particularly, to a driving device of a liquid crystal display for controlling a gray voltage supplied to a liquid crystal display.

Recently, display devices are also required to be lighter and thinner in accordance with the light weight and thickness of personal computers and televisions, and according to such demands, flat displays such as liquid crystal displays (LCDs) instead of cathode ray tubes (CRTs) are required. Panel type displays are being developed.

An LCD is a display device that obtains a desired image signal 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. Such LCDs are typical of portable flat panel displays, and among them, TFT-LCD using a thin film transistor (TFT) as a switching element is mainly used.

In general, an LCD includes a plurality of gate lines for transmitting a scan signal and data lines intersecting the gate lines, and data lines for transmitting image data. The LCD is formed in an area surrounded by the gate lines and the data lines, respectively. It includes a plurality of pixels in the form of a matrix connected through a switching element.

As a method of applying image data to each pixel in such an LCD, first, a gate-on signal, which is a scanning signal, is sequentially applied to gate lines to sequentially turn on a switching element connected to the gate line, and simultaneously to the gate line. An image signal (more specifically, a gradation voltage) to be applied to the corresponding pixel row is supplied to each data line. Then, the image signal supplied to the data line is applied to each pixel through the turned-on switching element. At this time, the gate-on signal is sequentially applied to all the gate lines for one frame period to apply the image signal to all the pixel rows, thereby eventually displaying the image of one frame.

As such, the gray scale voltage applied to the data line of the LCD refers to the voltage applied to the source electrode of the thin film transistor to generate gray scale (typically, the color is bright and dark). In the color TFT LCD, the gray scale is a graphic controller. It is determined by the number of bits of red (R), green (G), and blue (G) data coming from the data. That is, for example, if the R data comes in 6 bits, gray scales of 2 ⁶ = 64 are generated, so that 64 gray scales can be represented.

According to these gray scales, various color expressions are made on the LCD, and gray scale expressions are made to be closer to natural colors. However, although efforts have been made to improve color reproducibility by improving the performance of color filters in LCDs, there is a lack of countermeasures to more accurately reproduce the difference in brightness.

In general, color photographs display the brightness in the same surface reflection type as natural images, but because LCD displays the brightness in transmissive type, there is a difference between the brightness expression of the image of the color picture drawn on the photo paper and the brightness expression of the image on the LCD. Occurs. In other words, color pictures have the same reflectance by natural light as natural objects, so you can feel the same brightness as natural light depending on the amount of light in the surrounding environment.However, in the transmissive LCD, it has a constant transmittance regardless of the amount of light in the surrounding environment. For this reason, the expression of the tone changes according to the illumination.

For example, assuming that an object is seen in an environment having an illuminance of 100, such as natural light, with respect to two natural objects having a difference in reflectance of 0.1, the luminance difference is 100 × 0.1 = 10 to recognize the object. If the illuminance is 200, a luminance difference of 200 × 0.1 = 20 should occur to have a good expression of natural materials.

However, since the transmissive LCD always has a fixed transmittance, the image appears dark in bright places and the image looks bright in dark places, thereby providing an unnatural feel in an environment other than a specific illuminance. That is, if the luminance of the backlight is 100 and the transmittance of the two systems is 0.1, when the illuminance is 100, the luminance difference expressed by the LCD becomes 10, so that an image having the same feeling as that of natural objects can be displayed. Even though the luminance difference must be 20, the luminance difference is still only 10, so that an image with a feeling that is not the same as that of natural objects is displayed. Accordingly, LCD has a disadvantage of poor visibility.

Therefore, the technical problem to be achieved by the present invention is to solve the above disadvantages, and to improve the visibility of the liquid crystal display device.

According to an aspect of the present invention, there is provided a driving apparatus of a liquid crystal display device, wherein a plurality of gate lines and data lines are formed in row and column directions, respectively, and are defined as intersections of the gate lines and data lines. A drive device for a liquid crystal display device comprising a liquid crystal panel having a plurality of pixels having switching elements connected to the gate line and the data line, respectively, the device comprising: a scan driver configured to supply a gate voltage to the gate line; A data driver supplying a corresponding gray voltage to the data line according to an applied data signal; A timing controller which generates a digital signal for driving the data driver and scan driver; And a gray voltage generator for generating a plurality of gray voltages and supplying the gray voltages to the data driver, wherein the gray voltage levels vary according to the ambient luminance.

In particular, in the normal white mode, the potential difference between the gradation voltage and the common electrode voltage when the ambient luminance is greater than the reference value is smaller than the potential difference between the gradation voltage and the common electrode voltage when the ambient luminance is smaller than the reference value. In the normal black mode, the potential difference between the gradation voltage and the common electrode voltage when the ambient luminance is greater than the reference value is greater than the potential difference between the gradation voltage and the common electrode voltage when the ambient luminance is smaller than the reference value.

The gray voltage generator may include a first resistor string configured to generate a plurality of positive gray voltages; A second resistor string generating a plurality of negative gray voltages; A luminance measuring unit measuring ambient luminance; And a controller configured to vary the amount of current applied to the first resistor string and the second resistor string to vary the positive gray voltage and the negative gray voltage level according to the ambient luminance measured by the luminance measurer.

The controller may include a first variable resistor connected to a reference voltage terminal of the first resistor string; A second variable resistor connected to the reference low voltage terminal of the second resistor row; And a switching element operated according to a signal output from the luminance measuring unit to vary the amount of current applied to the first and second resistor strings through the first and second variable resistors.

The luminance measuring unit is mounted outside the liquid crystal display to measure the peripheral luminance, and may be formed of a photo diode.

Hereinafter, with reference to the drawings will be described in detail an embodiment of the present invention.                     

In the liquid crystal display according to the exemplary embodiment of the present invention, in order to improve visibility, an image having the same feeling as that of natural objects is displayed by changing a gamma characteristic of the liquid crystal display according to ambient brightness.

That is, in a bright environment, the gamma constant showing gamma curve characteristics is made smaller than the reference gamma constant, and in a dark environment, the gamma constant is made larger than the reference gamma constant to improve the visibility of the liquid crystal display device.

1 illustrates a structure of a liquid crystal display device showing an embodiment of the present invention.

As shown in FIG. 2, a liquid crystal display according to an exemplary embodiment of the present invention includes an LCD panel 1, a gate driver 2, a data driver 3, a driving voltage generator 4, and a timing controller ( 5), the gray voltage generator 6 and the luminance measuring unit 7 are included.

Herein, a normal black mode liquid crystal display is described as an example, but the present invention is not limited thereto and may be equally applied to a normally white mode liquid crystal display.

The data driver 3 is also called a source driver and serves to lower the voltage value transmitted to each pixel in the LCD panel 1 by one line. More specifically, the data driver 3 stores the digital data from the timing controller 5, which will be described later, in a shift register in the data driver, and then a signal (LOAD signal) for instructing the LCD panel 1 to lower the data. In this case, the voltage corresponding to each data is selected and the voltage is transferred to the LCD panel 1.                     

The gate driver 2 is also called a scan driver, and serves to open a way for data from the data driver 3 to be transferred to the pixel. Each pixel of the LCD panel 1 is turned on or off by a TFT serving as a switch, which is turned on and off by applying a constant voltage (Von, Voff) to a gate.

In this way, the Von voltage for turning on the gate and the Voff voltage for turning off the gate signal are generated by the driving voltage generator 4. The driving voltage generator 4 generates not only the above-mentioned Von and Voff voltages but also a Vcom voltage which is a reference for the data voltage difference in the TFT.

The timing controller 5 generates a digital signal for driving the data driver 3 and the gate driver 2. Specifically, the timing controller 5 generates a signal that enters the drivers 2 and 3, adjusts timing of data, and adjusts clock. It plays a role.

The gray voltage generator 6 generates a gray voltage entering the data driver 3, and in particular, generates a gray voltage according to the ambient brightness measured by the luminance measuring unit 7 according to an exemplary embodiment of the present invention. Supply to the drive part 3 is supplied.

2 shows an example of mounting the luminance measuring unit according to the embodiment of the present invention. As shown in FIG. 2, the luminance measuring unit 7 is installed on a portion of the top chassis of the LCD module in which the liquid crystal is injected between the color filter substrate and the thin film transistor substrate, for example, depending on the amount of light received. It consists of a photodiode or a transistor for outputting an electrical signal.

3 illustrates a structure of a gray voltage generator according to an exemplary embodiment of the present invention, which generates a gray voltage that is variable according to a signal output from the luminance measuring unit.

As shown in FIG. 3, the gray voltage generator 6 according to the exemplary embodiment of the present invention is connected to the luminance measuring unit 7 and operated according to a signal output from the luminance measuring unit 7. A negative gradation voltage is connected in series with Q1, a plurality of first resistor rows R1 to R5 for generating a positive gradation voltage, and a series of first resistor rows R1 to R5. It consists of a plurality of second row of resistance (R6 ~ R10) for generating a.

The control transistor Q1 has a base terminal connected to the output terminal of the luminance measuring unit 7 and turned off according to a signal applied to the base terminal.

The first resistor rows R1 to R5 are a plurality of resistors connected in series between a first voltage and a common voltage level applied from the outside to generate a plurality of gray voltages for the positive charging of the liquid crystal. The contact point between the voltage AVDD and each resistor becomes the VREF1 + to VREF5 + gradation voltages.

Here, the collector terminal of the control transistor Q1 is connected to the contact between the resistor R3 and the resistor R4 through the variable resistor RF, and the first resistor strings R1 to R5 are connected according to the potential of the collector terminal. The amount of current flowing through it is variable.

The second resistor strings R6 to R10 are a plurality of resistors connected in series between the common voltage level and the second voltage in order to generate a plurality of gray voltages for negative charging of the liquid crystal. The contact between them becomes VREF6--VREF10- gradation voltage. Here, since the emitter terminal of the control transistor Q1 is connected to the contact between the resistor R7 and the resistor R8 through the variable resistor RG, the second resistor string R6 depending on the potential of the emitter terminal. The amount of current flowing through R10) is variable.

In the gray voltage generator 6 having such a structure, the potential of the collector terminal of the control transistor Q1 and the potential of the emitter terminal are respectively varied according to the signal output from the luminance measuring unit 7. Since the amount of current flowing through the second resistance row is variable, the positive gray voltages (VREF1 + to VREF5 +) and the negative gray voltages (VREF6- to VREF10-) generated in accordance with the measured ambient brightness substantially vary.

Therefore, the control transistor Q1 and the variable resistors RF and RG function as means for controlling the gray voltage level generated according to the luminance measured by the luminance measuring unit.

In the present exemplary embodiment, the luminance measurer may be included in the gray voltage generator or may be formed separately from the gray voltage generator.

The operation of the liquid crystal display according to the embodiment of the present invention having such a structure will be described.

More specifically, as shown in FIG. 2, the luminance measuring unit 7 mounted on the outside of the top chassis of the liquid crystal display outputs an electrical signal according to the intensity of light received according to the luminance of the surrounding environment. do. The signal output from the luminance measuring unit 7 is input to the base terminal of the control transistor Q1 of the gray voltage generator 6 shown in FIG. 3, and according to the signal input to the base terminal, the control transistor Q1 is Turn on / off.

When the control transistor Q1 is turned off, the first voltage applied from the outside flows to the diode D1 through the first resistor strings R1 to R5, so that the first to fifth resistors connected in series ( The voltage is divided by R1 to R5, thereby generating positive gray voltages VREF1 + to VREF5. The current flowing through the diode D1 is charged to the capacitor C1. When the charging of the capacitor C1 is completed, the current flows through the diode D4 to the second row of resistors R6 to R10, and is connected in series. The negative gray scale voltages VREF6-VREF10- are generated by the voltage divided by the sixth to tenth resistors R6 to R10.

On the other hand, when the luminance of the surrounding environment is high and the amount of light received is large, the amount of current IDC applied to the base terminal of the control transistor Q1 is increased and the control transistor Q1 is turned on.

When the control transistor Q1 is turned on, a current applied from the outside flows to the control transistor Q1 through the first to third resistors R1 to R3 of the first resistor strings R1 to R6. The current passing through the control transistor Q1 flows through the resistor RG to the eighth through tenth resistors R8 through R10 of the second row of resistors.

Accordingly, the amount of current flowing through the first to third resistors R1 to R3 increases to increase the voltage drop, and the amount of current flowing to the fourth and fifth resistors R4 and R5 is relatively decreased, thereby decreasing the voltage drop. Becomes smaller.

In addition, the amount of current flowing through the eighth through tenth resistors R8 through R10 increases to increase the voltage drop, and the amount of current flowing through the sixth and seventh resistors R6 and R7 decreases, thereby decreasing the voltage drop. Becomes smaller.

As a result, the positive gray voltages generated at the contacts of the first to fifth resistors R1 to R5, respectively, in particular, the second to fourth gray voltages VREF2 to VREF4 are reduced, so that the fifth voltage is the white voltage. Negative gray voltages generated at the contacts of the sixth to tenth resistors R6 to R10, in particular, the seventh to ninth gray voltages VREF7 to VREF9 are increased. The display moves to the sixth gray voltage VREF5.

At this time, the degree to which the voltage is changed in accordance with the amount of ambient light irradiation is determined by the reference voltage regulating resistor provided between the control transistor Q1, the first resistor strings R1 to R5, and the second resistor strings R6 to R10. RF, RG). Therefore, by adjusting the resistance values of the reference voltage adjusting resistors RF and RG, it is possible to appropriately adjust the amount of voltage which varies according to the ambient luminance.

4 is a waveform diagram showing the relationship between the amount of ambient luminance measured by the luminance measuring unit and the gray scale voltage.

For example, assuming that the current flowing at the driving voltage of the control transistor at the general office luminance level is 4 mA, and the current amount increases according to the increase in luminance, as shown in FIG. 4, the intermediate gray voltages VREF2 to VREF4. And VREF6 to VREF9 are driven to VREF5 and VREF6, which are white voltages, respectively. On the other hand, when the luminance decreases and the current amount decreases, the intermediate gray voltages VREF2 to VREF4 and VREF6 to VREF9 are driven to the black voltages VREF5 and VREF6, respectively.

Therefore, when the reference gamma constant is 1, the gamma constant becomes smaller than 1 when the surrounding environment is brighter than the reference luminance, and the gamma constant becomes larger than 1 when it is darker than the reference luminance. This is done.                     

FIG. 5 shows an example in which the gradation display of the displayed image changes in accordance with the change of the gamma constant value.

Compared to the image displayed when the gamma constant has a value of 1, the image is displayed as a whole brighter when the gamma constant has a value smaller than 1, and when the gamma constant has a value greater than 1, the image is displayed as a whole dark. do.

As mentioned above, although embodiment of this invention was described, this invention is not limited only to the above-mentioned embodiment, A various other deformation | transformation and a change are possible.

According to the present invention described above, gamma correction is performed according to the luminance of the surrounding environment, whereby the visibility of the liquid crystal display device can be further improved. Therefore, even when the surrounding environment is dark or bright, the image displayed on the liquid crystal display may be easily identified.

Claims (6)

A plurality of gate lines and data lines are formed in the row and column directions, respectively, and a plurality of pixels having switching elements connected to the gate line and the data line are formed in an area defined by the intersection of the gate line and the data line, respectively. In the drive device of the liquid crystal display device containing the liquid crystal panel, A scan driver supplying a gate voltage to the gate line; A data driver supplying a corresponding gray voltage to the data line according to an applied data signal; A timing controller which generates a digital signal for driving the data driver and scan driver; And A luminance measuring unit for outputting a control signal according to the luminance of the surroundings, and And a gray voltage generator for generating a plurality of gray voltages and supplying them to the data driver and varying a level of the gray voltages in response to a control signal of the luminance measuring unit. The method of claim 1, In normal white mode The potential difference between the gradation voltage and the common electrode voltage when the ambient luminance is greater than the reference value is smaller than the potential difference between the gradation voltage and the common electrode voltage when the ambient luminance is smaller than the reference value, In normal black mode And a potential difference between the gradation voltage and the common electrode voltage when the peripheral luminance is greater than the reference value is greater than a potential difference between the gradation voltage and the common electrode voltage when the peripheral luminance is smaller than the reference value. The method of claim 1, The gray voltage generator A first resistor string generating a plurality of positive gray voltages; A second resistor string generating a plurality of negative gray voltages; A controller configured to vary the amount of current applied to the first resistor string and the second resistor string to vary the positive gray voltage and the negative gray voltage level according to the ambient luminance measured by the brightness measurer; Driving device for a liquid crystal display comprising a. The method of claim 3, The control unit A first variable resistor connected to the reference voltage terminal of the first resistor row; A second variable resistor connected to the reference voltage terminal of the second resistor row; A switch element operated according to the signal output from the luminance measuring unit to vary the amount of current applied to the first and second resistance strings through the first and second variable resistors. Driving device for a liquid crystal display comprising a. The method of claim 3, And the luminance measuring unit is mounted outside the liquid crystal display. The method of claim 3, And the luminance measuring unit is formed of a photodiode or a phototransistor.

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