KR20030046684A - device for driving liquid crystal device - Google Patents

Abstract

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

The present invention provides a gate voltage to a gate line on a liquid crystal panel in which a plurality of gate lines and data lines are formed in row and column directions, respectively, and pixels are formed in regions defined by intersections of the gate lines and data lines. A scan driver; A data driver supplying a corresponding gray voltage to the data line according to an applied data signal; A gray voltage generator generates a plurality of gray voltages and supplies them to the data driver, wherein the gray voltage levels vary according to the ambient temperature.

According to the present invention, the gray scale voltage is changed according to the change in the ambient temperature, so that the same gray scale characteristic can be obtained even if the temperature is changed.

Description

Device for driving liquid crystal device

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 adjusting the intensity of the electric field to adjust the amount of light transmitted through the substrate. 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 means a voltage applied to the source electrode of the thin film transistor to generate gray scale. Gradation is a step-by-step division of the amount of light that a human's vision feels. In an LCD, an image is displayed by artificially adjusting the degree of light passing through a liquid crystal. The voltage is used as the control means, and in general, the transmittance (T) of light of the liquid crystal is changed in a constant relationship according to the magnitude of the voltage (V) applied across the liquid crystal, that is, the intensity of the electric field passing through the liquid crystal. . Therefore, there exists a relationship as shown in FIG. 1 between the voltage across the liquid crystal and the transmittance through which the liquid crystal passes light, and this curve is called a V-T curve.

FIG. 1 is a graph showing V-T characteristics of a conventional liquid crystal display.

In the normal white mode liquid crystal display, when the voltage is initially applied (white) and when a very large voltage (black) is applied, there is little change in transmittance even when the voltage is changed, while in the middle portion It can be seen that the transmittance changes almost in proportion to the voltage to be obtained. The voltage at the point where voltage is first applied and the change in transmittance starts to occur in earnest is called the threshold voltage of the liquid crystal. When this threshold voltage increases, the voltage to be applied to the liquid crystal also increases. do.

In addition, the liquid crystal threshold voltage has a characteristic of decreasing with temperature characteristics, and each time the temperature increases by 1 ° C, the liquid crystal threshold voltage decreases by about 2 to 8 kV depending on the type of liquid crystal. This is because liquid crystals have liquid properties, so when the temperature rises, the viscosity of the liquid decreases, and when the temperature decreases, the viscosity of the liquid increases.

In general, the temperature characteristic of the liquid crystal threshold voltage is -2 to -4 mA / ° C. Since the temperature negative characteristic of such a liquid crystal is a gradation voltage based on a normal temperature of 25 ° C., the same gradation characteristic cannot be obtained at 50 ° C.

That is, in the conventional liquid crystal display device, the threshold voltage of the liquid crystal is changed according to a temperature change, thereby causing a problem in that the same gray scale characteristic cannot be obtained.

Therefore, the technical problem to be achieved by the present invention is to solve the above problems, and the liquid crystal display device to have the same gradation characteristics regardless of the temperature change.

1 is a graph showing the V-T characteristics of a conventional liquid crystal display.

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

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

4 is an output waveform diagram of a gray voltage generator according to an exemplary embodiment of the present invention.

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 gray voltage generator generates a plurality of gray voltages and supplies them to the data driver, wherein the gray voltage levels vary according to the ambient temperature.

The gray voltage generator may include a first resistor string configured to generate a plurality of positive gray voltages, including a plurality of resistors connected in series between a first voltage and a center voltage; A second row of resistors generating a plurality of negative gray voltages, including a plurality of resistors connected in series between the center voltage and the second voltage; And a temperature compensator disposed between the first and second resistor rows to compensate the positive gray voltage and the negative gray voltage by varying a common potential difference, which is a potential difference between the first and second resistor rows, according to an ambient temperature. Include.

Here, the temperature compensator is composed of at least one series connected diode.

Specifically, the temperature compensator may include: first and second diodes positioned between the first resistor string and the center voltage such that the voltage is changed according to a temperature change so that the common potential difference is varied; And third and fourth diodes positioned between the center voltage and the second resistance string so that the voltage is changed according to a temperature change so that the common all positions are varied. Each of these diodes is a forward diode.

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

2 shows 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) and a gradation voltage generator 6.

Herein, a normal white 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 black 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 adaptively according to a temperature change and supplies the gray voltage to the data driver 3.

In the exemplary embodiment of the present invention, the gradation voltage set on the basis of a specific temperature is shifted according to the temperature change so that the gradation characteristic to be displayed on the liquid crystal display is accurately realized.

For example, in the case where the temperature characteristic of the liquid crystal threshold voltage is -2 to -4 Pa / C, and the temperature negative characteristic of such a liquid crystal is set based on the room temperature of 25 C, -2 to -4 Pa / C x (50 C) -25 ° C) = -25 to -100 mA / ° C, and a gradation voltage shift of 25 to 100 mA / ° C is achieved.

3 illustrates the structure of the gray voltage generator according to the exemplary embodiment of the present invention.

The gray voltage generator 6 is connected in series with a plurality of first resistor strings R1 to R5 and the first resistor strings R1 to R5 for generating a positive gray voltage. It is located between the plurality of second resistor rows R6 to R10 and the first resistor rows R1 to R5 and the second resistor rows R6 to R10 that generate a gray voltage of. It includes a temperature compensation unit 61 to perform.

The first resistor strings R1 to R5 are disposed between a first voltage and a center voltage (first voltage> central voltage> second voltage) applied from the outside to generate a plurality of gray voltages for the positive charge of the liquid crystal. A plurality of resistors are connected in series, and the contact point between the first voltage AVDD and each resistor becomes a VREF1 + to VREF5 + gray voltage.

The second row of resistors R6 to R10 are a plurality of resistors connected in series between the center voltage Vcent and the second voltage to generate a plurality of gray voltages for the negative charge of the liquid crystal, and the center voltage Vcent. ) And the contact between each resistor become the VREF6--VREF10- gradation voltage.

The temperature compensator 61 includes a plurality of diodes D1 to D4 having a characteristic in which a voltage is reduced in accordance with a temperature change. The diodes D1 to D4 are PN diodes whose forward voltage characteristics are -2 mA / ° C, which decreases by 2 dB each time they are increased by 1 ° C.

Here, since the temperature characteristic of the liquid crystal threshold voltage is -2 to -4 mA / ° C, four diodes are connected in series so as to double the temperature change rate of the liquid crystal threshold voltage. As a result, the diode temperature change rate is divided by half between the positive gray voltage and the negative gray voltage of the liquid crystal, so that the temperature characteristic and the gray voltage characteristic of the liquid crystal coincide.

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

When the threshold voltage of the liquid crystal display is set at the set temperature and the voltage corresponding to the gray level to be displayed is set accordingly, when the ambient temperature is increased, the first resistance rows R1 to R5 of the gray voltage generator 6 are set. The voltage drop caused by the temperature compensator 61 positioned between the second and second resistor lines R6 to R10 is generated, so that the common potential differences VREF5 to VREF6 vary substantially.

That is, the voltage applied to the first resistor strings R1 to R5 is varied by the voltage drop of the diodes D1 and D2, so that the gray level voltage of the positive polarity generated by the voltage division of the first resistor strings R1 to R5 is changed. The level of (VVREF1 + to VREF5) also varies. In addition, the voltage applied to the second resistor strings R6 to R10 by the voltage drop of the diodes D2 and D4 is also varied, so that the gray scale of negative polarity generated by the voltage division of the second resistor strings R6 to R10 is reduced. The voltages VREF6-VREF10- also vary.

As a result, the positive grayscale voltages VREF7 to VREF9 generated at the contacts of the first to fifth resistors R1 to R5 are reduced to move to the center voltage Vcent, and the sixth to tenth resistors are reduced. The negative gray voltages VREF7 to VREF9 generated at the contacts of R6 to R10 are increased to move to the center voltage Vcent.

At this time, the degree of change in voltage in accordance with the change in the ambient temperature is determined by the number of diodes of the temperature compensator 61, as described above, since the diodes are arranged identically based on the center voltage (Vcent). The rate of temperature change by the diode is equally distributed between the positive gray voltage and the negative gray voltage.

4 is a graph illustrating an output change according to a temperature change of a gray voltage generator according to an exemplary embodiment of the present invention.

As can be seen in FIG. 4, when the temperature increases with respect to room temperature (about 25 ° C.), the positive gray voltage and the negative gray voltage become close to the center voltage (Vcent), and when the temperature decreases, the positive gray voltage and the negative polarity The gray voltage of is away from the center voltage Vcent.

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, the gray scale voltage is changed in accordance with the change in the ambient temperature, so that the same gray scale characteristic can be obtained even if the temperature is changed. Therefore, an image displayed with the same gray scale may be obtained regardless of a change in ambient temperature.

Claims (5)

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 gray voltage generator which generates a plurality of gray voltages and supplies them to the data driver; The gray voltage level is changed in accordance with the ambient temperature driving device of the liquid crystal display device. The method of claim 1, The gray voltage generator, A first resistor string for generating a plurality of positive gray voltages, including a plurality of resistors connected in series between the first voltage and the center voltage; A second row of resistors generating a plurality of negative gray voltages, including a plurality of resistors connected in series between the center voltage and the second voltage; And A temperature compensator configured to compensate the positive gray voltage and the negative gray voltage by varying a common potential difference, which is a potential difference between the first resistor string and the second resistor string, between the first resistor string and the second resistor string according to an ambient temperature; Driving device for a liquid crystal display comprising a. The method of claim 2, And the temperature compensator comprises at least one series-connected diode. The method of claim 2, The temperature compensator First and second diodes positioned between the first resistor string and a center voltage to change a common preposition by changing a voltage according to a temperature change; And Third and fourth diodes positioned between the center voltage and the second resistor string so that the voltage changes according to a temperature change so that the common potential difference is varied; Driving device for a liquid crystal display comprising a. The method according to claim 3 or 4, The diode is a driving device of the liquid crystal display device, characterized in that the forward diode.