KR100925469B1 - Driving apparatus of liquid crystal display - Google Patents

Abstract

The present invention relates to a driving device of a liquid crystal display device which can eliminate a wave phenomenon. By using a pulse width modulation signal, which is an inverter control dimming signal, a low gray level voltage is selected during a backlight lighting period, and a high gray level voltage is selected during a backlight lighting period, thereby changing the gray voltage value according to the pulse width modulation signal. It can eliminate the wave phenomenon.

Wave phenomenon, inverter, dimming, frequency, pulse width modulation, data driver, liquid crystal panel assembly, pixel

Description

DRIVING APPARATUS OF 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 an example of a gray voltage generator according to an exemplary embodiment of the present invention.

4 is an example of a gray voltage generator according to another exemplary embodiment of the present invention.

A typical liquid crystal display (LCD) includes an upper panel including a reference electrode, a plurality of color filters, a plurality of thin film transistors, and a plurality of pixel electrodes. and a lower panel on which a pixel electrode and the like are formed. An alignment layer is coated on inner surfaces of the upper panel and the lower panel, and a liquid crystal layer is injected into a gap between the two alignment layers. A voltage is applied to the pixel electrode and the reference electrode. If the voltages applied to the two electrodes are different from each other, an electric field is formed. When the intensity and / or direction of the electric field is changed, the arrangement of the liquid crystal molecules of the liquid crystal layer is changed and thus the transmittance of light passing through the liquid crystal layer is changed. Therefore, a desired image can be obtained by adjusting the voltage difference applied to the pixel electrode and the reference electrode. Such a liquid crystal display is a typical flat panel display, and among these, a TFT LCD using a thin film transistor as a switching element is mainly used.

On the other hand, the active layer forming the channel of the transistor of the TFT LCD is made of a silicon (Si) material such as amorphous silicon (a-Si) or polycrystalline silicon (poly-Si). In particular, the amorphous silicon layer is sensitive to light and thus has a property of a conductor or an insulator upon irradiation with light, causing an increase in overall parasitic capacitance, causing poor image quality.

In the design of TFT LCDs, several light blocking structures are introduced to prevent the amorphous silicon layer from being exposed to light. However, such a light blocking structure is a laminated form, and light reaches the amorphous silicon layer through various reflection paths between the layers. It is most desirable to remove the exposed portions of the amorphous silicon layer between the layers, but there is a problem in that the cost is increased due to the change or addition of a process, and the process simplification structure of the TFT, for example, a four-mask Or particularly in a five-sheet mask process. Therefore, in some regions, exposed portions of the amorphous silicon layer are inevitably present, and in particular, the presence of the amorphous silicon layer under the data line is generally used.

On the other hand, in the above structure, there is no problem in image quality when the backlight light is constantly irradiated. Recently, however, a pulse width modulation (PWM) scheme, which is realized by controlling the blink rate of the lamp itself as a method for increasing the dimming ratio of the backlight device, has been mainly used. In this regard, undesirable phenomena occur in terms of uniformity.

For example, adjusting the brightness of the LCD monitor changes the duty ratio of the PWM signal. In this case, the light-sensitive amorphous silicon layer reacts to the light and affects the charging voltage of the liquid crystal capacitor, that is, the pixel voltage. In other words, the amorphous silicon layer has the properties of a conductor when light is irradiated, and an insulator when there is no light, so that the resistance decreases during the light irradiation and the resistance increases during the absence of light, thereby changing the pixel voltage. Bring. This change in pixel voltage causes a regular flow of bands called water-falls on the screen.

Specifically, when the frame frequency is 60 Hz and the PWM frequency is 180 Hz, the backlight flashes three times in one frame. In this case, the pixel to which the data voltage is applied while the backlight is turned on may appear brighter by increasing the pixel voltage than the pixel to which the data voltage is applied while the backlight is turned off. As a result, three pairs of bright and dark bands are formed on the entire screen, causing a wave phenomenon.

Accordingly, an object of the present invention is to provide a driving device of a liquid crystal display device for removing such a wave phenomenon.

According to an aspect of the present invention, a device for driving a liquid crystal display including a plurality of pixels and a light source for supplying light to the pixels includes a light source controller, a gray voltage generator, and a data driver. . The light source controller generates a light source control signal for controlling the light source, the gray voltage generator generates a plurality of gray voltages whose values change according to the light source control signal, and the data driver generates a gray voltage corresponding to an image signal. Is applied to the pixel as a data voltage.

Here, the gray voltage generator selects a low gray voltage during the lighting period of the light source, and selects a high gray voltage during the light off period of the light source. In this case, the liquid crystal display is preferably in a normally black mode.

The gray voltage generator may select a high gray voltage during the lighting period of the light source and a low gray voltage during the light off period of the light source. In this case, the liquid crystal display may be in a normally white mode.

The light source control signal may be a pulse width modulation signal.

Meanwhile, the plurality of gray voltages include a first gray voltage and a second gray voltage, which are intermediate gray voltages, and the first gray voltage and the second gray voltage include voltages corresponding to the same gray level, respectively. It is preferable that the values of the corresponding voltages are different. Here, each of the first gray voltage and the second gray voltage may include a positive gray voltage and a negative gray voltage.

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.

First, 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.

First, a liquid crystal display according to an exemplary embodiment of the present invention will be described in detail with reference to the 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, a data driver 500, and a data driver 500 connected thereto. The gray voltage generator 800 connected to the 500, the lamp unit 910 for irradiating light to the liquid crystal panel assembly 300, the inverter 920 connected to the lamp unit 910, and the inverter connected to the inverter 920. A control unit 930, and a signal controller 600 for controlling them.

As shown in FIG. 2, the liquid crystal panel assembly 300 includes a lower panel 100 and an upper panel 200 and a liquid crystal layer 3 interposed therebetween, as shown in FIG. 1. Similarly, the equivalent circuit includes a plurality of display signal lines G ₁ -G _n , D ₁ -D _m , and a plurality of pixels connected thereto and arranged in a substantially matrix form.

The display signal lines G ₁ -G _n and D ₁ -D _m are provided on the lower panel 100 and transmit a plurality of gate lines G ₁ -G _n to transfer a gate signal (also called a “scan signal”). And a data signal line or data line D ₁ -D _m for transmitting a data signal. 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 , 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 superimposing 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 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.

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.

The gray voltage generator 800 generates a plurality of gray voltages related to the luminance of the liquid crystal display.

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, selects the gray voltage from the gray voltage generator 800, and uses the data lines D ₁ -D as data signals. _m ).

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

The gate control signal CONT1 includes a vertical synchronization start signal STV for indicating the start of output of the gate-on pulse (high period of the gate signal), a gate clock signal CPV for controlling the output timing of the gate-on pulse, and a gate-on pulse. And an output enable signal OE that defines the width of the signal.                     

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 gray voltage generator 800 generates a plurality of gray voltages related to the luminance of the liquid crystal display and applies them to the data driver 500.

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 equal to one period of the horizontal sync signal Hsync, the data enable signal DE, and the gate clock CPV], and the data driver 400 assigns each data voltage to a corresponding data line 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.

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").

On the other hand, the inverter 920 converts and converts the inverter driving voltage VIN, which is a direct current, into an alternating voltage according to the inverter control signal ICS from the inverter control unit 930 and applies it to the lamp unit 910. Accordingly, each lamp unit 910 blinks and the brightness of the lamp unit 910 is controlled.

The inverter controller 930 compares the feedback signal VFB with the brightness control voltage V _dim and according to the result, an inverter control signal which is a pulse width modulation (PWM) signal that controls the operation of the inverter 920. (ICS) is applied to the inverter 920. In this embodiment, the pulse width modulation signal is also applied to the gray voltage generator 800 to change the voltage values of the positive voltage and the negative voltage according to the signal.

The brightness control voltage V _dim may be directly input from a separate input device that can be adjusted by the user or may be input through the signal controller 600.

The structure and operation of the gray voltage generator will be described in more detail.

3 and 4 are circuit diagrams illustrating an example of a gray voltage generator according to an exemplary embodiment of the present invention.

The gray voltage generator 800 according to an embodiment of the present invention includes a plurality of gray voltage generator circuits. The gray voltage generator according to an embodiment of the present invention includes an inverting amplifier 810, a non-inverting amplifier 830, and a resistor string 850.

As described above, the inverter controller 930 supplies the inverter control signal ICS to the gray voltage generator 800, and an embodiment according to the present invention is a pulse width modulation as the inverter control signal ICS. , PWM) dimming control signal (hereinafter referred to as "PWM signal") is used.

In the drawings, only a part of the resistor string 850 is shown for convenience of description, and there are typically as many resistors as necessary to generate an appropriate number of gray voltages.

3 illustrates a liquid crystal display in a normally black mode, in which the output of the inverting amplifier 810 is connected to the positive gray voltage node N1 of the resistor string 850 and the negative gray scale. The output of the non-inverting amplifier 830 is connected to the voltage node N2. In contrast, the embodiment of FIG. 4 is for the liquid crystal display of the normally white mode, and the output of the non-inverting amplifier 830 is connected to the positive gray voltage node N1 of the resistor string 850 and the negative gray voltage. The output of the inverting amplifier 810 is connected to the node N2.

In the figure, inverting amplifier 810 is shown as an inverter and non-inverting amplifier 830 as a buffer.

The PWM signal is divided into a signal applied through the inverting amplifier 810 and the non-inverting amplifier 830, and is applied to the positive halftone voltage and the negative halftone voltage of the positive polarity. The reason for applying to the halftone voltage is to consider visibility.

In the normally black mode LCD of FIG. 3, the brighter the gray voltage is, the brighter the gray voltage is. In the period in which the PWM signal is high, that is, in the section in which the backlight is turned on, the gray level is applied by applying a low gray level to the gray level voltage of the positive polarity. The voltage value is lowered and the gray level voltage is increased by applying a high inversion signal in a low section, that is, a section where the backlight is turned off. In contrast to the negative gradation voltage, a non-inverting signal is applied.

On the contrary, in the case of the normally white mode liquid crystal display device, which becomes darker as the gray scale voltage of FIG. 4 increases, the voltage value is increased by applying a non-inverting signal high to the gray scale voltage of positive polarity in the period where the PWM signal is high. In the low period, the voltage value is lowered by applying the low, non-inverting signal. In contrast to the negative gradation voltage, an inversion signal is applied.

In this way, the wave phenomenon is eliminated by changing the gray scale voltage value based on the PWM signal.                     

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.

Therefore, the wave phenomenon can be eliminated by changing the gray scale voltage value in accordance with the PWM signal.

Claims (8)

An apparatus for driving a liquid crystal display device comprising a plurality of pixels and a light source for supplying light to the pixels. A light source controller configured to generate a pulse width modulated signal for controlling the light source; A gray voltage generator for generating a plurality of gray voltages whose values change according to the pulse width modulation signal, and A data driver which selects a gray voltage corresponding to an image signal and applies it to the pixel as a data voltage; Containing Driving device for liquid crystal display device. In claim 1, An inverting amplifier inverting the pulse width modulation signal and outputting the inverted signal to a first node; A non-inverting amplifier for outputting the pulse width modulated signal to a second node; A plurality of first resistors connected in series between a first power source and the first node, A plurality of second resistors connected in series between the first node and the second node, and A plurality of third resistors connected in series between the second node and a second power supply lower than the first power supply; Including; The plurality of gray voltages are generated by the plurality of first to third resistors. In claim 2, The liquid crystal display device is a driving device of the liquid crystal display device in a normally black mode. In claim 1, A non-inverting amplifier inverting the pulse width modulation signal and outputting the inverted pulse signal to a first node; An inverting amplifier for outputting the pulse width modulated signal to a second node; A plurality of first resistors connected in series between a first power source and the first node, A plurality of second resistors connected in series between the first node and the second node, and A plurality of third resistors connected in series between the second node and a second power supply lower than the first power supply; Including; The plurality of gray voltages are generated by the plurality of first to third resistors. In claim 4, The liquid crystal display device is a driving device of the liquid crystal display device in a normally white mode. delete In claim 1, The plurality of gray voltages may include a first gray voltage and a second gray voltage which are intermediate gray voltages. The first gray voltage and the second gray voltage include voltages corresponding to the same gray level, and have different values of voltages corresponding to the respective gray levels.  Driving device for liquid crystal display device. In claim 7, And each of the first gray voltage and the second gray voltage includes a positive gray voltage and a negative gray voltage.

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