KR101332062B1 - Liquid Crystal Display Device - Google Patents

Abstract

The present invention provides a liquid crystal display device suitable for preventing the deterioration of color sharpness and the increase of unnecessary load.

A liquid crystal display device includes: a liquid crystal panel having liquid crystal pixels formed in each of regions divided by a plurality of gate lines and a plurality of data lines and connected to a corresponding gate line and a corresponding data line; A data driver to supply pixel driving signals to the data lines in response to pixel data of one line; A voltage generator configured to generate a pre-charge voltage for charging the liquid crystal pixels; A precharge unit configured to charge the pre-charge voltage from the voltage generator to the liquid crystal pixels through the data lines in a period where the pixel driving signals from the data driver are not supplied to the data line; A control switch for switching the pre-charge voltage to be supplied from the voltage generator to the pre-charge unit; And a pre-charge mode control unit for controlling the switching operation of the control switch based on the gray level value of the pixel data for one line to be supplied to the data driver.

Optional, pre-charge, inversion, gray level, power, CR, black, luminance.

Description

Liquid crystal display device with selective pre-charging function

1 is a waveform diagram illustrating a voltage state pre-charged by a pixel on a liquid crystal panel.

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

FIG. 3 is a detailed block diagram illustrating the pre-charge mode controller of FIG. 2 in detail.

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

BRIEF DESCRIPTION OF THE DRAWINGS

10: liquid crystal panel

12: gate driver

14: data driver

16: timing controller

18: pre-charge part

20: pre-charge voltage generator

22: pre-charge mode control unit

30,36: comparator

32: counter

34: latch

SW1: Control switch

The present invention relates to a liquid crystal display device for displaying an image on a liquid crystal panel, and more particularly, to a liquid crystal display device having a function of pre-charging data lines of a liquid crystal panel.

A typical liquid crystal panel adjusts the light transmittance of liquid crystals according to video data so that an image corresponding to the video data is displayed. The liquid crystal panel has a thin thickness and a light weight. In addition, a liquid crystal panel is easier to implement a larger screen than a conventional cathode ray tube. In view of this, liquid crystal panels are used in display devices such as computers and televisions in place of cathode ray tubes.

In order to display an image corresponding to video data, the liquid crystal display includes drive circuits for driving the liquid crystal panel. The liquid crystal panel includes liquid crystal cells arranged in a matrix form. Each of the liquid crystal cells responds to a pixel drive signal from the drive circuit. Each of these liquid crystal cells orientates liquid crystal molecules in a direction corresponding to a potential difference between a pixel driving signal and a common voltage serving as a reference voltage. The amount of light passing through the liquid crystal cell is adjusted in accordance with the alignment direction of the liquid crystal molecules, so that an image is displayed.

The liquid crystal display drives the liquid crystal cells on the liquid crystal panel in an inversion manner so as to suppress generation of afterimages and flicker noise due to the charge and discharge characteristics of the liquid crystal cell. The inversion scheme allows the pixel driving signal to be supplied to the liquid crystal cell to have positive and negative voltages alternately at every frame period based on the reference voltage. As the pixel driving signal alternately has a positive voltage and a negative voltage, power consumed by the liquid crystal panel and its driving circuit is increased, and the response speed of the liquid crystal cell is inevitably slowed.

In order to solve these problems of power consumption and response speed, a charge sharing method is applied to liquid crystal displays. The charge sharing method allows the lines that transfer the pixel drive signal to the liquid crystal cells to share the charge remaining in the idle period when the signal is not transferred to each other, thereby pre-charging to a reference voltage (ie, a common voltage) or a voltage close to the reference voltage. To be. By the charge sharing method, the problem of power consumption and response speed in the liquid crystal display device can be solved to some extent.

However, as the liquid crystal display device starts to display a moving image signal such as a television signal, the occurrence of motion blurring in the image displayed on the liquid crystal panel has intensified. Motion blurring not only degrades the quality of the image but also makes viewing of the image difficult.

In order to minimize the occurrence of the motion blur phenomenon, the liquid crystal display device shortens the period for displaying an image on the liquid crystal panel. In other words, the recent liquid crystal display increases the frame frequency from the existing 60 Hz to 120 Hz so that 120 images are displayed on the liquid crystal panel per second. The increase in the frame frequency not only increases the power consumption but also increases the load on the driving circuit of the liquid crystal panel, thereby generating a lot of heat. The heat may even damage the drive circuit.

In order to solve the heat generation problem and the load of the driving circuit, a pre-charge method in which a predetermined voltage from a separate voltage source separated from the pixel driving signal is charged in advance to the liquid crystal cell (ie, the pixel) is used in the liquid crystal display device. It is introduced. The pre-charging method substantially reduces the load of the driving circuit of the liquid crystal panel and serves as an important factor for solving heat generation in the driving circuit.

In fact, as in the left half of Fig. 1, when a high gradation pixel driving signal is supplied to the liquid crystal cell during the " C " period (i.e., the scanning period), the liquid crystal is separated from a voltage source separate from the driving circuit in the " B " period. The constant voltage charged to the cell substantially reduces the load on the drive circuit. On the other hand, when the pixel driving signal of low gradation (for example, gradation of "0") is applied to the liquid crystal cell, as in the right half of FIG. 1, the liquid crystal cell is charged from a separate voltage source in the "B" period. This constant voltage unnecessarily increases the load of the driving circuit and increases the power consumption. In addition, a constant voltage pre-charged in the liquid crystal cell higher than the voltage of the pixel driving signal increases the luminance of black to deteriorate the color sharpness.

Accordingly, an object of the present invention is to provide a liquid crystal display device suitable for preventing the deterioration of color sharpness.

Another object of the present invention is to provide a liquid crystal display device suitable for preventing an unnecessary increase in load.

Another object of the present invention is to provide a liquid crystal display device suitable for reducing power consumption.

The liquid crystal display according to the embodiment of the present invention for achieving the above object is connected to a corresponding gate line and a corresponding data line in each of the regions divided by a plurality of gate lines and a plurality of data lines. A liquid crystal panel having formed liquid crystal pixels; A data driver to supply pixel driving signals to the data lines in response to pixel data of one line; A voltage generator configured to generate a pre-charge voltage for charging the liquid crystal pixels; A precharge unit configured to charge the pre-charge voltage from the voltage generator to the liquid crystal pixels through the data lines in a period where the pixel driving signals from the data driver are not supplied to the data line; A control switch for switching the pre-charge voltage to be supplied from the voltage generator to the pre-charge unit; And a pre-charge mode control unit for controlling the switching operation of the control switch based on the gradation value of the pixel data for one line to be supplied to the data driver.

According to another exemplary embodiment, a liquid crystal display device includes liquid crystal pixels formed to be connected to a corresponding gate line and a corresponding data line, respectively, in regions divided by a plurality of gate lines and a plurality of data lines. A liquid crystal panel; A data driver to supply pixel driving signals to the data lines in response to pixel data of one line; A voltage generator configured to generate a pre-charge voltage for charging the liquid crystal pixels; A precharge unit configured to charge the pre-charge voltage from the voltage generator to the liquid crystal pixels through the data lines in a period where the pixel driving signals from the data driver are not supplied to the data line; A timing controller controlling operation timing of the data driver and the pre-charge unit; A control switch for switching a timing control signal to be supplied to the pre-charge part from the timing control path; And a pre-charge mode control unit for controlling the switching operation of the control switch based on the gradation value of the pixel data for one line to be supplied to the data driver.

Other objects, other features, and other advantages of the present invention in addition to the above objects will become apparent from the detailed description of the embodiments associated with the accompanying drawings.

Best Mode for Carrying Out the Invention Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

2 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention. 2, a liquid crystal display according to an exemplary embodiment of the present invention includes a gate driver 12 driving a plurality of gate lines GL1 to GLn on the liquid crystal panel 10, and a plurality of liquid crystal panels 10 on the liquid crystal panel 10. A data driver 14 for driving the data lines DL1 to DLm of the data line, and a timing controller 16 for generating a gate control signal and a data control signal for controlling the gate driver 12 and the data driver 14. ).

The plurality of gate lines GL1 to GLn and the plurality of data lines DL1 to DLm are formed to cross each other on the liquid crystal panel 10. The pixel regions are divided by the gate lines GL1 to GLn and the data lines DL1 to DLm. In each of the pixel regions, a pixel including the thin film transistor MT and the liquid crystal cell CLC is formed. The thin film transistor MT includes a gate electrode and a source electrode connected to a corresponding gate line GL and a corresponding data line, respectively. The liquid crystal cell CLc is connected between the drain electrode of the thin film transistor MT and the common electrode Vcom.

The gate driver 12 sequentially and exclusively drives the gate lines GL1 to GLn on the liquid crystal panel 10. To this end, the gate driver 12 sequentially and exclusively applies one horizontal synchronization signal to the gate lines GL1 to GLn on the liquid crystal panel 10 in response to the gate control signal GCS supplied from the timing controller 16. N scan signals are enabled for each period. In other words, the gate driver 124 supplies the gate high voltage Vgh to the first to nth gate lines GL1 to GLn sequentially and alternately for each period of one horizontal synchronization signal.

The data driver 14 generates a plurality of data lines on the liquid crystal panel 10 whenever any one of the gate lines GL1 to GLn is enabled in response to the data control signal DCS generated by the timing controller 16. The pixel driving signal is supplied to each of DL1 to DLm. To this end, the data driver 14 inputs pixel data VDd for one line and converts pixel data VDd for one line into an analog form according to the data control signal. Each of the pixel driving signals converted as described above is supplied to the data line DL on the corresponding liquid crystal panel 10. Then, the thin film transistors MT connected to the enabled gate line GL are turned on so that the pixel driving signal on the corresponding data line DL is charged in the corresponding liquid crystal cell CLc. In addition, the data driver 14 may output the pixel driving signals to be supplied to the data lines DL based on the common voltage Vcom in response to the polarity inversion signal POL from the timing controller 16. Alternate polarity. For example, when the liquid crystal panel 10 is driven in a line inversion manner, all of the pixel driving signals have voltages of opposite polarities as the gate line being enabled is changed (that is, every period of the horizontal synchronization signal). . In addition, all of the pixel driving signals corresponding to the data lines DL1 to DLm have voltages of the same polarity.

The timing controller 16 converts the pixel data from the external video signal source (for example, a graphics card or a television signal recovery unit of a computer system), not shown, by the pixel data VDi and the synchronization signals SYNC by one frame. Enter). The synchronization signals SYNC include a vertical synchronization signal Vsync, a horizontal synchronization signal Hsync, a data enable signal DE, a data clock Dclk, and the like. The timing controller 16 generates the gate control signal GCS and the data control signal DCS by using the data clock Dclk, the horizontal and vertical synchronization signals Hsync and Vsync, and the pixel data by one line. Supply to the data driver 14. One line of pixel data VDd supplied to the data driver 14 includes red, green, and blue pixel data.

The liquid crystal display of FIG. 2 includes a pre-charge unit 18 connected between the data driver 14 and the data lines DL1 to DLm on the liquid crystal panel 10. This pre-charge unit 18

The pre-charge unit 18 may include a pre-charge voltage generator in a period in which the pixel driving signals are not supplied to the data lines DL1 to DLm (for example, a horizontal blanking period of the horizontal synchronization signal Hsync). A constant level of pre-charge voltage from 20 is supplied to the data lines DL1 to DLm. Then, the pixel (ie, the liquid crystal cell CLC) connected to each of the data lines DL1 to DLm is charged with the pre-charge voltage. The pre-charge operation of the pre-charge unit 18 is controlled by the pre-charge control signal PCS from the timing control path 16. The pre-charge control signal PCS is enabled in a specific logic (eg, high logic) state in a period in which the pixel driving signal is not supplied to the data line DL. On the contrary, in the period where the pixel driving signals are supplied from the data driver 18, the pre-charger 18 transfers the supplied pixel driving signals to the data lines DL1 to DLm on the liquid crystal panel 10.

In addition, the liquid crystal display according to the embodiment of the present invention, the control switch (SW1) for switching the pre-charge voltage to be supplied to the pre-charge unit 18 from the pre-charge voltage generator 20; And a pre-charge mode control unit 22 for inputting pixel data VDd for each line from the timing controller 22 together with the data driver 14. The pre-charge mode controller 22 detects whether the average gradation value of pixel data for one line is equal to or less than a constant gradation value. According to the detection result, the pre-charge mode controller 22 turns on or off the control switch SW1 to selectively block the pre-charge voltage to be supplied to the pre-charge unit 18. For example, if the average gradation value of pixel data for one line is lower than a constant gradation value (for example, any one of 25 to 40 gradation values), the pre-charge mode controller 18 switches the control switch SW1. Generate a pre-charge mode control signal PMS of a particular logic (e.g., high logic) that turns off. At this time, the pre-charge voltage to be supplied to the pre-charge part 18 is cut off, so that the pixel (liquid crystal cell CLD) connected to the data line DL on the liquid crystal panel 10 cannot be pre-charged. . Conversely, if the average gradation value of the pixel data for one line is higher than a constant gradation value (for example, any one of 25 to 40 gradation values), the pre-charge mode controller 18 turns the control switch SW1 on. Generate a pre-charge mode control signal PMS of base logic (e.g., low logic) that is turned on. In this case, the pre-charge voltage may be supplied to the pixel (liquid crystal cell CLD) connected to the data line DL on the liquid crystal panel 10 via the control switch SW1 and the pre-charge unit 18. . As a result, the pixel (liquid crystal cell CLD) is charged to a pre-charge voltage of a constant voltage level.

In this case, most of the pixel data of one line are not pre-charged when they have a low gray scale value, and thus are charged to a pre-charge voltage of a level higher than the voltage of the pixel driving signal and discharged to the voltage level of the pixel driving signal again. No action is taken. The power consumption is reduced by unnecessary charge and discharge operations, and the load of the data driver is reduced, thereby reducing the amount of heat generated. In addition, the brightness of black gradations does not increase, and color clarity does not deteriorate.

FIG. 3 is a detailed block diagram illustrating the pre-charge mode controller 22 shown in FIG. 2 in detail. Referring to FIG. 3, the pre-charge mode controller 22 includes a counter 32, a latch 34, and a second comparator 36 connected in series with the first comparator 30. The first comparator 30 compares the gray value of the pixel data input from the timing controller 16 of FIG. 2 with a reference gray value (for example, 50 gray levels) GLref. When the gray scale value of the pixel data is lower than the reference gray scale value, the first comparator 30 generates a first comparison signal of a specific logic (for example, high logic). Conversely, when the gray scale value of the pixel data is higher than the reference gray scale value, the first comparator 30 generates a first comparison signal of the basis logic (eg, the low logic). The reference gradation value is a value obtained through experiments, and pixel data below 50 gradation values as described above does not affect the temperature and does not have a large voltage level. Accordingly, gray scale values of 50 or less may be set as a reference gray scale value for identifying low gray scale pixel data.

The counter 32 is initialized to a value of "0" in the horizontal blanking period of the horizontal sync signal Hsync, and then the counter 32 of the specific logic generated in the first comparator 30 during the scan period of the horizontal sync signal Hsync. Count the number. In other words, the counter 32 counts the number of pixel data having a low gradation (for example, 50 gradations) or less. The period of the count operation is controlled by the data clock Dclk. The latch 34 transmits the number of comparison signals of a particular logic counted by the counter 32 during the horizontal scanning period to the second comparator 36. The transfer of the count value by the latch 34 is performed at the time of the horizontal retrace period. The transfer operation of this latch 34 is controlled by the horizontal synchronizing signal.

The second comparator 36 compares the number of low gradation pixel data counted from the latch 34 with the reference pixel number PNref to detect whether the average gradation value of the pixel data for one line is equal to or less than the low gradation reference value. For example, if the number of counted low gradation pixel data is lower than the reference pixel number, the second comparator 36 determines that the average gradation of pixel data for one line is lower than the low gradation reference value, and thus the pre- Generates a charge mode control signal PMS. On the contrary, if the number of counted low grayscale pixel data is higher than the reference pixel count, the second comparator 36 determines that the average grayscale of one line of pixel data is higher than the low grayscale reference value and thus the pre-charge operation may be performed. Generate a base logic pre-charge mode control signal (PMS). The reference pixel number PNref may be adjusted according to the low gradation reference value, but is preferably set in a range of 50 to 70% of the number of pixels per line. Accordingly, the low gradation reference value is set to any one of the gradation values in the range of approximately 25 to 35.

4 is a block diagram illustrating a liquid crystal display according to another exemplary embodiment of the present invention. In the liquid crystal display of FIG. 4, the control switch SW1 selectively blocks the pre-charge control signal PCS to be supplied from the timing controller 16 to the pre-charge unit 18. Except that the pre-charge voltage from 20 is directly supplied to the pre-charge part 18, it has the same structure as the liquid crystal display of FIG.

Components of FIG. 4 that have the same operations, functions, and effects as those shown in FIG. 2 will be referred to by the same name and reference numerals, and further details will be omitted as will be apparent from the description of FIG. 2.

In Fig. 4, the control switch SW1 is turned off and timing while the pre-charge mode control signal PMS of a specific logic is supplied from the pre-charge mode control section 22 (when low grayscale pixel data is displayed). The precharge control signal PCS to be supplied from the controller 16 to the precharge unit 18 is blocked. At this time, the pre-charge unit 18 cannot perform the pre-charge operation because the pre-charge control signal PCS is not supplied. The pre-charge voltage is also not charged in the pixel (liquid crystal cell). As a result, unnecessary charge / discharge operation of the pixel (ie, the liquid crystal cell) reduces power consumption, thereby reducing the load of the data driver, thereby reducing heat generation. In addition, the brightness of black gradations does not increase, and color clarity does not deteriorate.

As described above, the liquid crystal display and the driving method thereof according to the present invention block the supply of the pre-charge voltage or block the pre-charge control signal when the average gray level value of the pixel data for one line is low. An operation of charging to a pre-charge voltage of a level higher than the voltage of the pixel driving signal and discharging to the voltage level of the pixel driving signal again does not occur. As a result, power consumption due to unnecessary charge / discharge operations is reduced, and as a result, the load of the data driver is reduced, thereby reducing the amount of heat generated. In addition, the brightness of black gradations does not increase, and color clarity does not deteriorate.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, It will be apparent that various modifications, alterations, and other equivalent embodiments are possible without departing from the scope of the present invention. Accordingly, the technical idea and scope of the present invention to be protected must be determined by the appended claims.

Claims (4)

A liquid crystal panel having liquid crystal pixels formed to be connected to a corresponding gate line and a corresponding data line in each of the regions divided by the plurality of gate lines and the plurality of data lines; A data driver to supply pixel driving signals to the data lines in response to pixel data of one line; A voltage generator configured to generate a pre-charge voltage for charging the liquid crystal pixels; A pre-charge unit configured to charge the liquid crystal pixels through the data lines with the pre-charge voltage from the voltage generator in a period where the pixel driving signals from the data driver are not supplied to the data line; A control switch for switching the pre-charge voltage to be supplied from the voltage generator to the pre-charge unit; And And a pre-charge mode control unit for controlling the switching operation of the control switch based on the gradation value of the pixel data for one line to be supplied to the data driver, And the pre-charge mode controller opens the control switch when the average value of pixel data of one line is lower than a low gray scale reference value. delete A liquid crystal panel having liquid crystal pixels formed to be connected to a corresponding gate line and a corresponding data line in each of the regions divided by the plurality of gate lines and the plurality of data lines; A data driver to supply pixel driving signals to the data lines in response to pixel data of one line; A voltage generator configured to generate a pre-charge voltage for charging the liquid crystal pixels; A pre-charge unit configured to charge the liquid crystal pixels through the data lines with the pre-charge voltage from the voltage generator in a period where the pixel driving signals from the data driver are not supplied to the data line; A timing controller controlling operation timing of the data driver and the pre-charge unit; A control switch for switching a timing control signal to be supplied from the timing controller to the pre-charge unit; And And a pre-charge mode control unit for controlling the switching operation of the control switch based on the gradation value of the pixel data for one line to be supplied to the data driver, And the pre-charge mode controller opens the control switch when the average value of pixel data of one line is lower than a low gray scale reference value. delete

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