KR20080072377A - Liquid crystal display and method for driving the same - Google Patents

Abstract

An LCD device and a driving method thereof are provided to enhance image quality by improving flicker or crosstalk due to non-uniformity of common voltages based on image position. An LCD(Liquid Crystal Display) device includes an LCD panel(110), a first shift register(251), a voltage compensator(252), and a second shift register(253). The LCD panel includes plural feedback common lines. The first shift register receives sequentially display common voltages from the feedback common lines. The voltage compensator generates a feedback common voltage which compensates for the display common voltages using difference between the display common voltages and a reference common voltage. The second shift register sequentially outputs the feedback common voltage to the feedback common lines.

Description

Liquid crystal display and method for driving the same {Liquid crystal display and method for driving the same}

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

FIG. 2 is a detailed configuration diagram of the common voltage corrector shown in FIG. 1.

FIG. 3 is a detailed configuration diagram of the voltage compensator shown in FIG. 2.

4 is a flowchart illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention.

(Explanation of symbols for the main parts of the drawing)

110: liquid crystal panel 210: timing controller unit

220: gate driver 230: data driver

240: power supply unit 250: common voltage correction unit

251: First shift register 252: Voltage compensation unit

253: second shift register

The present invention relates to a liquid crystal display device and a driving method thereof, and more particularly, to a liquid crystal display device and a driving method thereof to which an optimized common voltage is applied.

The liquid crystal display device forms a liquid crystal layer having anisotropic dielectric constant between upper and lower substrates, which are transparent insulating substrates, and then adjusts the intensity of the electric field formed in the liquid crystal layer to change the molecular arrangement of the liquid crystal material, thereby The display device expresses a desired image by adjusting the amount of light transmitted through the upper substrate. As a liquid crystal display device, a thin film transistor liquid crystal display device (TFT LCD) using a thin film transistor (TFT) as a switching element is mainly used.

Such a liquid crystal display is largely divided into a liquid crystal panel for displaying an image and a driver for driving the liquid crystal panel.

Looking at the equivalent circuit of each pixel constituting the liquid crystal panel, a gate line and a data line are formed to cross each other, a thin film transistor and a pixel electrode are disposed at the intersection, and a liquid crystal capacitor, a storage capacitor, and the like are formed in units of pixels.

The equivalent circuit of each pixel comprised in this way operates as follows.

First, when a scan signal is applied and the thin film transistor is turned on, a data voltage corresponding to video data of each pixel is selected and applied to each pixel from the data line. The video data is a digital signal representing gray levels, and is generally set to have a value between 0 and 255.

Then, an electric field generated by the difference between the data voltage and the common voltage applied to each pixel is supplied to the liquid crystal capacitor to transmit light with a transmittance corresponding to the intensity of the electric field. At this time, the storage capacitor maintains the data voltage applied to the pixel for one frame period. The data voltage applied through the data line is generally applied while the positive voltage and the negative voltage are switched around the common voltage to reduce the flicker phenomenon.

Each pixel operates individually according to the applied data voltage. The common voltage becomes the center potential of the pixel when driven in pixel units. Therefore, to improve image quality, the same common voltage is applied to all pixels regardless of the position of the liquid crystal panel. It must be authorized.

However, since the common voltage is generally applied from one side of the liquid crystal panel and transferred to the other side, the level of the common voltage applied to each pixel is substantially changed according to the position of the liquid crystal panel, so that crosstalk, There is a problem that a defect such as flicker occurs.

In particular, as the liquid crystal display becomes larger and the resolution becomes higher, such defects become more severe and cause deterioration of image quality.

Accordingly, an object of the present invention is to provide a liquid crystal display and a driving method thereof capable of minimizing the variation of the common voltage according to the position of the liquid crystal panel.

Another object of the present invention is to provide a liquid crystal display and a method of driving the same, which can improve image quality by improving defects such as flicker and crosstalk caused by unevenness of common voltage when implementing a large screen.

Technical problems to be achieved by the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned above will be clearly understood by those skilled in the art from the following description. Could be.

According to an aspect of the present invention, there is provided a liquid crystal display device including: a liquid crystal panel in which a plurality of feedback common lines are arranged; a first shift register sequentially receiving a display common voltage from the plurality of feedback common lines; A voltage compensator for generating a feedback common voltage for correcting the display common voltage using a difference between a display common voltage and a reference common voltage, and a second shift for sequentially outputting the feedback common voltage to the plurality of feedback common lines Contains registers

According to an exemplary embodiment of the present invention, a method of driving a liquid crystal display includes sequentially receiving a display common voltage output from a plurality of feedback common lines disposed on a liquid crystal panel by a first shift register, and wherein the voltage compensator is configured to receive the display common voltage and the reference. Generating a feedback common voltage for correcting the display common voltage using a difference of the common voltage, and sequentially outputting the feedback common voltage to the plurality of feedback common lines by a second shift register.

Specific details of other embodiments are included in the detailed description and the drawings. Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. Like reference numerals refer to like elements throughout.

Hereinafter, a liquid crystal display according to an exemplary embodiment and a driving method thereof will be described in detail with reference to the accompanying drawings.

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

Referring to FIG. 1, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal panel 110, a timing controller 210, a gate driver 220, a data driver 230, a power supply 240, and a common controller. And a voltage corrector 250.

The liquid crystal panel 110 includes a plurality of pixels separated by gate lines GL1, GL2,... GLn and data lines DL1, DL2... DLm that cross each other. Although not shown, a thin film having a gate electrode, an active layer, a source electrode, and a drain electrode at the intersection of the gate lines GL1, GL2, ..., GLn and the data lines DL1, DL2, ..., DLm. The transistor TFT is disposed.

Each pixel is filled with a liquid crystal material equivalent to the liquid crystal cell Clc, and a storage capacitor Cst is formed to maintain a constant voltage charged in the liquid crystal cell Clc.

The liquid crystal panel 110 is sequentially shifted and scan signals supplied through the gate lines GL1, GL2, ..., GLn and data voltages supplied through the data lines DL1, DL2, ..., DLm. As a result, an image is displayed on each pixel. Here, the scan signal is a pulse signal in which the gate high voltage VGH supplied only for one horizontal period and the gate low voltage VGL supplied for the remaining period are alternated.

The thin film transistor TFT is turned on when the gate high voltage VGH is supplied from the gate lines GL1, GL2,..., GLn, and is transferred from the data lines DL1, DL2,..., DLm. The data voltage is supplied to the liquid crystal cell Clc.

Although not shown, the liquid crystal cell Clc is formed between the pixel electrode to which the data voltage is applied from the data lines DL1 to DLm and the common electrode to which the common voltage is applied. When the thin film transistor TFT of each pixel is turned on and a data voltage is applied to the pixel electrode, an image is displayed while the liquid crystal cell Clc is charged with a difference voltage between the data voltage and the common voltage.

When the gate low voltage VGL is supplied from the gate lines GL1, GL2,..., GLn, the thin film transistor TFT is turned off and the data voltage charged in the liquid crystal cell Clc is stored in the storage capacitor ( Cst) for one frame period.

The gate driver 220 supplies a scan signal sequentially shifted to the gate lines GL1, GL2,..., GLn according to the gate control signal GCS supplied from the timing controller 210.

The data driver 230 stores red, green, and blue video data (R, G, B) input from the timing controller 210 in response to the data control signal DCS supplied from the timing controller 210. It converts to voltage and supplies it to the data lines DL1, DL2, ..., DLm. The data voltage is a gamma voltage selected in response to the red, green, and blue video data R, G, and B that are input from the outside among the gamma voltages Vgma of the various levels supplied from the gamma voltage generator 241. .

The timing controller 210 rearranges the red, green, and blue video data R, G, and B input from the outside and supplies the rearranged video data to the data driver 230. In addition, the driving timing of the gate control signal GCS and the data driving 230 for controlling the driving timing of the gate driver 220 are controlled by using the vertical and horizontal synchronization signals Vsync and Hsync and the clock CLK. A data control signal DCS is generated.

The gate control signal GCS includes a gate start pulse (GSP), a gate shift clock (GSC), a gate output enable signal (GOE), and the like. The data control signal DCS includes a source start pulse (SSP), a source shift clock (SSC), a source output enable (SOE), and a polarity signal (POL). Etc. are included.

The power supply unit 240 includes a gamma voltage generator 241, a gate voltage generator 242, and a common voltage generator 243.

The gamma voltage generator 241 compensates the gamma characteristics of the liquid crystal panel 110. The gamma voltage generator 241 generates gamma voltages Vgma of various levels required for the digital / analog conversion of the data driver 230 within the gray scale, for each gray level. To the data driver 230.

The gate voltage generator 242 generates a gate high voltage VGH and a gate low voltage VGL for turning on and off the thin film transistor TFT and supplies the generated gate high voltage VGH to the gate driver 220.

The common voltage generator 243 generates a common voltage Vcom serving as a center potential of the pixel driving and supplies the generated common voltage Vcom to the common voltage corrector 250.

The common voltage corrector 250 receives the common voltage Vcom from the common voltage generator 243. In addition, while receiving feedback of the change of the display common voltage Vcom_out at regular intervals from various feedback points of the liquid crystal panel 110, the LCD panel 110 adjusts the feedback voltage to a constant level of the feedback common voltage Vcom_in to adjust the liquid crystal panel 110. Feed back to each feedback point.

FIG. 2 is a detailed configuration diagram of the common voltage corrector shown in FIG. 1, and FIG. 3 is a detailed configuration diagram of the voltage compensator shown in FIG. 2.

Referring to FIG. 2, a plurality of feedback common lines CL1, CL2,..., And CLk are disposed on the liquid crystal panel 110, and the feedback common lines CL1, CL2,. The connected common voltage corrector 250 includes a first shift register 251, a voltage compensator 252, and a second shift register 253.

The first shift register 251 sequentially receives the display common voltage Vcom_out from the plurality of feedback common lines CL1, CL2,..., CLk and provides the voltage to the voltage compensator 252.

The voltage compensator 252 uses the difference between the display common voltage Vcom_out output from the first shift register 251 and the reference common voltage Vcom provided from the common voltage generator 243 to determine the display common voltage ( The feedback common voltage Vcom_in is generated by correcting Vcom_out).

The second shift register 253 receives the feedback common voltage Vcom_in from the voltage compensator 252, and receives the feedback common voltage Vcom_in from the plurality of feedback common lines CL1, CL2,..., CLk. Will be printed sequentially.

Here, a plurality of feedback common lines CL1, CL2,..., And CLk are disposed on the liquid crystal panel 110, and optimum feedback common to each of the common lines CL1, CL2,..., CLk. As the voltage Vcom_in is applied and a feedback of the display common voltage Vcom_out periodically output from the liquid crystal panel 110 is made according to the control clock, a constant level of common voltage is continuously applied to the liquid crystal panel 110. do.

As described above, the common voltage corrector 250 receives the display common voltage Vcom_out of each feedback common line CL1, CL2,..., CLk in accordance with the control clock through the first shift register 251. This is transferred to the voltage compensator 252. Thereafter, the feedback common voltages Vcom_in are generated by comparing them with the reference common voltage Vcom in order so that the common voltages applied to the respective feedback common lines CL1, CL2,..., And CLk can be maintained at a constant level. do.

The number of bits Bit of the first shift register 251 and the second shift register 253 is equal to the number of the plurality of feedback common lines CL1, CL2,..., CLk arranged in the liquid crystal panel 110. Can be determined. The feedback common lines CL1, CL2, ..., CLk and each bit of the first and second shift registers 251, 253 correspond one-to-one (1: 1) or one-to-many (1: multi). Can correspond.

The frequency of the control clock may vary depending on the correction period (one horizontal period, one frame period, etc.) of the common voltage. For example, when the common voltage is to be compensated for every one frame period (for example, 1/60 sec), the control clocks of the first shift register 251 and the second shift register 253 may be controlled. Is used in synchronism with the clock CLK inputted to the timing controller 210 from FIG.

FIG. 3 is a detailed configuration diagram of the voltage compensator shown in FIG. 2.

The voltage compensator 252 includes a differential amplifier circuit for amplifying a voltage corresponding to a difference between the display common voltage Vcom_out and the reference common voltage Vcom. The voltage compensator 252 applies a compensation circuit using inverted amplification to the liquid crystal panel 110. Minimize fluctuations in the common voltage occurring at

The differential amplifier circuit forming the voltage compensator 252 may be configured using an operational amplifier OP and resistors R1 and R2.

The reference common voltage Vcom provided from the common voltage generator 243 is applied to the positive input terminal of the operational amplifier OP, and the first resistor R1 is applied to the negative input terminal of the associative amplifier OP. One side of is connected, and the display common voltage Vcom_out provided from the first shift register 251 is applied to the other side of the connected first resistor R1.

The second resistor R2 is connected between the negative input terminal and the output terminal of the operational amplifier OP.

The display common voltage Vcom_out is sequentially output from the first shift register 251 to the operational amplifier OP in accordance with the control clock, and the operational amplifier OP is input to the input display common voltage Vcom_out and the reference common voltage Vcom. Compare the to compensate for the difference.

When the display common voltage Vcom_out input from the first shift register 251 is greater than the reference common voltage Vcom provided from the common voltage generator 243, the differential amplifier circuit constituting the voltage compensator 252 is larger. A negative voltage is provided to generate a feedback common voltage Vcom_in which reduces the display common voltage Vcom_out. When the display common voltage Vcom_out provided from the first shift register 251 is smaller than the reference common voltage Vcom input from the common voltage generator 243, the display common voltage Vcom_out is provided by providing a positive voltage. To generate a feedback common voltage Vcom_in.

The voltage of which the difference of the common voltage amplified by the voltage compensator 252 is compensated for, that is, the magnitude of the feedback common voltage Vcom_in may be adjusted by the ratio R2 / R1 of the resistors.

The voltage compensator 252 continuously receives the display common voltage Vcom_out applied to the input terminal from the liquid crystal panel 110 through the first shift register 251 and adjusts the compensation ratio R2 / R1 to the output terminal. By outputting the feedback common voltage Vcom_in that compensates for the display common voltage Vcom_out, the feedback voltage is controlled at a constant level while feeding back the variation of the common voltage generated on the liquid crystal panel 110.

Here, the display common voltage Vcom_out is a common voltage input from the liquid crystal panel 110 to the voltage compensator 252 via the first shift register 251, and the feedback common voltage Vcom_in is the voltage compensator 252. ) Is a common voltage fed back to the liquid crystal panel 110 via the second shift register 253.

The first shift register 251 and the second shift register 253 have a plurality of common lines CL1 and CL2 arranged in the liquid crystal panel 110 for a predetermined period (one horizontal period, one frame period, etc.) according to the control clock. The display common voltage Vcom_out provided from, ..., CLk is input, compensated for, and output as a feedback common voltage Vcom_in.

4 is a flowchart illustrating a method of driving a liquid crystal display according to an exemplary embodiment of the present invention, based on the liquid crystal display of FIGS. 1 to 3.

First, in step S110, the timing controller 210 generates a gate control signal GCS and a data control signal DCS for controlling the driving timing of the gate driver 220 and the data driver 230, respectively.

Next, in operation S120, the common voltage compensator 252 uses the display common voltage Vcom_out input from the feedback common lines CL1, CL2,..., CLk to provide feedback common to the liquid crystal panel 110. The voltage Vcom_in is determined and the determined feedback common voltage Vcom_in is supplied back to the feedback common lines CL1, CL2,..., CLk of the liquid crystal panel 110.

The step S120 is subdivided into steps S121 to S123.

First, in operation S121, the first shift register 251 of the common voltage compensator 252 is output from the plurality of feedback common lines CL1, CL2,..., CLk arranged in the liquid crystal panel 110. The common voltage Vcom_out is sequentially input.

In operation S122, the voltage compensator 252 generates a feedback common voltage Vcom_in for correcting the display common voltage Vcom_out by using a difference between the display common voltage Vcom_out and the reference common voltage Vcom. .

In operation S123, the second shift register 253 sequentially outputs the feedback common voltage Vcom_in to the plurality of feedback common lines CL1, CL2,..., CLk.

Here, the first shift register 251 periodically receives the display common voltage Vcom_out output from the feedback common lines CL1, CL2,..., And CLk of the liquid crystal panel 110 by a control clock. The second shift register 253 periodically outputs the feedback common voltage Vcom_in by the control clock to periodically correct the common voltage of the liquid crystal panel 110.

The correction period of the common voltage is determined according to the frequency of the control clock, and the correction period of the common voltage may be adjusted in one horizontal period and one frame period by changing the control clock.

Next, in step S130, the gate driver 220 supplies a scan signal to the gate lines GL1, GL2,... GLn of the liquid crystal panel 110 according to the gate control signal GCS.

Next, in step S140, the data driver 230 supplies the data voltages to the data lines DL1, DL2,..., DLm of the liquid crystal panel according to the data control signal DCS.

Next, in step S150, the thin film transistor TFT of each pixel is turned on for one horizontal period according to the scan signal supplied from the gate lines GL1, GL2,..., GLn, and the thin film transistor TFT In the turn-on state, the liquid crystal cell Clc of each pixel is charged with a difference voltage between the data voltage and the feedback common voltage Vcom_in to display an image for each pixel.

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. I can understand that.

Therefore, since the embodiments described above are provided to completely inform the scope of the invention to those skilled in the art, it should be understood that they are exemplary in all respects and not limited. The invention is only defined by the scope of the claims.

According to the present invention made as described above, the deviation of the common voltage according to the position on the screen can be minimized, and when the large screen is implemented, defects such as flicker or crosstalk caused by unevenness of the common voltage are improved to improve image quality. Can be improved.

Claims (10)

A liquid crystal panel in which a plurality of feedback common lines are arranged; And A first shift register receiving a display common voltage sequentially from the plurality of feedback common lines; A voltage compensator configured to generate a feedback common voltage for correcting the display common voltage by using a difference between the display common voltage and a reference common voltage; And A second shift register configured to sequentially output the feedback common voltage to the plurality of feedback common lines Liquid crystal display comprising a. The method of claim 1, The first shift register and the second shift register, And the number of bits is determined by the number of the plurality of feedback common lines. The method of claim 1, The first shift register and the second shift register, The control clock is determined according to the correction period of the common voltage. The method of claim 3, The correction period of the common voltage is, It is one frame period, The liquid crystal display device characterized by the above-mentioned. The method of claim 1, The voltage compensator, When the display common voltage is greater than the reference common voltage, the display common voltage is decreased. And when the display common voltage is smaller than the reference common voltage, increasing the display common voltage. The method of claim 1, The voltage compensator, And a differential amplifier circuit for amplifying a voltage corresponding to a difference between the display common voltage and the reference common voltage. Sequentially receiving a display common voltage output from the plurality of feedback common lines arranged on the liquid crystal panel by the first shift register; Generating, by the voltage compensator, a feedback common voltage for correcting the display common voltage using a difference between the display common voltage and a reference common voltage; And A second shift register sequentially outputting the feedback common voltage to the plurality of feedback common lines Method of driving a liquid crystal display comprising a. The method of claim 7, wherein The first shift register, And a display clock voltage is periodically input by a control clock. The method of claim 7, wherein The second shift register, And periodically correcting the common voltage of the liquid crystal panel by periodically outputting the feedback common voltage by a control clock. The method of claim 9, The correction period of the common voltage is, It is one frame period, The driving method of the liquid crystal display device characterized by the above-mentioned.

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