KR20080013190A - Driver and liquid crystal display - Google Patents

Abstract

A driver and a liquid crystal display device are provided to improve image quality by preventing afterimages from a displayed image on the LCD(Liquid Crystal Display) device. An LCD driver includes a detector(710), a feedback signal output unit(720), and a gate-off voltage output unit(730). The detector is electrically connected to a gate line. The detector detects a voltage level of a gate-off voltage which is applied on the gate line, and outputs a detection signal. The feedback signal output unit outputs the feedback signal whose voltage level is varied in response to the detection signal. The gate-off voltage output unit outputs the compensated gate-off voltage according to a voltage level of the feedback signal. The detector includes a TFT with a gate electrode. The gate electrode of the TFT(Thin Film Transistor) is electrically connected to the gate line.

Description

Driver and liquid crystal display

1 is a block diagram illustrating a driving apparatus according to an embodiment of the present invention.

FIG. 2 is an internal circuit diagram of the sensing unit of FIG. 1.

3A is an internal circuit diagram of the feedback signal output unit of FIG. 1.

3B is an equivalent circuit diagram for describing a feedback signal output unit when the sensing signal of FIG. 3A is at a first level.

3C is an equivalent circuit diagram for describing a feedback signal output unit when the sensing signal of FIG. 3A is at a second level.

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

FIG. 5 is an equivalent circuit diagram of one pixel of FIG. 4.

6 is an internal circuit diagram of the sensing unit of FIG. 4.

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

10: liquid crystal display device 100: first display panel

150: liquid crystal layer 200: second display panel

300: liquid crystal panel assembly 400: gate driver

500: data driver 600: signal controller

700: drive unit 710: detection unit

720: feedback signal output unit 730: gate off voltage output unit

800: gray voltage generator

The present invention relates to a drive device and a liquid crystal display device, and more particularly, to a drive device and a liquid crystal display device that can improve the display quality by preventing afterimages.

The liquid crystal display includes a liquid crystal panel including a thin film transistor, a first display panel including a pixel electrode, a second display panel provided with a common electrode, and a liquid crystal layer having dielectric anisotropy injected between the first and second display panels. And a driving device for generating a gate on voltage and a gate off voltage for turning on or off the thin film transistor.

In the first display panel, a plurality of gate lines and a plurality of data lines are disposed, for example, in a matrix form, and the thin film transistor is positioned in an area where each gate line and each data line cross each other. Each gate line is connected to a gate electrode of each thin film transistor, and a gate on voltage or a gate off voltage is applied to each gate line.

When the gate-off voltage is applied, the thin film transistor is turned off. The gate-off voltage applied to the gate line may change due to a deviation in device values or a problem on the liquid crystal panel, and the variation in the gate off voltage causes an afterimage of the liquid crystal panel. Let's do it.

The technical problem to be solved by the present invention is to provide a driving apparatus which can improve display quality.

Another object of the present invention is to provide a liquid crystal display device capable of improving display quality.

The technical problem of the present invention is not limited to the technical problem mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a driving apparatus including: a sensing unit electrically connected to a gate line and sensing a voltage level of a gate-off voltage applied to the gate line to output a sensing signal; A feedback signal output unit configured to output a feedback signal having a variable voltage level in response to the sensing signal, and a gate off voltage output unit configured to output a gate off voltage corrected according to the voltage level of the feedback signal.

According to another aspect of the present invention, a liquid crystal display device includes a plurality of gate lines, a plurality of data lines, and a plurality of switching elements electrically connected to the gate lines and the data lines. A sensing unit electrically connected to the liquid crystal panel and the gate lines, the sensing unit sensing a voltage level of each gate line and outputting a sensing signal, and outputting a feedback signal having a voltage level varying in response to the sensing signal. And a driving device including a feedback signal output unit and a gate off voltage output unit configured to output a gate off voltage according to the voltage level of the feedback signal.

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. The embodiments disclosed below relate to a driving device and a liquid crystal display, but the present invention is not limited thereto and may be implemented as various display devices for displaying image information using a driving voltage such as an organic EL and a driving device used therein. The present embodiments are merely provided to complete the disclosure of the present invention and to fully inform the scope of the invention to those skilled in the art to which the present invention pertains. It is only defined by Like reference numerals refer to like elements throughout.

1 is a block diagram illustrating a driving apparatus according to an embodiment of the present invention.

The driving apparatus 700 according to an exemplary embodiment of the present invention illustrated in FIG. 1 senses the gate off voltages Vg1,..., Vgn applied to a gate line (not shown), and senses the sensed gate off voltages Vg1. When Vgn is not a voltage level for completely turning off a plurality of switching elements (not shown) on the liquid crystal panel (not shown), the voltage is corrected by correcting the levels of the gate-off voltages Vg1, ..., Vgn. The gate off voltage Voff 'is output. The driving device 700 outputs a corrected gate-off voltage Voff 'that completely turns off a plurality of switching elements (not shown) on the liquid crystal panel (not shown), thereby reducing afterimages of the liquid crystal panel (not shown). , Improve the display quality.

Specifically, referring to FIG. 1, the driving apparatus 700 includes a sensing unit 710, a feedback signal output unit 720, and a gate off voltage output unit 730.

The sensing unit 710 is electrically connected to a gate line (not shown) on the liquid crystal panel (not shown), and detects the gate off voltages Vg1,..., And Vgn applied to each gate line (not shown). Outputs (SIG). The sensing signal SIG may include a plurality of voltages Vg1,..., And Vgn of the gate-off voltages applied to the gate lines (not shown), and are electrically connected to gate lines (not shown) on the liquid crystal panel (not shown). This signal indicates whether or not the voltage level is to completely turn off the switching element. For example, when the sensed gate off voltages Vg1, ..., Vgn are voltage levels that completely turn off a plurality of switching elements (not shown), the sense signal SIG is high level, otherwise it is low. May be a level. Internal circuits and specific operations of the sensing unit 710 will be described later with reference to FIG. 2.

The feedback signal output unit 720 outputs a feedback signal FB having a variable voltage level in response to the sensing signal SIG provided from the sensing unit 710. The feedback signal FB determines the voltage level of the corrected gate off voltage Voff '. That is, the feedback signal output unit 720 may output the feedback signal (i) to output the corrected gate-off voltage Voff 'of a voltage level that completely turns off the plurality of switching elements (not shown) according to the sensing signal SIG. FB). An internal circuit and a detailed operation of the feedback signal output unit 720 will be described later with reference to FIGS. 3A to 3B.

The gate off voltage output unit 730 receives the feedback signal FB and outputs a corrected gate off voltage Voff '. The corrected gate off voltage Voff 'varies with the voltage level of the feedback signal FB. Here, the internal circuit of the gate off voltage output unit 730 is not limited, and may be a known gate off voltage output circuit.

Here, the sensing unit 710 of FIG. 1 will be described in detail with reference to FIG. 2. FIG. 2 is an internal circuit diagram of the sensing unit of FIG. 1.

Referring to FIG. 2, the sensing unit 710 includes a plurality of sub sensing units 710_1,..., 710_n that sense voltage levels of gate-off voltages applied to each gate line (not shown). For example, the first sub detector 710_1 may include the thin film transistor DUMMY_TFT and the comparator CPR.

 The gate electrode of the thin film transistor DUMMY_TFT is electrically connected to a first gate line (not shown) to receive a gate off voltage Vg1 applied to the first gate line (not shown). The thin film transistor DUMMY_TFT may be the same thin film transistor, for example, an a-Si TFT, as a plurality of switching elements (not shown) on a liquid crystal panel (not shown).

When the gate off voltage Vg1 applied to the first gate line (not shown) is a voltage level at which the plurality of switching elements (not shown) electrically connected to the first gate line (not shown) are not completely turned off, The thin film transistor DUMMY_TFT also does not turn off completely. At this time, the first node N1 is at a high level. That is, the thin film transistor DUMMY_TFT is turned on to apply the first DC voltage Vdc1 to the first node N1.

On the other hand, when the gate off voltage Vg1 applied to the first gate line (not shown) is a voltage level when the plurality of switching elements (not shown) electrically connected to the first gate line (not shown) are completely turned off. The thin film transistor DUMMY_TFT is also completely turned off. At this time, the first node N1 is at a low level.

Here, the first node N1 is electrically connected to the input of the comparator CPR. That is, the thin film transistor DUMMY_TFT provides the comparator CPR with the high or low level state signals SS1,..., And SSn according to the gate-off voltages Vg1,..., And Vgn.

The comparator CPR compares the high level or low level state signals SS1,..., SSn from the thin film transistor DUMMY_TFT with a reference signal to output the sensing signal SIG of the first level or the second level. Here, the comparator CPR may be an operational amplifier, the reference signal may be a ground voltage, the swing range of the output of the comparator CPR is 0V to a second DC voltage Vdc2, and the lower limit is a negative voltage lower than 0V. It could be

In detail, the comparator CPR may receive the state signals SS1,..., And SSn through the positive input (+), and the ground voltage through the negative input (−). The detection signal SIG becomes the second DC voltage Vdc2 when the status signals SS1, ..., SSn are at the high level, and the detection signal SIG is the low level when the status signals SS1, ..., SSn are at the low level. It becomes the ground voltage.

Meanwhile, although the first to nth sub-sensing units 710_1 to 710_n each include a comparator CPR, the comparators CPR may be removed.

The feedback signal output unit of FIG. 1 will be described with reference to FIGS. 3A to 3C. 3A is an internal circuit diagram of the feedback signal output unit of FIG. 1, FIG. 3B is an equivalent circuit diagram for describing a feedback signal output unit when the sensing signal of FIG. 3A is at a first level, and FIG. 3C is a circuit diagram of FIG. It is an equivalent circuit diagram for demonstrating the feedback signal output part in case of two levels.

Referring to FIG. 3A, the feedback signal output unit 720 includes a first feedback signal output unit including a first switching element SW_N and a digital variable resistor DVR that are enabled for the first level sensing signal SIG. The second feedback signal output unit 720 and the common resistor R2 including the second switching element SW_P and the fixed resistor R1 enabled at 720_1 and the sensing signal SIG of the second level. Include. Hereinafter, the first switching device SW_N is an N-MOS, the second switching device SW_P is a PMOS, a first level is a high level, and a second level is a low level. The case is described as an example.

First, when the first feedback signal output unit 720_1 is described, when the detection signal SIG of the first level is input, the second switching device SW_P is turned off and the first switching device SW_N is turned on. This can be represented by the equivalent circuit shown in FIG. 3B. That is, the digital variable resistor DVR and the common resistor R2 are connected in series between nodes to which the third DC voltage Vdc3 and the fourth DC voltage Vdc4 are respectively applied, and the feedback is performed at the second node N2. The signal FB is output.

Here, the resistance value of the digital variable resistor (DVR) changes according to an external resistance control signal, and the voltage level of the feedback signal (FB) is determined according to the resistance ratio of the digital variable resistor (DVR) and the common resistor (R2). . The apparatus may further include a resistance adjustment signal providing unit (not shown) that provides a resistance adjustment signal to adjust the resistance value of the digital variable resistor (DVR).

Referring to the second feedback signal output unit 720_2, when the second level detection signal SIG is input, the second switching device SW_P is turned on and the first switching device SW_N is turned off. It can be represented by the equivalent circuit shown in Figure 3c. That is, the fixed resistor R1 and the common resistor R2 are connected in series between the nodes to which the third DC voltage Vdc3 and the fourth DC voltage Vdc4 are applied, respectively, and the feedback signal at the second node N2. (FB) is output. The fixed resistor R1 and the common resistor R2 are both resistors having fixed resistances, and the voltage level of the feedback signal FB is determined according to the resistance ratio between the fixed resistor R1 and the common resistor R2.

When the sensing unit (see 710 of FIG. 1) provides the sensing signal SIG of the first level, that is, when a plurality of switching elements (not shown) on the liquid crystal panel (not shown) are not completely turned off, 1 The feedback signal output unit 720 provides a feedback signal FB, where the feedback signal FB is a signal whose voltage level is adjusted by a resistance value of the digital variable resistor DVR. When the level of the feedback signal FB is adjusted, the gate off voltage output unit 730 changes the voltage level accordingly and outputs the corrected gate off voltage Voff '. That is, a plurality of switching elements (not shown) on the liquid crystal panel (not shown) are corrected to a voltage level capable of turning off completely.

When the sensing unit (see 710 of FIG. 1) provides the sensing signal SIG of the second level, that is, when a plurality of switching elements (not shown) on the liquid crystal panel (not shown) are completely turned on, the second The feedback signal output unit 720 provides the feedback signal FB, where the feedback signal FB is a signal determined according to a resistance ratio between the fixed resistor R1 and the common resistor R2, and the feedback signal FB. Is not changed and becomes a signal of a constant level. In this case, the gate-off voltage output unit 730 maintains the output voltage level without changing the voltage level.

According to such a driving apparatus (see 700 of FIG. 1), a corrected gate off voltage (see Voff ′ of FIG. 1) is provided to a plurality of switching elements (not shown) on a liquid crystal panel (not shown). (Not shown) may be completely turned off to prevent afterimages.

Hereinafter, a liquid crystal display according to an exemplary embodiment of the present invention will be described with reference to FIGS. 4 to 6. 4 is a block diagram illustrating a liquid crystal display according to an exemplary embodiment of the present invention, FIG. 5 is an equivalent circuit diagram of one pixel of FIG. 4, and FIG. 6 is an internal circuit diagram of the sensing unit 710 of FIG. 4. . Components having substantially the same functions as those of FIGS. 1 to 3C have the same reference numerals, and detailed descriptions of the components will be omitted for convenience of description.

Referring to FIG. 4, the liquid crystal display 10 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. And a gray voltage generator 800 connected to the signal, and a signal controller 600 and a driving device 700 for controlling the gray voltage generator 800.

The liquid crystal panel assembly 300 includes a plurality of display signal lines G1 -Gn and D1 -Dm and a plurality of pixels PX connected to the display signal lines G1 -Gn and D1 -Dm and arranged in a matrix form.

The display signal lines G1 -Gn and D1 -Dm include a plurality of gate lines G1 -Gn for transmitting a gate signal and a plurality of data lines D1 -Dm for transmitting a data signal. The gate lines G1 -Gn extend substantially in the row direction and are substantially parallel to each other, and the data lines D1 -Dm extend substantially in the column direction and are substantially parallel to each other.

Here, referring to FIG. 5, one pixel PX includes a first display panel 100, a second display panel 200, and a liquid crystal layer 150 interposed therebetween.

The color filter CF may be formed in a portion of the common electrode CE of the second display panel 200 to face the pixel electrode PE of the first display panel 100. Each pixel, for example, a pixel connected to the i-th (i = 1, 2, ..., n) gate line Gi and the j-th (j = 1, 2, ..., m) data line Dj, is connected to the signal line Gi. And a switching element Q connected to Dj, a liquid crystal capacitor Clc, and a storage capacitor Cst connected thereto. The holding capacitor Cst can be omitted as necessary.

The liquid crystal panel assembly 300 includes a plurality of dummy thin film transistors DUMMY_TFT, and each dummy thin film transistor DUMMY_TFT is electrically connected to each gate line G1 -Gn.

Each dummy thin film transistor DUMMY_TFT includes a gate electrode electrically connected to each gate line G1 -Gn, thereby enabling or disabling a state according to a gate-off voltage applied to each gate line G1 -Gn. The status signals SS1, ..., SSn indicated are outputted. The dummy thin film transistor DUMMY_TFT is the same as the thin film transistor of the driving apparatus of the previous embodiment (see DUMMY_TFT in FIG. 2). That is, the dummy thin film transistor DUMMY_TFT on the liquid crystal panel assembly 300 is used instead of the thin film transistor of the driving device (see DUMMY_TFT of FIG. 2).

When the gate-off voltage level applied to each gate line G1 -Gn is a voltage level at which the plurality of switching devices (see Q in FIG. 5) are not completely turned off, each dummy thin film transistor DUMMY_TFT is enabled and is high. Outputs state signals SS1, ..., SSn, and the gate-off voltage level applied to each gate line G1-Gn is a voltage level for completely turning off the plurality of switching elements (see Q in FIG. 5). In this case, each dummy thin film transistor DUMMY_TFT is disabled to output low level status signals SS1,..., SSn.

The gate driver 400 applies a gate-on voltage Von to the gate lines G1 -Gn according to the gate control signal CONT1 from the signal controller 600, and is connected to the gate lines G1 -Gn. Turn on (see Q in FIG. 5). Then, the data signal applied to the data lines D1 -Dm is applied to the pixel PX through the turned on switching element (see Q in FIG. 5).

The difference between the voltage of the data signal applied to the pixel PX and the common voltage Vcom is charged in the liquid crystal capacitor Clc to serve as the pixel voltage. The arrangement of the liquid crystal molecules varies according to the magnitude of the pixel voltage. Accordingly, the polarization of the light passing through the liquid crystal layer 150 changes, thereby displaying an image.

The data driver 500 is connected to the data lines D1 -Dm of the liquid crystal panel assembly 300 to select an image data voltage corresponding to the image data DAT among the gray voltages provided from the gray voltage generator 800. And the selected image data voltage pixel. Here, when the gray voltage generator 800 does not provide all the voltages for all grays, but only the basic gray voltages, the data driver 500 divides the basic gray voltages to generate gray voltages for all grays. The video data voltage can be selected from these.

The gate driver 400 or the data driver 500 may be mounted directly on the liquid crystal panel assembly 300 in the form of a plurality of driving integrated circuit chips, or may be mounted on a flexible printed circuit film (not shown). The liquid crystal panel assembly 300 may be attached to the liquid crystal panel assembly 300 in the form of a tape carrier package. Alternatively, the gate driver 400 or the data driver 500 may be integrated in the liquid crystal panel assembly 300 together with the display signal lines G1 -Gn and D1-Dm and the switching elements (see Q in FIG. 5). .

The signal controller 600 receives the input image signals R, G, and B and an input control signal for controlling the display thereof from an external graphic controller (not shown). Examples of the input control signal include a vertical sync signal Vsinc, a vertical sync signal Hsync, a main clock MCLK, and a data enable signal DE.

The signal controller 600 generates a gate control signal CONT1 and a data control signal CONT2 based on the input image signals R, G, and B and the input control signal, and generates the gate control signal CONT1 by the gate driver 400. ), The data control signal CONT2 and the image data DAT are sent to the data driver 500.

The driving device 701 includes a detector 711, a feedback signal output unit 720, and a gate-off voltage output unit 730. The driving device 701 receives the state signals SS1,..., SSn from the dummy thin film transistor DUMMY_TFT of the liquid crystal panel assembly 300 to completely turn off the plurality of switching elements (see Q in FIG. 5). The output gate off voltage Voff '.

Here, the sensing unit 711 does not include the thin film transistor DUMMY_TFT, unlike the sensing unit of the driving apparatus (see 710 of FIG. 2) according to an exemplary embodiment. Referring to FIG. 6, each of the sub-sensing units 711_1,..., 711_n includes status signals SS1,..., SSn provided from a dummy thin film transistor (see DUMMY_TFT in FIG. 4) of the liquid crystal panel assembly (see 300 in FIG. 4). And ground voltage as reference signal. The comparison result is output as the detection signal SIG.

The feedback signal output unit 720 receives the sensing signal SIG and outputs a feedback signal FB having a variable voltage level.

The gate off voltage output unit 730 receives the feedback signal FB and outputs a gate off voltage Voff 'corrected according to the voltage level of the feedback signal FB.

The driving device 701 may further include a gate on / off voltage generator (not shown) and a common voltage generator (not shown).

The gray voltage generator 800 receives the driving voltage AVDD from the driving device 700 to generate the gray voltage.

The gray voltage generator 800 includes a plurality of resistors connected in series between the node to which the driving voltage AVDD is applied and the ground to distribute the voltage levels of the driving voltage AVDD to generate the gray voltage. Not shown. The internal circuit of the gray voltage generator 800 is not limited thereto, and may be variously implemented.

Such a liquid crystal display (see 10 of FIG. 4) has a gated voltage (see G1-Gn of FIG. 5) with a corrected gate off voltage Voff 'that completely turns off a plurality of switching elements (see Q of FIG. 5). As a result, the afterimage can be prevented and the display quality can be improved.

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, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

As described above, according to the driving device and the liquid crystal display device according to the present invention, afterimage can be prevented and display quality can be improved.

Claims (10)

A sensing unit electrically connected to a gate line and sensing a voltage level of a gate-off voltage applied to the gate line to output a sensing signal; A feedback signal output unit configured to output a feedback signal having a variable voltage level in response to the sensing signal; And And a gate off voltage output unit configured to output a gate off voltage corrected according to the voltage level of the feedback signal. The method of claim 1, The sensing unit includes a thin film transistor including a gate electrode electrically connected to the gate line. The method of claim 1, The sensing unit may be electrically connected to the gate line and provide a state signal corresponding to a voltage level of the gate off voltage, and the sensing signal of the first level or the second level by comparing the state signal with a reference signal. Drive device including a comparator for outputting. The method of claim 3, wherein The feedback signal output unit may include a first switching element and a variable resistor enabled for the sensing signal of the first level, and output a first feedback signal for varying a voltage level according to a resistance value of the variable resistor. And a second feedback signal output unit including an output unit, a second switching element enabled to sense signals of the second level, and a fixed resistor, and outputting the feedback signal of a predetermined level. The method of claim 4, wherein The variable resistor is a digital variable resistor, and the first feedback signal output unit further includes a resistance adjustment signal providing unit for providing a resistance adjustment signal to the digital variable resistor. A liquid crystal panel assembly including a plurality of gate lines, a plurality of data lines, each of the gate lines, a plurality of switching elements electrically connected to each of the data lines, and a dummy thin film transistor electrically connected to each of the gate lines; And A sensing unit for outputting a sensing signal whose voltage level is varied according to whether the dummy thin film transistor is enabled, a feedback signal output unit for outputting a feedback signal having a voltage level varying in response to the sensing signal, and a And a driving device including a gate off voltage output unit configured to output a gate off voltage according to a voltage level. The method of claim 6, And the plurality of switching elements are the same thin film transistors as the dummy thin film transistor, and the sensing signal is a signal indicating whether the gate off voltage turns off the plurality of switching elements. The method of claim 7, wherein The sensing unit includes a comparator for outputting the sensing signal of the first level when the dummy thin film transistor is enabled, and outputting the sensing signal of the second level when the dummy thin film transistor is disabled. The method of claim 8, The feedback signal output unit includes a first switching element and a variable resistor, the first feedback signal output unit outputting the feedback signal having a variable voltage level, the first switching element being enabled to the sensing signal of the first level, and the second level. And a second feedback signal output unit configured to output the feedback signal at a predetermined level, including a second switching element enabled for the sensing signal and a fixed resistor. The method of claim 9, The variable resistor may be a digital variable resistor, and the first feedback signal output unit may further include a resistance control signal providing unit configured to provide a resistance control signal to the digital variable resistor.

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