KR20110069321A - Liquid crystal display - Google Patents

Abstract

PURPOSE: A liquid crystal display is provided to prevent phenomena from being turned on before a TFT of a liquid cell normally scanning by switching a common voltage in a horizontal line unit according to a panel scanning when driving a common voltage swing. CONSTITUTION: A liquid crystal display panel is crossed with a plurality of data lines and a plurality of gate lines. The liquid crystal display panel has a common electrodes(2) which is patterned into a horizontal line unit by facing a pixel electrodes of the liquid crystal cells and a plurality of liquid crystal cells arranged on a matrix form by the crossing structure. A common voltage generating circuit generates a common voltage which is swung in a constant period. A common voltage switching unit(15) switches a common voltage in the horizontal line unit according to a panel scan. The liquid display panel has a valid display area displaying an image including the liquid crystal cells and a non display area of a valid display area. The common voltage switching unit is formed on the non display area.

Description

Liquid Crystal Display

The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device for swing driving a common voltage.

Conventional liquid crystal display devices display an image by adjusting the light transmittance of the liquid crystal using an electric field. To this end, the liquid crystal display includes a liquid crystal display panel in which liquid crystal cells are arranged in a matrix, and a driving circuit for driving the liquid crystal display panel.

As shown in FIG. 1, the liquid crystal display panel includes a thin film transistor for driving the liquid crystal cell Clc at the intersection of the gate line GL and the data line DL and at the intersection of the gate line GL and the data line GL. Thin Film Transistor (hereinafter referred to as "TFT") is formed. In addition, a storage capacitor Cst is formed in the liquid crystal display panel to maintain the voltage of the liquid crystal cell Clc. The liquid crystal cell Clc includes a pixel electrode Ep to which a data voltage is applied, a common electrode Ec to which a common voltage Vcom is applied, and a liquid crystal layer. The liquid crystal molecules forming the liquid crystal layer control the amount of light transmitted as the arrangement is changed by an electric field applied between the pixel electrode Ep and the common electrode Ec.

The common voltage Vcom is typically driven at a DC level, but in some cases, the common voltage Vcom may be swing driven at a predetermined period. For example, the common voltage Vcom may be swing driven at one frame period as shown in FIG. 2. As shown in FIG. 2, the liquid crystal cell is specified by the common voltage Vcom applied to the first level L1 and the data voltage Vdata applied to the second level L2 (L2 <L1) in the nth frame. Assuming that the first voltage Vp1 is applied, the potential difference applied to the specific liquid crystal cell even in the n + 1th frame until a new data voltage is applied by the scan in the n + 1th frame for the specific liquid crystal cell. Must be maintained at the first voltage Vp1. In other words, before the scan of the specific liquid crystal cell in the n + 1th frame, if the common voltage Vcom is lowered to the second level L2, the data voltage Vdata charged in the specific liquid crystal cell is also the second level. It must be lowered to the third level L3 (L3 <L2) so as to maintain the potential difference by the common voltage Vcom of L2 and the first voltage Vp1. Prior to the scan for the specific liquid crystal cell, the TFT connected to the specific liquid crystal cell is kept turned off. Since the TFT is turned off, the data voltage Vdata charged in the specific liquid crystal cell may be lowered from the second level L2 to the third level L3 due to the coupling effect.

However, the TFT is turned on unconditionally when its gate-source voltage difference Vgs becomes greater than or equal to the threshold voltage as shown in FIG. When the level of the data voltage Vdata is lowered by the swing of the common voltage Vcom, the gate-source voltage difference Vgs of the TFT becomes large, and as a result, the TFT can be turned on before normal scanning. If the TFT is turned on before scanning, a data voltage to be applied to another liquid crystal cell flows into the specific liquid crystal cell, and the potential difference applied to the specific liquid crystal cell in the n + 1 th frame as shown in FIG. 2 is maintained at the first voltage Vp1. And may change to an unwanted second voltage Vp2. This problem is caused by the common voltage applied to all liquid crystal cells swinging simultaneously regardless of the scan operation. If the potential difference applied to the specific liquid crystal cell before scanning is changed, the image quality deteriorates.

Accordingly, an object of the present invention is to provide a liquid crystal display device capable of switching the common voltage in units of horizontal lines according to a panel scan during common voltage swing driving.

In order to achieve the above object, a liquid crystal display device according to an embodiment of the present invention, a plurality of liquid crystal cells are arranged in a matrix form by a plurality of data lines and a plurality of gate lines are crossed, and A liquid crystal display panel facing the pixel electrodes of the liquid crystal cells and having a plurality of common electrodes patterned in units of horizontal lines; A common voltage generating circuit generating a common voltage swinging at a predetermined period; And a common voltage switching unit for switching the common voltage in units of the horizontal line according to a panel scan.

The liquid crystal display panel includes an effective display area for displaying an image including the liquid crystal cells and a non-display area outside the effective display area; The common voltage switching unit is formed in the non-display area.

The common voltage switching unit includes: a common wiring to which the common voltage is applied; And a switch array for switching the common voltage on the common wiring to the common electrodes of the horizontal line unit.

The switch array includes a plurality of common voltage application switches, one for each horizontal line.

The common voltage applying switch formed on the nth horizontal line among the common voltage applying switches included in the switch array is connected between the common line and the common electrode formed on the nth horizontal line and is applied to the nth gate line. It is driven by the scan pulse.

The switch array includes a plurality of common voltage applying switches allocated to two horizontal lines.

The first common voltage applying switch formed on the nth horizontal line among the common voltage applying switches included in the switch array is connected between the common line and the common electrode formed on the nth horizontal line and connected to the nth gate line. Driven by an applied scan pulse; The second common voltage applying switch formed on the n-th horizontal line among the common voltage applying switches included in the switch array is connected between the common line and the common electrode formed on the n-th horizontal line, and has an n-1 th gate. It is driven by a scan pulse applied to the line.

The common voltage is swinged between the first level and the second level in one frame period.

The common voltage swings between the first level and the second level in one horizontal period.

The liquid crystal display according to the present invention switches the common voltage in units of horizontal lines according to the panel scan during common voltage swing driving, thereby preventing the TFT of the liquid crystal cell from turning on before normal scanning in common voltage swing. Can be. As a result, the liquid crystal display according to the present invention can maintain the potential difference between the pixel electrode and the common electrode of the liquid crystal cell at a desired value, thereby improving image quality.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 3 to 7.

3 shows a liquid crystal display device according to an embodiment of the present invention.

3, a liquid crystal display according to an exemplary embodiment of the present invention includes a liquid crystal display panel 10, a timing controller 11, a data driving circuit 12, a gate driving circuit 13, and a common voltage generating circuit ( 14).

The liquid crystal display panel 10 includes two glass substrates and a liquid crystal layer formed therebetween. In the liquid crystal display panel, a plurality of liquid crystal cells Clc are formed in a matrix form by the cross structure of the plurality of data lines DL and the plurality of gate lines GL.

Data lines DL, gate lines GL, TFTs, and storage capacitors Cst are formed on the lower glass substrate of the liquid crystal display panel 10. The liquid crystal cells Clc are connected to the TFT and driven by an electric field applied between the pixel electrodes 1 and the common electrodes 2. The black matrix, the color filter, and the common electrodes 2 are formed on the upper glass substrate of the liquid crystal display panel 10. The common electrodes 2 are formed on the upper glass substrate in a vertical electric field driving method such as twisted nematic (TN) mode and vertical alignment (VA) mode, and are in an in plane switching (IPS) mode and a fringe field switching (FFS) mode. In the horizontal electric field driving method as described above, the pixel electrodes 1 are formed on the lower glass substrate. The common electrodes 2 are patterned in units of horizontal lines. The electric field is applied to the liquid crystal layer by the data voltage applied to the pixel electrodes 1 and the common voltage Vcom applied to the common electrodes 2. This electric field allows the liquid crystal molecules of the liquid crystal layer to adjust the amount of light transmitted as the arrangement thereof changes. A polarizing plate is attached to each of the upper glass substrate and the lower glass substrate of the liquid crystal display panel 10, and an alignment layer for setting the pre-tilt angle of the liquid crystal is formed.

The liquid crystal display panel 10 includes an effective display area AA including liquid crystal cells Clc to display an image, and a non-display area NAA outside the effective display area AA. The common voltage switching unit 15 is formed in the non-display area NAA to switch the common voltage Vcom in units of horizontal lines according to a panel scan.

The timing controller 11 receives timing signals such as a data enable signal (DE), a dot clock (CLK), and the like to control operation timing of the data driver circuit 12 and the gate driver circuit 13. Generate signals GDC, DDC.

The data control signal DDC for controlling the operation timing of the data driving circuit 12 is a source sampling instructing the latch operation of data in the data driving circuit 12 based on a rising or falling edge. A polarity of the data voltage to be supplied to the clock (Source Sampling Clock SSC), the source output enable signal SOE indicating the output of the data driving circuit 12, and the liquid crystal cells Clc of the liquid crystal display panel 10. And a polarity control signal POL indicating.

The gate control signal GDC for controlling the operation timing of the gate driving circuit 13 may include a gate start pulse (GSP) indicating a start horizontal line at which scanning starts in one vertical period in which one screen is displayed; A gate shift clock signal (Gate Shift) generated at a pulse width corresponding to an ON period of a TFT as a timing control signal input to a shift register in the gate driving circuit 13 to sequentially shift the gate start pulse GSP. Clock (GSC), and a gate output enable signal (GOE) for controlling the output of the gate driving circuit 13 and the like.

In addition, the timing controller 11 rearranges the digital video data RGB input from an external system board to the data driving circuit 12 according to the resolution of the liquid crystal display panel 10.

The data driving circuit 12 based on the digital video data RGB based on the gamma reference voltages GMA from the gamma reference voltage generator (not shown) in response to the data control signal DDC from the timing controller 11. The analog gamma compensation voltage is converted into an analog gamma compensation voltage, and the analog gamma compensation voltage is supplied to the data lines DL of the liquid crystal display panel 10 as a data voltage. The data driving circuit 12 stores a shift line for sampling a clock signal, a register for temporarily storing digital video data (RGB), and one line for storing data in response to a clock signal from the shift register. Latch for outputting data at the same time, digital / analog converter for selecting positive / negative gamma voltage under reference to gamma reference voltage in response to digital data value from latch, and selection of positive / negative gamma voltage A plurality of data drive ICs include a multiplexer for selecting the data line DL to which the generated data voltage is supplied, and an output buffer connected between the multiplexer and the data line DL.

The gate driving circuit 13 sequentially generates a gate signal Sg including a shift register array to select a horizontal line of the liquid crystal display panel 10 to which a data voltage is supplied. The gate driving circuit 13 may further include a level shifter for converting the output signal of the shift register array into a swing width suitable for driving the TFT of the liquid crystal cell Clc. The shift register array may be directly formed through a gate in panel (GIP) method on a non-display area (NAA) of a lower glass substrate, or may be directly integrated in a gate drive IC together with a level shifter. When the shift register array is formed on the non-display area NAA of the lower glass substrate, the level shifter may be mounted on the control board together with the timing controller 11.

The common voltage generation circuit 14 generates a common voltage Vcom swinging at a predetermined period and supplies the common voltage Vcom to the common wiring formed in the non-display area NAA.

4 shows an example of the common voltage switching unit 15.

Referring to FIG. 4, the common voltage switching unit 15 includes the common lines 151 to which the common voltage Vcom is applied, and the common electrodes patterning the common voltage Vcom on the common line 151 in units of horizontal lines. And a switch array for switching to (2).

The common voltage Vcom swinging at a predetermined period is applied to the common wiring 151. The common voltage Vcom may swing between the first level L1 and the second level L2 at the interval of one frame period 1V as shown in FIG. 6, and further, one horizontal period 1H as shown in FIG. 7. The swing may be performed between the first level L1 and the second level L2.

The switch array includes a plurality of common voltage application switches 152 allocated one for each horizontal line. The common voltage application switches 152 may be implemented with a TFT.

The common voltage applying switch 152 formed on the n th horizontal line HLn is connected between the common wiring 151 and the common electrode 2 formed on the n th horizontal line HLn, and the n th gate line GLn. It is driven by the scan pulse applied to). The common voltage applying switch 152 formed on the n-th horizontal line HLn is turned on during the n-th scan pulse maintaining the turn-on level so that the common voltage Vcom on the common line 151 is n-th horizontal. It is applied to the common electrode 2 formed in the line HLn, and is turned off during the period in which the nth scan pulse maintains the turn off level, thereby floating the common electrode 2 formed in the nth horizontal line HLn.

The common voltage applying switch 152 formed on the n + 1th horizontal line HLn + 1 is connected between the common wiring 151 and the common electrode 2 formed on the n + 1th horizontal line HLn + 1. And is driven by a scan pulse applied to the n + 1th gate line GLn + 1. The common voltage applying switch 152 formed on the n + 1th horizontal line HLn + 1 is turned on for a period during which the n + 1th scan pulse maintains a turn-on level, so that the common voltage on the common line 151 Vcom) is applied to the common electrode 2 formed on the n + 1th horizontal line HLn + 1, and is turned off during the period in which the n + 1th scan pulse maintains the turn-off level. The common electrode 2 formed on HLn + 1 is floated.

5 shows another example of the common voltage switching unit 15.

Referring to FIG. 5, the common voltage switching unit 15 includes the common lines 151 to which the common voltage Vcom is applied, and the common electrodes patterning the common voltage Vcom on the common line 151 in units of horizontal lines. And a switch array for switching to (2).

The common voltage Vcom swinging at a predetermined period is applied to the common wiring 151. The common voltage Vcom may swing between the first level L1 and the second level L2 at intervals of one frame period 1V as shown in FIG. 6.

The switch array includes a plurality of common voltage application switches 152A and 152B, which are allocated two for each horizontal line. The common voltage applying switches 152A and 152B may be implemented with TFTs.

The first common voltage applying switch 152A formed on the nth horizontal line HLn is connected between the common wiring 151 and the common electrode 2 formed on the nth horizontal line HLn, and the nth gate line It is driven by a scan pulse applied to GLn. The first common voltage applying switch 152A formed on the nth horizontal line HLn is turned on for a period during which the nth scan pulse maintains a turn on level, thereby changing the common voltage Vcom on the common line 151 to n. Applied to the common electrode 2 formed on the first horizontal line HLn, and turned off during the period in which the nth scan pulse maintains the turn-off level, thereby floating the common electrode 2 formed on the nth horizontal line HLn. .

The second common voltage applying switch 152B formed on the nth horizontal line HLn is connected between the common wiring 151 and the common electrode 2 formed on the nth horizontal line HLn, and the n-1th It is driven by a scan pulse applied to the gate line GLn-1. The second common voltage applying switch 152B formed on the nth horizontal line HLn is turned on during the n−1th scan pulse to maintain the turn on level, so that the common voltage Vcom on the common wiring 151 is turned on. Is applied to the common electrode 2 formed on the nth horizontal line HLn, and the common electrode 2 formed on the nth horizontal line HLn is turned off while the n-1th scan pulse maintains the turn-off level. )).

When the common voltage of the corresponding horizontal line is switched by using two common voltage applying switches, the load applied to the switch can be reduced to 1/2 compared to when using one common voltage applying switch, and one common voltage is applied. Each switch capacity can be reduced by half compared to when using a voltage application switch.

As described above, the liquid crystal display according to the present invention switches the common voltage in units of horizontal lines according to the panel scan during the common voltage swing driving, and thus the TFT of the liquid crystal cell is turned on before the normal scan during the common voltage swing. It can prevent it beforehand. As a result, the liquid crystal display according to the present invention can maintain the potential difference between the pixel electrode and the common electrode of the liquid crystal cell at a desired value, thereby improving image quality.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the present invention should not be limited to the details described in the detailed description but should be defined by the claims.

1 is an equivalent circuit diagram of a typical liquid crystal cell.

2 is a view for explaining a phenomenon in which the TFT is turned on before scanning during common voltage swing driving;

3 illustrates a liquid crystal display according to an exemplary embodiment of the present invention.

4 is a diagram illustrating an example of a common voltage switching unit.

5 is a view illustrating another example of the common voltage switching unit.

6 and 7 illustrate swing periods of a common voltage.

<Description of Symbols for Main Parts of Drawings>

10 liquid crystal display panel 11 timing controller

12: data driving circuit 13: gate driving circuit

14 common voltage generating circuit 15 common voltage switching unit

151: common wiring 152,152A, 152B: common voltage application switch

Claims (9)

A plurality of data lines and a plurality of gate lines intersect, and a plurality of liquid crystal cells arranged in a matrix form by the crossing structure, and a plurality of common patterns facing each other and the pixel electrodes of the liquid crystal cells and patterned in units of horizontal lines A liquid crystal display panel having electrodes; A common voltage generating circuit generating a common voltage swinging at a predetermined period; And And a common voltage switching unit for switching the common voltage in units of horizontal lines according to a panel scan. The method of claim 1, The liquid crystal display panel includes an effective display area for displaying an image including the liquid crystal cells and a non-display area outside the effective display area; And the common voltage switching unit is formed in the non-display area. The method of claim 2, The common voltage switching unit, A common wiring to which the common voltage is applied; And And a switch array configured to switch the common voltage on the common line to the common electrodes in the horizontal line unit. The method of claim 3, wherein The switch array, And a plurality of common voltage applying switches allocated one by one for each horizontal line. The method of claim 4, wherein The common voltage applying switch formed on the nth horizontal line among the common voltage applying switches included in the switch array is connected between the common line and the common electrode formed on the nth horizontal line and is applied to the nth gate line. A liquid crystal display device driven by a scan pulse. The method of claim 3, wherein The switch array, And a plurality of common voltage applying switches allocated to two horizontal lines. The method of claim 6, The first common voltage applying switch formed on the nth horizontal line among the common voltage applying switches included in the switch array is connected between the common line and the common electrode formed on the nth horizontal line, and the nth gate line Driven by a scan pulse applied to; The second common voltage applying switch formed on the n-th horizontal line among the common voltage applying switches included in the switch array is connected between the common line and the common electrode formed on the n-th horizontal line, and has an n-1 th gate. A liquid crystal display device driven by a scan pulse applied to a line. The method of claim 1, The common voltage is And a swing between the first level and the second level at one frame period. The method of claim 1, The common voltage is And a swing between the first level and the second level at intervals of one horizontal period.

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