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JP2005055562A - Liquid crystal display device and method for driving the same - Google Patents

Liquid crystal display device and method for driving the same Download PDF

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JP2005055562A
JP2005055562A JP2003284616A JP2003284616A JP2005055562A JP 2005055562 A JP2005055562 A JP 2005055562A JP 2003284616 A JP2003284616 A JP 2003284616A JP 2003284616 A JP2003284616 A JP 2003284616A JP 2005055562 A JP2005055562 A JP 2005055562A
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liquid crystal
pixel
display device
potential
electrode
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Shizuo Nishihara
静夫 西原
Hidenobu Kuroi
英伸 黒井
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Sony Corp
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Sony Corp
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Priority to JP2003284616A priority Critical patent/JP2005055562A/en
Priority to PCT/JP2004/011314 priority patent/WO2005012986A1/en
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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N9/00Details of colour television systems
    • H04N9/12Picture reproducers
    • H04N9/31Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
    • H04N9/3102Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators
    • H04N9/312Driving therefor
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • G09G3/3611Control of matrices with row and column drivers
    • G09G3/3648Control of matrices with row and column drivers using an active matrix
    • GPHYSICS
    • G02OPTICS
    • G02FOPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/136Liquid crystal cells structurally associated with a semi-conducting layer or substrate, e.g. cells forming part of an integrated circuit
    • G02F1/1362Active matrix addressed cells
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00Control of display operating conditions
    • G09G2320/04Maintaining the quality of display appearance
    • G09G2320/043Preventing or counteracting the effects of ageing
    • G09G2320/046Dealing with screen burn-in prevention or compensation of the effects thereof

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Liquid Crystal Display Device Control (AREA)
  • Liquid Crystal (AREA)
  • Control Of Indicators Other Than Cathode Ray Tubes (AREA)

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display device whose operating life of a liquid crystal panel is extended by alleviating an image persistence phenomenon caused by absorption of ions, produced by photo- or thermal-decomposition of an organic material due to long time irradiation of intense light on the liquid crystal panel, to an alignment layer and/or an electrode interface, and a method for driving the same. <P>SOLUTION: The ions giving rise to the image persistence phenomenon are made to be dissociated from the alignment layer 22A, 22B and/or the electrode interface by reducing at least an electric potential, preferably both electric potentials of a pixel electrode 21B and a counter electrode 21A of a liquid crystal cell in the pixel to the ground level in a time period other than an operating time to carry out a picture display, especially in a stand-by mode state aiming at power saving. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は、液晶表示装置およびその駆動方法に関する。   The present invention relates to a liquid crystal display device and a driving method thereof.

液晶表示装置では、長時間、同じ画像や文字等を表示したままにしておくと、その部分が劣化し、次回にその部分がかすれたり、変色したりして正常に表示されなくなったりする「焼き付き」と称される現象が発生することが知られている。従来、この焼き付きを防止するために、全画面を1ラインずつ描画する通常の描画とは別に、通常の描画よりも短時間で焼き付き防止を目的とする市松パターンを描画するようにしていた(例えば、特許文献1参照)。   In a liquid crystal display device, if the same image or character is displayed for a long time, the part deteriorates and the part is faded or discolored next time and may not be displayed normally. Is known to occur. Conventionally, in order to prevent this burn-in, a checkerboard pattern intended to prevent burn-in has been drawn in a shorter time than normal drawing apart from normal drawing in which the entire screen is drawn line by line (for example, , See Patent Document 1).

特開2000−131671号公報JP 2000-131671 A

ところで、液晶の焼き付き現象には2つの要因がある。その一つは直流電圧の印加であり、もう一つはイオンである。直流電圧の印加に起因して起こる焼き付き現象を防止するために為されたのが、上記特許文献1記載の従来技術である。したがって、当該従来技術では、イオンに起因して起こる焼き付き現象を防止することはできない。このイオンに起因して起こる焼き付き現象について以下に述べる。   There are two factors in the image sticking phenomenon of the liquid crystal. One is the application of a DC voltage and the other is ions. The prior art described in Patent Document 1 has been made to prevent a burn-in phenomenon that occurs due to the application of a DC voltage. Therefore, the conventional technique cannot prevent the image sticking phenomenon caused by the ions. The seizure phenomenon caused by the ions will be described below.

二枚のガラス基板間に液晶層を挟持してなる液晶パネルには、液晶、配向膜、シール剤といった有機材料が使われており、液晶パネルに強い光を長時間照射すると、当該パネル内に使用されている有機材料に劣化が起きる。すなわち、光により有機材料が分解され、イオンが発生する。発生したイオンは長時間の直流成分のため、配向膜あるいは電極界面にドリフトして付着する。エネルギー的に安定であれば、長い緩和時間を持って吸収される。したがって、電界を除去した後もイオンは界面にとどまる。そして、界面に停留したイオンは印加電界とは逆の電界を形成する。この逆電界は、液晶にかかる電圧を印加電圧よりも低くし、コントラストや表示品質に悪影響を及ぼす。   A liquid crystal panel that has a liquid crystal layer sandwiched between two glass substrates uses organic materials such as liquid crystals, alignment films, and sealing agents. Degradation occurs in the organic materials used. That is, the organic material is decomposed by light, and ions are generated. Since the generated ions are DC components for a long time, they drift and adhere to the alignment film or the electrode interface. If it is energetically stable, it is absorbed with a long relaxation time. Therefore, ions remain at the interface even after the electric field is removed. The ions that remain at the interface form an electric field opposite to the applied electric field. This reverse electric field makes the voltage applied to the liquid crystal lower than the applied voltage, and adversely affects contrast and display quality.

特に、青色光は、他の色の光、即ち緑色光、赤色光に比べてエネルギーが大きい。したがって、例えば青色、緑色、赤色のそれぞれに対応して液晶パネルを配置してなる3板式液晶表示装置(液晶プロジェクタ)において、特に青色光が入射する液晶パネルに光による有機材料の劣化が起きる可能性が高い。通常の劣化過程としては、液晶パネルに焼き付き現象が起こった後、配向膜に起因する画質劣化が発生し、最終的に気泡に到る。   In particular, blue light has higher energy than other colors of light, that is, green light and red light. Therefore, for example, in a three-plate type liquid crystal display device (liquid crystal projector) in which liquid crystal panels are arranged corresponding to each of blue, green, and red, deterioration of the organic material due to light may occur particularly in the liquid crystal panel on which blue light is incident. High nature. As a normal deterioration process, after a burn-in phenomenon occurs in the liquid crystal panel, image quality deterioration due to the alignment film occurs, and finally bubbles are reached.

図6に、焼き付き現象が発生する過程を示す。図6において、(A)対向側基板の内面に配された透明電極101および配向膜102と、TFT側基板の内面に配された透明電極103および配向膜104との間に液晶層105を挟持してなる液晶パネル100に光が入射すると、(B)光や熱で有機材料が分解してイオンが発生する。そして、(C)2枚の基板間に印加される直流成分により、発生したイオンが配向膜102,104の表面に吸着する。   FIG. 6 shows a process in which the burn-in phenomenon occurs. In FIG. 6, (A) the liquid crystal layer 105 is sandwiched between the transparent electrode 101 and the alignment film 102 disposed on the inner surface of the opposite substrate and the transparent electrode 103 and the alignment film 104 disposed on the inner surface of the TFT substrate. When light enters the liquid crystal panel 100, (B) the organic material is decomposed by light or heat, and ions are generated. Then, (C) the generated ions are adsorbed on the surfaces of the alignment films 102 and 104 by the DC component applied between the two substrates.

本発明は、上記課題に鑑みてなされたものであって、その目的とするところは、光や熱で有機材料が分解してイオンが発生し、配向膜あるいは電極界面に吸着することに起因して発生する焼き付き現象を軽減し、液晶パネルの長寿命化が可能にした表示装置およびその駆動方法を提供することにある。   The present invention has been made in view of the above problems, and the object of the present invention is that the organic material is decomposed by light or heat to generate ions, which are adsorbed on the alignment film or the electrode interface. It is an object of the present invention to provide a display device and a driving method thereof that can reduce the image sticking phenomenon that occurs and extend the life of the liquid crystal panel.

上記目的を達成するために、本発明では、液晶セルおよび画素トランジスタを含む画素が行列状に2次元配置されてなる画素アレイ部を備えた液晶表示装置において、画像表示を行う動作時以外のときに、液晶セルの画素電極および対向電極の少なくとも一方の電位をグランドレベルにする構成を採っている。   In order to achieve the above object, according to the present invention, in a liquid crystal display device having a pixel array portion in which pixels including liquid crystal cells and pixel transistors are two-dimensionally arranged in a matrix, when the image display is not performed. In addition, a configuration is adopted in which the potential of at least one of the pixel electrode and the counter electrode of the liquid crystal cell is set to the ground level.

液晶パネルにおいて、光や熱で有機材料が分解してイオンが発生し、当該イオンが配向膜や電極界面に吸着しても、液晶セルの画素電極および対向電極の少なくとも一方、好ましくは両方の電位をグランドレベルにすることで、配向膜や電極界面に吸着したイオンが解離する。   In the liquid crystal panel, even if the organic material is decomposed by light or heat to generate ions and the ions are adsorbed to the alignment film or the electrode interface, the potential of at least one of the pixel electrode and the counter electrode of the liquid crystal cell, preferably both By setting to the ground level, ions adsorbed on the alignment film and the electrode interface are dissociated.

本発明によれば、光や熱で有機材料が分解して発生して配向膜や電極界面に吸着したイオンを解離できることにより、当該イオンに起因して発生する焼き付き現象を軽減できるため、液晶パネルの長寿命化を図ることができる。   According to the present invention, since the organic material is decomposed by light or heat and the ions adsorbed on the alignment film or the electrode interface can be dissociated, the image sticking phenomenon caused by the ions can be reduced. It is possible to extend the service life.

以下、本発明の実施の形態について図面を参照して詳細に説明する。   Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

図1は、本発明の一実施形態に係る液晶表示装置を示す概略構成図である。図1において、透明絶縁基板、例えばガラス基板11上には、画素12が行列状に2次元配置されてなる画素アレイ部13が形成されている。ガラス基板11は、もう一枚のガラス基板と所定の間隙を持って対向配置され、両基板間に液晶材料を封止することで液晶パネル(LCDパネル)10を構成している。   FIG. 1 is a schematic configuration diagram showing a liquid crystal display device according to an embodiment of the present invention. In FIG. 1, on a transparent insulating substrate, for example, a glass substrate 11, a pixel array unit 13 in which pixels 12 are two-dimensionally arranged in a matrix is formed. The glass substrate 11 is disposed opposite to another glass substrate with a predetermined gap, and a liquid crystal panel (LCD panel) 10 is configured by sealing a liquid crystal material between the two substrates.

画素12の各々は、画素トランジスタであるTFT(Thin Film Transistor;薄膜トランジスタ)121と、このTFT121のドレイン電極に画素電極が接続された液晶セル122と、TFT121のドレイン電極に一方の電極が接続された保持容量123とを有する構成となっている。ここで、液晶セル122は、画素電極とこれに対向して形成される対向電極との間で発生する液晶容量を意味する。   Each of the pixels 12 includes a TFT (Thin Film Transistor) 121 which is a pixel transistor, a liquid crystal cell 122 having a pixel electrode connected to the drain electrode of the TFT 121, and one electrode connected to the drain electrode of the TFT 121. The storage capacitor 123 is included. Here, the liquid crystal cell 122 means a liquid crystal capacitance generated between the pixel electrode and a counter electrode formed opposite to the pixel electrode.

図2に、液晶パネル10の断面構造を示す。図2から明らかなように、液晶パネル10は、所定の間隙を持って対向配置された2枚のガラス基板11A,11B間に、透明電極(例えば、ITO膜)21A,21Bおよび配向膜22A,22Bを介して液晶層23を挟持した構造となっている。ここで、透明電極22A,22Bは、液晶セル122の対向電極および画素電極に相当する。   FIG. 2 shows a cross-sectional structure of the liquid crystal panel 10. As is apparent from FIG. 2, the liquid crystal panel 10 includes transparent electrodes (for example, ITO films) 21A and 21B and alignment films 22A, between two glass substrates 11A and 11B arranged to face each other with a predetermined gap. The liquid crystal layer 23 is sandwiched through 22B. Here, the transparent electrodes 22A and 22B correspond to the counter electrode and the pixel electrode of the liquid crystal cell 122.

この画素構造において、TFT121はゲート電極がゲート線(走査線)14に接続され、ソース電極が信号線15に接続されている。液晶セル122は対向電極がVCOM線16に対して各画素共通に接続されている。そして、液晶セル122の対向電極には、VCOM線16を介してコモン電圧VCOM(VCOM電位)が各画素共通に与えられる。保持容量123は他方の電極(対向電極側の端子)がCS線17に対して各画素共通に接続されている。   In this pixel structure, the TFT 121 has a gate electrode connected to a gate line (scanning line) 14 and a source electrode connected to a signal line 15. The liquid crystal cell 122 has a common electrode connected to the VCOM line 16 in common for each pixel. A common voltage VCOM (VCOM potential) is applied to the common electrode of the liquid crystal cell 122 via the VCOM line 16. In the storage capacitor 123, the other electrode (terminal on the counter electrode side) is connected to the CS line 17 in common for each pixel.

ここで、1H(Hは水平期間)反転駆動または1F(Fはフィールド期間)反転駆動を行う場合は、各画素に書き込まれる表示信号は、VCOM電位を基準として極性反転を行うことになる。また、VCOM電位の極性を一定周期、例えば1H周期または1F周期で反転させるコモン反転駆動を1H反転駆動または1F反転駆動と併用する場合には、CS線17に与えられるCS電位の極性もVCOM電位に同期して反転する。ただし、本実施形態に係る液晶表示装置は、VCOM反転駆動に限られるものではない。   Here, in the case of performing 1H (H is a horizontal period) inversion driving or 1F (F is a field period) inversion driving, the display signal written to each pixel is inverted in polarity with the VCOM potential as a reference. In addition, when common inversion driving that inverts the polarity of the VCOM potential at a constant period, for example, 1H period or 1F period, is used together with 1H inversion driving or 1F inversion driving, the polarity of the CS potential applied to the CS line 17 is also VCOM potential. Invert in sync with. However, the liquid crystal display device according to the present embodiment is not limited to the VCOM inversion driving.

画素アレイ部13と同じガラス基板11上には、例えば、画素アレイ部13の左右に垂直駆動回路18L,18Rが、画素アレイ部13の上側に水平駆動回路19がそれぞれ搭載されている。垂直駆動回路18L,18Rは各々、シフトレジスタにより構成される。これら垂直駆動回路18L,18Rにおいて、シフトレジスタは、タイミングジェネレータ(図示せず)から供給される垂直スタートパルスVSTに応答してシフト動作を開始し、同じくタイミングジェネレータから供給される垂直クロックパルスVCKに同期して1垂直期間に順次転送していく走査パルスを生成する。   On the same glass substrate 11 as the pixel array unit 13, for example, vertical drive circuits 18L and 18R are mounted on the left and right of the pixel array unit 13, and a horizontal drive circuit 19 is mounted on the upper side of the pixel array unit 13, respectively. Each of the vertical drive circuits 18L and 18R is configured by a shift register. In these vertical drive circuits 18L and 18R, the shift register starts a shift operation in response to a vertical start pulse VST supplied from a timing generator (not shown), and also generates a vertical clock pulse VCK supplied from the timing generator. A scan pulse that is sequentially transferred in one vertical period is generated in synchronization.

垂直駆動回路18L,18Rで生成される走査パルスは、バッファ20L,20Rを通して画素アレイ部13の左右両側からゲート線14に順次与えられることで、画素アレイ部13の各画素12を行単位で選択する。このように、ゲート線14に対して画素アレイ部13の左右両側から走査パルスを与えるのは、ゲート線14の配線抵抗や寄生容量に起因する伝搬遅延によって生ずる走査パルスの波形のなまりを抑えるためであり、水平方向の画素数が多くなる程その効果は大である。   Scan pulses generated by the vertical drive circuits 18L and 18R are sequentially applied to the gate lines 14 from the left and right sides of the pixel array unit 13 through the buffers 20L and 20R, thereby selecting each pixel 12 of the pixel array unit 13 in units of rows. To do. As described above, the scanning pulse is applied to the gate line 14 from both the left and right sides of the pixel array unit 13 in order to suppress the rounding of the waveform of the scanning pulse caused by the propagation delay caused by the wiring resistance and parasitic capacitance of the gate line 14. As the number of pixels in the horizontal direction increases, the effect becomes greater.

水平駆動回路19は、垂直駆動回路18L,18Rによる垂直走査により、画素アレイ部13の各画素12が行(ライン)単位で順に選択されると、この選択された1ライン分の画素12に対して、信号線15を介して1ライン分の映像信号を書き込む。このライン単位の映像信号の書き込み動作が繰り返して実行されることにより、1画面分の画表示が行われる。   When the pixels 12 of the pixel array unit 13 are sequentially selected in units of rows (lines) by the vertical scanning by the vertical driving circuits 18L and 18R, the horizontal driving circuit 19 applies the selected pixels 12 for one line. Thus, the video signal for one line is written through the signal line 15. By repeating this video signal writing operation in units of lines, an image for one screen is displayed.

上記構成の液晶表示装置において、本発明では、当該液晶表示装置(以下、単に「装置本体」と記す場合もある)の画像表示を行う動作時以外、特に省電力を目的とするスタンバイモード状態のときに、画素12における液晶セル122の画素電極および対向電極の少なくとも一方の電位、好ましくは両方の電位をグランドレベルに落とすようにしたことを特徴としている。   In the liquid crystal display device having the above-described configuration, in the present invention, the liquid crystal display device (hereinafter sometimes simply referred to as “device main body”) is in a standby mode state particularly for power saving except during an operation of displaying an image. In some cases, the potential of at least one of the pixel electrode and the counter electrode of the liquid crystal cell 122 in the pixel 12 and preferably both potentials are dropped to the ground level.

このように、液晶セル122の画素電極および対向電極の各電位をグランドレベルとすることにより、光や熱で有機材料が分解して発生して配向膜22A,22Bの表面に吸着し、焼き付き現象を起こす要因となるイオンが、図3に示すように、配向膜22A,22Bから解離する。その結果、配向膜22A,22Bあるいは電極21A,21Bの界面に吸着するイオンに起因して発生する焼き付き現象を軽減できる。この焼き付き現象の軽減により、液晶パネルの表示品質が従来比で約1.2〜1.5倍程度に長寿命化できることが本願発明者によって確認されている。   In this way, by setting the potentials of the pixel electrode and the counter electrode of the liquid crystal cell 122 to the ground level, the organic material is decomposed by light or heat and is adsorbed on the surfaces of the alignment films 22A and 22B, thereby causing a burn-in phenomenon. As shown in FIG. 3, ions that cause the dissociation are dissociated from the alignment films 22A and 22B. As a result, it is possible to reduce the image sticking phenomenon that occurs due to the ions adsorbed on the interface between the alignment films 22A and 22B or the electrodes 21A and 21B. It has been confirmed by the present inventor that the display quality of the liquid crystal panel can be extended to about 1.2 to 1.5 times longer than that of the prior art by reducing the image sticking phenomenon.

次に、スタンバイモード状態のときに、液晶セル122の画素電極および対向電極の各電位をグランドレベルに設定するための制御手段の具体的な構成について述べる。   Next, a specific configuration of control means for setting each potential of the pixel electrode and the counter electrode of the liquid crystal cell 122 to the ground level in the standby mode state will be described.

先ず、液晶セル122の対向電極の電位をグランドレベルに落とす手法の一例について説明する。液晶セル122の対向電極には、先述したように、VCOM線16を介してVCOM電位が各画素共通に与えられるようになっている。そこで、例えば図1に示すように、VCOM線16の電位供給端16AにスイッチSW1の可動接点aを接続する。このスイッチSW1は、2入力切り替えスイッチであり、VCOM電位を一方の固定接点bの入力とするとともに、グランドレベルを他方の固定接点cの入力としている。   First, an example of a technique for dropping the potential of the counter electrode of the liquid crystal cell 122 to the ground level will be described. As described above, the VCOM potential is commonly applied to each pixel via the VCOM line 16 to the counter electrode of the liquid crystal cell 122. Therefore, for example, as shown in FIG. 1, the movable contact a of the switch SW1 is connected to the potential supply terminal 16A of the VCOM line 16. This switch SW1 is a two-input changeover switch, and the VCOM potential is input to one fixed contact b, and the ground level is input to the other fixed contact c.

このスイッチSW1において、画像表示を行う装置本体の動作時には、可動接点aを固定接点b側に切り替えてVCOM電位を選択することで、当該VCOM電位がVCOM線16を介して画素12の対向電極に対して各画素共通に与えられる。これにより、映像信号に応じて画素12の画素電極に書き込まれる電位に応じた通常の画像表示が行われる。一方、スタンバイモード状態では、スタンバイモード信号に応答して可動接点aを固定接点c側に切り替えてグランドレベルを選択することで、当該グランドレベルがVCOM線16を介して画素12の対向電極に対して各画素共通に与えられる。これにより、液晶セル122の対向電極の電位がグランドレベルとなり、対向電極側の配向膜あるいは電極界面に吸着したイオンが解離するため、焼き付き現象を軽減できる。   In this switch SW1, when the apparatus main body that performs image display is operated, the movable contact a is switched to the fixed contact b side and the VCOM potential is selected, so that the VCOM potential is applied to the counter electrode of the pixel 12 via the VCOM line 16. For each pixel, it is given in common. Thereby, normal image display according to the potential written in the pixel electrode of the pixel 12 according to the video signal is performed. On the other hand, in the standby mode state, in response to the standby mode signal, the movable contact a is switched to the fixed contact c side and the ground level is selected, so that the ground level is applied to the counter electrode of the pixel 12 via the VCOM line 16. Are given in common to each pixel. As a result, the potential of the counter electrode of the liquid crystal cell 122 becomes the ground level, and ions adsorbed on the alignment film on the counter electrode side or the electrode interface are dissociated, so that the image sticking phenomenon can be reduced.

続いて、液晶セル122の画素電極の電位をグランドレベルに落とす手法の一例について説明する。先ず、垂直駆動回路18L,18Rの各々とゲート線14との間に介在するバッファ20L,20Rは、例えば図4に示すように、ゲート電極およびドレイン電極がそれぞれ共通に接続されたPchMOSトランジスタQpおよびNchMOSトランジスタQnからなるCMOSインバータによって構成されている。   Next, an example of a technique for dropping the potential of the pixel electrode of the liquid crystal cell 122 to the ground level will be described. First, buffers 20L and 20R interposed between each of the vertical drive circuits 18L and 18R and the gate line 14 include, for example, a PchMOS transistor Qp having a gate electrode and a drain electrode connected in common as shown in FIG. The CMOS inverter is composed of an Nch MOS transistor Qn.

PchMOSトランジスタQpのソース電極には、電源電圧VDDが印加されている。NchMOSトランジスタQnのソース電極は、スイッチSW2の可動接点aに接続されている。このスイッチSW2は、2入力切り替えスイッチであり、グランドレベルを一方の固定接点bの入力とするとともに、画素トランジスタであるTFT122を導通状態にする電位、例えば電源電圧VDDを他方の固定接点cの入力としている。   A power supply voltage VDD is applied to the source electrode of the PchMOS transistor Qp. The source electrode of the Nch MOS transistor Qn is connected to the movable contact a of the switch SW2. This switch SW2 is a two-input changeover switch, and the ground level is input to one fixed contact b, and a potential for turning on the TFT 122, which is a pixel transistor, for example, a power supply voltage VDD is input to the other fixed contact c. It is said.

このバッファ20L,20Rにおいて、画像表示を行う装置本体の動作時には、スイッチSW2は可動接点aを固定接点b側に切り替えてグランドレベルを選択する。この状態において、垂直駆動回路18L,18Rから低レベルの走査パルスが出力され、バッファ20L,20Rに入力すると、PchMOSトランジスタQpが導通状態となるため、VDDレベルの走査パルスがゲート線14に印加され、行の選択が行われる。垂直駆動回路18L,18Rから低レベルの走査パルスが出力されないときは、NchMOSトランジスタQnが導通状態となるため、ゲート線14の電位がグランドレベルに固定される。これにより、選択対象の行以外の行の画素が選択されるという誤動作を防止できる。   In the buffers 20L and 20R, when the apparatus main body that performs image display is operated, the switch SW2 switches the movable contact a to the fixed contact b side to select the ground level. In this state, when a low level scan pulse is output from the vertical drive circuits 18L and 18R and is input to the buffers 20L and 20R, the PchMOS transistor Qp becomes conductive, so that a VDD level scan pulse is applied to the gate line 14. , Row selection is performed. When the low-level scan pulse is not output from the vertical drive circuits 18L and 18R, the Nch MOS transistor Qn is in a conductive state, so that the potential of the gate line 14 is fixed to the ground level. Thereby, it is possible to prevent a malfunction that a pixel in a row other than the selection target row is selected.

一方、垂直駆動回路18L,18Rから走査パルスが出力されることのないスタンバイモード状態では、スイッチSW2はスタンバイモード信号に応答して可動接点aを固定接点c側に切り替えてVDDレベルを選択する。この状態では、NchMOSトランジスタQnのソース電位がVDDレベルになるため、バッファ20L,20Rの入力電位、即ちNchMOSトランジスタQnのゲート電位が高レベル状態であっても、当該MOSトランジスタQnが導通し、全てのゲート線14の電位がVDDレベルになるため、全ての画素12のTFT121が導通状態になる。   On the other hand, in the standby mode state where no scanning pulse is output from the vertical drive circuits 18L and 18R, the switch SW2 switches the movable contact a to the fixed contact c side in response to the standby mode signal and selects the VDD level. In this state, the source potential of the Nch MOS transistor Qn is at the VDD level. Therefore, even if the input potential of the buffers 20L and 20R, that is, the gate potential of the Nch MOS transistor Qn is in the high level state, the MOS transistor Qn becomes conductive. Since the potential of the gate line 14 becomes the VDD level, the TFTs 121 of all the pixels 12 become conductive.

このとき、全ての信号線15に対して水平駆動回路19からグランドレベルを与えるようにする。これにより、画素アレイ部13の全ての画素12において、導通状態にあるTFT121を通して液晶セル122の画素電極にグランドレベルが書き込まれる。すなわち、全ての画素12において、液晶セル122の画素電極の電位がグランドレベルとなることで、画素電極側の配向膜あるいは電極界面に吸着したイオンが解離するため、焼き付き現象を軽減できる。   At this time, the ground level is applied to all the signal lines 15 from the horizontal drive circuit 19. As a result, the ground level is written to the pixel electrode of the liquid crystal cell 122 through the TFT 121 in the conductive state in all the pixels 12 in the pixel array unit 13. That is, in all the pixels 12, the potential of the pixel electrode of the liquid crystal cell 122 becomes the ground level, so that ions adsorbed on the alignment film on the pixel electrode side or the electrode interface are dissociated, so that the image sticking phenomenon can be reduced.

なお、本例では、スタンバイモード状態のときに、バッファ20L,20Rのグランド側にグランドレベルに代えてVDDレベルを与えることによって全てのゲート線14の電位をVDDレベルにするとしたが、これは一例に過ぎず、この手法に限られるものではなく、要は、スタンバイモード状態のときに全てのゲート線14の電位を、画素トランジスタを導通状態にする電位に設定できる手法であれば良い。例えば、一般的には、スタンバイモード状態では、垂直駆動回路18L,18Rから走査パルスが出力されることはないが、敢えて、スタンバイモード状態のときに垂直駆動回路18L,18Rから走査パルスを全ラインに対して一斉に、あるいは順次に出力するようにすれば、スタンバイモード状態のときに全てのラインの画素トランジスタを導通状態にすることができる。   In this example, in the standby mode state, the potentials of all the gate lines 14 are set to the VDD level by applying the VDD level to the ground side of the buffers 20L and 20R instead of the ground level. However, the present invention is not limited to this method. In short, any method can be used as long as the potentials of all the gate lines 14 can be set to potentials for turning on the pixel transistors in the standby mode state. For example, in general, in the standby mode state, scanning pulses are not output from the vertical drive circuits 18L and 18R. However, in the standby mode state, all lines of the scanning pulses are output from the vertical drive circuits 18L and 18R. If the outputs are made simultaneously or sequentially, the pixel transistors of all the lines can be made conductive in the standby mode.

(適用例)
以上説明した本実施形態に係る液晶表示装置は、例えば3板式液晶プロジェクタ装置に用いて好適なものである。
(Application example)
The liquid crystal display device according to this embodiment described above is suitable for use in, for example, a three-plate liquid crystal projector device.

図5に、液晶プロジェクタ装置の構成の概略を示す。図5において、光源31から発せられる白色光は、第1のビームスプリッタ32で特定の色成分、例えば一番波長の短い青色光(B)の光成分のみが透過し、残りの色の光成分は反射される。第1のビームスプリッタ32を透過した青色光の光成分は、ミラー33で光路が変更され、レンズ34を通して青色用のLCDパネル(液晶パネル)35Bに照射される。   FIG. 5 shows an outline of the configuration of the liquid crystal projector apparatus. In FIG. 5, the white light emitted from the light source 31 is transmitted through the first beam splitter 32 only through a specific color component, for example, the light component of blue light (B) having the shortest wavelength, and the light components of the remaining colors. Is reflected. The light component of the blue light transmitted through the first beam splitter 32 is changed in optical path by the mirror 33 and irradiated to the blue LCD panel (liquid crystal panel) 35B through the lens.

第1のビームスプリッタ32で反射された光成分については、第2のビームスプリッタ36で例えば緑色光(G)の光成分が反射され、赤色光(R)の光成分が透過する。第2のビームスプリッタ36で反射された緑白光の光成分は、レンズ37を通して緑色用のLCDパネル35Gに照射される。第2のビームスプリッタ36を透過した赤色光の光成分は、ミラー38,39で光路が変更され、レンズ40を通して赤色のLCDパネル35Rに照射される。   For the light component reflected by the first beam splitter 32, for example, the light component of green light (G) is reflected by the second beam splitter 36, and the light component of red light (R) is transmitted. The green / white light component reflected by the second beam splitter 36 is applied to the green LCD panel 35G through the lens 37. The optical component of the red light transmitted through the second beam splitter 36 is irradiated to the red LCD panel 35R through the lens 40 after the optical path is changed by the mirrors 38 and 39.

LCDパネル35R,35G,35Bは各々、複数の画素がマトリクス状に配置されてなる第1の基板と、この第1の基板に対して所定の間隔をもって対向配置された第2の基板と、これら基板間に保持された液晶層と、各色に対応したフィルタ層とを有する構成となっている。これらLCDパネル35R,35G,35Bを経た赤色、緑色、青色の各光は、クロスプリズム41で光合成される。そして、このクロスプリズム41から出射される合成光は、投射プリズム42によってスクリーン43に投射される。   Each of the LCD panels 35R, 35G, and 35B includes a first substrate in which a plurality of pixels are arranged in a matrix, a second substrate that is opposed to the first substrate with a predetermined interval, and these The liquid crystal layer held between the substrates and a filter layer corresponding to each color are provided. The red, green, and blue lights that have passed through the LCD panels 35R, 35G, and 35B are combined by the cross prism 41. The combined light emitted from the cross prism 41 is projected onto the screen 43 by the projection prism 42.

かかる構成の3板式液晶プロジェクタ装置において、LCDパネル35R,35G,35Bとして先述した実施形態に係る液晶表示装置を用いることで、当該液晶表示装置では光や熱で有機材料が分解してイオンが発生し、当該イオンが配向膜や電極界面に吸着することに起因して発生する焼き付き現象を軽減できるため、LCDパネル35R,35G,35Bの寿命を延命できるとともに、焼き付き現象に起因する画質不良を解消できる。青色光は、緑色光、赤色光に比べてエネルギーが大きいため、青色用のLCDパネル35Bに光による有機材料の劣化が起きる可能性が高いが、3板式液晶プロジェクタ装置において、特に青色用のLCDパネル35Bに先述した実施形態に係る液晶表示装置を適用することで、イオンによる焼き付き現象の軽減効果が大である。   By using the liquid crystal display device according to the above-described embodiment as the LCD panels 35R, 35G, and 35B in the three-plate liquid crystal projector device having such a configuration, in the liquid crystal display device, organic materials are decomposed by light or heat to generate ions. In addition, the burn-in phenomenon that occurs due to the ions adsorbing to the alignment film or the electrode interface can be reduced, so the life of the LCD panels 35R, 35G, and 35B can be extended, and image quality defects due to the burn-in phenomenon can be eliminated. it can. Since blue light has higher energy than green light and red light, there is a high possibility that the organic material will be deteriorated by light in the blue LCD panel 35B. By applying the liquid crystal display device according to the above-described embodiment to the panel 35B, the effect of reducing the image sticking phenomenon due to ions is great.

本発明の一実施形態に係る液晶表示装置を示す概略構成図である。It is a schematic block diagram which shows the liquid crystal display device which concerns on one Embodiment of this invention. 液晶パネルの断面構造図である。It is a cross-section figure of a liquid crystal panel. 配向膜からイオンが解離する様子を示す図である。It is a figure which shows a mode that ion dissociates from alignment film. バッファの構成の一例を示す回路図である。It is a circuit diagram which shows an example of a structure of a buffer. 本発明が適用される液晶プロジェクタ装置の構成の一例を示すブロック図である。It is a block diagram which shows an example of a structure of the liquid crystal projector device with which this invention is applied. 焼き付き現象が発生する過程を示す図である。It is a figure which shows the process in which the image sticking phenomenon occurs.

符号の説明Explanation of symbols

10…液晶パネル、11,11A,11B…ガラス基板、12…画素、13…画素アレイ部、14…ゲート線、15…信号線、18L,18R…垂直駆動回路、19…水平駆動回路、20L,20R…バッファ、21A,21B…透明電極、22A,22B…配向膜、23…液晶層、121…TFT(画素トランジスタ)、122…液晶セル、123…保持容量   DESCRIPTION OF SYMBOLS 10 ... Liquid crystal panel, 11, 11A, 11B ... Glass substrate, 12 ... Pixel, 13 ... Pixel array part, 14 ... Gate line, 15 ... Signal line, 18L, 18R ... Vertical drive circuit, 19 ... Horizontal drive circuit, 20L, 20R ... buffer, 21A, 21B ... transparent electrode, 22A, 22B ... alignment film, 23 ... liquid crystal layer, 121 ... TFT (pixel transistor), 122 ... liquid crystal cell, 123 ... retention capacitor

Claims (6)

液晶セルおよび画素トランジスタを含む画素が行列状に2次元配置されてなる画素アレイ部と、
画像表示を行う動作時以外のときに、前記液晶セルの画素電極および対向電極の少なくとも一方の電位をグランドレベルにする制御手段と
を備えたことを特徴とする液晶表示装置。
A pixel array unit in which pixels including liquid crystal cells and pixel transistors are two-dimensionally arranged in a matrix;
A liquid crystal display device comprising: control means for setting a potential of at least one of the pixel electrode and the counter electrode of the liquid crystal cell to a ground level when the image display is not performed.
前記制御手段は、画像表示を行う動作時以外のときに、前記液晶セルの対向電極に対して全画素共通に所定の電位を与える配線の電位をグランドレベルにする
ことを特徴とする請求項1記載の液晶表示装置。
2. The control means sets the potential of a wiring that applies a predetermined potential in common to all the pixels to the counter electrode of the liquid crystal cell to a ground level at a time other than an operation for performing image display. The liquid crystal display device described.
前記制御手段は、画像表示を行う動作時以外のときに、前記画素トランジスタを導通状態にするとともに、当該画素トランジスタに映像信号を供給する信号線の電位をグランドレベルにする
ことを特徴とする請求項1記載の液晶表示装置。
The control means makes the pixel transistor conductive when it is not during an image display operation and sets the potential of a signal line for supplying a video signal to the pixel transistor to a ground level. Item 2. A liquid crystal display device according to item 1.
液晶セルおよび画素トランジスタを含む画素が行列状に2次元配置されてなる画素アレイ部を備えた液晶表示装置の駆動方法であって、
画像表示を行う動作時以外のときに、前記液晶セルの画素電極および対向電極の少なくとも一方の電位をグランドレベルにする
ことを特徴とする液晶表示装置の駆動方法。
A method of driving a liquid crystal display device including a pixel array unit in which pixels including liquid crystal cells and pixel transistors are two-dimensionally arranged in a matrix,
A method for driving a liquid crystal display device, characterized in that, at a time other than during an image display operation, the potential of at least one of the pixel electrode and the counter electrode of the liquid crystal cell is set to a ground level.
画像表示を行う動作時以外のときに、前記液晶セルの対向電極に対して全画素共通に所定の電位を与える配線の電位をグランドレベルにする
ことを特徴とする請求項4記載の液晶表示装置の駆動方法。
5. The liquid crystal display device according to claim 4, wherein a potential of a wiring that applies a predetermined potential to all the pixels in common with respect to the counter electrode of the liquid crystal cell is set to a ground level when the image display is not performed. Driving method.
画像表示を行う動作時以外のときに、前記画素トランジスタを導通状態にするとともに、当該画素トランジスタに映像信号を供給する信号線の電位をグランドレベルにする
ことを特徴とする請求項4記載の液晶表示装置の駆動方法。
5. The liquid crystal according to claim 4, wherein the pixel transistor is set in a conductive state at a time other than an operation for performing image display, and a potential of a signal line for supplying a video signal to the pixel transistor is set to a ground level. A driving method of a display device.
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US8068079B2 (en) 2007-10-18 2011-11-29 Canon Kabushiki Kaisha Liquid crystal display apparatus
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