JP4477160B2 - Gradation method of bistable liquid crystal cell - Google Patents
Gradation method of bistable liquid crystal cell Download PDFInfo
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- 239000004973 liquid crystal related substance Substances 0.000 title claims description 98
- 210000002858 crystal cell Anatomy 0.000 title claims description 61
- 238000000034 method Methods 0.000 title claims description 23
- 238000012935 Averaging Methods 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 2
- 239000010409 thin film Substances 0.000 claims description 2
- 230000009977 dual effect Effects 0.000 claims 1
- 238000010586 diagram Methods 0.000 description 10
- 238000002834 transmittance Methods 0.000 description 9
- 230000007704 transition Effects 0.000 description 5
- 230000003446 memory effect Effects 0.000 description 4
- 230000005684 electric field Effects 0.000 description 3
- 238000010998 test method Methods 0.000 description 3
- 239000010408 film Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 239000004988 Nematic liquid crystal Substances 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 210000004027 cell Anatomy 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL 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
- G02F1/00—Devices 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
- G02F1/01—Devices 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
- G02F1/13—Devices 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
- G02F1/137—Devices 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 characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
- G02F1/139—Devices 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 characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
- G02F1/1391—Bistable or multi-stable liquid crystal cells
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control 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
- G09G3/34—Control 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
- G09G3/36—Control 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
- G09G3/3611—Control of matrices with row and column drivers
- G09G3/3622—Control of matrices with row and column drivers using a passive matrix
- G09G3/3629—Control of matrices with row and column drivers using a passive matrix using liquid crystals having memory effects, e.g. ferroelectric liquid crystals
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control 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
- G09G3/34—Control 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
- G09G3/36—Control 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
- G09G3/3611—Control of matrices with row and column drivers
- G09G3/3648—Control of matrices with row and column drivers using an active matrix
- G09G3/3651—Control of matrices with row and column drivers using an active matrix using multistable liquid crystals, e.g. ferroelectric liquid crystals
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G2300/00—Aspects of the constitution of display devices
- G09G2300/04—Structural and physical details of display devices
- G09G2300/0469—Details of the physics of pixel operation
- G09G2300/0478—Details of the physics of pixel operation related to liquid crystal pixels
- G09G2300/0482—Use of memory effects in nematic liquid crystals
- G09G2300/0486—Cholesteric liquid crystals, including chiral-nematic liquid crystals, with transitions between focal conic, planar, and homeotropic states
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- General Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- Theoretical Computer Science (AREA)
- Nonlinear Science (AREA)
- Optics & Photonics (AREA)
- Liquid Crystal (AREA)
- Liquid Crystal Display Device Control (AREA)
- Control Of Indicators Other Than Cathode Ray Tubes (AREA)
Description
【０００１】
【発明の属する技術分野】
本発明は双安定液晶セル（Bistable Twisted Nematic Cell）の階調方法に関する。さらに詳しくは、とくに二つの準安定状態をもつ双安定液晶セルに印加する電圧レベルを調節して多階調を具現できる双安定液晶セルの階調方法に関する。
【０００２】
【従来の技術】
液晶は物質特性上、長軸方向と短軸方向の誘電率が異なるために、外部の電界によって配列方向が変わる。
【０００３】
とくに、ネマティック液晶にカイラル物質が添加された双安定液晶は、０度と３６０度の二つの準安定状態をもつものであり、このような双安定液晶を採用した液晶表示装置は、そのスイッチング速度を速くすることが可能でありながらも低電力駆動が可能なため、動画像の具現により有利である。またその視野角が広くコントラスト比が高いという長所をもっているなどの全般的に優秀な特性をもっているので、未来の情報化時代に主導的な役割をする表示装置の一つとして注目されている。
【０００４】
双安定液晶セルは、印加される電界によって二つの準安定状態になる双安定特性をもっており、多階調を具現するのに有利である。
【０００５】
このような特性をもった双安定液晶セルのスイッチングタイムを減らして多階調を具現できるようにした駆動方式に関して、本出願人は韓国特許出願第９８−８５２号を出願している。
【０００６】
この出願では、単に双安定液晶セルに印加する駆動信号であるリセットパルスと選択パルスとのあいだに休止時間を与えて、液晶分子が応答するスイッチングタイムを２μｓまで減らすようにすることによって、フレーム変調による動画像の多階調を具現した。
【０００７】
しかし、前述した双安定液晶セルの階調方法は、複数個のフレームを一つの単位として階調表示を行なうものであり、何段階の階調が可能かどうかは前記スイッチングタイムに依存する。そのために、高解像度画面において動画像の多階調を具現するには限界があり、現在はスイッチングタイムを支援するドライバー接続素子さえ開発できずにいる実情であって実用化が難しいという問題点を抱えている。
【０００８】
【発明が解決しようとする課題】
前述した従来の問題点を解決するためになされた本発明は、双安定液晶セルがもっている双安定特性を利用してスイッチングタイムを減らさなくても高解像度の動画像で、多階調を具現できる双安定液晶セルの階調方法を提供することを目的とする。
【０００９】
【課題を解決するための手段】
本発明の双安定液晶セルの階調方法は、初期配向角がθ１のツイスト状態にある液晶分子が、リセットパルスの印加後に印加される選択パルスの電圧レベルによって、前記初期角度θ１から液晶分子の転移角度θ２を引いた角度θ１−θ２にツイストされる第１準安定状態と、前記初期角度θ１に液晶分子の転移角度θ２を加算した角度θ１＋θ２にツイストされる第２準安定状態をもつ双安定液晶セルの多階調を表示する方法であって、二つの準安定状態が混在して現われる混在領域内で液晶セルに印加する電圧を調整することによって、前記二つの準安定状態の混在比率を変化させて多階調を表示することを特徴とする。
【００１０】
前記混在領域が、前記第１準安定状態と第２準安定状態を混在させる臨界電圧と、第１準安定状態と第２準安定状態が混在する状態から第２準安定状態に突入させる飽和電圧とのあいだであるのが好ましい。
【００１１】
前記混在領域が、液晶セルに印加される電圧の上昇により第１臨界電圧と第１飽和電圧とのあいだにおいて形成される第１混在領域と、第２臨界電圧と第２飽和電圧とのあいだにおいて形成される第２混在領域として現われるのが好ましい。
【００１２】
前記第１混在領域と第２混在領域の中のどちらか一つの領域内において電圧を調整することにより多階調を表現するのが好ましい。
【００１３】
前記二つの準安定状態の混在比率は、液晶セルに印加するリセットパルスと選択パルスの電圧の両方を変化させて調整するのが好ましい。
【００１４】
前記二つの準安定状態の混在比率は、液晶セルに印加する前記リセットパルスの電圧を固定し、前記選択パルスの電圧を変化させて調整するのが好ましい。
【００１５】
前記液晶セルに印加する電圧は、時分割駆動方式の電圧平均化法により調整するのが好ましい。
【００１６】
前記電圧平均化法は、コモン電圧のハイレベルをリセット電圧の臨界電圧未満にし、コモン電圧のローレベルを選択電圧の臨界電圧未満にし、セグメント電圧を所定の範囲内で変化させることによって、液晶セルに印加するリセット電圧と選択電圧を調整するのが好ましい。
【００１７】
前記液晶セルに信号電圧を印加するスイッチング手段として、薄膜トランジスターを使用するのが好ましい。
【００１８】
【発明の実施の形態】
以下、図面を参照しながら本発明をより具体的に説明する。
【００１９】
まず、本発明の理解を助けるため、図６〜図７を参照しつつ本発明にかかわる通常の双安定液晶セルの動作特性について説明する。
【００２０】
無電界の初期状態において、双安定液晶セル１０内の液晶分子１１は図６（ａ）のようにツイスト角度がθ１の配向状態をしている。
【００２１】
このような初期状態において、図８に図示したように一定電圧（Freedericksz電圧）以上のリセットパルスを所定電圧Ｖｒで所定時間Ｗｒ印加すると、液晶分子１１は、図６（ｂ）のように基板１０ａ面に対して垂直に立つホメオトロピック（homeotropic）状態になり、リセット電圧Ｖｒが下がって休止時間Ｗｄの経過後、液晶分子のツイスト角度は初期のθ１の状態に戻らず、図７（ｂ）に図示したように、θ１＋θ２の第２準安定状態（ブラックモード）になり、これがメモリー効果によって所定時間維持されたのち、初期状態に戻る。
【００２２】
一方、双安定液晶セル１０にリセットパルスを印加し、休止時間を与えたのち、再び臨界電圧より高い選択パルスの電圧Ｖｓを一定時間Ｗｓ印加すると、液晶分子１１はホメオトロピック状態から図７（ａ）に図示したように、θ１−θ２の第１準安定状態（ホワイトモード）になり、それを所定時間維持する。
【００２３】
前記θ１は、配向膜のラビングによって変化する初期配向角であり、前記θ２は液晶分子がツイストされる転移角度であり、今まで知られているのは１８０度程度である。
【００２４】
したがって、前記θ１を１８０度になるように液晶分子を配向させ、図９のような波形のパルスを印加した場合、ＰＳ１区間において液晶分子は３６０度にツイストされたブラックモードになり、ＰＳ２区間では液晶分子は０度ツイストされたホワイトモードになる。ただし、前記ホワイトモードとブラックモードは偏光板の付着角度によりお互いに反転する。
【００２５】
本発明は図５（ａ）および図５（ｂ）に図示したように、パネル２上の単位画素２４内にホワイトモードＷとブラックモードＢを混在させると同時に、その混在比率を液晶セルに印加する電圧レベルを変化させて調整することによって、動画像のフルカラーを具現できるようにする。
【００２６】
つまり、本発明の初期角度θ１から液晶分子の転移角度θ２を引いた角度θ１−θ２にツイストされてホワイトモードを表示する第１準安定状態と、初期角度θ１に液晶分子の転移角度θ２を加算した角度θ１＋θ２にツイストされてブラックモードを表示する第２準安定状態とが単位画素２４内に混在して現われる混在領域内において、液晶セルの単位電極に印加する電圧を変化させることによって、前記二つの準安定状態、すなわちホワイトモードとブラックモードの混在比率を変化させるのである。
【００２７】
ここで、前記混在領域は、第１準安定状態と第２準安定状態が混在し始める臨界電圧と第１準安定状態と第２準安定状態が混在する状態から第２準安定状態に突入させる飽和電圧とのあいだである。
【００２８】
したがって、双安定液晶セルに印加する駆動信号の電圧レベルを臨界電圧と飽和電圧とのあいだで調節すれば、単位画素内に分布する液晶分子をツイスト角がθ１−θ２である第１準安定状態とツイスト角がθ１＋θ２である第２準安定状態で混在させることができ、この混在比率を調整して液晶の透過度を変化させることができる。
【００２９】
図１は、本発明における電圧の変化に対する液晶セルの透過度（Transmittance）を示した特性線図である。この図は一定区間において液晶セルに印加するリセットパルスおよび選択パルスの電圧に依存して液晶の透過度が変化することを示している。
【００３０】
前記のような結果データは、双安定液晶セルに印加するリセットパルスの電圧Ｖｒと選択パルスの電圧Ｖｓの比を５０：７、リセットパルスの幅Ｗｒは５００ｍｓ、選択パルスの幅Ｗｓは５０μｓ、リセットパルスと選択パルスとのあいだに与える休止時間の幅Ｗｄは５００ｍｓとし、そしてリセットパルスの電圧Ｖｒを３０Ｖから５０Ｖまでゆっくりと変化させながら液晶セルの透過度の変化を測定して得たものである。
【００３１】
前記結果により、液晶の透過度が可変させられる電圧の範囲（混在領域ＭＤ）は、液晶セルに印加する電圧が臨界電圧Ｖｔｈになる時点、つまりブラックモードＢの領域がおわる部分から現われ、前記混在領域ＭＤ内における混在比率は液晶セルに印加される電圧の上昇にしたがって変化して液晶の透過度を増加させる。液晶セルに印加される電圧が飽和電圧Ｖｓａｔに至れば、混在領域ＭＤは消え、ホワイトモードＷになることが分かる。
【００３２】
したがって、リセットパルスおよび選択パルスの電圧を同じ変動率にして可変させると多階調を表示できる。このようにリセットパルスと選択パルスの電圧を調節するためには、図２に示したようにコモン電圧とセグメント電圧の電位差を与える電圧平均化法を使うことが望ましい。
【００３３】
図示したコモン電圧のハイレベルＶＨは、リセットパルスの電圧を与えるためのものであり、コモン電圧のローレベルＶＬは選択パルスの電圧を与えるためのものである。このとき、前記コモン電圧のＶＨおよびＶＬのレベルは、前述したリセットパルスおよび選択パルスの臨界電圧Ｖｔｈ未満にしなければならないが、それはセグメント電圧の調節によって、前記リセットパルスおよび選択パルスの臨界電圧Ｖｔｈ以上の駆動電圧を付与するためである。
【００３４】
つまり、液晶セルをスキャンニングするコモン電圧のＶＨおよびＶＬにそれぞれリセット電圧および選択電圧の臨界電圧Ｖｔｈ未満の電圧を加え、セグメント電圧によって前記リセット電圧および選択電圧を臨界電圧Ｖｔｈ以上に調節して図１に図示した混在領域ＭＤからホワイトモードＷ領域まで透過図を変化できるようにする。
【００３５】
図３は、コモン電圧をＶＨとＶＬに固定してセグメント電圧を変化させながら測定した液晶の透過度特性を示している。
【００３６】
このような測定データは、本出願人の繰り返し試験によって得られたものであり、つぎの実施例を通じて試験に使用した液晶表示装置の試験方法と駆動条件について説明する。
実施例
本発明の実施例で使用した液晶表示装置の試験方法は、下記のごとくである。
【００３７】
使用液晶：ＺＬＩ−１５５７（ドイツのメルック(Merck)社製）
配向剤：ＳＥ−３１４０（日本のニッサン化学社製）
Ｃｅｌｌ−Ｇａｐ：２．２μｍ
液晶の初期配向角：１８０度
上下偏光板の角度：配向膜のラビング角度に対して４５度にし、二枚の偏光板をお互いにクロスさせる。
【００３８】
そして、前述した試験方法で製作した液晶表示装置を、図２に図示したようにコモン電圧とセグメント電圧による電圧平均化法で駆動させる。その電圧レベルは、コモン電圧のＶＨを５０Ｖにして５００ｍｓ、コモン電圧のＶＬは２Ｖにして５０μｓ間印加して固定し、セグメント電圧の時間幅は５０μｓにして−３Ｖから−６Ｖまでゆっくりと変化させる。
【００３９】
このようにコモン電圧のＶＨおよびＶＬをそれぞれリセットパルスおよび選択パルスの臨界電圧Ｖｔｈ未満に固定し、セグメント電圧を変化させることによって、リセットパルスおよび選択パルスの電圧をそれぞれ臨界電圧Ｖｔｈと飽和電圧Ｖｓａｔとのあいだで可変させる。それにより単位画素２４内に一緒に分布している第１準安定状態のホワイトモードＷと第２準安定状態のブラックモードＢの混在比率を調節して液晶の透過度を変化させることによって多階調を具現できる。
【００４０】
このように単位画素当たりの透過度を調節することができる双安定液晶セルは、前記の混在領域ＭＤ内においても液晶分子が０度および３６０度の準安定状態と同じメモリー効果をもっていてこそ多階調の具現が可能である。
【００４１】
それを確認するために行なった数回の反復試験によると、特定の電圧範囲内において液晶分子は０度および３６０度の準安定状態と同じメモリー効果をもつことが確認され、そのメモリー時間はつぎの表１に示したとおりである。ただし、コモン電圧はＶＨを５０Ｖにして５００ｍｓ、ＶＬを２Ｖにして５０μｓ間印加する。
【００４２】
【表１】
このように双安定液晶セルの液晶分子は、混在領域ＭＤ内においてもメモリー効果をもつことにより多階調の画像表示を可能にする。
【００４４】
一方、前記の混在領域ＭＤは、液晶材料の物性やパルス印加方法によって多数回現われることもあるので、本発明の階調方法は前述したような一回の混在領域の特性をもった双安定液晶セルに適用することに限らず、複数回の混在領域の特性をもった液晶セルにも適用できる。
【００４５】
たとえば、図４に図示したように液晶セルに印加する電圧の上昇によって、第１臨界電圧Ｖｔｈ１と第１飽和電圧Ｖｓａｔ１とのあいだに存在する第１混在領域ＭＤ１と、第２臨界電圧Ｖｔｈ２と第２飽和電圧Ｖｓａｔ２とのあいだに存在する第２混在領域ＭＤ２が現われる場合、このような特性をもった液晶セルを採用した液晶表示装置は、前記の第１混在領域ＭＤ１と第２混在領域ＭＤ２の中から一つの領域だけを選択して液晶セルに印加する電圧を調整することによって多階調を表示できる。
【００４６】
【発明の効果】
以上説明したように、本発明は双安定液晶セルに印加する電圧の調節によって、単位画素内に双安定液晶セルがもっている二つの準安定状態が混在されるようにすると同時に、その混在比率を調節することによって階調表示が可能になって高解像度の動画像をフルカラーで具現できる。
【００４７】
一方、本発明は特定の望ましい実施例に限られることなく、請求項に記載された範囲内において当業界の通常の知識によって多様な応用が可能であることは勿論である。
【図面の簡単な説明】
【図１】本発明における電圧変化に対する液晶セルの透過度の特性線図である。
【図２】本発明の実施例による液晶セルの駆動信号波形図である。
【図３】図２の波形で駆動させた液晶セルの透過度の特性線図である。
【図４】本発明の実施例による混在領域を示したグラフである。
【図５】本発明によって具現される二つの準安定の混在状態を示したパネルの正面図およびそのパネルを形成する画素の液晶層配列状態図である。
【図６】本発明にかかわる通常の双安定液晶セルのツイスト状態図である。
【図７】本発明にかかわる通常の双安定液晶セルのツイスト状態図である。
【図８】本発明にかかわる通常の双安定液晶セルの駆動パルス波形図である。
【図９】本発明にかかわる通常の双安定液晶セルの駆動パルス波形図である。
【符号の説明】
２４ 単位画素
Ｗ ホワイト領域
Ｂ ブラック領域
ＭＤ 混在領域域[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a gradation method for a bistable liquid crystal cell. More particularly, the present invention relates to a gradation method for a bistable liquid crystal cell that can implement multiple gradations by adjusting the voltage level applied to the bistable liquid crystal cell having two metastable states.
[0002]
[Prior art]
Since liquid crystals have different dielectric constants in the major axis direction and the minor axis direction due to material properties, the alignment direction is changed by an external electric field.
[0003]
In particular, a bistable liquid crystal in which a chiral substance is added to a nematic liquid crystal has two metastable states of 0 degrees and 360 degrees, and a liquid crystal display device employing such a bistable liquid crystal has a switching speed of Since it is possible to drive at low power while being able to increase the speed, it is more advantageous to implement a moving image. In addition, it has excellent characteristics such as wide viewing angle and high contrast ratio, so it has attracted attention as one of the display devices that play a leading role in the future information age.
[0004]
The bistable liquid crystal cell has a bistable characteristic in which two metastable states are brought about by an applied electric field, which is advantageous for realizing multi-gradation.
[0005]
The present applicant has filed Korean Patent Application No. 98-852 regarding a drive system that can realize multi-gradation by reducing the switching time of a bistable liquid crystal cell having such characteristics.
[0006]
In this application, frame modulation is performed by providing a pause time between a reset pulse, which is a driving signal applied to a bistable liquid crystal cell, and a selection pulse, thereby reducing the switching time to which liquid crystal molecules respond to 2 μs. Realized the multi-gradation of the moving image by.
[0007]
However, the gradation method of the bistable liquid crystal cell described above performs gradation display using a plurality of frames as one unit, and how many gradations are possible depends on the switching time. For this reason, there is a limit to the realization of multi-gradation of moving images on a high-resolution screen, and it is currently difficult to develop even a driver connection element that supports switching time, which is difficult to put into practical use. I have it.
[0008]
[Problems to be solved by the invention]
The present invention, which has been made to solve the above-mentioned conventional problems, realizes multi-gradation with a high-resolution moving image without reducing the switching time by utilizing the bistable characteristics of the bistable liquid crystal cell. An object is to provide a gradation method for a bistable liquid crystal cell.
[0009]
[Means for Solving the Problems]
According to the gray scale method of the bistable liquid crystal cell of the present invention, the liquid crystal molecules in the twisted state having an initial alignment angle of θ1 are changed from the initial angle θ1 to the liquid crystal molecules according to the voltage level of the selection pulse applied after the reset pulse is applied. A bistable state having a first metastable state twisted to an angle θ1−θ2 obtained by subtracting the transition angle θ2 and a second metastable state twisted to an angle θ1 + θ2 obtained by adding the transition angle θ2 of liquid crystal molecules to the initial angle θ1. A method of displaying multi-gradation of a liquid crystal cell, wherein the mixing ratio of the two metastable states is adjusted by adjusting the voltage applied to the liquid crystal cell in a mixed region where two metastable states appear together. It is characterized by displaying multiple gradations by changing.
[0010]
The mixed region includes a critical voltage for mixing the first metastable state and the second metastable state, and a saturation voltage for entering the second metastable state from a state where the first metastable state and the second metastable state are mixed. It is preferable to be between.
[0011]
The mixed region is formed between the first critical voltage and the first saturation voltage and the second critical voltage and the second saturation voltage formed between the first critical voltage and the first saturation voltage due to an increase in voltage applied to the liquid crystal cell. It preferably appears as a second mixed region to be formed.
[0012]
It is preferable to express multi-gradation by adjusting the voltage in one of the first mixed region and the second mixed region.
[0013]
The mixing ratio of the two metastable states is preferably adjusted by changing both the reset pulse voltage and the selection pulse voltage applied to the liquid crystal cell.
[0014]
The mixing ratio of the two metastable states is preferably adjusted by fixing the voltage of the reset pulse applied to the liquid crystal cell and changing the voltage of the selection pulse.
[0015]
The voltage applied to the liquid crystal cell is preferably adjusted by a time-division driving voltage averaging method.
[0016]
In the voltage averaging method, the high level of the common voltage is made less than the critical voltage of the reset voltage, the low level of the common voltage is made less than the critical voltage of the selection voltage, and the segment voltage is changed within a predetermined range. It is preferable to adjust the reset voltage and the selection voltage applied to.
[0017]
A thin film transistor is preferably used as a switching means for applying a signal voltage to the liquid crystal cell.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described more specifically with reference to the drawings.
[0019]
First, in order to help understanding of the present invention, the operation characteristics of a normal bistable liquid crystal cell according to the present invention will be described with reference to FIGS.
[0020]
In the initial state of no electric field, the
[0021]
In such an initial state, when a reset pulse of a predetermined voltage (Freedericksz voltage) or more is applied at a predetermined voltage Vr for a predetermined time Wr as shown in FIG. 8, the
[0022]
On the other hand, when a reset pulse is applied to the bistable
[0023]
The θ1 is an initial alignment angle that changes due to the rubbing of the alignment film, and the θ2 is a transition angle at which the liquid crystal molecules are twisted.
[0024]
Therefore, when the liquid crystal molecules are aligned so that θ1 is 180 degrees and a pulse having a waveform as shown in FIG. 9 is applied, the liquid crystal molecules are in a black mode twisted at 360 degrees in the PS1 section, and in the PS2 section. The liquid crystal molecules enter a white mode twisted 0 degree. However, the white mode and the black mode are reversed to each other depending on the adhesion angle of the polarizing plate.
[0025]
In the present invention, as shown in FIGS. 5A and 5B, the white mode W and the black mode B are mixed in the
[0026]
That is, the first metastable state in which the white mode is displayed by twisting to the angle θ1-θ2 obtained by subtracting the transition angle θ2 of the liquid crystal molecules from the initial angle θ1 of the present invention, and the transition angle θ2 of the liquid crystal molecules is added to the initial angle θ1. By changing the voltage applied to the unit electrode of the liquid crystal cell in the mixed region where the second metastable state in which the black mode is displayed by being twisted at the angle θ1 + θ2 appears mixedly in the
[0027]
Here, the mixed region enters the second metastable state from the critical voltage at which the first metastable state and the second metastable state begin to coexist, and the state where the first metastable state and the second metastable state coexist. Between the saturation voltage.
[0028]
Therefore, if the voltage level of the driving signal applied to the bistable liquid crystal cell is adjusted between the critical voltage and the saturation voltage, the liquid crystal molecules distributed in the unit pixel are in the first metastable state where the twist angle is θ1−θ2. Can be mixed in the second metastable state in which the twist angle is θ1 + θ2, and the transmittance of the liquid crystal can be changed by adjusting the mixing ratio.
[0029]
FIG. 1 is a characteristic diagram showing the transmittance of a liquid crystal cell with respect to a change in voltage in the present invention. This figure shows that the transmissivity of the liquid crystal changes depending on the voltage of the reset pulse and the selection pulse applied to the liquid crystal cell in a certain interval.
[0030]
The above result data shows that the ratio of the reset pulse voltage Vr to the selection pulse voltage Vs applied to the bistable liquid crystal cell is 50: 7, the reset pulse width Wr is 500 ms, the selection pulse width Ws is 50 μs, and the reset pulse is reset. The width Wd of the pause time given between the pulse and the selection pulse is 500 ms, and the change in the transmittance of the liquid crystal cell is measured while slowly changing the voltage Vr of the reset pulse from 30 V to 50 V. .
[0031]
As a result, the voltage range (mixed region MD) in which the transmittance of the liquid crystal can be varied appears when the voltage applied to the liquid crystal cell reaches the critical voltage Vth, that is, from the portion where the black mode B region ends. The mixing ratio in the region MD changes as the voltage applied to the liquid crystal cell increases to increase the transmittance of the liquid crystal. It can be seen that when the voltage applied to the liquid crystal cell reaches the saturation voltage Vsat, the mixed region MD disappears and the white mode W is entered.
[0032]
Therefore, multi-gradation can be displayed by varying the reset pulse voltage and the selection pulse voltage with the same variation rate. In order to adjust the voltages of the reset pulse and the selection pulse in this way, it is desirable to use a voltage averaging method that gives a potential difference between the common voltage and the segment voltage as shown in FIG.
[0033]
The high level VH of the illustrated common voltage is for applying a reset pulse voltage, and the low level VL of the common voltage is for applying a selection pulse voltage. At this time, the levels of the VH and VL of the common voltage must be lower than the critical voltage Vth of the reset pulse and the selection pulse described above, which is higher than the critical voltage Vth of the reset pulse and the selection pulse by adjusting the segment voltage. This is because a driving voltage of 1 is applied.
[0034]
That is, a voltage lower than the critical voltage Vth of the reset voltage and the selection voltage is applied to the common voltages VH and VL for scanning the liquid crystal cell, respectively, and the reset voltage and the selection voltage are adjusted to the critical voltage Vth or more by the segment voltage. The transmission diagram can be changed from the mixed area MD shown in 1 to the white mode W area.
[0035]
FIG. 3 shows the transmittance characteristics of the liquid crystal measured while changing the segment voltage while fixing the common voltage to VH and VL.
[0036]
Such measurement data is obtained by the applicant's repeated test, and the test method and driving conditions of the liquid crystal display device used for the test will be described through the following examples.
Examples The test method of the liquid crystal display device used in the examples of the present invention is as follows.
[0037]
Liquid crystal used: ZLI-1557 (Merck, Germany)
Orienting agent: SE-3140 (manufactured by Nissan Chemical Industries, Japan)
Cell-Gap: 2.2 μm
Initial alignment angle of liquid crystal: 180 degrees Angle of upper and lower polarizing plates: 45 degrees with respect to rubbing angle of alignment film, and two polarizing plates are crossed with each other.
[0038]
Then, the liquid crystal display device manufactured by the test method described above is driven by a voltage averaging method using a common voltage and a segment voltage as shown in FIG. The voltage level is 500 ms with the common voltage VH of 50 V, the VL of the common voltage is fixed to 2 V and applied for 50 μs, and the time width of the segment voltage is slowly changed from −3 V to −6 V with 50 μs. .
[0039]
In this way, by fixing the common voltages VH and VL below the critical voltage Vth of the reset pulse and the selection pulse, respectively, and changing the segment voltage, the voltages of the reset pulse and the selection pulse are changed to the critical voltage Vth and the saturation voltage Vsat, respectively. It is made variable between. As a result, by adjusting the mixing ratio of the white mode W in the first metastable state and the black mode B in the second metastable state that are distributed together in the
[0040]
In this way, the bistable liquid crystal cell in which the transmittance per unit pixel can be adjusted is multi-level only if the liquid crystal molecules have the same memory effect as the metastable states of 0 degrees and 360 degrees in the mixed region MD. Realization of the key is possible.
[0041]
According to several repeated tests conducted to confirm this, liquid crystal molecules have been confirmed to have the same memory effect as the metastable states of 0 degrees and 360 degrees within a specific voltage range. As shown in Table 1. However, the common voltage is applied for 50 ms by setting VH to 50 V and 500 ms, and VL to 2 V.
[0042]
[Table 1]
Thus, the liquid crystal molecules of the bistable liquid crystal cell enable multi-tone image display by having a memory effect even in the mixed region MD.
[0044]
On the other hand, the mixed region MD may appear many times depending on the physical properties of the liquid crystal material and the pulse application method. Therefore, the gradation method of the present invention is a bistable liquid crystal having the characteristics of a single mixed region as described above. The present invention can be applied not only to a cell but also to a liquid crystal cell having a mixed region characteristic multiple times.
[0045]
For example, as shown in FIG. 4, the first mixed region MD1 existing between the first critical voltage Vth1 and the first saturation voltage Vsat1, the second critical voltage Vth2 and the second critical voltage Vth1 due to the increase in the voltage applied to the liquid crystal cell. When the second mixed region MD2 existing between the two saturation voltages Vsat2 appears, the liquid crystal display device adopting the liquid crystal cell having such characteristics has the first mixed region MD1 and the second mixed region MD2 described above. Multiple gradations can be displayed by selecting only one region from the inside and adjusting the voltage applied to the liquid crystal cell.
[0046]
【The invention's effect】
As described above, according to the present invention, by adjusting the voltage applied to the bistable liquid crystal cell, two metastable states having the bistable liquid crystal cell are mixed in the unit pixel, and at the same time, the mixing ratio is set. By adjusting, gradation display becomes possible, and a high-resolution moving image can be realized in full color.
[0047]
On the other hand, the present invention is not limited to a specific preferred embodiment, and it is needless to say that various applications are possible by ordinary knowledge in the art within the scope of the claims.
[Brief description of the drawings]
FIG. 1 is a characteristic diagram of transmittance of a liquid crystal cell with respect to voltage change in the present invention.
FIG. 2 is a drive signal waveform diagram of a liquid crystal cell according to an embodiment of the present invention.
FIG. 3 is a characteristic diagram of transmittance of a liquid crystal cell driven with the waveform of FIG. 2;
FIG. 4 is a graph showing a mixed area according to an embodiment of the present invention.
FIG. 5 is a front view of a panel showing two metastable mixed states embodied by the present invention and a liquid crystal layer arrangement state diagram of pixels forming the panel.
FIG. 6 is a twist state diagram of a normal bistable liquid crystal cell according to the present invention.
FIG. 7 is a twist state diagram of a normal bistable liquid crystal cell according to the present invention.
FIG. 8 is a drive pulse waveform diagram of a normal bistable liquid crystal cell according to the present invention.
FIG. 9 is a drive pulse waveform diagram of a normal bistable liquid crystal cell according to the present invention.
[Explanation of symbols]
24 unit pixel W white area B black area MD mixed area area
Claims (7)
前記電圧の調整は、リセットパルスおよび選択パルスの電圧を同じ変動率にして可変させる
ことを特徴とする双安定液晶セルの階調方法。In the bistable liquid crystal cell having the characteristics of the first metastable state and the second metastable state, the voltage applied to the liquid crystal cell is adjusted in the mixed region where the two metastable states appear together. Multi-gradation is displayed by changing the mixing ratio of two metastable states ,
The gradation adjustment method for a bistable liquid crystal cell, wherein the voltage adjustment is performed by changing the voltage of the reset pulse and the selection pulse at the same fluctuation rate .
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1998-18106 | 1998-05-20 | ||
| KR1019980018106A KR100297686B1 (en) | 1998-05-20 | 1998-05-20 | Method of the gray-leveling for bistable twisted nematic cell |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH11352466A JPH11352466A (en) | 1999-12-24 |
| JP4477160B2 true JP4477160B2 (en) | 2010-06-09 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP12403299A Expired - Lifetime JP4477160B2 (en) | 1998-05-20 | 1999-04-30 | Gradation method of bistable liquid crystal cell |
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| JP (1) | JP4477160B2 (en) |
| KR (1) | KR100297686B1 (en) |
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|---|---|---|---|---|
| CN1823364A (en) * | 2003-07-17 | 2006-08-23 | 皇家飞利浦电子股份有限公司 | Electrophoretic or bistable display device and driving method thereof |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US5631752A (en) * | 1992-12-24 | 1997-05-20 | Casio Computer Co., Ltd. | Antiferroelectric liquid crystal display element exhibiting a precursor tilt phenomenon |
| US5847799A (en) * | 1995-05-31 | 1998-12-08 | Casio Computer Co., Ltd. | Antiferroelectric liquid crystal display device |
-
1998
- 1998-05-20 KR KR1019980018106A patent/KR100297686B1/en not_active Expired - Fee Related
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1999
- 1999-04-30 JP JP12403299A patent/JP4477160B2/en not_active Expired - Lifetime
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| Publication number | Publication date |
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| KR100297686B1 (en) | 2001-08-07 |
| JPH11352466A (en) | 1999-12-24 |
| KR19990085592A (en) | 1999-12-06 |
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