JP3871088B2 - Driving method of simple matrix liquid crystal display device - Google Patents

Description

【００１９】
そして、ある列の４つの液晶素子の輝度を、式２、式３あるいは式４に示すパターンに対応させた表示をさせたい場合には、式５、式６あるいは式７の式の右辺に示す値に応じた電圧波形の電圧（カラム電圧系列）を当該列電極に印加する。式２から式４は、例えば「＋１」が明表示、「−１」が暗表示を意味し、同一の数値が記載された位置の液晶素子は同一の輝度に制御されることを意味する。また、式５から式７において、プラスの値は走査電圧と逆極性の印加電圧を意味し、マイナスの値は走査電圧と同極性の印加電圧を意味し、絶対値の大きさは基本カラム電圧を何倍するのかを意味する。また、カラム電圧は１行目から順番に印加される。
【００２０】
【数２】

【００２１】
【数３】

【００２２】
【数４】

【００２３】
【数５】

【００２４】
【数６】

【００２５】
【数７】

【００２６】
そして、このような式１に示す走査電圧系列および式５、式６あるい式７に示すカラム電圧系列を上記同士選択グループの列方向に並んだ４つの液晶素子に印加すれば、当該４つの液晶素子を上記式２、式３あるいは式４に示す輝度分布に制御することができる。式５に示す行列式を行電極および列電極に印加する動作シーケンスを図５に示す。同図において、１は同時選択される複数の画素（液晶素子）を意味し、２は同時選択グループを意味し、３は同時選択グループの複数の走査電圧系列、３ａ，３ｂ，３ｃ，３ｄは当該走査電圧系列を構成して各サブフレーム周期毎に行電極に印加される走査電圧であり、４は１フレーム周期あたりに列電極に印加されるカラム電圧系列であり、４ａ，４ｂ，４ｃ，４ｄは当該カラム電圧系列を構成して各サブフレーム周期毎に列電極に印加されるカラム電圧である。また、同図において（ａ），（ｂ），（ｃ），（ｄ）は各サブフレーム周期を意味する。
【００２７】
次に、このようなカラム電圧系列を数フレーム分連続的に印加する場合において、スプライシングの発生メカニズムを説明する。なお、式８から式１２においては同一の同時選択グループに対して連続的に選択電圧を印加し続けた場合の例である。式８は上記式５に示すカラム電圧系列を３回つづけて印加して、その間上記同時選択グループの４つの画素を式２の行列に対応する輝度に制御しつづけている場合（静止画像の場合）の例であり、式９は上記式６に示すカラム電圧系列を３回つづけて印加して、その間上記同時選択グループの４つの画素を式３の行列に対応する輝度に制御しつづけている場合（静止画像の場合）の例であり、式１０は上記式７に示すカラム電圧系列を３フレーム周期連続的に印加して、その間上記同時選択グループの４つの画素を式４の行列に対応する輝度に制御しつづけている場合（静止画像の場合）の例であり、式１１は上記式５に示すカラム電圧系列から上記式６に示すカラム電圧系列に変化した場合（動画の場合）の例であり、式１２は上記式７に示すカラム電圧系列から上記式６に示すカラム電圧系列に変化した場合（動画の場合）の例である。
【００２８】
（０ ４ ０ ０ ０ ４ ０ ０ ０ ４ ０ ０） ・・・式８
【００２９】
（４ ０ ０ ０ ４ ０ ０ ０ ４ ０ ０ ０） ・・・式９
【００３０】
（２ ２ ２ ２ ２ ２ ２ ２ ２ ２ ２ ２） ・・・式１０
【００３１】
（０ ４ ０ ０ ４ ０ ０ ０ ４ ０ ０ ０） ・・・式１１
【００３２】
（２ ２ ２ ２ ４ ０ ０ ０ ４ ０ ０ ０） ・・・式１２
【００３３】
これらの各例を比較する。式８から式１０に示す例の場合、つまり静止画像においては、連続した４つのカラム電圧の二乗平均値を計算すると、どのサブフレーム周期におけるカラム電圧から数えても、４つのカラム電圧を二乗して加算した値の平均値（二乗平均値）は、常に４となる。これに対して式１１に示す例では、先頭から２番目から５番目のカラム電圧の当該二乗平均値は８となり、式１２に示す例では、先頭から８番目のカラム電圧を印加する間に、二乗平均値が「４ ４ ４ ４ ７ ６ ５ ４」と変化する。
【００３４】
ところで、この連続した４つのカラム電圧の二乗平均値は、各液晶素子に印加されるカラム電圧の二乗平均値を意味し、ひいては各液晶素子に１フレーム周期に相当する時間当たりに印加される実効値電圧に対応する値である。従って、上記式１１の例では、５番目のカラム電圧が印加された時点から液晶素子に印加される実効値電圧が変動し、当該液晶素子の透過率（輝度）が変動してしまうことを意味している。つまり、動画を表示する際には、表示画像が変化すると、その切り替わる際のカラム電圧の実効値が変動し、瞬時的な輝度変動を生じてしまう。
【００３５】
そして、このような瞬時的な輝度変動が各行電極毎にランダムに生じた場合には、隣接する行電極との間で輝度差を生じ、それがスプライシングとして視認されてしまう。特に、上記行電極同士の輝度変動差が大きかったり、画像の更新周期が遅かったりしする場合には、顕著に発生してしまう。
【００３６】
なお、線順次駆動方式では、一般的に、画像が切り替わったとしても各画素に独立に印加するカラム電圧の極性を切り替える制御を行うだけなので、１フレーム周期あたりのカラム電圧の二乗平均値は常に一定となり、動画表示の際に上記ＭＬＡ駆動方式におけるスプライシングの問題は生じない。
【００３７】
次に、従来の階調方式について説明する。従来、この種の単純マトリックス液晶表示装置において階調表現を行うための技術として、液晶素子に印加するカラム電圧の大きさを制御することで透過率を調整し、これにより１フレーム周期毎に表示画像の階調表現を行う所謂アンプリチュードモジュレーション方式（以下、ＡＭ方式と呼ぶ）や、液晶素子へ印加するカラム電圧のパルス幅を制御することで透過率を調整し、これにより１フレーム周期毎に表示画像の階調表現を行うパルスウィズスモジュレーション方式（以下、ＰＷＭ方式と呼ぶ）や、複数のフレーム周期を１つの表示画像を表示させるために使用し、各フレーム周期において液晶素子に印加するカラム電圧を制御することで表示画像の階調表現を行うフレームレートコントロール方式（以下、ＦＲＣ方式と呼ぶ）などが知られている。
【００３８】
上記ＡＭ方式とは、各画素に印加するカラム電圧の大きさを制御することで、当該画素に印加する実効値電圧を変化させ、これにより当該画素の輝度を制御する階調方式である。この階調方式は、所定の画素に印加する実効値電圧を変化させるためにカラム電圧の大きさを変更してしまうので、階調数に応じてカラム電圧のレベル数を増加させなければならず、しかも、列電圧の実効値電圧を一定にするために各列電極には補正用カラム電圧を印加しなければならないので、表示したい階調数よりも多い電圧レベルに制御できるようにしなければならない。従って、６４階調を表現させることは現実的ではない。
【００３９】
上記ＰＷＭ方式とは、各画素に印加するカラム電圧のパルス幅を制御することで、当該画素に印加する実効値電圧を変化させ、これにより当該画素の輝度を制御する階調方式である。この階調方式は、階調数を確保するためにはカラム電圧のパルス幅を細分化する必要がある。従って、細分化するにつれてカラム電圧が高周波となって波形鈍りの問題が生じ、その結果、選択画素において十分な輝度が得られなくなるとか、輝度分布が不均一なってしまうといった問題が生じる。従って、従来、このＰＷＭ方式の階調表現と上記ＭＬＡ駆動方式とを組み合わせることを提案した所謂シェーファーの特許（特開平６−８９０８２号公報）があるが、現状の技術では、１２インチ以上の大画面の液晶表示装置においては１画像サブフレーム当たりにおいて３分割程度（つまり不均一分割であっても８階調程度）を確保するのが限界であり、自然画像を表示するために十分な６４以上の階調を確保することはできない。
【００４０】
上記ＦＲＣ方式とは、複数のフレーム周期を１つの表示画像を表示させるために使用して、各フレーム周期において液晶素子に印加するカラム電圧をＯＮ，ＯＦＦ制御することで表示画像の階調を表現する階調方式である。この方式は、階調数を確保するためには階調サブフレームの数を増加させる必要があり、その数が大きくなると全体が１つの表示画像として視認されなくなって、ちらついた画像が表示させたように見えてしまうという問題がある。従って、１画像を表現するための階調サブフレーム数としては８〜１６個程度（つまり階調数としては９〜１７階調程度）が限界であり、自然画像を表示するために十分な６４以上の階調を確保することはできない。また、特開平８−３０２３８号公報に提案されるＡＭ方式とこのＦＲＣ方式とを組み合わせて６４階調の階調表現を実現化することも考えられるが、そのためにはサブフレーム毎にダミーデータを印加するための時間を確保する必要があり、その結果、駆動デューティが実質的に４／３倍となってしまい、大型の液晶表示装置では現実的に利用できるものとはならない。
【００４１】
なお、上記ＭＬＡ駆動方式においては、上記ＦＲＣ方式のちらつきを抑制する技術として、位相フレームという技術がある。この位相フレームとは、隣接する複数の画素の階調制御の順番を異なるものに設定することで、当該複数の隣接画素が全て同一階調である場合に、各フレームにおける輝度の平均値がほぼ一致するようにすることで、階調画像間のちらつきを抑制する技術である。具体例を図６に示す。同図においては、４つのフレーム周期を１組とした４ＦＲＣ方式の例であり、各フレーム周期での分割画像の輝度は、４つの液晶素子Ａ，Ｂ，Ｃ，Ｄ全てがＯＮである場合の約３／４の輝度に安定する。
【００４２】
この発明は上記のような課題を解決するためになされたもので、先ず、動画表示の際に発生するスプライシングの発生を抑制した単純マトリックス液晶表示装置の駆動方法を得ることを目的とする。
【００４３】
また、この発明は、自然画像を表現するために必要な６４階調による階調表現を行うことができる単純マトリックス液晶表示装置の駆動方法を得ることを目的とする。
【００４４】
【課題を解決するための手段】
請求項１記載の発明に係る単純マトリックス液晶表示装置の駆動方法は、複数の行電極と複数の列電極とから所定の電圧が印加されることで各画素毎に設けられた液晶素子の透過率を制御し、複数のフレーム周期を１つの表示画像を表示させるために使用して、各フレーム周期において液晶素子に印加するカラム電圧をＯＮ、ＯＦＦ制御することで表示画像の階調を表現する単純マトリックス液晶表示装置の駆動方法において、動画表示が行われ、その際に、上記複数の行電極を複数本ずつの同時選択グループに分割した上で、当該同時選択グループ毎に行電極に走査電圧を印加するとともに、複数の列電極に対してもそれと同時にカラム電圧を印加することで、同一のカラム電圧が印加される複数の液晶素子に対して同時に選択電圧を印加し、これを少なくとも上記同時選択行数と同数回以上繰り返すことにより各液晶素子へ印加する実効値電圧を制御して所定の輝度の１つの表示画像を形成するマルチラインアドレッシング駆動方式にて駆動するとともに、各列電極における複数の画素の輝度の配列が２つの画素を単位として繰り返される輝度配列である場合に各列電極に印加されるカラム電圧系列のうち、最大の絶対値を有するカラム電圧を二乗し、これを当該カラム電圧系列の二乗平均値で割った時の除算値が１．５以下であり、表示画像の表示階調を各分割画像での分割階調に分割する際には、各分割画像が市松模様の表示画像と同様な階調分布となるように分割される位相フレームを用いて階調表示を行うものである。
【００４５】
請求項２記載の発明に係る単純マトリックス液晶表示装置の駆動方法は、複数の行電極と複数の列電極とから所定の電圧が印加されることで各画素毎に設けられた液晶素子の透過率を制御し、複数のフレーム周期を１つの表示画像を表示させるために使用して、各フレーム周期において液晶素子に印加するカラム電圧をＯＮ、ＯＦＦ制御することで表示画像の階調を表現する単純マトリックス液晶表示装置の駆動方法において、動画表示が行われ、その際に、上記複数の行電極を複数本ずつの同時選択グループに分割した上で、当該同時選択グループ毎に行電極に走査電圧を印加するとともに、複数の列電極に対してもそれと同時にカラム電圧を印加することで、同一のカラム電圧が印加される複数の液晶素子に対して同時に選択電圧を印加し、これを少なくとも上記同時選択行数と同数回以上繰り返すことにより各液晶素子へ印加する実効値電圧を制御して所定の輝度の１つの表示画像を形成するマルチラインアドレッシング駆動方式にて駆動するとともに、各列電極における複数の画素の輝度の配列が４つの画素を単位として繰り返されるとともに、当該４つの画素を連続する２つの画素ずつに２分割した際にペアとなった２つの画素の輝度がそれぞれ同一である輝度配列である場合においても、上記除算値が１．５以下であり、表示画像の表示階調を各分割画像での分割階調に分割する際には、各分割画像が同一階調が２画素ずつ交互にくる場合の表示画像と同様な階調分布となるように分割される位相フレームを用いて階調表示を行うものである。
【００４６】
請求項３記載の発明に係る単純マトリックス液晶表示装置の駆動方法は、各列電極における複数の画素の輝度の配列が全て同一となる輝度配列である場合においても、上記除算値が１．５以下であるものである。
【００４７】
請求項４記載の発明に係る単純マトリックス液晶表示装置の駆動方法は、複数の行電極と複数の列電極とから所定の電圧が印加されることで各画素毎に設けられた液晶素子の透過率を制御し、複数のフレーム周期を１つの表示画像を表示させるために使用して、各フレーム周期において液晶素子に印加するカラム電圧をＯＮ、ＯＦＦ制御することで表示画像の階調を表現する単純マトリックス液晶表示装置の駆動方法において、動画表示が行われ、その際に、上記複数の行電極を複数本ずつの同時選択グループに分割した上で、当該同時選択グループ毎に行電極に走査電圧を印加するとともに、複数の列電極に対してもそれと同時にカラム電圧を印加することで、同一のカラム電圧が印加される複数の液晶素子に対して同時に選択電圧を印加し、これを少なくとも上記同時選択行数と同数回以上繰り返すことにより各液晶素子へ印加する実効値電圧を制御して所定の輝度の１つの表示画像を形成するマルチラインアドレッシング駆動方式にて駆動するとともに、
各列電極における複数の画素の輝度の配列が２つの画素を単位として繰り返される輝度配列である場合に各列電極に印加されるカラム電圧系列のうち、最大の絶対値を有するカラム電圧を二乗し、これを当該カラム電圧系列の二乗平均値で割った時の除算値が、上記カラム電圧系列とは異なる少なくとも１のカラム電圧系列における当該除算値よりも小さく、表示画像の表示階調を各分割画像での分割階調に分割する際には、各分割画像が一様な表示画像と同様な階調分布となるように分割される位相フレームを用いて階調表示を行うものである。
【００４８】
請求項５記載の発明に係る単純マトリックス液晶表示装置の駆動方法は、各列電極における複数の画素の輝度の配列が４つの画素を単位として繰り返されるとともに、当該４つの画素を連続する２つの画素ずつに２分割した際にペアとなった２つの画素の輝度がそれぞれ同一である輝度配列である場合においても、上記除算値が、上記カラム電圧系列とは異なる少なくとも１のカラム電圧系列における当該除算値よりも小さいことものである。
【００４９】
請求項６記載の発明に係る単純マトリックス液晶表示装置の駆動方法は、各列電極における複数の画素の輝度の配列が全て同一となる場合においても、上記除算値が、上記カラム電圧系列とは異なる少なくとも１のカラム電圧系列における当該除算値よりも小さいことものである。
【００５０】
請求項７記載の発明に係る単純マトリックス液晶表示装置の駆動方法は、ＦＲＣ方式とＰＷＭ方式とを併用して階調表現を行なうものである。
【００５１】
請求項８記載の発明に係る単純マトリックス液晶表示装置の駆動方法は、ＦＲＣ方式とＰＷＭ方式とを併用して階調表現を行なうとともに、ＦＲＣの各フレーム周期毎に形成される複数の分割画像のうち少なくとも１の分割画像における各列電極に係る複数の画素の輝度配列が、２つの画素を単位として繰り返される輝度配列か、あるいは、４つの画素を単位として繰り返されるとともに、当該４つの画素を連続する２つの画素ずつに２分割した際に各ペアの輝度が同一となる輝度配列となるように、各フレーム周期におけるパルス幅変調を決定するものである。
【００５２】
請求項９記載の発明に係る単純マトリックス液晶表示装置の駆動方法は、複数の分割画像のうち、少なくとも１の分割画像においてはその他の分割画像とは異なる分割比にてパルス幅変調を行うものである。
【００５３】
【発明の実施の形態】
以下、この発明の実施の一形態を説明する。
【００５４】
実施の形態１．
単純マトリックス液晶表示装置として（１０２４画素×７２８画素×ＲＧＢ）個のＳＴＮ素子がマトリックス状に配列された１５インチのＸＧＡ液晶パネルを使用した。この液晶表示装置は、２４０度のツイスト角のＳＴＮ方式にて駆動する液晶に、位相補償を行う２枚の位相フィルムと、内面カラーフィルタと、液晶バックライトとを組み合わせた構造のものであり、高精度表示が可能である。また、上記液晶を駆動させる駆動系は、画面の上部を駆動する上部駆動系と下部を駆動する下部駆動系との２つが設けられ、各分割駆動系には６ビットパラレルの画像信号を介して独立に６０Ｈｚの低周波の周期ごとに更新される入力画像を入力できるように駆動制御系を構成した。同時に、表示画像はこの入力画像に同期して６０Ｈｚ毎に更新されるようにして、入力信号を記憶するために必要となるメモリを１画面分にまで削減している。なお、上記１０２４画素×７２８画素の表示画面はパソコンなどに利用されるＸＧＡ水準の画像品質に相当する。
【００５５】
そして、本実施の形態１では特に、画像のコントラストを確保するためにＭＬＡ駆動方式を採用するとともに、同時選択行数Ｌ＝４、同時選択列数Ｋ＝４として同時選択される行電極への走査電圧系列が正方行列として表記されるようにした。
【００５６】
また、この正方行列は、同一のカラム電圧４ａ，４ｂ，４ｃ，４ｄが印加される列方向において少なくとも隣接する４以上の画素１，１，１，１に対して同一の画像を表示させる白あるいは黒の一様な表示画像を表示する場合、列方向の配列において隣接する４以上の画素１，１，１，１に対して白と黒とが交互にくる市松模様の表示画像を表示する場合、および、列方向の配列において隣接する４以上の画素１，１，１，１に対して「白白黒黒」あるいは「黒黒白白」とくる表示画像を表示する場合に、下記式１３のように、各列電極へ印加されるカラム電圧系列４の二乗平均和と一致するような直交行列を用いた。
【００５７】
【数８】

【００５８】
念のため、一様な表示画像を表示する場合のカラム電圧系列４の演算結果を式１４に、および、白黒の市松模様の表示画像を表示する際に場合のカラム電圧系列４の演算結果を式１５に、更に、白と黒とが２画素ずつ交互にくる場合のカラム電圧系列４の演算結果を式１６に示す。また、図１に式１４に基づく各種の印加電圧の変化を示す。同図において、１は液晶素子（画素）、２は同時選択される４つの画素、３は行電極に印加される走査電圧系列、３ａ，３ｂ，３ｃ，３ｄは走査電圧系列を構成して各サブフレーム周期毎に印加される走査電圧、４は行電極に印加されるカラム電圧系列、４ａ，４ｂ，４ｃ，４ｄはカラム電圧系列を構成して各サブフレーム周期毎に印加されるカラム電圧である。また、（ａ）から（ｄ）は各サブフレーム周期を意味する。これらの演算結果から明らかなように、各サブフレームにおけるカラム電圧４ａ，４ｂ，４ｃ，４ｄはそれぞれ、当該カラム電圧系列４の二乗平均値「４」と一致している。また、最大の絶対値（「２」）を有するカラム電圧は、カラム電圧がとりうる最大値「４」よりもカラム電圧の平均値「２」に近い値となっている。それゆえ、例えば、入力画像に従って、式１４に示すカラム電圧系列４から式１５に示すカラム電圧系列４に変化する場合（図２（ａ））や、式１５に示すカラム電圧系列４から式１４に示すカラム電圧系列４に変化する場合（同図（ｂ））などにおいては、画像が切り替わったとしてもカラム電圧による瞬時的な実効値電圧は全く変動しない。
【００５９】
【数９】

【００６０】
【数１０】

【００６１】
【数１１】

【００６２】
なお、上記式１３に示すような直交行列は、白あるいは黒が連続する場合や、白と黒とが交互にくる場合や、白と黒とが２画素ずつ交互にくるような表示画像では、全てのカラム電圧４ａ，４ｂ，４ｃ，４ｄが一定の絶対値となる特殊解と考えられる。実際には、液晶素子１の応答速度によるコントラスト低下を抑制するために同時選択行数（ここでは４本）を決定し、アダマール行列（Ｈａｄａｍａｒｄ行列）の各行や各列を極性反転したり、各行を並べ替えることによって、所定の条件を満たすような直交行列を得ることができる。これらの最適化はシミュレーションなどを使用して効率良く行なうことができる。
【００６３】
また、列電極に印加するカラム電圧４ａ，４ｂ，４ｃ，４ｄの絶対値の平均値の、行電極に印加する走査電圧３ａ，３ｂ，３ｃ，３ｄの絶対値の平均値に対する電圧比は１／１０とした。
【００６４】
次に本実施の形態１における階調表現について説明する。本実施の形態における階調方式は、８つの分割画像にて１つの表示画像の表示階調を表現するＦＲＣ方式と、各分割画像においてカラム電圧のパルス幅（印加時間）を二分割して各分割画像の階調を制御するＰＷＭ方式とを併用した。具体的には、カラム電圧の最大の印加時間を０．３：０．７にて固定的に分割した。この不均一な分割比の場合には、単純に０．５：０．５の均等な分割比にて分割した場合に比べて、複数の分割画像を重ね合わせた場合における表示階調数を確保することができる。ちなみに、４階調ＰＷＭを２階調サブフレーム使用すると９階調以上、４階調ＰＷＭを４階調サブフレーム使用すると２５階調以上の階調を確保することが可能である。そして、本実施の形態では入力信号の６ビットにて区別することができる６４階調にて階調表現を行う。
【００６５】
なお、０．３：０．７の分割比で２つのフレームにより表わすことができる階調を表１に示す。他方、０．５：０．５の分割比で２つのフレームにより表わすことができる階調を表２に示す。
【００６６】
また、各表示画像の表示階調を各分割画像での分割階調に分割する際には、各分割画像が上記一様な表示画像と同様な階調分布か、上記市松模様の表示画像と同様な階調分布か、あるいは、同一階調が２画素ずつ交互にくる場合の表示画像と同様な階調分布となるように分割するようにした。具体例を図３に示す。同図は４フレーム周期で切り替わるＦＲＣ方式の場合の例であり、（ａ），（ｂ），（ｃ），（ｄ）がそれぞれ１フレーム周期における分割画像を意味する。同図において、［ｄ１，ｄ２，ｄ３，ｄ４］が１の表示階調を表現するための各分割画像の階調であり、これが１フレーム周期（（ａ）から（ｄ））毎に各列電極に印加されるカラム電圧系列の基本的となる。このようにすることによりカラム電圧系列が切り替わる際の実効値の変動は最小限に抑えられる。
【００６７】
そして、このような駆動方法により駆動される液晶表示装置に、１ビットからなる文字画像からなる画像データを入力して、白地背景の上に、８×８画素からなる黒文字を５行×２００列にて表示させた。
【００６８】
その結果、コントラストの高い、クロストークの少ない表示を得ることができた。また、列電極の配列方向に画面をスクロールさせた際に、スプライシングや各分割画像間の表示むらは全く発生しなかった。
【００６９】
また、６０Ｈｚごとに更新される６４階調の表示画像を６ビットの入力信号を介して入力して、人間の顔などの自然な陰影のある動画を表示させるテストも行った。６ビットの中間調を発生する手段としては、０．３：０．７の二分割ＰＷＭ方式と、４，５，６，７，８フレームで１つの表示画像を完成させるＦＲＣ方式とを組み合わせた。また、各階調において上記の表示画像となるように分割画像の組み合わせを決定している。
【００７０】
その結果、顔の輪郭や陰影を忠実に再現することができた。また、顔の表示が変化したとしても、スプライシングが発生することはなく、しかも、各表示画像においてもスプライシングやちらつきなどの画質劣化が発生することがない自然な画質を得ることができた。
【００７１】
以上のように、本実施の形態１では、１５インチの大画面に高精度、高コントラストの静止画像を表示することができると同時に、ちらつき（フリッカー）やクロストーク、スプライシングなどの画質劣化を伴わない高品質な動画を高速に表示させることができた。特に、入力画像の更新周期と表示画像の更新周期とを一致させて、各カラム電圧のパルス幅を最大限に確保しているので電圧波形鈍りによる画質劣化は全く発生しなかった。
【００７２】
また、上記式１３に示される直交行列に応じた走査電圧系列を各行電極に印加しているので、一様な表示画像、白と黒とが交互にくる市松模様の表示画像、白白と黒黒とが交互にくる市松模様の表示画像、並びに、各種の分割画像においては、スプライシングが全く発生することはなかった。その結果、通常の動画表示においては動画のかなりの部分においてスプライシングが視認されなくなり、マルティメディア対応モニターや、車載用高密度情報表示装置、携帯パソコン、携帯情報端末（ＰＤＡ）などにおいて、コンパクトディスク−リードオンリーメモリ（ＣＤ−ＲＯＭ）などに記憶された自然画像などの高品質の画像を表示するために利用しても十分な品質（高速、高コントラスト、高表示品位）の動画表示および自然画表示が可能であることが確認された。なお、ＳＴＮ素子からなる液晶表示装置は、同解像度のＴＦＴ素子からなる液晶表示装置よりも安価に製造することができる。
【００７３】
以下に、同時選択される複数の列電極に印加される複数のカラム電圧のうち、最大の絶対値を有するカラム電圧を二乗し、これを当該複数のカラム電圧の二乗平均値で割った除算値と、スプライシングの視認性との関係を表３に示す。式１３、式１７および式１８の直交行列に走査電圧系列として印加した状態で、式１４から式１６にしめす表示画像を表示させた場合の表示画面を表示させた場合でスプライシングの発生確認を行なった。この表から明らかなように上記除算値が２よりも小さい場合には、大半の人がスプライシングが抑制されて表示品位が向上したと認めた。特に、上記除算値が１．５よりも小さい場合には、スプライシングが全くといっていいほど視認されることはなかった。
【００７４】
【数１２】

【００７５】
【数１３】

【００７６】
【表１】

【００７７】
【表２】

【００７８】
【表３】

【００７９】
比較の形態１．
ＭＬＡ駆動方式に換えて６０Ｈｚの画像更新周期で動作する線順次駆動方式を採用した以外は、実施の形態１と同様の構成である。
【００８０】
そして、白地背景の上に、８×８画素からなる黒文字を５行×２００列にて表示させた。
【００８１】
その結果、コントラストが低すぎ、十分な品質の画質を得ることができなかった。
【００８２】
比較の形態２．
画像更新周期を６０Ｈｚから４倍の２４０Ｈｚに変更した以外は、比較の形態１と同様の構成である。
【００８３】
そして、白地背景の上に、８×８画素からなる黒文字を５行×２００列にて表示させた。
【００８４】
その結果、十分に高いコントラストを得ることはできたが、画面の電圧印加側の部位と反対側の部位とで輝度差が大きく、波形鈍りによるクロストークが発生してしまっていた。
【００８５】
比較の形態３．
直交関数として、各行各列に奇数個の異符号（−１）が含まれる４×４のアダマール行列（Ｈａｄａｍａｒｄ行列）を使用した以外は、実施の形態１と同様の構成である。当該アダマール行列を式１９に示す。
【００８６】
【数１４】

【００８７】
ちなみに、一様な表示画像におけるカラム電圧の演算結果を式２０に、および、白黒の市松模様の表示画像におけるカラム電圧の演算結果を式２１に示す。これらの演算結果から明らかなように、各画像サブフレームにおけるカラム電圧は偏ったものとなっている。また、最大の絶対値（「４」）を有するカラム電圧は、カラム電圧がとりうる最大値４に一致している。それゆえ、例えば、入力画像に従って、式２０に示すカラム電圧系列から式２１に示すカラム電圧系列に変化する場合や、式２１に示すカラム電圧系列から式２０に示すカラム電圧系列に変化する場合などのように、画像が切り替わる際に瞬時的な実効値電圧の変動が生じる。
【００８８】
【数１５】

【００８９】
【数１６】

【００９０】
そして、白地背景の上に、８×８画素からなる黒文字を５行×２００列にて表示させた。
【００９１】
その結果、コントラストが高く且つクロストークのない静止画像を表示することができた。しかしながら、列電極の配列方向に画面をスクロールさせた際に、強いスプライシングや表示むらが発生してしまった。
【００９２】
比較の形態４．
位相テーブルとして図４に示す４×４の魔方陣を使用した以外は、実施の形態１と同様のものである。同図において（ａ），（ｂ），（ｃ），（ｄ）は各フレーム周期における分割画像を意味する。
【００９３】
そして、実施の形態１と同様の人間の顔などの自然な陰影のある動画を表示させた。
【００９４】
その結果、静止状態にある顔の輪郭や陰影は忠実に再現することができたが、顔の表示が変化した部位においては、全体的に見れば比較の形態３よりも弱いスプライシングではあったが、スプライシングがはっきり見えたり、薄く見えたりすることがあった。
【００９５】
これは、位相テーブルの大きさが直交行列よりも大きいため、同一の表示階調を表示させる際に各分割画像間の平均的な輝度を安定化させることができず、その結果、分割画像間のちらつきを抑制する効果が得られないためであると考えられる。
【００９６】
実施の形態２．
４ＦＲＣの各分割データ［ｄ１，ｄ２，ｄ３，ｄ４］におけるパルス幅を異ならせた。具体的には、［ｄ１，ｄ２］は分割比３：４でのＰＷＭ方式であり、［ｄ３，ｄ４］は分割比７：３のＰＷＭ方式でＰＷＭ変調を行なった。ちなみに、この分割例の組み合わせでは、２ＦＲＣで１５階調と、４ＦＲＣで６０階調といったように少ないフレーム数で多階調を表現することが可能である。
【００９７】
これにより、少ないフレーム数で所定の階調を表現することができ、ＦＲＣ方式の欠点である画面のちらつきをより効果的に抑えることができた。
【００９８】
また、図３に示す位相テーブルを使用した場合であっても、２つを組として分割比を異ならせているので、各列ごとに同じ分割の演算を行なうことができ、１種類の分割比を用いた場合と同様の制御を行なうことができる。
【００９９】
なお、３：４の分割比であるフレーム周期と７：３の分割比であるフレーム周期とからなる２つのフレーム周期により表わすことができる階調（１５階調）を表４に示す。
【０１００】
【表４】

【０１０１】
【発明の効果】
以上のように、請求項１記載の発明によれば、ＭＬＡ駆動方式にて駆動するとともに、各列電極における複数の画素の輝度の配列が２つの画素を単位として繰り返される輝度配列である場合に各列電極に印加されるカラム電圧系列のうち、最大の絶対値を有するカラム電圧を二乗し、これを当該カラム電圧系列の二乗平均値で割った時の除算値が１．５以下であるので、上記２つの画素を単位として繰り返される輝度配列を基本とする表示画像を表示している状態では、画像の一部あるいは全部を切り替えるためにカラム電圧を変化させたとしても、上記除算値の変動は殆ど生じない。従って、当該表示画像の表示部分においてはスプライシングが視認され難くなり、実質的にスプライシングの発生を抑制することができる効果がある。特に、背景画像として上記パターンの表示画像を使用すれば、画面のほとんどの部分においてスプライシングを抑制することができる効果がある。
【０１０２】
請求項２記載の発明によれば、各列電極における複数の画素の輝度の配列が４つの画素を単位として繰り返されるとともに、当該４つの画素を連続する２つの画素ずつに２分割した際にペアとなった２つの画素の輝度がそれぞれ同一である輝度配列である場合においても、上記除算値が１．５以下であるので、上記４つの画素を単位として繰り返される輝度配列を基本とする表示画像を表示している状態では、画像の一部あるいは全部を切り替えるためにカラム電圧を変化させたとしても、上記除算値の変動は殆ど生じない。従って、当該表示画像の表示部分においてはスプライシングが視認され難くなり、実質的にスプライシングの発生を抑制することができる効果がある。特に、背景画像として上記パターンの表示画像を使用すれば、画面のほとんどの部分においてスプライシングを抑制することができる効果がある。
【０１０３】
請求項３記載の発明によれば、各列電極における複数の画素の輝度の配列が全て同一となる輝度配列である場合においても、上記除算値が１．５以下であるので、上記４つの画素を単位として繰り返される輝度配列を基本とする表示画像を表示している状態では、画像の一部あるいは全部を切り替えるためにカラム電圧を変化させたとしても、上記除算値の変動は殆ど生じない。従って、当該表示画像の表示部分においてはスプライシングが視認され難くなり、実質的にスプライシングの発生を抑制することができる効果がある。特に、背景画像として上記パターンの表示画像を使用すれば、画面のほとんどの部分においてスプライシングを抑制することができる効果がある。
【０１０４】
請求項４記載の発明によれば、ＭＬＡ駆動方式にて駆動するとともに、各列電極における複数の画素の輝度の配列が２つの画素を単位として繰り返される輝度配列である場合に各列電極に印加されるカラム電圧系列のうち、最大の絶対値を有するカラム電圧を二乗し、これを当該カラム電圧系列の二乗平均値で割った時の除算値が、上記カラム電圧系列とは異なる少なくとも１のカラム電圧系列における当該除算値よりも小さいので、上記２つの画素を単位として繰り返される輝度配列を基本とする表示画像を表示している状態では、画像の一部あるいは全部を切り替えるためにカラム電圧を変化させたとしても、上記除算値の変動は殆ど生じない。従って、当該表示画像の表示部分においてはスプライシングが視認され難くなり、実質的にスプライシングの発生を抑制することができる効果がある。特に、背景画像として上記パターンの表示画像を使用すれば、画面のほとんどの部分においてスプライシングを抑制することができる効果がある。
【０１０５】
請求項５記載の発明によれば、各列電極における複数の画素の輝度の配列が４つの画素を単位として繰り返されるとともに、当該４つの画素を連続する２つの画素ずつに２分割した際にペアとなった２つの画素の輝度がそれぞれ同一である輝度配列である場合においても、上記除算値が、上記カラム電圧系列とは異なる少なくとも１のカラム電圧系列における当該除算値よりも小さいので、上記４つの画素を単位として繰り返される輝度配列を基本とする表示画像を表示している状態では、画像の一部あるいは全部を切り替えるためにカラム電圧を変化させたとしても、上記除算値の変動は殆ど生じない。従って、当該表示画像の表示部分においてはスプライシングが視認され難くなり、実質的にスプライシングの発生を抑制することができる効果がある。特に、背景画像として上記パターンの表示画像を使用すれば、画面のほとんどの部分においてスプライシングを抑制することができる効果がある。
【０１０６】
請求項６記載の発明によれば、各列電極における複数の画素の輝度の配列が全て同一となる場合においても、上記除算値が、上記カラム電圧系列とは異なる少なくとも１のカラム電圧系列における当該除算値よりも小さいので、上記４つの画素を単位として繰り返される輝度配列を基本とする表示画像を表示している状態では、画像の一部あるいは全部を切り替えるためにカラム電圧を変化させたとしても、上記除算値の変動は殆ど生じない。従って、当該表示画像の表示部分においてはスプライシングが視認され難くなり、実質的にスプライシングの発生を抑制することができる効果がある。特に、背景画像として上記パターンの表示画像を使用すれば、画面のほとんどの部分においてスプライシングを抑制することができる効果がある。
【０１０７】
請求項７記載の発明によれば、ＦＲＣ方式とＰＷＭ方式とを併用して階調表現を行なうので、各種の画質劣化を抑制しつつ自然画表示に必要な６４階調を表現することが可能となる効果がある。
【０１０８】
請求項８記載の発明によれば、ＦＲＣ方式とＰＷＭ方式とを併用して階調表現を行なうとともに、ＦＲＣの各フレーム周期毎に形成される複数の分割画像のうち少なくとも１の分割画像における各列電極に係る複数の画素の輝度配列が、２つの画素を単位として繰り返される輝度配列か、あるいは、４つの画素を単位として繰り返されるとともに、当該４つの画素を連続する２つの画素ずつに２分割した際に各ペアの輝度が同一となる輝度配列となるように、各フレーム周期におけるパルス幅変調を決定するので、各サブフレーム周期毎に形成される分割画像が切り替わる際にスプライシングの発生を抑制することができる効果がある。
【０１０９】
請求項９記載の発明によれば、複数の分割画像のうち、少なくとも１の分割画像においてはその他の分割画像とは異なる分割比にてパルス幅変調を行うので、全ての分割画像を同一の分割比にてパルス幅変調を行った場合に比べて、複数の分割画像を重ね合わせることにより得られる各画素の実効値電圧の種類を増加させることができる。その結果、階調数も増加させることができる効果がある。
【図面の簡単な説明】
【図１】 この発明の実施の形態１による電圧印加シーケンスの例である。
【図２】 この発明の実施の形態１による画像切換え時のカラム電圧波形の例である。
【図３】 この発明の実施の形態１による位相フレームである。
【図４】 この発明の比較の形態４による魔方陣である。
【図５】 従来における電圧印加シーケンスの例である。
【図６】 従来の位相テーブルの例である。
【符号の説明】
１ 液晶素子、２ 同時選択グループ、３ 走査電圧系列、３ａ，３ｂ，３ｃ，３ｄ 走査電圧、４ カラム電圧系列、４ａ，４ｂ，４ｃ，４ｄ カラム電圧。[0001]
BACKGROUND OF THE INVENTION
In the present invention, a plurality of row electrodes and a plurality of column electrodes are provided to drive a plurality of liquid crystal elements provided for each pixel by a super twisted nematic method (hereinafter referred to as STN method). A simple matrix liquid crystal display that changes a predetermined transmittance of each liquid crystal element by applying a voltage having a predetermined voltage waveform to the display image, thereby displaying a predetermined display image on a display image composed of a matrix of the plurality of liquid crystal elements. In particular, it is possible to display high-quality still images that do not cause display unevenness or contrast reduction, even on a large screen with a high accuracy of 12 inches or more, and also display high-quality moving images. The present invention relates to a driving method of a possible simple matrix liquid crystal display device.
[0002]
[Prior art]
A simple matrix liquid crystal display device provided with a plurality of row electrodes and a plurality of column electrodes and a liquid crystal display device using a thin film transistor (hereinafter referred to as TFT) are widely used in personal computers and the like, particularly as a display device. Since it has the advantages of light weight and thinness and low power consumption, so-called notebook personal computers that can be easily carried and perform data processing have become key devices for their spread. As the display standard of personal computers has changed from VGA to S-VGA, and further from S-VGA to XGA, liquid crystal display devices have also been increased in size and accuracy.
[0003]
On the other hand, the processing capability of recent personal computers has been dramatically improved, and the function of the operating system is being enhanced at the same time. As a result, it has become easy to capture a natural image or the like on a personal computer via an input device such as a read-only compact disc (CD-ROM) and display it on a liquid crystal display device. In addition, so-called desktop personal computers used in offices and the like are used in place of display devices using cathode ray tubes (CRTs) in order to reduce the space of offices due to the appearance of large-sized liquid crystal display devices. It is starting to become.
[0004]
However, in the present situation, in the simple matrix liquid crystal display device, when the display screen is enlarged, the capacitive load of each electrode increases, and the waveform of the voltage applied to the electrode becomes blunt. As a result, the voltage applied to the liquid crystal element located on the terminal end side of the electrode is lower than the voltage applied to the liquid crystal element located on the voltage application end side of the electrode, resulting in a difference in luminance at both ends of the display screen. Image quality is degraded. Therefore, at present, the simple matrix liquid crystal display device is rarely used in large liquid crystal display devices of 12 inches or more, and is limited to those using TFTs. However, even in a liquid crystal display device using this TFT, it is necessary to provide a switching function for selecting each liquid crystal element for each liquid crystal element, and the basic structure is complicated. However, when it is made more expensive, it becomes an expensive module that is very complicated and does not have a good yield. As a result, it has not been widely spread.
[0005]
In light of the current state of such large liquid crystal display devices, the inventors have started to develop a large simple matrix liquid crystal display device of the STN method. Specifically, it is to establish a driving method capable of displaying a high-quality still image and capable of displaying a moving image even when displaying a large screen with high accuracy of 12 inches or more.
[0006]
For this purpose, the inventors replaced the 15-inch STN liquid crystal display device with a so-called line-sequential drive method that has been generally used in the past, and disclosed in Japanese Patent Laid-Open Nos. Hei 6-27904 and Hei 8-62574. The multi-line addressing driving method (hereinafter referred to as the MLA driving method) disclosed in the Japanese Patent Publication is considered.
[0007]
The line-sequential driving method is a driving method in which a luminance control voltage is applied to each row by sequentially applying a scanning voltage to each row electrode and applying a column voltage to a plurality of column electrodes in synchronization therewith. Each liquid crystal element has an average effective value in the luminance control voltage (more precisely, the time until the voltage is applied once to all the row electrodes (hereinafter referred to as one frame period). And a predetermined image can be displayed for each frame period.
[0008]
In the MLA driving method, a plurality of row electrodes are divided into a plurality of simultaneous selection groups and a scanning voltage is applied to the row electrodes for each of the simultaneous selection groups, and simultaneously to a plurality of column electrodes. This is a driving method in which a selection voltage is applied simultaneously to a plurality of liquid crystal elements to which the same column voltage is applied by applying a column voltage, and this is repeated at least as many times as the number of simultaneously selected rows. Thereby, each liquid crystal element is controlled to a transmittance according to the effective value voltage applied per time (one frame period) until the repetition is completed, and one display image is formed for each one frame period. Is done.
[0009]
Hereinafter, advantages of the MLA driving method over the line sequential driving method in achieving the above object will be described. In the MLA driving method, a selection voltage is simultaneously applied to a plurality of liquid crystal elements arranged in the column direction by simultaneously applying a scanning voltage to a plurality of row electrodes. A predetermined voltage can be applied to all the liquid crystal elements every period (hereinafter referred to as one subframe period) obtained by dividing the frame period by the number of simultaneous selections. This brings a number of advantages over the line sequential drive method of the MLA drive method.
[0010]
The purpose of this development is to establish a driving method capable of displaying a high-quality still image and displaying a moving image even when displaying a large screen with high accuracy of 12 inches or more. Therefore, since the display screen becomes large, the number of row electrodes increases, and moreover, the number of liquid crystal elements driven by each row electrode increases and the load capacity also increases. Further, it is necessary to use a liquid crystal element with good response characteristics so that the previous image does not remain as an afterimage when displaying a moving image.
[0011]
Under such conditions of the liquid crystal display device, if one frame period is suppressed to a short time as in the conventional case, the time for applying a voltage to each row electrode is shortened, and the voltage pulse becomes a high frequency pulse. The pulse voltage applied to each row electrode is significantly dull. Therefore, the difference in luminance between the left and right of the image is noticeably generated. Therefore, it is necessary to ensure the voltage application time to each row electrode by making one frame period longer than the conventional one.
[0012]
In the line-sequential driving method, since the voltage is applied to each liquid crystal element every frame period, the longer frame period directly becomes the longer voltage application interval for each liquid crystal element. The liquid crystal element exhibits a so-called frame response characteristic. This frame response characteristic means that each liquid crystal element exhibits a characteristic that responds to an applied voltage pulse. When such a characteristic is exhibited, the luminance of the liquid crystal element for which the transmittance is desired to be controlled is high. On the other hand, in the liquid crystal element whose transmittance is desired to be controlled low, the luminance increases, and the brightness difference (contrast) between the bright and dark portions of the image decreases. In particular, when a liquid crystal element having a high response speed is used in order to suppress the afterimage phenomenon at the time of moving image display as in the present case, this frame response characteristic is remarkably generated, and the contrast is significantly reduced.
[0013]
On the other hand, in the MLA driving method, even if the frame period is extended, a pulse voltage is applied to each liquid crystal element every subframe period. Compared to the system, the frame response characteristic is shortened by an amount corresponding to the number of subframe periods per frame period, and the frame response characteristics as described above are suppressed. Therefore, even if a liquid crystal display device with a large screen and a high response speed is driven, it is possible to suppress a difference in luminance between the left and right sides of the image while suppressing a decrease in contrast as compared with the line sequential driving method. In the line sequential driving method, in order to suppress a decrease in contrast as in the MLA driving method, one frame cycle must be set to a cycle equivalent to one subframe cycle in the MLA driving method. The brightness difference between the left and right sides of the screen becomes even more remarkable.
[0014]
Further, in the MLA driving method, as described above, a voltage can be applied to all the liquid crystal elements every subframe period. Therefore, the voltage applied to each liquid crystal element in each subframe period can be extended by extending one frame period. Even if the application time is secured, the setting can be made so as not to cause a problem such as the frame response characteristics described above. Therefore, it is possible to suppress the decrease in contrast while further uniforming the luminance of each pixel by taking a longer time to apply one voltage to each liquid crystal element than in the line sequential driving method. At this time, in particular, if one frame period coincides with the update period of the input image, it is possible to operate with a memory for one screen.
[0015]
[Problems to be solved by the invention]
However, when the inventors have driven a large-screen liquid crystal display device at a low frequency using the MLA driving method, an instantaneous luminance change appears on the screen as if it rained when displaying a moving image. It was visually recognized. Such a phenomenon is generally called splicing.
[0016]
Conventionally, in the driving method of the simple matrix liquid crystal display device, there has not been a gradation method that can secure 64 gradations that are at least required for displaying a natural image.
[0017]
First, a splicing generation mechanism under the above conditions will be described using a specific example. For convenience of explanation, the number of simultaneously selected rows is L = 4, the number of subframe periods per frame cycle is K = 4, and the four simultaneously selected row electrodes correspond to the orthogonal matrix shown in Equation 1. Apply waveform voltage. The matrix of Expression 1 is an orthogonal matrix composed of “+1” and “−1”, “+1” means the scanning voltage + Vr, and “−1” means the scanning voltage −Vr. Further, each row means a voltage waveform (scanning voltage series) applied to one row electrode, and is applied in order from the first column.
[0018]
[Expression 1]

[0019]
Then, the luminance of the four liquid crystal elements in a certain column is displayed corresponding to the pattern shown in Equation 2, Equation 3, or Equation 4. The If not, a voltage having a voltage waveform (column voltage series) corresponding to the value shown on the right side of Expression 5, 6 or 7 is applied to the column electrode. In Expressions 2 to 4, for example, “+1” means bright display and “−1” means dark display, and liquid crystal elements at positions where the same numerical values are written are controlled to have the same luminance. In Expressions 5 to 7, a positive value means an applied voltage having a polarity opposite to the scanning voltage, a negative value means an applied voltage having the same polarity as the scanning voltage, and the magnitude of the absolute value is the basic column voltage. Means how many times The column voltage is applied in order from the first row.
[0020]
[Expression 2]

[0021]
[Equation 3]

[0022]
[Expression 4]

[0023]
[Equation 5]

[0024]
[Formula 6]

[0025]
[Expression 7]

[0026]
When the scanning voltage series shown in Formula 1 and the column voltage series shown in Formula 5, Formula 6, or Formula 7 are applied to the four liquid crystal elements arranged in the column direction of the selection group, the four The liquid crystal element can be controlled to have a luminance distribution represented by the above formula 2, formula 3 or formula 4. FIG. 5 shows an operation sequence for applying the determinant shown in Equation 5 to the row electrode and the column electrode. In the figure, 1 denotes a plurality of pixels (liquid crystal elements) that are simultaneously selected, 2 denotes a simultaneous selection group, 3 denotes a plurality of scanning voltage series of the simultaneous selection group, 3a, 3b, 3c, and 3d The scanning voltage series constitutes the scanning voltage applied to the row electrode every subframe period, and 4 is the column voltage series applied to the column electrode per frame period, 4a, 4b, 4c, Reference numeral 4d denotes a column voltage that constitutes the column voltage series and is applied to the column electrode every subframe period. In the figure, (a), (b), (c), and (d) mean each subframe period.
[0027]
Next, the splicing generation mechanism when such a column voltage series is continuously applied for several frames will be described. Expressions 8 to 12 are examples in the case where the selection voltage is continuously applied to the same simultaneous selection group. In Formula 8, when the column voltage series shown in Formula 5 is applied three times in succession, the four pixels in the simultaneous selection group are controlled to have the luminance corresponding to the matrix of Formula 2 during that time (in the case of a still image) 9 is an example in which the column voltage series shown in Equation 6 is applied three times in succession, and the four pixels of the simultaneous selection group are continuously controlled to the luminance corresponding to the matrix of Equation 3 during that time. This is an example of the case (in the case of a still image), and Equation 10 applies the column voltage series shown in Equation 7 above continuously for 3 frame periods, and in the meantime, the four pixels of the simultaneous selection group correspond to the matrix of Equation 4 This is an example of the case where the brightness is continuously controlled (in the case of a still image). Equation 11 is a case where the column voltage sequence shown in Equation 5 is changed to the column voltage sequence shown in Equation 6 (in the case of a moving image). For example, Equation 12 is From to the column voltage sequence is an example in which changes to the column voltage sequence shown in Equation 6 (for video).
[0028]
(0 4 0 0 0 4 0 0 0 4 4 0 0) ... Equation 8
[0029]
(4 0 0 0 4 0 0 0 0 4 0 0 0) ... Equation 9
[0030]
(2 2 2 2 2 2 2 2 2 2 2 2) Formula 10
[0031]
(0 4 0 0 4 0 0 0 0 4 0 0 0) Equation 11
[0032]
(2 2 2 2 4 0 0 0 4 0 0 0) (12)
[0033]
Compare each of these examples. In the case of the example shown in Expression 8 to Expression 10, that is, in the still image, if the mean square value of four consecutive column voltages is calculated, the four column voltages are squared regardless of the column voltage in any subframe period. The average value (root mean square value) of the added values is always 4. On the other hand, in the example shown in Expression 11, the root mean square value of the second to fifth column voltages from the head is 8, and in the example shown in Expression 12, while the eighth column voltage from the head is applied, The root mean square value changes to “4 4 4 4 7 6 5 4”.
[0034]
By the way, the mean square value of the four consecutive column voltages means the mean square value of the column voltages applied to each liquid crystal element, and as a result, the effective value applied to each liquid crystal element per time corresponding to one frame period. It is a value corresponding to the value voltage. Therefore, in the example of the above formula 11, it means that the effective value voltage applied to the liquid crystal element fluctuates from the time when the fifth column voltage is applied, and the transmittance (luminance) of the liquid crystal element fluctuates. is doing. That is, when a moving image is displayed, if the display image changes, the effective value of the column voltage at the time of switching changes, resulting in an instantaneous luminance fluctuation.
[0035]
When such an instantaneous luminance variation occurs randomly for each row electrode, a luminance difference is produced between adjacent row electrodes, which is visually recognized as splicing. In particular, when the luminance fluctuation difference between the row electrodes is large or the image update cycle is slow, the problem occurs remarkably.
[0036]
In the line-sequential driving method, generally, even if the image is switched, only the control of switching the polarity of the column voltage applied independently to each pixel is performed, so the mean square value of the column voltage per frame period is always There is no problem of splicing in the MLA driving method when displaying a moving image.
[0037]
Next, a conventional gradation method will be described. Conventionally, as a technique for performing gradation expression in this type of simple matrix liquid crystal display device, the transmittance is adjusted by controlling the magnitude of the column voltage applied to the liquid crystal element, thereby displaying the image every frame period. The transmissivity is adjusted by controlling the pulse width of the column voltage applied to the liquid crystal element, so-called amplitude modulation method (hereinafter referred to as AM method) that expresses the gradation of the image, and thereby, every frame period. A column that applies a pulse width modulation method (hereinafter referred to as a PWM method) that expresses a gradation of a display image or a plurality of frame periods to display one display image, and that is applied to a liquid crystal element in each frame period. Frame rate control method (hereinafter referred to as FRC method) that displays the gradation of the displayed image by controlling the voltage, etc. It is known.
[0038]
The AM method is a gradation method in which the effective voltage applied to the pixel is changed by controlling the magnitude of the column voltage applied to each pixel, thereby controlling the luminance of the pixel. In this gradation method, the column voltage is changed in order to change the effective value voltage applied to a predetermined pixel. Therefore, the number of column voltage levels must be increased in accordance with the number of gradations. Not In addition, since the column voltage for correction must be applied to each column electrode in order to make the effective value voltage of the column voltage constant, it is necessary to be able to control the voltage level higher than the number of gradations to be displayed. . Therefore, it is not realistic to express 64 gradations.
[0039]
The PWM method is a gradation method in which the effective voltage applied to the pixel is changed by controlling the pulse width of the column voltage applied to each pixel, thereby controlling the luminance of the pixel. In this gradation method, it is necessary to subdivide the pulse width of the column voltage in order to ensure the number of gradations. Therefore, as the subdivision is performed, the column voltage becomes high frequency and the waveform becomes dull. As a result, there is a problem that sufficient luminance cannot be obtained in the selected pixel or the luminance distribution becomes non-uniform. Therefore, there is a so-called Schaefer patent (Japanese Patent Laid-Open No. 6-89082) that proposed combining the PWM gradation expression and the MLA driving method, but the current technology has a large size of 12 inches or more. In the liquid crystal display device of the screen, it is the limit to secure about 3 divisions (that is, about 8 gradations even in the case of non-uniform division) per image sub-frame, and 64 or more sufficient for displaying a natural image Cannot be ensured.
[0040]
The FRC method uses a plurality of frame periods to display one display image, and represents the gradation of the display image by controlling the column voltage applied to the liquid crystal element in each frame period. This is a gradation method. In this method, it is necessary to increase the number of gradation subframes in order to secure the number of gradations, and when the number increases, the whole image is not visually recognized as one display image, and a flickering image is displayed. There is a problem that it looks like. Accordingly, the number of gradation subframes for expressing one image is about 8 to 16 (that is, the number of gradations is about 9 to 17 gradations), which is 64 enough to display a natural image. The above gradation cannot be ensured. Also, it is conceivable to realize the gradation expression of 64 gradations by combining the AM method proposed in Japanese Patent Laid-Open No. 8-30238 and this FRC method. For this purpose, dummy data is provided for each subframe. It is necessary to secure the time for applying, and as a result, the drive duty is substantially 4/3 times, and it cannot be practically used in a large liquid crystal display device.
[0041]
In the MLA driving method, there is a technology called a phase frame as a technology for suppressing the flickering of the FRC method. In this phase frame, by setting the order of gradation control of a plurality of adjacent pixels to be different, when the plurality of adjacent pixels are all at the same gradation, the average value of luminance in each frame is approximately This is a technique for suppressing flicker between gradation images by making them coincide. A specific example is shown in FIG. In the figure, an example of a 4FRC system in which four frame periods are set as one set, the luminance of a divided image in each frame period is the case where all four liquid crystal elements A, B, C, and D are ON. Stable to about 3/4 brightness.
[0042]
The present invention has been made in order to solve the above-described problems. First, an object of the present invention is to obtain a driving method of a simple matrix liquid crystal display device that suppresses the occurrence of splicing that occurs during moving image display.
[0043]
Another object of the present invention is to provide a driving method for a simple matrix liquid crystal display device that can perform gradation expression with 64 gradations necessary for expressing a natural image.
[0044]
[Means for Solving the Problems]
A driving method of a simple matrix liquid crystal display device according to the invention of claim 1 is: In order to control the transmittance of the liquid crystal element provided for each pixel by applying a predetermined voltage from a plurality of row electrodes and a plurality of column electrodes, and to display one display image with a plurality of frame periods In the driving method of the simple matrix liquid crystal display device that expresses the gradation of the display image by controlling ON / OFF the column voltage applied to the liquid crystal element in each frame period, moving image display is performed. The plurality of row electrodes are divided into a plurality of simultaneous selection groups, and a scanning voltage is applied to the row electrodes for each of the simultaneous selection groups, and a column voltage is simultaneously applied to a plurality of column electrodes. By simultaneously applying a selection voltage to a plurality of liquid crystal elements to which the same column voltage is applied, this is repeated at least as many times as the number of simultaneously selected rows. Multiline addressing to form one display image of a predetermined brightness by controlling the effective voltage applied to the liquid crystal element The maximum absolute value among the column voltage series applied to each column electrode when the driving method is used and the luminance array of a plurality of pixels in each column electrode is a luminance array repeated in units of two pixels When a column voltage having a value is squared and divided by the mean square value of the column voltage series, the division value is 1.5 Is Therefore, when the display gradation of the display image is divided into the divided gradations in each divided image, a phase frame that is divided so that each divided image has the same gradation distribution as the checkered display image is used. Gradation display Is.
[0045]
A driving method of a simple matrix liquid crystal display device according to the invention of claim 2 is as follows: In order to control the transmittance of the liquid crystal element provided for each pixel by applying a predetermined voltage from a plurality of row electrodes and a plurality of column electrodes, and to display one display image with a plurality of frame periods In the driving method of the simple matrix liquid crystal display device that expresses the gradation of the display image by controlling ON / OFF the column voltage applied to the liquid crystal element in each frame period, moving image display is performed. The plurality of row electrodes are divided into a plurality of simultaneous selection groups, and a scanning voltage is applied to the row electrodes for each of the simultaneous selection groups, and a column voltage is simultaneously applied to a plurality of column electrodes. By simultaneously applying a selection voltage to a plurality of liquid crystal elements to which the same column voltage is applied, this is repeated at least as many times as the number of simultaneously selected rows. Together to control the effective voltage applied to the liquid crystal element is driven by multiline addressing drive method for forming one display image of a predetermined brightness, The array of the luminance values of the plurality of pixels in each column electrode is repeated in units of four pixels, and the luminance values of the two pixels paired when the four pixels are divided into two consecutive pixels, respectively. Even in the case of the same luminance array, the above division value is 1.5 Is Thus, when the display gradation of the display image is divided into the divided gradations in each divided image, each divided image has the same gradation distribution as the display image in the case where the same gradation is alternately arranged by two pixels. Gradation display using phase frames divided in this way Is.
[0046]
According to a third aspect of the present invention, there is provided a driving method for a simple matrix liquid crystal display device, wherein the divided value is obtained even when the luminance arrangement of a plurality of pixels in each column electrode is the same. 1.5 It is the following.
[0047]
The driving method of the simple matrix liquid crystal display device according to the invention of claim 4 is as follows: In order to control the transmittance of the liquid crystal element provided for each pixel by applying a predetermined voltage from a plurality of row electrodes and a plurality of column electrodes, and to display one display image with a plurality of frame periods In the driving method of the simple matrix liquid crystal display device that expresses the gradation of the display image by controlling ON / OFF the column voltage applied to the liquid crystal element in each frame period, moving image display is performed. The plurality of row electrodes are divided into a plurality of simultaneous selection groups, and a scanning voltage is applied to the row electrodes for each of the simultaneous selection groups, and a column voltage is simultaneously applied to a plurality of column electrodes. By simultaneously applying a selection voltage to a plurality of liquid crystal elements to which the same column voltage is applied, this is repeated at least as many times as the number of simultaneously selected rows. Multiline addressing to form one display image of a predetermined brightness by controlling the effective voltage applied to the liquid crystal element Drive with the drive system,
When the luminance arrangement of a plurality of pixels in each column electrode is a luminance arrangement repeated in units of two pixels, the column voltage having the maximum absolute value is squared among the column voltage series applied to each column electrode. The division value when this is divided by the mean square value of the column voltage series is smaller than the division value in at least one column voltage series different from the column voltage series. In addition, when the display gradation of the display image is divided into the divided gradations in each divided image, a phase frame that is divided so that each divided image has the same gradation distribution as that of the uniform display image is used. Gradation display Is.
[0048]
According to a fifth aspect of the present invention, there is provided a driving method for a simple matrix liquid crystal display device, wherein the arrangement of the luminances of a plurality of pixels in each column electrode is repeated in units of four pixels, and the four pixels are consecutive. Even in the case of a luminance array in which the luminance of two pixels paired when divided into two at the same time is the same, the division value is the division in at least one column voltage series different from the column voltage series. It is smaller than the value.
[0049]
In the driving method of the simple matrix liquid crystal display device according to the sixth aspect of the present invention, the divided value is different from the column voltage series even when the luminance arrangement of the plurality of pixels in each column electrode is all the same. It is smaller than the division value in at least one column voltage series.
[0050]
According to a seventh aspect of the present invention, there is provided a driving method for a simple matrix liquid crystal display device which performs gradation expression using both the FRC method and the PWM method.
[0051]
A driving method of a simple matrix liquid crystal display device according to an eighth aspect of the present invention performs gradation expression by using both the FRC method and the PWM method, and a plurality of divided images formed for each frame period of the FRC. Among them, the luminance array of a plurality of pixels related to each column electrode in at least one divided image is a luminance array that is repeated in units of two pixels, or is repeated in units of four pixels, and the four pixels are continuous. The pulse width modulation in each frame period is determined so as to obtain a luminance array in which the luminance of each pair is the same when the two pixels are divided into two.
[0052]
According to a ninth aspect of the present invention, there is provided a driving method for a simple matrix liquid crystal display device in which at least one divided image is subjected to pulse width modulation at a division ratio different from other divided images among a plurality of divided images. is there.
[0053]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below.
[0054]
Embodiment 1 FIG.
As a simple matrix liquid crystal display device, a 15-inch XGA liquid crystal panel in which (1024 pixels × 728 pixels × RGB) STN elements were arranged in a matrix was used. This liquid crystal display device has a structure in which two phase films that perform phase compensation, an inner color filter, and a liquid crystal backlight are combined with liquid crystal that is driven by an STN method with a twist angle of 240 degrees. High-precision display is possible. The driving system for driving the liquid crystal is provided with an upper driving system for driving the upper part of the screen and a lower driving system for driving the lower part. Each divided driving system is connected via a 6-bit parallel image signal. The drive control system was configured so that an input image updated independently for each 60 Hz low frequency period could be input. At the same time, the display image is updated every 60 Hz in synchronization with the input image, so that the memory required for storing the input signal is reduced to one screen. The display screen of 1024 pixels × 728 pixels corresponds to the image quality of the XGA level used for a personal computer or the like.
[0055]
In the first embodiment, in particular, the MLA driving method is adopted to ensure the contrast of the image, and simultaneously selected row numbers L = 4 and simultaneously selected column numbers K = 4. The scanning voltage series was expressed as a square matrix.
[0056]
The square matrix is white or white for displaying the same image on at least four or more adjacent pixels 1, 1, 1, 1 in the column direction to which the same column voltage 4a, 4b, 4c, 4d is applied. When displaying a black uniform display image, when displaying a checkered pattern display image in which white and black alternate with respect to four or more adjacent pixels 1, 1, 1, 1 in an array in the column direction And when displaying a display image of “white black and white black” or “black black white white” for four or more adjacent pixels 1, 1, 1, 1 in the arrangement in the column direction, In addition, an orthogonal matrix that matches the root mean square of the column voltage series 4 applied to each column electrode was used.
[0057]
[Equation 8]

[0058]
As a precaution, the calculation result of the column voltage series 4 when displaying a uniform display image is shown in Expression 14 and the calculation result of the column voltage series 4 when displaying a monochrome checkered display image is shown. Formula 15 further shows the calculation result of the column voltage series 4 when white and black alternate by two pixels. FIG. 1 shows changes in various applied voltages based on Equation 14. In the figure, 1 is a liquid crystal element (pixel), 2 is four simultaneously selected pixels, 3 is a scanning voltage series applied to the row electrode, and 3a, 3b, 3c, and 3d constitute a scanning voltage series, and each A scanning voltage applied every subframe period, 4 is a column voltage series applied to the row electrode, and 4a, 4b, 4c and 4d are column voltages applied to each subframe period forming a column voltage series. is there. Further, (a) to (d) mean each subframe period. As is apparent from these calculation results, the column voltages 4 a, 4 b, 4 c, 4 d in each subframe coincide with the root mean square value “4” of the column voltage series 4. In addition, the column voltage having the maximum absolute value (“2”) is closer to the average value “2” of the column voltage than the maximum value “4” that the column voltage can take. Therefore, for example, when the column voltage series 4 shown in Expression 14 changes to the column voltage series 4 shown in Expression 15 according to the input image (FIG. 2A), or from the column voltage series 4 shown in Expression 15 to Expression 14 In the case of changing to the column voltage series 4 shown in FIG. 4 (FIG. 2B), the instantaneous effective value voltage due to the column voltage does not change at all even if the image is switched.
[0059]
[Equation 9]

[0060]
[Expression 10]

[0061]
[Expression 11]

[0062]
Note that the orthogonal matrix as shown in the above equation 13 has a display image in which white or black continues, in which white and black alternate, or in which a white and black alternate every two pixels. All column voltages 4a, 4b, 4c and 4d are considered to be special solutions in which the absolute values are constant. Actually, the number of simultaneously selected rows (four in this case) is determined in order to suppress a decrease in contrast due to the response speed of the liquid crystal element 1, and each row or column of the Hadamard matrix (Hadamard matrix) is inverted in polarity, An orthogonal matrix that satisfies a predetermined condition can be obtained by rearranging. These optimizations can be performed efficiently using simulation or the like.
[0063]
The voltage ratio of the average value of the column voltages 4a, 4b, 4c, and 4d applied to the column electrodes to the average value of the absolute values of the scanning voltages 3a, 3b, 3c, and 3d applied to the row electrodes is 1 / It was set to 10.
[0064]
Next, gradation expression in the first embodiment will be described. The gradation method in this embodiment includes an FRC method that expresses the display gradation of one display image with eight divided images, and a pulse width (application time) of the column voltage in each divided image by dividing it into two. The PWM method for controlling the gradation of the divided image was also used. Specifically, the maximum application time of the column voltage was fixedly divided at 0.3: 0.7. In the case of this non-uniform division ratio, the number of display gradations when a plurality of divided images are superimposed is ensured as compared with the case where the division is simply performed with an even division ratio of 0.5: 0.5. can do. By the way, when 4 gradation PWM is used in 2 gradation subframes, it is possible to secure 9 gradations or more, and when 4 gradation PWM is used in 4 gradation subframes, it is possible to secure gradations of 25 gradations or more. In this embodiment, gradation expression is performed with 64 gradations that can be distinguished by 6 bits of the input signal.
[0065]
Table 1 shows gradations that can be represented by two frames with a division ratio of 0.3: 0.7. On the other hand, Table 2 shows gradations that can be represented by two frames with a 0.5: 0.5 division ratio.
[0066]
Further, when the display gradation of each display image is divided into the division gradations in each divided image, each divided image has the same gradation distribution as the uniform display image or the checkered display image. The display is divided so as to have a similar gradation distribution or a gradation distribution similar to that of a display image in the case where the same gradation is alternated by two pixels. A specific example is shown in FIG. This figure is an example of the FRC system that switches at a cycle of 4 frames, and (a), (b), (c), and (d) mean divided images in one frame cycle. In the same figure, [d1, d2, d3, d4] is the gradation of each divided image for expressing one display gradation, and this is for each column period ((a) to (d)). This is the basic column voltage series applied to the electrodes. By doing so, fluctuations in the effective value when the column voltage series is switched can be minimized.
[0067]
Then, image data consisting of a 1-bit character image is input to a liquid crystal display device driven by such a driving method, and black characters consisting of 8 × 8 pixels are arranged in 5 rows × 200 columns on a white background. Was displayed.
[0068]
As a result, it was possible to obtain a display with high contrast and little crosstalk. In addition, when the screen was scrolled in the column electrode arrangement direction, splicing and display unevenness between the divided images did not occur at all.
[0069]
In addition, a test for displaying a moving image with a natural shadow such as a human face by inputting a display image of 64 gradations updated every 60 Hz via a 6-bit input signal was also performed. As a means for generating a 6-bit halftone, a 0.3: 0.7 divided PWM method and an FRC method for completing one display image in 4, 5, 6, 7, and 8 frames are combined. . Further, the combination of the divided images is determined so that the display image is obtained in each gradation.
[0070]
As a result, we were able to faithfully reproduce the outline and shadow of the face. Even if the face display changes, Shi In addition, it was possible to obtain a natural image quality in which no deterioration in image quality such as splicing or flickering occurred in each display image.
[0071]
As described above, the first embodiment can display a high-accuracy and high-contrast still image on a 15-inch large screen, and is accompanied by image quality degradation such as flicker, crosstalk, and splicing. It was possible to display high-quality videos that were not at high speed. In particular, since the update cycle of the input image and the update cycle of the display image are matched to ensure the maximum pulse width of each column voltage, image quality deterioration due to voltage waveform dullness did not occur at all.
[0072]
Further, since the scanning voltage series corresponding to the orthogonal matrix shown in the above equation 13 is applied to each row electrode, a uniform display image, a checkered display image in which white and black alternate, white white and black black No splicing occurred in the checkered pattern display image and the various divided images. As a result, in normal video display, splicing is not visually recognized in a substantial part of the video, and compact disc-lead is used in multimedia compatible monitors, in-vehicle high-density information display devices, portable personal computers, personal digital assistants (PDAs), etc. Even when used to display high-quality images such as natural images stored in only memory (CD-ROM), video and natural images with sufficient quality (high speed, high contrast, high display quality) can be displayed. It was confirmed that it was possible. Note that a liquid crystal display device including STN elements can be manufactured at a lower cost than a liquid crystal display device including TFT elements having the same resolution.
[0073]
The divided value obtained by squaring the column voltage having the maximum absolute value among the plurality of column voltages applied to the plurality of column electrodes selected simultaneously and dividing the result by the square mean value of the plurality of column voltages. Table 3 shows the relationship between and the splicing visibility. Orthogonal matrix of Equation 13, Equation 17 and Equation 18 In The splicing occurrence was confirmed when the display screen in the case where the display image shown in Expression 14 to Expression 16 was displayed in the state where the scanning voltage series was applied. As apparent from this table, when the division value is smaller than 2, most people recognized that splicing was suppressed and display quality was improved. In particular, when the division value was smaller than 1.5, splicing was not recognized as much as possible.
[0074]
[Expression 12]

[0075]
[Formula 13]

[0076]
[Table 1]

[0077]
[Table 2]

[0078]
[Table 3]

[0079]
Comparative form 1.
The configuration is the same as that of the first embodiment except that a line sequential driving method that operates at an image update period of 60 Hz is adopted instead of the MLA driving method.
[0080]
Then, black characters consisting of 8 × 8 pixels were displayed in 5 rows × 200 columns on a white background.
[0081]
As a result, the contrast was too low to obtain a sufficient quality image.
[0082]
Comparative form 2.
The configuration is the same as that of the comparative example 1 except that the image update cycle is changed from 60 Hz to 240 Hz, which is four times.
[0083]
Then, black characters consisting of 8 × 8 pixels were displayed in 5 rows × 200 columns on a white background.
[0084]
As a result, a sufficiently high contrast could be obtained, but there was a large luminance difference between the voltage application side portion and the opposite side portion of the screen, and crosstalk due to waveform dullness occurred.
[0085]
Comparative form 3.
The configuration is the same as that of Embodiment 1 except that a 4 × 4 Hadamard matrix (Hadamard matrix) including an odd number of different codes (−1) in each row and column is used as the orthogonal function. The Hadamard matrix is shown in Equation 19.
[0086]
[Expression 14]

[0087]
Incidentally, the calculation result of the column voltage in the uniform display image is shown in Expression 20, and the calculation result of the column voltage in the black and white checkered display image is shown in Expression 21. As is apparent from these calculation results, the column voltages in each image subframe are biased. In addition, the column voltage having the maximum absolute value (“4”) matches the maximum value 4 that the column voltage can take. Therefore, for example, according to the input image, the column voltage series shown in Expression 20 changes to the column voltage series shown in Expression 21, or the column voltage series shown in Expression 21 changes to the column voltage series shown in Expression 20, etc. As described above, when the images are switched, an instantaneous effective voltage fluctuation occurs.
[0088]
[Expression 15]

[0089]
[Expression 16]

[0090]
Then, black characters consisting of 8 × 8 pixels were displayed in 5 rows × 200 columns on a white background.
[0091]
As a result, a still image with high contrast and no crosstalk could be displayed. However, when the screen is scrolled in the arrangement direction of the column electrodes, strong splicing and display unevenness have occurred.
[0092]
Comparative form 4.
This embodiment is the same as the first embodiment except that the 4 × 4 magic square shown in FIG. 4 is used as the phase table. In the figure, (a), (b), (c), and (d) mean divided images in each frame period.
[0093]
Then, a moving image with a natural shadow such as a human face similar to that in the first embodiment is displayed.
[0094]
As a result, it was possible to faithfully reproduce the contours and shadows of the face in a stationary state, but the splicing was weaker than the comparative form 3 as a whole at the part where the face display changed. , Splicing could be seen clearly or thinly.
[0095]
This is because the size of the phase table is larger than the orthogonal matrix, so that the average luminance between the divided images cannot be stabilized when displaying the same display gradation. This is probably because the effect of suppressing flickering cannot be obtained.
[0096]
Embodiment 2. FIG.
The pulse widths of the divided data [d1, d2, d3, d4] of 4FRC were varied. Specifically, [d1, d2] is a PWM method with a division ratio of 3: 4, and [d3, d4] is PWM modulated with a PWM method of a division ratio of 7: 3. By the way, with this combination of division examples, it is possible to express multiple gradations with a small number of frames, such as 15 gradations with 2FRC and 60 gradations with 4FRC.
[0097]
Thereby, a predetermined gradation can be expressed with a small number of frames, and flickering of the screen, which is a drawback of the FRC method, can be more effectively suppressed.
[0098]
Further, even when the phase table shown in FIG. 3 is used, since the division ratios are different for the two groups, the same division calculation can be performed for each column, and one type of division ratio is used. The same control as when using is possible.
[0099]
Table 4 shows gradations (15 gradations) that can be represented by two frame periods, which are a frame period having a division ratio of 3: 4 and a frame period having a division ratio of 7: 3.
[0100]
[Table 4]

[0101]
【The invention's effect】
As described above, according to the first aspect of the present invention, when driving by the MLA driving method and the luminance array of a plurality of pixels in each column electrode is a luminance array repeated in units of two pixels. Of the column voltage series applied to each column electrode, the square value of the column voltage having the maximum absolute value is squared, and the divided value obtained by dividing this by the mean square value of the column voltage series is 1.5 In the state where the display image based on the luminance array repeated in units of the two pixels is being displayed, even if the column voltage is changed in order to switch part or all of the image, Fluctuation of the division value hardly occurs. Therefore, it is difficult for the splicing to be visually recognized in the display portion of the display image, and it is possible to substantially suppress the occurrence of splicing. In particular, if a display image having the above pattern is used as a background image, there is an effect that splicing can be suppressed in most parts of the screen.
[0102]
According to the second aspect of the present invention, the luminance array of the plurality of pixels in each column electrode is repeated in units of four pixels, and the four pixels are paired when divided into two consecutive pixels. Even in the case of a luminance array in which the luminances of the two pixels are the same, the above division value is 1.5 In the state where the display image based on the luminance array repeated with the above four pixels as a unit is displayed, even if the column voltage is changed to switch part or all of the image, Fluctuation of the division value hardly occurs. Therefore, it is difficult for the splicing to be visually recognized in the display portion of the display image, and it is possible to substantially suppress the occurrence of splicing. In particular, if a display image having the above pattern is used as a background image, there is an effect that splicing can be suppressed in most parts of the screen.
[0103]
According to the third aspect of the present invention, even when the luminance arrangement is such that the luminance arrangement of the plurality of pixels in each column electrode is the same, the division value is 1.5 In the state where the display image based on the luminance array repeated with the above four pixels as a unit is displayed, even if the column voltage is changed to switch part or all of the image, Fluctuation of the division value hardly occurs. Therefore, it is difficult for the splicing to be visually recognized in the display portion of the display image, and it is possible to substantially suppress the occurrence of splicing. In particular, if a display image having the above pattern is used as a background image, there is an effect that splicing can be suppressed in most parts of the screen.
[0104]
According to the fourth aspect of the present invention, driving is performed by the MLA driving method, and is applied to each column electrode when the luminance arrangement of a plurality of pixels in each column electrode is a luminance arrangement repeated in units of two pixels. At least one column having a division value obtained by squaring the column voltage having the largest absolute value among the column voltage series and dividing the result by the mean square value of the column voltage series. Since it is smaller than the division value in the voltage series, the column voltage is changed in order to switch a part or all of the image in a state where a display image based on the luminance array repeated in units of the two pixels is displayed. Even if this is done, the division value hardly fluctuates. Therefore, it is difficult for the splicing to be visually recognized in the display portion of the display image, and it is possible to substantially suppress the occurrence of splicing. In particular, if a display image having the above pattern is used as a background image, there is an effect that splicing can be suppressed in most parts of the screen.
[0105]
According to the fifth aspect of the present invention, the luminance array of the plurality of pixels in each column electrode is repeated in units of four pixels, and the four pixels are paired when divided into two consecutive pixels. Even in the case of the luminance array in which the luminances of the two pixels become the same, the division value is smaller than the division value in at least one column voltage series different from the column voltage series. In a state where a display image based on a luminance array that is repeated in units of one pixel is displayed, even if the column voltage is changed to switch part or all of the image, the above-described variation in the division value hardly occurs. Absent. Therefore, it is difficult for the splicing to be visually recognized in the display portion of the display image, and it is possible to substantially suppress the occurrence of splicing. In particular, if a display image having the above pattern is used as a background image, there is an effect that splicing can be suppressed in most parts of the screen.
[0106]
According to the sixth aspect of the present invention, even when the luminance arrays of the plurality of pixels in each column electrode are all the same, the division value is at least one column voltage series different from the column voltage series. Since it is smaller than the division value, even if the column voltage is changed in order to switch part or all of the image in the state where the display image based on the luminance array repeated in units of the above four pixels is displayed. The division value hardly fluctuates. Therefore, it is difficult for the splicing to be visually recognized in the display portion of the display image, and it is possible to substantially suppress the occurrence of splicing. In particular, if a display image having the above pattern is used as a background image, there is an effect that splicing can be suppressed in most parts of the screen.
[0107]
According to the seventh aspect of the present invention, since gradation expression is performed using both the FRC method and the PWM method, it is possible to express 64 gradations necessary for natural image display while suppressing various image quality deteriorations. There is an effect.
[0108]
According to the eighth aspect of the present invention, gradation expression is performed using both the FRC method and the PWM method, and each of at least one divided image among a plurality of divided images formed for each frame period of the FRC. The luminance array of a plurality of pixels related to the column electrode is a luminance array that is repeated in units of two pixels, or is repeated in units of four pixels, and the four pixels are divided into two consecutive two pixels. Since the pulse width modulation in each frame period is determined so that the luminance array of each pair has the same luminance, the occurrence of splicing is suppressed when the divided images formed in each subframe period are switched. There is an effect that can be done.
[0109]
According to the ninth aspect of the present invention, since at least one divided image among the plurality of divided images is subjected to pulse width modulation at a different division ratio from the other divided images, all the divided images are divided into the same divided image. Compared to the case where the pulse width modulation is performed with the ratio, the types of effective value voltages of each pixel obtained by superimposing a plurality of divided images can be increased. As a result, the number of gradations can be increased.
[Brief description of the drawings]
FIG. 1 is an example of a voltage application sequence according to a first embodiment of the present invention.
FIG. 2 is an example of a column voltage waveform at the time of image switching according to the first embodiment of the present invention.
FIG. 3 is a phase frame according to the first embodiment of the present invention.
FIG. 4 is a magic square according to a fourth embodiment of the present invention.
FIG. 5 is an example of a conventional voltage application sequence.
FIG. 6 is an example of a conventional phase table.
[Explanation of symbols]
1 liquid crystal element, 2 simultaneous selection group, 3 scanning voltage series, 3a, 3b, 3c, 3d scanning voltage, 4 column voltage series, 4a, 4b, 4c, 4d column voltage.

Claims (9)

In order to control the transmittance of the liquid crystal element provided for each pixel by applying a predetermined voltage from a plurality of row electrodes and a plurality of column electrodes, and to display one display image with a plurality of frame periods In a driving method of a simple matrix liquid crystal display device that expresses gradation of a display image by controlling ON / OFF of a column voltage applied to a liquid crystal element in each frame period ,
When a moving image is displayed, the plurality of row electrodes are divided into a plurality of simultaneous selection groups, and a scanning voltage is applied to the row electrodes for each of the simultaneous selection groups. On the other hand, by applying a column voltage at the same time, a selection voltage is simultaneously applied to a plurality of liquid crystal elements to which the same column voltage is applied, and this is repeated at least as many times as the number of simultaneously selected rows. The pixel is driven by a multi-line addressing driving method for controlling one effective voltage applied to each liquid crystal element to form one display image having a predetermined luminance, and two pixels are arranged in luminance for each column electrode. Of the column voltage series applied to each column electrode in the case of a luminance array repeated in units of Quotient when divided by the mean square value of the ram voltage series Ri der 1.5 or less, when dividing a display gradation of the display image on the split tone in each divided image, the divided image is checkered A driving method of a simple matrix liquid crystal display device, characterized in that gradation display is performed using a phase frame divided so as to have a gradation distribution similar to a display image of a pattern . In order to control the transmittance of the liquid crystal element provided for each pixel by applying a predetermined voltage from a plurality of row electrodes and a plurality of column electrodes, and to display one display image with a plurality of frame periods In a driving method of a simple matrix liquid crystal display device that expresses gradation of a display image by controlling ON / OFF of a column voltage applied to a liquid crystal element in each frame period ,
When a moving image is displayed, the plurality of row electrodes are divided into a plurality of simultaneous selection groups, and a scanning voltage is applied to the row electrodes for each of the simultaneous selection groups. On the other hand, by applying a column voltage at the same time, a selection voltage is simultaneously applied to a plurality of liquid crystal elements to which the same column voltage is applied, and this is repeated at least as many times as the number of simultaneously selected rows. The pixel is driven by a multi-line addressing driving method for controlling one effective voltage applied to each liquid crystal element to form one display image having a predetermined luminance, and the luminance array of a plurality of pixels in each column electrode has four pixels. Are repeated as a unit, and the luminance of the two pixels paired when the four pixels are divided into two consecutive two pixels is the same. Of the column voltage sequence applied to each column electrode when a degree sequence, division value when squared column voltage, which was divided by the mean square value of the column voltage sequence having a maximum absolute value of 1 .5 Ri der below, when dividing a display gradation of the display image on the split tone in each divided image, similar to the display image when the respective divided image is same tone comes alternately by two pixels A driving method of a simple matrix liquid crystal display device, wherein gradation display is performed using a phase frame divided so as to have a gradation distribution . In the case where the array of brightness of a plurality of pixels in each column electrode is the same brightness array, the column voltage having the maximum absolute value is squared among the column voltage series applied to each column electrode, and this 3. The driving method of a simple matrix liquid crystal display device according to claim 1, wherein a division value obtained by dividing by a mean square value of the column voltage series is 1.5 or less. In order to control the transmittance of the liquid crystal element provided for each pixel by applying a predetermined voltage from a plurality of row electrodes and a plurality of column electrodes, and to display one display image with a plurality of frame periods In a driving method of a simple matrix liquid crystal display device that expresses gradation of a display image by controlling ON / OFF of a column voltage applied to a liquid crystal element in each frame period ,
When a moving image is displayed, the plurality of row electrodes are divided into a plurality of simultaneous selection groups, and a scanning voltage is applied to the row electrodes for each of the simultaneous selection groups. On the other hand, by applying a column voltage at the same time, a selection voltage is simultaneously applied to a plurality of liquid crystal elements to which the same column voltage is applied, and this is repeated at least as many times as the number of simultaneously selected rows. The pixel is driven by a multi-line addressing driving method for controlling one effective voltage applied to each liquid crystal element to form one display image having a predetermined luminance, and two pixels are arranged in luminance for each column electrode. Of the column voltage series applied to each column electrode in the case of a luminance array repeated in units of Quotient when divided by the mean square value of the ram voltage series, the column voltage sequence and rather smaller than the quotient of different at least one column voltage sequence, the display gradation of the display image in each divided image A simple matrix liquid crystal that performs gradation display using a phase frame that is divided so that each divided image has a gradation distribution similar to that of a uniform display image when divided into divided gradations. A driving method of a display device.   The array of the luminance values of the plurality of pixels in each column electrode is repeated in units of four pixels, and the luminance values of the two pixels paired when the four pixels are divided into two consecutive pixels, respectively. Divide by dividing the column voltage having the maximum absolute value among the column voltage series applied to each column electrode in the case of the same luminance array, and dividing this by the mean square value of the column voltage series 5. The driving method of a simple matrix liquid crystal display device according to claim 4, wherein the value is smaller than the division value in at least one column voltage series different from the column voltage series.   In the case where the array of brightness of a plurality of pixels in each column electrode is the same brightness array, the column voltage having the maximum absolute value is squared among the column voltage series applied to each column electrode, and this 5. The simple matrix liquid crystal display according to claim 4, wherein a division value obtained by dividing by a mean square value of the column voltage series is smaller than the division value in at least one column voltage series different from the column voltage series. Device driving method.   A frame rate control system that uses a plurality of frame periods to display one display image, and controls the column voltage applied to the liquid crystal element in each frame period to express the gradation of the display image, and each frame period And a pulse width modulation method that expresses the gradation of the divided image formed at each frame period by controlling the pulse width of the column voltage applied to the liquid crystal element. The driving method of the simple matrix liquid crystal display device according to claim 1. A frame rate control system that uses a plurality of frame periods to display one display image, and controls the column voltage applied to the liquid crystal element in each frame period to express the gradation of the display image, and each frame period And a pulse width modulation method that expresses the gray level of the divided image formed for each frame period by controlling the pulse width of the column voltage applied to the liquid crystal element in FIG.
The luminance array of a plurality of pixels in each column electrode of at least one of the plurality of divided images is a luminance array that is repeated in units of two pixels, or is repeated in units of four pixels, 2. The pulse width modulation in each frame period is determined so as to obtain a luminance array in which the luminance of each pair is the same when the four pixels are divided into two consecutive two pixels. A driving method of a simple matrix liquid crystal display device according to any one of claims 1 to 6.   Among the plurality of divided images that are superimposed to express the gradation of one display image, at least one divided image is subjected to pulse width modulation at a different division ratio from the other divided images. A driving method of a simple matrix liquid crystal display device according to claim 7 or 8.

Images