JP4604455B2 - Electro-optical device, driving method of electro-optical device, and electronic apparatus - Google Patents

Description

階調データ（０００）は一つの画素３０に階調度０の表示（黒表示：有機ＥＬ素子３１の発光強度が０の表示）をするためのデータであり、階調データ（１１１）は一つの画素３０に階調度７の表示（白表示：有機ＥＬ素子３１の発光強度が７の表示）をするためのデータである。また、階調データ（００１）〜（１１０）はそれぞれ、一つの画素３０に中間の階調度１〜６の表示（有機ＥＬ素子３１の発光強度１〜６の表示）をするためのデータである。
【００５３】
データ線駆動回路２３は、走査線Ｙ１〜Ｙｍの一つが順に選択される各選択期間ｔ１に、選択された一つの走査線に対応する各画素３０にデータ信号として、上記の表１及び図６に示すようにＬ（電圧０）又はＨ（電圧Ｖ１）のいずれか一方を一斉に出力するようになっている。この電圧に応じ、図４，５で動作で発光する。その際は、階調データの階調度に応じた強度でも発光する。
【００５４】
下記の表２は、上述した８種類の階調度に応じた階調データと、１フレームにおけるサブフィールドＳＦ１（１回目の選択期間ｔ１）、ＳＦ２（２回目と３回目の各選択期間ｔ１）及びＳＦ３（４回目〜７回目の各選択期間ｔ１）で一つの画素３０に書き込まれるデータ信号との関係を示してある。
【００５５】
【表２】

例えば、図６（ａ）の階調データ（０００）で各画素３０に階調度０の表示をする場合、表２に示すように、サブフィールドＳＦ１（１回目の選択期間ｔ１）、ＳＦ２（２回目と３回目の各選択期間ｔ１）及びＳＦ３（４回目〜７回目の各選択期間ｔ１）の７回の選択期間ｔ１でＬのデータ信号各画素３０に書き込まれる。また、図６（ｂ）の階調データ（００１）で各画素３０に階調度１の表示をする場合、表２に示すように、１回目の選択期間ｔ１にのみＨのデータ信号が書き込まれ、２回目〜７回目までの各選択期間ｔ１にはＬのデータ信号が書き込まれる。以下同様に、図６（ｃ）〜（ｈ）の階調データ（０１０）〜（１１１）で各画素３０に階調度２〜７の表示をする場合、表２に示すように、１フレームにおいて７回の各選択期間ｔ１でＬ又はＨのデータ信号が書き込まれるようになっている。
【００５６】
このように、１フレームにおいて７回の各選択期間ｔ１で、Ｌ又はＨのデータ信号が書き込まれることにより、各画素３０の有機ＥＬ素子３１は図６（ａ）〜（ｈ）の階調データ（０００）〜（１１１）に応じた発光強度で発光し、各画素３０で８階調の階調表示を行うようになっている。
【００５７】
図８（ａ）は、１フレームにおける７回の各選択期間ｔ１で、電圧Ｖ１（Ｈのデータ信号）が画素３０に連続して書き込まれる場合のデータ信号の波形を示している。また、図８（ｂ）は、各選択期間ｔ１で電圧Ｖ１のデータ信号が画素３０に書き込まれることで保持用キャパシタＣ１に蓄積される電荷Ｑの変化と、トランジスタＱｓがオフしてからの電荷Ｑの変化とを示している。また、図８（ｃ）は、電圧Ｖ１のデータ信号が画素３０に書き込まれたときの有機ＥＬ素子３１に流れる電流Ｉ_ELの変化を示している。この図８（ｃ）では、選択期間ｔ１終了直前の電流Ｉ_EL（電流値Ｉ₁）、電圧Ｖ１が印加されている状態で定常的に流れる電流を意味しており、選択期間ｔ１終了時から有機ＥＬ素子３１に流れる電流Ｉ_ELは保持用キャパシタＣ１に蓄積された電荷Ｑを電流源とする電流に切り替わる。また、図８（ｃ）では、選択期間ｔ１終了直前での電流Ｉ_ELの（電流値Ｉ₁）と電荷Ｑの電流源に切り替わったときの電流Ｉ_ELの（電流値Ｉ₂）とが一致するように示されているが、両者の電圧値が必ずしも一致するとは限らない。そして、図８（ｄ）は、電圧Ｖ１のデータ信号が画素３０に書き込まれるときの有機ＥＬ素子３１の発光強度Ｌ_Iの変化を示している。
【００５８】
図８（ａ）〜（ｄ）から分かるように、各選択期間ｔ１で電圧Ｖ１のデータ信号が画素３０に書き込まれると、トランジスタＱｓがオンしている選択期間ｔ１の間に保持用キャパシタＣ１に電圧Ｖ１に応じた電荷Ｑが蓄積される。各選択期間ｔ１の終了時にトランジスタＱｓがオン状態からオフ状態になると、保持用キャパシタＣ１に蓄積された電荷Ｑが有機ＥＬ素子３１を通じて放電するので、その電荷Ｑが次第に減少する。この減少に伴い有機ＥＬ素子３１に流れる電流Ｉ_ELが次第に低下し、有機ＥＬ素子３１の発光強度Ｌ_Iが次第に低下する。
【００５９】
そして、本例では、前記周期Ｔの時間内に、各画素３０の有機ＥＬ素子３１に流れる電流Ｉ_ELが、選択期間ｔ１終了時における電流値Ｉ₁対して予め設定された相対値以下の電流値Ｉ₂になるように、有機ＥＬ素子３１の電圧／電流特性及び保持用キャパシタＣ１の容量を設定してある。例えば、周期Ｔの時間内で、次の選択期間ｔ１が開始される前の所定期間ｔ２になるまでに、電流値Ｉ₂が電流値Ｉ₁の１／２或いは１／１０になるように、有機ＥＬ素子３１の電圧／電流特性及び保持用キャパシタＣ１の容量を設定してある。このような設定により、各選択期間の前に、有機ＥＬ素子３１の発光強度が小さく、その発熱量が少ない冷却期間が設けられることになる。これにより、各有機ＥＬ素子３１の素子温度が低く抑えられる。なお、本例では、「周期Ｔ」が、各選択期間ｔ１の開始時から同じ走査線が次に選択されるまでの時間に相当する。
【００６０】
図９は、１フレームにおいて、走査線Ｙ１〜Ｙｋに対応する各画素３０に上記階調度０の表示（黒表示）をさせるとともに、走査線Ｙｋ＋１〜Ｙｍに対応する各画素３０に上記階調度７の表示（白表示）をさせる際に、各画素３０に書き込むデータ信号の波形を示している。この場合、１フレームに各画素３０へのデータ信号の書き込みを周期Ｔ毎に７回行う際に、各周期Ｔにおいて、走査線Ｙ１〜Ｙｋに対応する各画素３０には０（Ｖ）のデータ信号を書き込み、走査線Ｙｋ＋１〜Ｙｍに対応する各画素３０にはＶ１（Ｖ）のデータ信号を書き込む。これにより、図１０に示すような１フレームの表示画面が表示される。
【００６１】
以上のように構成された第１実施形態によれば、以下の作用効果を奏する。
（イ）各選択期間ｔ１に、選択する一つの走査線に接続された各画素３０のトランジスタＱｓがオン状態になると、複数のデータ線Ｘ１〜ＸｎからトランジスタＱｓを介して供給されるデータ信号の電圧に応じた電荷Ｑが保持用キャパシタＣ１に蓄積される。これとともに、データ信号に応じた電流が選択する一つの走査線に接続された各画素３０のトランジスタＱｓを通じて有機ＥＬ素子３１に流れ、その電流に応じた明るさで有機ＥＬ素子３１が発光する。また、各選択期間が終了しトランジスタＱｓがオフ状態になる非選択期間に、保持用キャパシタＣ１に蓄積された電荷Ｑが有機ＥＬ素子３１を通じて放電して有機ＥＬ素子３１に電流が流れ、有機ＥＬ素子３１が発光する。
【００６２】
このように、各選択期間ｔ１には、選択された走査線に対応する各画素３０の有機ＥＬ素子３１に、オン状態となったトランジスタＱｓを通じて電流を流すことで、その電流に応じた明るさで有機ＥＬ素子３１を発光させる。また、非選択期間には、保持用キャパシタＣ１に蓄積された電荷を電流源として各画素の有機ＥＬ素子３１を発光させる。
【００６３】
このような「パルス駆動」方式を採用しているため、各画素３０には一つのトランジスタＱｓを設けるだけでよい。これにより、１画素の等価回路が図３に示すように単純化し、製造コストを低減することができる。また、各画素３０の有効な発光領域が増える、即ち開口率が増加するので、各画素３０の有機ＥＬ素子３１に流す電流を減らして単位面積当たりの発光素子の発光強度を小さくすることができ、各有機ＥＬ素子３１の発熱量を低く抑えることが可能になる。したがって、製造コストを低減することができるとともに、発光素子の寿命を延ばすことができる。
【００６４】
（ロ）図８に示すように、各画素３０の有機ＥＬ素子３１に流れる電流Ｉ_EL（電流値Ｉ₂）が、選択期間ｔ１終了時での電流Ｉ_EL（電流値Ｉ₁）に対して予め設定された相対値以下になるように、有機ＥＬ素子３１の電圧／電流特性及び保持用キャパシタＣ１の容量を設定してある。このため、各選択期間ｔ１の前に有機ＥＬ素子３１の発光強度が小さく、その発熱量が少ない冷却期間ｔ２が設けられることになり、有機ＥＬ素子３１の発熱量を少なくして素子温度を低く抑えることができる。例えば、前記相対値を１／１０（図１３の横軸で示す相対値０．１）にすることで、その発熱量が１／１０になる冷却期間ｔ２を各選択期間ｔ１の前にとることができる。この場合、有機ＥＬ素子３１の素子温度は、従来では通常８０℃〜１００℃位になるのに対し、４０℃〜５０℃位になり、その結果、有機ＥＬ素子３１の寿命は１０⁵時間位に延ばすことができた。また、相対値を１／１０にするのが難しい場合には、相対値を１／２（図１３の横軸で示す相対値０．５）にすることにより、有機ＥＬ素子３１の寿命を２×１０⁴時間位に延ばすことができた。このように、有機ＥＬ素子３１の寿命を更に延ばすことができる。
【００６５】
（ハ）各画素３０の有機ＥＬ素子３１を上記パルス駆動により発光させるのに、上記サブフィールド駆動による階調制御を行なっている。つまり、１フレームにおいて７回の各選択期間ｔ１で、Ｌ又はＨのデータ信号が書き込まれることにより、各画素３０の有機ＥＬ素子３１は図６（ａ）〜（ｈ）の階調データ（０００）〜（１１１）に応じた発光強度で発光し、各画素３０で２３階調の階調表示を行なっている。これにより、データ信号の書き込み周期が短くなるので、各選択期間ｔ１に各保持用キャパシタＣ１に蓄積させる電荷Ｑが小さくてすむ。したがって、高精細でも、低消費電力でかつ明るい表示を実現することができる。
【００６６】
[第２実施形態]
図１１は、本発明を電気光学装置としてのＥＬ表示装置２０に適用した第２実施形態を示している。この実施形態の説明において、上記第１実施形態と同様の部材及び信号には、同じ符号を使って重複した説明を省略する。
【００６７】
この第２実施形態は、上記パルス駆動と上記サブフィールド駆動による階調制御を行う点では上記第１実施形態と同じであるが、走査線Ｙ１〜Ｙｍのいずれか一つに接続されている各画素３０の保持用キャパシタＣ１の端子ａが第１実施形態とは異なる配線に接続されている点で第１実施形態とは異なる。
【００６８】
つまり、各画素３０の保持用キャパシタＣ１の端子ａは、ゲート線（配線）４０を介して、ｍ行の走査線Ｙ１〜Ｙｍのうち１つ前に選択される前段（１行前）の走査線に接続されている。例えば、走査線Ｙｍとデータ線Ｘ１〜Ｘｎの各交差部にある各画素３０の保持用キャパシタＣ１の端子ａは、ゲート線４０を介して、１つ前に選択される前段の走査線である走査線Ｙｍ−１に接続されている。なお、第１行目の走査線Ｙ１に対応する各画素３０の保持用キャパシタＣ１の端子ａについては、第１行目の走査線Ｙ１に対する前段の走査線がないので、ダミーの走査線Ｙ０を設けてある。
【００６９】
このように構成された第２実施形態により、上記第１実施形態と同様に上記作用効果（イ）〜（ハ）を奏する。
[第３実施形態]
図１２は、第３実施形態に係るＥＬ表示装置２０を示している。
【００７０】
このＥＬ表示装置２０は、図２に示す上記第１実施形態において、各画素３０の保持用キャパシタＣ１を無くしたもので、各選択期間ｔ１の間に、データ信号に応じた電流が選択された一つの走査線に接続された各トランジスタＱｓを通じて有機ＥＬ素子３１に流れ、有機ＥＬ素子３１が発光するように構成されている。
【００７１】
また、このＥＬ表示装置２０は、各選択期間ｔ１の前に上記冷却期間ｔ２（図８（ｄ））を設けるために、各画素３０の有機ＥＬ素子３１に流れる電流Ｉ_ELが、選択期間ｔ１終了時での電流Ｉ_ELに対して予め設定された相対値以下になるように、有機ＥＬ素子３１の電圧／電流特性を設定してある。その他の構成は、上記第１実施形態と同様である。
【００７２】
このように構成された第３実施形態により、以下の作用効果を奏する。
（ニ）各選択期間ｔ１に、選択する一つの走査線に接続された各画素３０のトランジスタＱｓがオン状態になると、データ信号に応じた電流が各画素３０のトランジスタＱｓを通じて有機ＥＬ素子３１に流れ、その電流に応じた明るさで有機ＥＬ素子３１が発光する。このように、各選択期間ｔ１に、選択された走査線に対応する各画素３０の有機ＥＬ素子３１に、オン状態となったトランジスタＱｓを通じて電流を流すことでその電流に応じた明るさで有機ＥＬ素子３１を発光させる。このような「パルス駆動」方式を採用しているため、各画素３０には一つのトランジスタＱｓを設けるだけでよい。したがって、上記作用効果（イ）と同様に、製造コストを低減することができるとともに、発光素子の寿命を延ばすことができる。
【００７３】
（ホ）各画素３０の有機ＥＬ素子３１に流れる電流Ｉ_ELが、選択期間ｔ１終了時での電流Ｉ_ELに対して予め設定された相対値以下になるように、有機ＥＬ素子３１の電圧／電流特性を設定してある。このため、各選択期間ｔ１の前に有機ＥＬ素子３１の発光強度が小さく、その発熱量が少ない冷却期間ｔ２が設けられることになり、有機ＥＬ素子３１の発熱量を少なくして素子温度を低く抑えることができる。したがって、上記作用効果（ロ）と同様に、有機ＥＬ素子３１の寿命を更に延ばすことができる。
【００７４】
（ヘ）上記第１実施形態と同様に、各画素３０の有機ＥＬ素子３１を上記パルス駆動により発光させるのに、上記サブフィールド駆動による階調制御を行なうことにより、上記作用効果（ハ）を奏することができる。
【００７５】
（ト）各画素３０の保持用キャパシタＣ１を無くしたことにより、保持用キャパシタＣ１両側の端子ａ，ｂと保持容量線Ｌとが不要になるので、１画素の等価回路が図３に示す上記第１実施形態よりも更に単純化し（図１２参照）、製造コストを更に低減することができる。
【００７６】
［電子機器］
次に、上記各実施形態で説明したＥＬ表示装置２０の表示パネル部２１を用いた電子機器について説明する。表示パネル部２１は、図１４に示すようなモバイル型のパーソナルコンピュータに適用できる。図１４に示すパーソナルコンピュータ７０は、キーボード７１を備えた本体部７２と、表示パネル部２１を用いた表示ユニット７３とを備えている。この表示ユニット７３に用いた表示パネル部２１では、高精細でも、低消費電力でかつ明るい表示を実現することができる。
【００７７】
[変形例]
なお、この発明は以下のように変更して具体化することもできる。
・上記第１実施形態では、各画素３０の有機ＥＬ素子３１を上記パルス駆動により発光させるのに、上記サブフィールド駆動による階調制御を行なっているが、本発明はこれに限定されない。例えば、複数の走査線Ｙ１〜Ｙｍを１フレームに１回ずつ選択し、１フレーム当たり１回の選択期間ｔ１に、階調度に応じた電圧のデータ信号を各画素３０に印加して有機ＥＬ素子３１の発光強度を制御するアナログ階調制御にも本発明は適用可能である。
【００７８】
・上記第１実施形態では、前記相対値を、一例として１／２或いは１／１０にする場合について説明したが、その相対値は適宜変更可能で、周期Ｔの時間内で、次の選択期間ｔ１が開始される前の所定期間ｔ２になるまでに、相対値が１／２以下であれば顕著な効果が得られる。また、所定期間ｔ２において有機ＥＬ素子３１に流れる電流Ｉ_EL（電流値Ｉ₂）が０になるようにしてもよい。この場合には、各選択期間ｔ１の前に有機ＥＬ素子３１が非発光となり、発熱量をより少なくして素子温度をより低く抑えることができる。
【００７９】
・上記第１実施形態において、上述したサブフィールド駆動による階調制御に代えて、サブフィールド駆動による階調制御を次のように行う構成にも本発明は適用可能である。制御回路２４は、１フレームを同じ長さの期間（周期Ｔ）を有する２^Ｎ−１個のサブフィールドに分割し、サブフィールド毎に、上記階調データに基づき各画素に２値の電圧のいずれか一方を書き込み２^Ｎ階調の表示を行うように、走査線駆動回路２２及びデータ線駆動回路２３を制御する。下記の表３は、一例として２^３階調の表示を行う場合における８種類の階調データと、２^３−１（＝７）個のサブフィールドＳＦ１〜ＳＦ７毎に行う１回目〜７回目の各選択期間ｔ１で一つの画素３０に書き込まれるデータ信号との関係を示してある。
【００８０】
【表３】

例えば、階調データ（０００）で各画素３０に階調度０の表示をする場合、表３に示すように、サブフィールドＳＦ１（１回目の選択期間ｔ１）〜ＳＦ７（７回目の選択期間ｔ１）の各選択期間ｔ１でＬのデータ信号のみが各画素３０に書き込まれる。また、階調データ（００１）で各画素３０に階調度１の表示をする場合、表３に示すように、サブフィールドＳＦ１でのみＨのデータ信号が書き込まれ、サブフィールドＳＦ２〜ＳＦ７の各選択期間ｔ１にはＬのデータ信号が書き込まれる。以下同様に、階調データ（０１０）〜（１１１）で各画素３０に階調度２〜７の表示をする場合、表３に示すように、Ｌ又はＨのデータ信号が書き込まれるようになっている。このようなサブフィールド駆動による階調制御によって、上記第１実施形態と同様に上記作用効果（ハ）を奏することができる。
【００８１】
・上記第１実施形態では、２^３階調（２^ＮのＮ＝３で、８階調）の階調表示、即ち階調度０〜階調度７の階調表示を行う構成であるが、Ｎの値を適宜に設定して２^Ｎ階調の表示、即ち階調度０〜階調度２^Ｎ−１の階調表示を行う構成にも本発明は適用される。
・上記第１実施形態では、フレーム周波数を６０Ｈｚとしているが、フレーム周波数をその２倍（１２０Ｈｚ）以上とするＥＬ表示装置にも本発明は適用可能である。この場合にも、上記第１実施形態と同様の作用効果を奏する。
【００８２】
・上記第１実施形態では、複数の走査線Ｙ１〜Ｙｍを順に一つずつ選択する構成であるが、本発明はこの構成に限定されない。例えば、複数の走査線Ｙ１〜Ｙｍの２つ以上を順に選択する方式、飛び越し走査方式で複数の走査線Ｙ１〜Ｙｍを順に選択する構成にも本発明は適用される。
【００８３】
・上記各実施形態では、走査線駆動回路２２、データ線駆動回路２３、制御回路２４はスイッチング用トランジスタＱｓが形成される基板上に内蔵される必要はなく、外部回路として形成してもよい。また、それらのうち少なくとも１つを内蔵してもよい。ここで、「内蔵」とは、基板上にトランジスタを用いて直接形成した状態を指す。
【００８４】
・上記各実施形態では、電気光学装置をＥＬ表示装置２０として説明したが、本発明はこれに限るものではなく、有機ＥＬ素子以外の発光素子を用いた電気光学装置及び該電気光学装置を備えた電子機器に対しても適用可能である。
【００８５】
・本発明に用いられるスイッチング用トランジスタＱｓはポリシリコンＴＦＴ、アモルファスシリコンＴＦＴ、単結晶シリコンＴＦＴ等のシリコン薄膜をチャンネル層に用いたＴＦＴやシリコンゲルマニウム等の半導体薄膜をチャンネル層に用いたＴＦＴが用いられる。
【００８６】
・ＥＬ表示装置２０は、図１４に示すようなパーソナルコンピュータに限らず、携帯電話、デジタルカメラ等の各種の電子機器に適用できる。
【図面の簡単な説明】
【図１】 第１実施形態に係るＥＬ表示装置を示すブロック図。
【図２】 表示パネル部の等価回路と駆動回路を示すブロック図。
【図３】 １画素の等価回路を示す回路図。
【図４】 図３に示す等価回路におけるデータ書き込み時の動作を示す説明図。
【図５】 図３に示す等価回路における放電時の動作を示す説明図。
【図６】 （ａ）〜（ｈ）は階調データとデータ信号の関係を示す波形図。
【図７】 走査信号を示す波形図。
【図８】 （ａ）〜（ｄ）はデータ信号Ｖ１が印加されて有機ＥＬ素子が発光する様子を示す波形図。
【図９】 駆動の一例を示すデータ信号の波形図。
【図１０】 図９に示す駆動による表示例を示す説明図。
【図１１】 第２実施形態に係る表示パネル部の等価回路と駆動回路を示すブロック図。
【図１２】 第３実施形態に係る表示パネル部の等価回路と駆動回路を示すブロック図。
【図１３】 有機ＥＬ素子の寿命を示すグラフ。
【図１４】 ＥＬ表示装置を用いたパーソナルコンピュータを示す斜視図。
【符号の説明】
Ｖ０，Ｖ１…電圧、Ｑ…電荷、Ｔ…周期、ｔ１…選択期間、ｔ２…期間、Ｙ０，Ｙ１〜Ｙｍ…走査線、Ｉ_EL…電流、ＳＦ１〜ＳＦ７…サブフィールド、Ｘ１−Ｘｎ…データ線、２０…電気光学装置としてのＥＬ表示装置、２２…走査線駆動回路、２３…データ線駆動回路、２４…制御回路、Ｑｓ…スイッチング素子としてのスイッチング用トランジスタ、Ｃ１…容量素子としての保持用キャパシタ、３０…画素、３１…発光素子としての有機ＥＬ素子。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electro-optical device, a driving method for the electro-optical device, a driving circuit for the electro-optical device, and an electronic apparatus.
[0002]
[Prior art]
In recent years, an electro-optical device using an organic EL element as an electro-optical device has attracted attention as being superior to other devices in terms of low power consumption, a high viewing angle, and a high contrast ratio. As an electro-optical device using this type of organic EL element, each of a plurality of pixels includes a switching TFT, a current control TFT, an organic EL element, and a capacitor. There is known one that performs tone display (for example, Patent Document 1). In this electro-optical device, when the gate line is selected, the gate of the switching TFT is opened, the data signal of the source line is accumulated in the capacitor, and the gate of the current control TFT is opened. Then, after the gate of the switching TFT is closed, the gate of the current control TFT is kept open by the electric charge accumulated in the capacitor, and the organic EL element emits light during that time. Further, in order to perform gradation display, for example, 64 gradation display in a time division manner, one frame is divided into 16 at a frame frequency of 60 Hz, and the ratio between the writing period and the display period is determined to be 6:10. 6 times are written.
[0003]
[Patent Document 1]
JP 2001-222240 A
[0004]
[Problems to be solved by the invention]
By the way, in a conventional electro-optical device, for example, a conventional electro-optical device described in Patent Document 1, two or more transistors including a switching transistor and a current control transistor are provided in each of a plurality of pixels. in use. Thus, it is necessary to provide two or more transistors in each pixel, which increases the manufacturing cost and reduces the effective light-emitting area of each pixel (the aperture ratio decreases). When the aperture ratio decreases, it is necessary to increase the amount of current flowing through the organic EL element to increase the emission intensity of the organic EL element per unit area. If it does in this way, there was a possibility that the emitted-heat amount of the organic EL element in each pixel might increase, element temperature might become high, and it might lead to the lifetime deterioration of an organic EL element.
[0005]
Therefore, the present invention has been made in view of such conventional problems, and an object thereof is an electro-optical device capable of reducing manufacturing costs and extending the life of a light-emitting element, a driving method of the electro-optical device, An object of the present invention is to provide an optical device drive circuit and electronic equipment.
[0006]
[Means for Solving the Problems]
The electro-optical device according to the present invention includes a plurality of scanning lines, a plurality of data lines, a plurality of switching elements disposed corresponding to the intersections of the scanning lines and the data lines, and the switching elements. When the switching element corresponding to the scanning line to be selected is turned on during each selection period in which the plurality of scanning lines are sequentially selected, the light emitting element and the capacitive element are disposed, and the plurality of data lines are A charge corresponding to the voltage of the data signal supplied through the switching element is accumulated in the capacitor element, and a current corresponding to the data signal flows to the light emitting element through the switching element, so that the light emitting element emits light. The charge accumulated in the capacitor element is released through the light emitting element during the non-selection period when the selection period ends and the switching element is turned off. Current flows to the light emitting element and the light emitting element is summarized in that configured to emit.
[0007]
According to this, when the switching element corresponding to the scanning line to be selected is turned on during each selection period, the charge corresponding to the voltage of the data signal supplied from the plurality of data lines via the switching element is supplied to the capacitor element. Accumulated. At the same time, a current corresponding to the data signal flows to the light emitting element through the switching element, and the light emitting element emits light with brightness according to the current. In addition, during the non-selection period in which each selection period ends and the switching element is turned off, the charge accumulated in the capacitor element is discharged through the light emitting element, current flows to the light emitting element, and the light emitting element emits light.
[0008]
As described above, in each selection period, light is emitted with brightness according to the current of the data signal by flowing current through the switching element that is turned on to the light emitting element of each pixel corresponding to the selected scanning line. The device emits light. In the non-selection period, the light emitting elements of the respective pixels are caused to emit light using the electric charge accumulated in the capacitor as a current source. Because of this driving method, it is only necessary to provide one switching element for each pixel. Thereby, the equivalent circuit of one pixel can be simplified and the manufacturing cost can be reduced. In addition, since the effective light emitting area of each pixel increases, that is, the aperture ratio increases, the current flowing through the light emitting element of each pixel can be reduced, and the light emission intensity of the light emitting element per unit area can be reduced. It is possible to keep the element temperature low by reducing the amount of heat generated. Therefore, the manufacturing cost can be reduced and the lifetime of the light emitting element can be extended.
[0009]
In this electro-optical device, the current flowing through the light emitting element during the time from the start of each selection period to the next selection of the same scanning line among the plurality of scanning lines is The characteristics of the light emitting element and the capacitance of the capacitive element are set so as to be equal to or less than a preset relative value with respect to the current at.
[0010]
In the prior art described in the above-mentioned Patent Document 1, since the current of substantially the same value continues to flow through the organic EL element of each pixel during the display period, the amount of heat generated by the organic EL element is large and the element temperature becomes high. This leads to deterioration of the life of the organic EL element. On the other hand, according to this configuration, the current flowing through each light emitting element of each of the plurality of pixels within the time from the start of each selection period to the next selection of the same scanning line is It is made to become below the preset relative value with respect to the said current in. For this reason, a cooling period in which the light emitting element is not emitting light or its light emission intensity is low is provided before each selection period, and the amount of heat generated by the light emitting element of each pixel is reduced to keep the element temperature lower. be able to. Therefore, the lifetime of the light emitting element can be further extended.
[0011]
In this electro-optical device, the data signal is written so that charges corresponding to the voltage of the data signal are accumulated in the capacitive element of each of the plurality of pixels at a frame frequency of 120 Hz or more.
[0012]
According to this, since the writing of the data signal for accumulating charges corresponding to the voltage of the data signal in the capacitor element of each pixel is performed at a frame frequency of 120 Hz or more, the frame period is shortened. Accordingly, the data signal writing cycle is shortened, so that the charge accumulated in each capacitor element in each selection period can be reduced. Since the charge is represented by the product of the voltage of the data signal and the capacitance of the capacitor, at least one of the voltage and the capacitance can be reduced. The power consumption can be reduced by reducing the voltage, and the aperture ratio can be further increased by reducing the capacity. Therefore, even with high definition, a bright display with low power consumption can be realized. Note that the “data signal writing cycle” here refers to the time from the start of each selection period to the next selection of the same scanning line among a plurality of scanning lines. For example, when a plurality of scanning lines are selected once per frame, the frame period becomes the “data signal writing period”.
[0013]
In this electro-optical device, one frame is divided into N subfields having a length corresponding to each bit of N-bit gradation data, and the shortest sub-field among the N subfields is divided into one frame. Based on the gradation data, a data signal is written to store charges corresponding to one of binary voltages in the capacitive element of each of the plurality of pixels based on the gradation data. ^N It was configured to perform gradation display.
[0014]
According to this, data for accumulating charges corresponding to one of the binary voltages in the capacitance element of each pixel based on the grayscale data in the cycle of the shortest subfield among N subfields per frame. Write signal and 2 by digital gradation control ^N Displays gradation. In order to perform such gradation display, 2 frames with the shortest subfield period in one frame. ^N The data signal is written once. For example, 2 bits by 3-bit gradation data ³ When gradation display of gradation (8 gradations) is performed, the period of the three sub-feeds has a length corresponding to each bit, that is, 1 (2 ⁰ ): 2 (2 ¹ ): 4 (2 ² ) Ratio. The cycle of the shortest subfield among the three subfields set in this way is 7 times (2 ³ -1) Write data signal. Accordingly, the data signal writing cycle is shortened, so that the charge accumulated in each capacitor element in each selection period can be reduced. Therefore, even with high definition, a bright display with low power consumption can be realized.
[0015]
In this electro-optical device, one frame has a period of the same length. ^N A data signal is written that is divided into one subfield, and in each subfield, a charge corresponding to one of binary voltages is accumulated in the capacitive element of each of a plurality of pixels based on gradation data. 2 ^N It was configured to perform gradation display.
[0016]
According to this, one frame has a period of the same length 2 ^N -1 sub-field is divided, and for each sub-field, a data signal is written so that a charge corresponding to one of the binary voltages is accumulated in the capacitive element of each pixel based on the gradation data. ^N Digital gradation display of gradation is performed. In order to perform such gradation display, 2 for each subfield in one frame. ^N −1 time, either one of the binary voltages is written. Accordingly, the data signal writing cycle is shortened, so that the charge accumulated in each capacitor element in each selection period can be reduced. Therefore, even with high definition, a bright display with low power consumption can be realized.
[0017]
The electro-optical device according to the present invention includes a plurality of scanning lines, a plurality of data lines, a plurality of switching elements disposed corresponding to the intersections of the scanning lines and the data lines, and the switching elements. When the switching element corresponding to the scanning line to be selected is turned on during each selection period in which the plurality of scanning lines are sequentially selected, the plurality of data lines are connected via the switching element. The present invention is configured such that a current corresponding to the data signal supplied through the switching element flows to the light emitting element, and the light emitting element emits light.
[0018]
According to this, when the switching element corresponding to the scanning line to be selected is turned on in each selection period, a current corresponding to the data signal flows to the light emitting element through the switching element, and the light emitting element has a brightness corresponding to the current. Emits light. In addition, during the non-selection period in which each selection period ends and the switching element is turned off, the charge accumulated in the capacitor element is discharged through the light emitting element, current flows to the light emitting element, and the light emitting element emits light. As described above, in each selection period, light is emitted with brightness according to the current of the data signal by flowing current through the switching element that is turned on to the light emitting element of each pixel corresponding to the selected scanning line. The device emits light. In the non-selection period, the light emitting elements of the respective pixels are caused to emit light using the electric charge accumulated in the capacitor as a current source. With such a driving method, the manufacturing cost can be reduced and the lifetime of the light emitting element can be extended.
[0019]
In this electro-optical device, a data signal is written so that a current corresponding to the data signal is supplied to the light emitting element of each of a plurality of pixels at a frame frequency of 120 Hz or more.
[0020]
According to this, since the data signal writing cycle is shortened, the charge accumulated in each capacitor element during each selection period can be reduced. Since the charge is represented by the product of the voltage of the data signal and the capacitance of the capacitor, at least one of the voltage and the capacitance can be reduced. The power consumption can be reduced by reducing the voltage, and the aperture ratio can be further increased by reducing the capacity. Therefore, even with high definition, a bright display with low power consumption can be realized.
[0021]
In this electro-optical device, one frame is divided into N subfields having a length corresponding to each bit of N-bit gradation data, and the shortest sub-field among the N subfields is divided into one frame. Based on the gradation data, a data signal is written to store charges corresponding to any one of the binary voltages in the capacitance elements of the plurality of pixels based on the gradation data. ^N It was configured to perform gradation display.
[0022]
According to this, data for accumulating charges corresponding to one of the binary voltages in the capacitance element of each pixel based on the grayscale data in the cycle of the shortest subfield among N subfields per frame. Write signal and 2 by digital gradation control ^N Displays gradation. In order to perform such gradation display, 2 frames with the shortest subfield period in one frame. ^N Since the data signal writing cycle is shortened by writing the data signal once, the charge accumulated in each capacitor element in each selection period can be reduced. Therefore, even with high definition, a bright display with low power consumption can be realized.
[0023]
In this electro-optical device, one frame has a period of the same length. ^N A data signal is written that is divided into one subfield, and in each subfield, a charge corresponding to one of binary voltages is accumulated in the capacitive element of each of a plurality of pixels based on gradation data. 2 ^N It was configured to perform gradation display.
[0024]
According to this, one frame has a period of the same length 2 ^N -1 sub-field is divided, and for each sub-field, a data signal is written so that a charge corresponding to one of the binary voltages is accumulated in the capacitive element of each pixel based on the gradation data. ^N Digital gradation display of gradation is performed. In order to perform such gradation display, 2 for each subfield in one frame. ^N By writing one of the binary voltages once, the writing cycle of the data signal is shortened, so that the charge accumulated in each capacitor element during each selection period can be reduced. Therefore, even with high definition, a bright display with low power consumption can be realized.
[0025]
The electro-optical device driving method according to the present invention includes a plurality of scanning lines, a plurality of data lines, a plurality of switching elements arranged corresponding to intersections of the scanning lines and the data lines, and the switching elements. In a driving method of an electro-optical device including a corresponding light emitting element and a capacitive element, in each selection period in which the plurality of scanning lines are sequentially selected, the switching element corresponding to the selected scanning line is turned on Then, charge corresponding to the voltage of the data signal supplied from the plurality of data lines through the switching element is accumulated in the capacitor element, and current corresponding to the data signal is stored in the light emitting element through the switching element. In the non-selection period in which each of the selection periods ends and the switching element is turned off. The charge accumulated in the child is discharged through the light emitting element current flows to the light emitting element, is summarized in that for light emitting the light emitting element.
[0026]
According to this, when the switching element corresponding to the scanning line to be selected is turned on in each selection period, the charge corresponding to the voltage of the data signal supplied from the plurality of data lines via the switching element is supplied to the capacitor element. Accumulate. At the same time, a current corresponding to the data signal is supplied to the light emitting element through the switching element, and the light emitting element is caused to emit light with brightness according to the current. In addition, in the non-selection period in which each selection period ends and the switching element is turned off, the charge accumulated in the capacitor element is discharged through the light emitting element, and a current is caused to flow to the light emitting element to cause the light emitting element to emit light. Because of this driving method, it is only necessary to provide one switching element for each pixel. Therefore, the manufacturing cost can be reduced and the lifetime of the light emitting element can be extended.
[0027]
The electro-optical device driving method according to the present invention includes a plurality of scanning lines, a plurality of data lines, a plurality of switching elements arranged corresponding to intersections of the scanning lines and the data lines, and the switching elements. In a driving method of an electro-optical device including a correspondingly arranged light emitting element, when each of the switching elements corresponding to the scanning line to be selected is turned on in each selection period in which the plurality of scanning lines are sequentially selected, The gist is to cause a current corresponding to a data signal supplied from a plurality of data lines through the switching element to flow through the switching element to the light emitting element to cause the light emitting element to emit light.
[0028]
According to this, when the switching element corresponding to the scanning line to be selected is turned on during each selection period, a current corresponding to the data signal is supplied to the light emitting element through the switching element, and the light emitting element is turned on with brightness according to the current. Make it emit light. Since this driving method (pulse driving method) is used, it is only necessary to provide one switching element for each pixel. Therefore, the manufacturing cost can be reduced and the lifetime of the light emitting element can be extended.
[0029]
The driving circuit of the electro-optical device according to the present invention includes a plurality of scanning lines, a plurality of data lines, a plurality of switching elements arranged corresponding to intersections of the scanning lines and the data lines, and the switching elements. When the switching element corresponding to the selected scanning line is turned on during each selection period in which the plurality of scanning lines are sequentially selected, the plurality of data are provided. A charge corresponding to the voltage of the data signal supplied from the line via the switching element is accumulated in the capacitor element, and a current corresponding to the data signal flows to the light emitting element through the switching element, and the light emitting element In the non-selection period in which each selection period ends and the switching element is turned off, the charge accumulated in the capacitor element becomes the light-emitting element. Through discharged current flows to the light emitting element, the light emitting element is summarized in that configured to emit.
[0030]
According to this, when the switching element corresponding to the scanning line to be selected is turned on in each selection period, the charge corresponding to the voltage of the data signal supplied from the plurality of data lines via the switching element is supplied to the capacitor element. Accumulate. At the same time, a current corresponding to the data signal is supplied to the light emitting element through the switching element, and the light emitting element is caused to emit light with brightness according to the current. In addition, in the non-selection period in which each selection period ends and the switching element is turned off, the charge accumulated in the capacitor element is discharged through the light emitting element, and a current is caused to flow to the light emitting element to cause the light emitting element to emit light. Because of this driving method, it is only necessary to provide one switching element for each pixel. Therefore, the manufacturing cost can be reduced and the lifetime of the light emitting element can be extended.
[0031]
The driving circuit of the electro-optical device according to the present invention includes a plurality of scanning lines, a plurality of data lines, a plurality of switching elements arranged corresponding to intersections of the scanning lines and the data lines, and the switching elements. And when the switching element corresponding to the scanning line to be selected is turned on in each selection period in which the plurality of scanning lines are sequentially selected, the switching is performed from the plurality of data lines. The gist is that a current corresponding to a data signal supplied through the element flows to the light emitting element through the switching element, and the light emitting element emits light.
[0032]
According to this, when the switching element corresponding to the scanning line to be selected is turned on during each selection period, a current corresponding to the data signal is supplied to the light emitting element through the switching element, and the light emitting element is turned on with brightness according to the current. Make it emit light. Because of this driving method, it is only necessary to provide one switching element for each pixel. Therefore, the manufacturing cost can be reduced and the lifetime of the light emitting element can be extended.
[0033]
An electronic apparatus according to an aspect of the invention includes the electro-optical device according to any one of claims 1 to 9. According to this, the display quality of the electronic device can be improved.
Therefore, an electronic device with good visibility can be realized.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments embodying the present invention will be described with reference to the drawings.
[First embodiment]
A first embodiment in which the present invention is applied to an EL display device as an electro-optical device will be described with reference to FIGS.
[0035]
FIG. 1 shows a circuit configuration of an EL display device as an electro-optical device, FIG. 2 shows an equivalent circuit and a drive circuit of a display panel unit, and FIG. 3 shows an equivalent circuit of one pixel.
[0036]
In FIG. 1, the EL display device 20 includes a display panel unit 21, a scanning line driving circuit 22, a data line driving circuit 23, and a control circuit 24. The scanning line driving circuit 22 and the data line driving circuit 23 are controlled by the control circuit 24 to drive the plurality of scanning lines Y1 to Ym and the plurality of data lines X1 to Xn. The control circuit 24 receives a data signal, a synchronization signal, and a clock signal from an external circuit. In addition, a vertical synchronization signal, a clock signal, and the like are supplied from the control circuit 24 to the scanning line driving circuit 22 through a signal line. A data signal, a horizontal synchronizing signal, and the like are supplied from the control circuit 24 to the data line driving circuit 23 through the signal line.
[0037]
Each element 21 to 24 of the EL display device 20 may be composed of independent electronic components. For example, each element 21 to 24 may be constituted by a one-chip semiconductor integrated circuit device. Moreover, you may be comprised as an electronic component in which all or one part of each element 21-24 was united. For example, the scanning line driving circuit 22 and the data line driving circuit 23 may be integrally formed on the display panel unit 21. All or a part of each element 21 to 24 may be configured by a programmable IC chip, and the function may be realized by software by a program written in the IC chip.
[0038]
As shown in FIG. 2, the display panel unit 21 includes n columns of data lines X1 to Xn (n is an integer) extending along the column direction and m rows of scanning lines Y1 to Ym (m) extending along the row direction. Is provided with a plurality of (m × n) pixels 30 arranged in a matrix at the intersection with (integer).
[0039]
As shown in FIGS. 2 and 3, each pixel 30 has one switching transistor Qs as a switching element, an organic EL element 31 as a light emitting element, and a holding capacitor C1 as a capacitive element. ing.
[0040]
The switching transistor (hereinafter referred to as “transistor”) Qs is a thin film transistor (TFT). In this example, the transistor Qs is composed of an N-channel FET. The transistor Qs has a gate that is a control terminal, a source that is a first terminal, and a drain that is a second terminal. The gate of the transistor Qs is connected to one of the scanning lines Y1 to Ym, the source is connected to one of the data lines X1 to Xn, and the organic EL element 31 and the holding capacitor C1 are connected in parallel to the drain. It is connected.
[0041]
The organic EL element 31 is a light emitting element in which a light emitting layer is composed of an organic EL and emits light when a current is supplied. The terminal a of the holding capacitor C1 in each pixel 30 is connected to the drain of the transistor Qs, and the terminal b is connected to the holding capacitor line L. Further, the anode of the organic EL element 31 in each pixel 30 is connected to the drain of the transistor Qs, and the cathode is connected to a common electrode (cathode electrode) different from the storage capacitor line L. The potential of the cathode electrode is generally 0 (V) in this example, but any voltage value lower than V1 (V) that is the voltage value of the data signal can be used.
[0042]
Here, the operation of the equivalent circuit of each pixel 30 shown in FIGS. 2 and 3 having the above configuration will be briefly described.
In each selection period t1 (see FIG. 7) in which one of the scanning lines Y1 to Ym is sequentially selected, a plurality of scanning signals having the voltage V0 shown in FIG. 7 are connected to the scanning line. When applied to the gate of the transistor Qs, each transistor Qs is turned on. Thus, during each selection period t1 in which each transistor Qs of the plurality of pixels 30 corresponding to one scanning line to be selected is in the ON state, as shown in FIG. 4, each transistor is simultaneously transmitted from the plurality of data lines X1 to Xn. The voltage V1 of the data signal supplied via Qs is applied to the organic EL element 31 and each holding capacitor C1.
[0043]
As a result, during each selection period t1, a charge Q corresponding to the voltage V1 of the data signal is accumulated in each holding capacitor C1, and a current corresponding to the data signal flows to the organic EL element 31 through each transistor Qs. The organic EL element 31 emits light with brightness according to the current. The charge Q accumulated in each holding capacitor C1 when writing such a data signal is represented by Q = C0 × V1.
[0044]
During each non-selection period in which each transistor Qs of the plurality of pixels 30 corresponding to one scanning line to be selected is turned off after each selection period t1 is completed, the data is stored in each holding capacitor C1. The charged charge Q is discharged through the organic EL element 31, a current flows through the organic EL element 31, and the organic EL element 31 emits light again.
[0045]
As described above, in the EL display device 20 of this example, in each pixel 30, not only the current flowing through the organic EL element 31 but also the holding current accumulated during the selection period t1 in which the transistor Qs is turned on. A driving method is used in which the charge Q of the capacitor C1 is used as a current source and the organic EL element 31 emits light. In the following description, the driving method is referred to as “pulse driving”.
[0046]
Further, in the EL display device 20 of this example, the “pulse driving” is performed in combination with gradation control (digital gradation control) by subfield driving (time division driving).
[0047]
<Gradation control by subfield drive>
The control circuit 24 of the EL display device 20 controls the scanning line driving circuit 22 and the data line driving circuit 23 so that 2N gradation display is performed by subfield driving. In the “subfield driving”, one frame is divided into N subfields having a length corresponding to each bit of N-bit gradation data. Here, “one frame” refers to a period in which display of one screen is configured by sequentially selecting one of the scanning lines Y1 to Ym and writing data signals to all the pixels 30. The duration of the N subfeeds has a length corresponding to each bit, that is, 1 (2 ⁰ ): 2 (2 ¹ ): 4 (2 ² ) ... 2 ^N A ratio of −1 is set. One of the binary voltages is written to each pixel 30 based on the gradation data shown in FIG. 6 at the shortest subfield period T of the N subfields set in this way, and 2N gradation display is performed. .
[0048]
Specifically, the control circuit 24 of this example is 2 ³ Gradation (2 ^N N = 3 and 8 gradations), that is, gradation display of gradation degree 0 to gradation degree 7, so that one frame has three subfields SF1, SF2, and SF3 as shown in FIG. Respectively. Each period (time length) of the three subfields SF1, SF2, and SF3 is set to a length corresponding to each bit of the 3-bit gradation data (according to the binary system), that is, 1 (2 ⁰ ): 2 (2 ¹ ): 4 (2 ² ) Ratio. Accordingly, each period of the subfields SF2 and SF3 is twice or four times that of the subfield SF1. In this case, of the three subfields SF1, SF2 and SF3, the subfield having the shortest period is SF1, and a binary voltage is applied to each pixel 30 as a data signal in the period T (see FIG. 7) of the subfield SF1. Write one of these. The “binary voltage” mentioned here is an L level voltage 0 (V) and an H level voltage V1 (V).
[0049]
As described above, in the gradation control by the subfield driving of this example, the data signal is written to each pixel 30 at a frame frequency of 60 Hz (frame period is 1/60 sec), and each pixel 30 is set in one frame. One of binary voltages is written every period T. That is, as shown in FIG. 7, the writing of the data signal to each pixel 30 is performed 7 times per cycle T in one frame of 1/60 second (sec) (2 ³ -1 times) For this purpose, the control circuit 24 outputs a vertical scanning start signal DY (not shown) to the scanning line driving circuit 22 seven times at intervals of a period T in one frame based on the synchronization signal and the clock signal. .
[0050]
Each time a vertical scanning start signal DY (hereinafter simply referred to as a start signal DY) is input from the control circuit 24, the scanning line driving circuit 22 generates and outputs the scanning signals G1 to Gm in order, thereby outputting the scanning line. One of Y1 to Ym is sequentially selected. That is, when the first start signal DY is input at the beginning of one frame, the scanning line driving circuit 22 first scan signal G1 as shown in FIG. ₁ ~ Gm ₁ Are sequentially output, and the scanning lines Y1 to Ym are sequentially selected. This selection period is the first selection period t1 in one frame. Further, when the second to seventh start signals DY are input every time the period T elapses from when the first start signal DY is input, the scanning line driving circuit 22 performs the second scanning signal G1. ₂ ~ Gm ₂ ... Seventh scanning signal G1 ₇ ~ Gm ₇ Are sequentially output, and the scanning lines Y1 to Ym are sequentially selected. These selection periods are the second to seventh selection periods t1 in one frame. In this manner, the operation of sequentially selecting the scanning lines Y1 to Ym is repeated seven times in one frame.
[0051]
In addition to the synchronization signal and the clock signal, 3-bit gradation data is input to the control circuit 24 as a binary data signal that is an image signal in order to perform field driving. The gradation data are eight types of binary data signals from (000) to (111) as shown in Table 1 below and FIGS. 6 (a) to (h).
[0052]
[Table 1]

The gradation data (000) is data for displaying a gradation of 0 on one pixel 30 (black display: display of the light emission intensity of the organic EL element 31 of 0), and the gradation data (111) is one. This is data for displaying a gradation of 7 on the pixel 30 (white display: display of the light emission intensity of the organic EL element 31 of 7). The gradation data (001) to (110) are data for displaying an intermediate gradation degree 1 to 6 on one pixel 30 (displaying the light emission intensity 1 to 6 of the organic EL element 31). .
[0053]
The data line driving circuit 23 uses the above-described Table 1 and FIG. 6 as a data signal for each pixel 30 corresponding to one selected scanning line during each selection period t1 in which one of the scanning lines Y1 to Ym is sequentially selected. As shown in FIG. 4, either L (voltage 0) or H (voltage V1) is output simultaneously. In response to this voltage, light is emitted by operation in FIGS. In that case, light is emitted even at an intensity corresponding to the gradation level of the gradation data.
[0054]
Table 2 below shows gradation data corresponding to the above-described eight kinds of gradations, subfield SF1 (first selection period t1), SF2 (second and third selection periods t1) in one frame, and A relationship with a data signal written to one pixel 30 in SF3 (fourth to seventh selection periods t1) is shown.
[0055]
[Table 2]

For example, when the gradation data (000) in FIG. 6A is used to display the gradation degree 0 on each pixel 30, as shown in Table 2, subfields SF1 (first selection period t1), SF2 (2 The L data signal is written to each pixel 30 in seven selection periods t1 of the third and third selection periods t1) and SF3 (fourth to seventh selection periods t1). Further, when the gradation data (001) of FIG. 6B is used to display each pixel 30 with a gradation of 1, the H data signal is written only during the first selection period t1, as shown in Table 2. An L data signal is written in each selection period t1 from the second time to the seventh time. Similarly, when displaying gradation levels 2 to 7 on each pixel 30 with the gradation data (010) to (111) of FIGS. 6C to 6H, as shown in Table 2, in one frame, An L or H data signal is written in each of the seven selection periods t1.
[0056]
In this manner, when the L or H data signal is written in each of the seven selection periods t1 in one frame, the organic EL element 31 of each pixel 30 has the gradation data shown in FIGS. Light is emitted at a light emission intensity corresponding to (000) to (111), and each pixel 30 performs gradation display of eight gradations.
[0057]
FIG. 8A shows the waveform of the data signal when the voltage V1 (H data signal) is continuously written to the pixel 30 in each of the seven selection periods t1 in one frame. FIG. 8B shows the change in the charge Q accumulated in the holding capacitor C1 by writing the data signal of the voltage V1 to the pixel 30 in each selection period t1, and the charge after the transistor Qs is turned off. The change of Q is shown. FIG. 8C shows the current I flowing through the organic EL element 31 when the data signal of the voltage V1 is written into the pixel 30. _EL Shows changes. In FIG. 8C, the current I immediately before the end of the selection period t1. _EL (Current value I ₁ ), A current that constantly flows in a state where the voltage V1 is applied, and a current I that flows in the organic EL element 31 from the end of the selection period t1. _EL Switches to a current using the charge Q stored in the holding capacitor C1 as a current source. In FIG. 8C, the current I just before the selection period t1 ends. _EL (Current value I ₁ ) And current I when switched to the current source of charge Q _EL (Current value I ₂ ) Are shown to match, but the voltage values of the two do not necessarily match. 8D shows the light emission intensity L of the organic EL element 31 when the data signal of the voltage V1 is written to the pixel 30. FIG. _I Shows changes.
[0058]
As can be seen from FIGS. 8A to 8D, when the data signal of the voltage V1 is written to the pixel 30 in each selection period t1, it is stored in the holding capacitor C1 during the selection period t1 in which the transistor Qs is on. A charge Q corresponding to the voltage V1 is accumulated. When the transistor Qs changes from the on state to the off state at the end of each selection period t1, the charge Q accumulated in the holding capacitor C1 is discharged through the organic EL element 31, so that the charge Q gradually decreases. With this decrease, the current I flowing in the organic EL element 31 _EL Gradually decreases, and the emission intensity L of the organic EL element 31 is reduced. _I Gradually decreases.
[0059]
In this example, the current I that flows through the organic EL element 31 of each pixel 30 within the time period of the period T is set. _EL Is the current value I at the end of the selection period t1. ₁ Current value I that is less than or equal to the preset relative value ₂ Thus, the voltage / current characteristics of the organic EL element 31 and the capacitance of the holding capacitor C1 are set. For example, the current value I before the next selection period t1 is started within the time of the period T until the predetermined period t2 starts. ₂ Is the current value I ₁ The voltage / current characteristics of the organic EL element 31 and the capacitance of the holding capacitor C1 are set so as to be 1/2 or 1/10 of the above. With such a setting, a cooling period in which the emission intensity of the organic EL element 31 is small and the amount of generated heat is small is provided before each selection period. Thereby, the element temperature of each organic EL element 31 is suppressed low. In this example, “period T” corresponds to the time from the start of each selection period t1 until the same scanning line is selected next.
[0060]
In FIG. 9, in each frame, each pixel 30 corresponding to the scanning lines Y1 to Yk is displayed with the gradation 0 (black display), and each pixel 30 corresponding to the scanning lines Yk + 1 to Ym has the gradation 7 described above. The waveform of the data signal written to each pixel 30 when displaying (white display) is shown. In this case, when writing a data signal to each pixel 30 in one frame seven times for each period T, 0 (V) data is stored in each pixel 30 corresponding to the scanning lines Y1 to Yk in each period T. A signal is written, and a data signal of V1 (V) is written to each pixel 30 corresponding to the scanning lines Yk + 1 to Ym. As a result, a one-frame display screen as shown in FIG. 10 is displayed.
[0061]
According to 1st Embodiment comprised as mentioned above, there exist the following effects.
(A) When the transistor Qs of each pixel 30 connected to one scanning line to be selected is turned on in each selection period t1, the data signal supplied from the plurality of data lines X1 to Xn via the transistor Qs A charge Q corresponding to the voltage is accumulated in the holding capacitor C1. At the same time, a current corresponding to the data signal flows to the organic EL element 31 through the transistor Qs of each pixel 30 connected to one selected scanning line, and the organic EL element 31 emits light with brightness according to the current. In addition, during the non-selection period in which each selection period ends and the transistor Qs is turned off, the charge Q accumulated in the holding capacitor C1 is discharged through the organic EL element 31, and a current flows to the organic EL element 31, whereby the organic EL The element 31 emits light.
[0062]
As described above, in each selection period t1, a current corresponding to the current is supplied to the organic EL element 31 of each pixel 30 corresponding to the selected scanning line through the transistor Qs that is turned on. The organic EL element 31 is caused to emit light. In the non-selection period, the organic EL element 31 of each pixel is caused to emit light using the electric charge accumulated in the holding capacitor C1 as a current source.
[0063]
Since such a “pulse drive” method is employed, it is only necessary to provide one transistor Qs for each pixel 30. Thereby, the equivalent circuit of one pixel can be simplified as shown in FIG. 3, and the manufacturing cost can be reduced. In addition, since the effective light emitting area of each pixel 30 increases, that is, the aperture ratio increases, the current flowing through the organic EL element 31 of each pixel 30 can be reduced, and the light emission intensity of the light emitting element per unit area can be reduced. The amount of heat generated by each organic EL element 31 can be kept low. Therefore, the manufacturing cost can be reduced and the lifetime of the light emitting element can be extended.
[0064]
(B) As shown in FIG. 8, the current I flowing through the organic EL element 31 of each pixel 30 _EL (Current value I ₂ ) Is the current I at the end of the selection period t1 _EL (Current value I ₁ ), The voltage / current characteristics of the organic EL element 31 and the capacitance of the holding capacitor C1 are set to be equal to or less than a preset relative value. Therefore, a cooling period t2 in which the light emission intensity of the organic EL element 31 is small and the heat generation amount is small is provided before each selection period t1, and the heat generation amount of the organic EL element 31 is reduced to lower the element temperature. Can be suppressed. For example, by setting the relative value to 1/10 (relative value 0.1 shown by the horizontal axis in FIG. 13), the cooling period t2 in which the heat generation amount becomes 1/10 is taken before each selection period t1. Can do. In this case, the element temperature of the organic EL element 31 is normally about 80 ° C. to 100 ° C., whereas it is about 40 ° C. to 50 ° C. As a result, the lifetime of the organic EL element 31 is 10 times. ^Five I was able to extend the time. When it is difficult to reduce the relative value to 1/10, the lifetime of the organic EL element 31 is reduced to 2 by setting the relative value to 1/2 (relative value 0.5 shown by the horizontal axis in FIG. 13). × 10 ^Four I was able to extend the time. Thus, the lifetime of the organic EL element 31 can be further extended.
[0065]
(C) In order to cause the organic EL element 31 of each pixel 30 to emit light by the pulse drive, gradation control by the subfield drive is performed. In other words, when the L or H data signal is written in each of the seven selection periods t1 in one frame, the organic EL element 31 of each pixel 30 has the gradation data (000) of FIGS. ) To (111), and each pixel 30 performs gradation display of 23 gradations. As a result, the data signal writing cycle is shortened, so that the charge Q accumulated in each holding capacitor C1 during each selection period t1 can be reduced. Therefore, even with high definition, a bright display with low power consumption can be realized.
[0066]
[Second Embodiment]
FIG. 11 shows a second embodiment in which the present invention is applied to an EL display device 20 as an electro-optical device. In the description of this embodiment, the same members and signals as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted.
[0067]
The second embodiment is the same as the first embodiment in that gradation control is performed by the pulse drive and the subfield drive, but each of the scan lines Y1 to Ym connected to any one of the scan lines Y1 to Ym. This is different from the first embodiment in that the terminal a of the holding capacitor C1 of the pixel 30 is connected to a wiring different from that of the first embodiment.
[0068]
That is, the terminal a of the holding capacitor C1 of each pixel 30 is scanned through the gate line (wiring) 40 in the previous stage (one line before) selected one before the m scanning lines Y1 to Ym. Connected to the wire. For example, the terminal a of the holding capacitor C1 of each pixel 30 at each intersection of the scanning line Ym and the data lines X1 to Xn is a preceding scanning line that is selected one before through the gate line 40. It is connected to the scanning line Ym-1. For the terminal a of the holding capacitor C1 of each pixel 30 corresponding to the scanning line Y1 in the first row, there is no preceding scanning line with respect to the scanning line Y1 in the first row. It is provided.
[0069]
According to the second embodiment configured as described above, the above-described operational effects (a) to (c) are exhibited in the same manner as the first embodiment.
[Third embodiment]
FIG. 12 shows an EL display device 20 according to the third embodiment.
[0070]
The EL display device 20 is obtained by eliminating the holding capacitor C1 of each pixel 30 in the first embodiment shown in FIG. 2, and a current corresponding to the data signal is selected during each selection period t1. The organic EL element 31 is configured to emit light by flowing to the organic EL element 31 through each transistor Qs connected to one scanning line.
[0071]
Further, the EL display device 20 has a current I flowing through the organic EL element 31 of each pixel 30 in order to provide the cooling period t2 (FIG. 8D) before each selection period t1. _EL Is the current I at the end of the selection period t1 _EL The voltage / current characteristics of the organic EL element 31 are set so as to be equal to or less than a preset relative value. Other configurations are the same as those in the first embodiment.
[0072]
The third embodiment configured as described above provides the following operational effects.
(D) When the transistor Qs of each pixel 30 connected to one scanning line to be selected is turned on in each selection period t1, a current corresponding to the data signal is supplied to the organic EL element 31 through the transistor Qs of each pixel 30. The organic EL element 31 emits light with brightness according to the current. In this manner, in each selection period t1, a current is passed through the transistor Qs that is turned on to the organic EL element 31 of each pixel 30 corresponding to the selected scanning line, so that the organic light has a brightness corresponding to the current. The EL element 31 is caused to emit light. Since such a “pulse drive” method is employed, it is only necessary to provide one transistor Qs for each pixel 30. Accordingly, like the above-described effect (A), the manufacturing cost can be reduced and the lifetime of the light-emitting element can be extended.
[0073]
(E) Current I flowing in the organic EL element 31 of each pixel 30 _EL Is the current I at the end of the selection period t1 _EL The voltage / current characteristics of the organic EL element 31 are set so as to be equal to or less than a preset relative value. Therefore, a cooling period t2 in which the light emission intensity of the organic EL element 31 is small and the heat generation amount is small is provided before each selection period t1, and the heat generation amount of the organic EL element 31 is reduced to lower the element temperature. Can be suppressed. Therefore, the lifetime of the organic EL element 31 can be further extended, similarly to the above-described effect (b).
[0074]
(F) In the same manner as in the first embodiment, in order to cause the organic EL element 31 of each pixel 30 to emit light by the pulse drive, the above-mentioned operational effects (c) can be obtained by performing gradation control by the subfield drive. Can play.
[0075]
(G) Since the holding capacitor C1 of each pixel 30 is eliminated, the terminals a and b on both sides of the holding capacitor C1 and the holding capacitor line L become unnecessary, and therefore an equivalent circuit of one pixel is shown in FIG. It can be further simplified than the first embodiment (see FIG. 12), and the manufacturing cost can be further reduced.
[0076]
[Electronics]
Next, electronic devices using the display panel unit 21 of the EL display device 20 described in the above embodiments will be described. The display panel unit 21 can be applied to a mobile personal computer as shown in FIG. A personal computer 70 shown in FIG. 14 includes a main body 72 including a keyboard 71 and a display unit 73 using the display panel unit 21. The display panel unit 21 used in the display unit 73 can realize bright display with low power consumption even with high definition.
[0077]
[Modification]
In addition, this invention can also be changed and embodied as follows.
In the first embodiment, gradation control by the subfield drive is performed to cause the organic EL element 31 of each pixel 30 to emit light by the pulse drive. However, the present invention is not limited to this. For example, a plurality of scanning lines Y1 to Ym are selected once per frame, and a data signal having a voltage corresponding to the gradation is applied to each pixel 30 in a selection period t1 once per frame, thereby providing an organic EL element. The present invention can also be applied to analog gradation control for controlling the emission intensity 31.
[0078]
In the first embodiment, the case where the relative value is set to 1/2 or 1/10 has been described as an example. However, the relative value can be changed as appropriate, and the next selection period is within the period T. If the relative value is ½ or less before the predetermined period t2 before the start of t1, a remarkable effect is obtained. Further, the current I flowing through the organic EL element 31 in the predetermined period t2 _EL (Current value I ₂ ) May be 0. In this case, the organic EL element 31 does not emit light before each selection period t1, and the element temperature can be kept lower by reducing the amount of heat generation.
[0079]
In the first embodiment, the present invention can also be applied to a configuration in which gradation control by subfield driving is performed as follows instead of the gradation control by subfield driving described above. The control circuit 24 has one frame having the same length period (period T). ^N -1 subfield is divided, and for each subfield, one of binary voltages is written to each pixel based on the gradation data 2 ^N The scanning line driving circuit 22 and the data line driving circuit 23 are controlled so as to perform gradation display. Table 3 below shows 2 as an example ³ 8 kinds of gradation data in case of gradation display, 2 ³ A relationship with a data signal written to one pixel 30 in each of the first to seventh selection periods t1 performed every −1 (= 7) subfields SF1 to SF7 is shown.
[0080]
[Table 3]

For example, when displaying gradation level 0 on each pixel 30 with gradation data (000), as shown in Table 3, subfield SF1 (first selection period t1) to SF7 (seventh selection period t1). Only the L data signal is written in each pixel 30 in each selection period t1. In addition, when displaying gradation level 1 on each pixel 30 with gradation data (001), as shown in Table 3, an H data signal is written only in the subfield SF1, and each selection in the subfields SF2 to SF7 is performed. In the period t1, an L data signal is written. Similarly, when displaying gradation levels 2 to 7 on each pixel 30 with gradation data (010) to (111), an L or H data signal is written as shown in Table 3. Yes. By the gradation control by such subfield driving, the above-mentioned operational effect (C) can be obtained as in the first embodiment.
[0081]
In the first embodiment, 2 ³ Gradation (2 ^N N = 3 and 8 gradations), that is, gradation display of gradation degree 0 to gradation degree 7, but the value of N is set appropriately and 2 ^N Gradation display, that is, gradation degree 0 to gradation degree 2 ^N The present invention is also applied to a configuration that performs gradation display of -1.
In the first embodiment, the frame frequency is set to 60 Hz. However, the present invention can also be applied to an EL display device in which the frame frequency is twice (120 Hz) or more. Also in this case, the same effect as the first embodiment is obtained.
[0082]
In the first embodiment, the plurality of scanning lines Y1 to Ym are selected one by one in order, but the present invention is not limited to this configuration. For example, the present invention is applied to a configuration in which two or more of the plurality of scanning lines Y1 to Ym are sequentially selected and a configuration in which the plurality of scanning lines Y1 to Ym are sequentially selected by the interlaced scanning method.
[0083]
In each of the above embodiments, the scanning line driving circuit 22, the data line driving circuit 23, and the control circuit 24 do not need to be built on the substrate on which the switching transistor Qs is formed, and may be formed as an external circuit. Moreover, you may incorporate at least 1 of them. Here, “built-in” refers to a state of being directly formed on a substrate using a transistor.
[0084]
In each of the above embodiments, the electro-optical device has been described as the EL display device 20, but the present invention is not limited to this, and includes an electro-optical device using a light emitting element other than an organic EL element and the electro-optical device. It can also be applied to electronic devices.
[0085]
As the switching transistor Qs used in the present invention, a TFT using a silicon thin film such as a polysilicon TFT, an amorphous silicon TFT, or a single crystal silicon TFT as a channel layer or a TFT using a semiconductor thin film such as silicon germanium as a channel layer is used. It is done.
[0086]
The EL display device 20 is not limited to a personal computer as shown in FIG. 14, but can be applied to various electronic devices such as a mobile phone and a digital camera.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an EL display device according to a first embodiment.
FIG. 2 is a block diagram showing an equivalent circuit and a drive circuit of a display panel unit.
FIG. 3 is a circuit diagram showing an equivalent circuit of one pixel.
4 is an explanatory diagram showing an operation at the time of data writing in the equivalent circuit shown in FIG. 3;
5 is an explanatory diagram showing an operation during discharging in the equivalent circuit shown in FIG. 3. FIG.
FIGS. 6A to 6H are waveform diagrams showing the relationship between gradation data and data signals.
FIG. 7 is a waveform diagram showing a scanning signal.
8A to 8D are waveform diagrams showing how an organic EL element emits light when a data signal V1 is applied.
FIG. 9 is a waveform diagram of a data signal showing an example of driving.
10 is an explanatory diagram showing a display example by driving shown in FIG. 9. FIG.
FIG. 11 is a block diagram showing an equivalent circuit and a drive circuit of a display panel unit according to a second embodiment.
FIG. 12 is a block diagram showing an equivalent circuit and a drive circuit of a display panel unit according to the third embodiment.
FIG. 13 is a graph showing the lifetime of an organic EL element.
FIG. 14 is a perspective view showing a personal computer using an EL display device.
[Explanation of symbols]
V0, V1 ... voltage, Q ... charge, T ... period, t1 ... selection period, t2 ... period, Y0, Y1-Ym ... scanning line, I _EL ... Current, SF1 to SF7 ... Subfield, X1-Xn ... Data line, 20 ... EL display device as electro-optical device, 22 ... Scanning line drive circuit, 23 ... Data line drive circuit, 24 ... Control circuit, Qs ... Switching Switching transistor as element, C1... Holding capacitor as capacitor element, 30... Pixel, 31.

Claims (5)

In an electro-optical device,
A plurality of scanning lines, a plurality of data lines, a plurality of switching elements arranged corresponding to the intersections of the scanning lines and the data lines, a light emitting element arranged corresponding to the switching elements, and a capacitor With elements,
In each selection period in which the plurality of scanning lines are sequentially selected, when the switching element corresponding to the selected scanning line is turned on, the voltage of the data signal supplied from the plurality of data lines through the switching element is set. A corresponding charge is accumulated in the capacitor element, and a current according to the data signal flows to the light emitting element through the switching element, and the light emitting element emits light,
During the non-selection period when each selection period ends and the switching element is turned off, the charge accumulated in the capacitor element is discharged through the light emitting element, and a current flows through the light emitting element, so that the light emitting element emits light. Configured as
One frame is divided into N subfields having a length corresponding to each bit of N-bit grayscale data, and the one subframe has a period of the shortest subfield among the N subfields. The configuration is such that a 2 ^N gradation display is performed by writing a data signal for accumulating charges corresponding to one of binary voltages in the capacitive element of each of a plurality of pixels based on gradation data. Electro-optical device characterized. The electro-optical device according to claim 1.
The current flowing through the light emitting element within the time from the start of each selection period to the next selection of the same scanning line among the plurality of scanning lines is compared to the current at the end of each selection period. An electro-optical device, wherein the characteristics of the light emitting element and the capacitance of the capacitive element are set to be equal to or less than a preset relative value. The electro-optical device according to claim 1 or 2,
An electro-optical device configured to perform writing of a data signal for accumulating charges corresponding to a voltage of the data signal in each of the plurality of pixels at a frame frequency of 120 Hz or more. A plurality of scanning lines, a plurality of data lines, a plurality of switching elements arranged corresponding to the intersections of the scanning lines and the data lines, a light emitting element arranged corresponding to the switching elements, and a capacitor In a driving method of an electro-optical device including an element,
In each selection period in which the plurality of scanning lines are sequentially selected, when the switching element corresponding to the selected scanning line is turned on, the voltage of the data signal supplied from the plurality of data lines through the switching element is set. The charge corresponding to the capacitor element is accumulated in the capacitor element, and a current corresponding to the data signal is caused to flow to the light emitting element through the switching element to cause the light emitting element to emit light,
During the non-selection period in which each selection period ends and the switching element is turned off, the charge accumulated in the capacitor element is discharged through the light-emitting element to cause a current to flow through the light-emitting element, thereby causing the light-emitting element to emit light ,
One frame is divided into N subfields having a length corresponding to each bit of N-bit grayscale data, and the one subframe has a period of the shortest subfield among the N subfields. A ^2N gray scale display is performed by writing a data signal for accumulating electric charge corresponding to one of binary voltages in the capacitor element of each of a plurality of pixels based on gray scale data. Driving method of optical device.   An electronic apparatus comprising the electro-optical device according to claim 1.

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