Driving method of light emitting device and light emitting device

Abstract

A driving method of a light emitting device, in which when an N-type driving TFT is connected to an anode of a light emitting element or a P-type driving TFT is connected to a cathode thereof, the driving TFT operates in a saturation region and an image can be displayed with a desired gray scale level depending on a video signal. In addition, a light emitting device adopting the driving method is provided. According to the invention, when a potential having image data is supplied to a gate of a driving TFT depending on a video signal, a reverse bias voltage is applied to the driving TFT and a light emitting element which are connected in series with each other. Meanwhile, when a pixel displays an image depending on the video signal, a forward bias voltage is applied to the driving TFT and the light emitting element.

1 . (canceled) 
     
     
         2 . A method for driving a light emitting device comprising a first line, a second line, a third line, a first transistor, a second transistor, a capacitor and a light emitting element, wherein a gate of the first transistor is electrically connected to the first line, wherein one of a source and a drain of the first transistor is electrically connected to the second line, wherein the other of the source and the drain of the first transistor is electrically connected to a gate of the second transistor, wherein one of a source and a drain of the second transistor is electrically connected to a first electrode of the light emitting element, wherein the other of the source and the drain of the second transistor is electrically connected to the third line, wherein a first electrode of the capacitor is electrically connected to the gate of the second transistor and wherein a second electrode of the capacitor is electrically connected to the one of the source and the drain of the second transistor, the method comprising the steps of:
 supplying a first potential to the third line; and   supplying a second potential to the third line,   wherein a frame period comprises a first period and a second period after the first period,   wherein the first period comprises a first timing,   wherein the second period comprises a second timing,   wherein the first transistor is in an on-state at the first timing,   wherein a potential of the third line is the first potential at the first timing,   wherein a potential of a second electrode of the light emitting element is a third potential at the first timing,   wherein the first transistor is in an off-state at the second timing,   wherein the potential of the third line is the second potential at the second timing,   wherein the potential of the second electrode of the light emitting element is the third potential at the second timing,   wherein the second potential is higher than the first potential, and   wherein the second potential is higher than the third potential.   
     
     
         3 . The method according to  claim 2 , wherein supplying the first potential to the third line begins before the first transistor is turned on and ends after the first transistor is turned off. 
     
     
         4 . The method according to  claim 2 , wherein a potential of the second line is a video signal potential at the first timing. 
     
     
         5 . The method according to  claim 2 ,
 wherein the first period is a writing period, and   wherein the second period is a display period.   
     
     
         6 . A method for driving a light emitting device comprising a first line, a second line, a third line, a first transistor, a second transistor, a capacitor and a light emitting element, wherein a gate of the first transistor is electrically connected to the first line, wherein one of a source and a drain of the first transistor is electrically connected to the second line, wherein the other of the source and the drain of the first transistor is electrically connected to a gate of the second transistor, wherein one of a source and a drain of the second transistor is electrically connected to a first electrode of the light emitting element, wherein the other of the source and the drain of the second transistor is electrically connected to the third line, wherein a first electrode of the capacitor is electrically connected to the gate of the second transistor and wherein a second electrode of the capacitor is electrically connected to the one of the source and the drain of the second transistor, the method comprising the steps of:
 supplying a first potential to the third line; and   supplying a second potential to the third line,   wherein a frame period comprises a first period and a second period after the first period,   wherein the first period comprises a first timing,   wherein the second period comprises a second timing,   wherein the first transistor is in an on-state at the first timing,   wherein a potential of the third line is the first potential at the first timing,   wherein a potential of a second electrode of the light emitting element is a third potential at the first timing,   wherein the first transistor is in an off-state at the second timing,   wherein the potential of the third line is the second potential at the second timing,   wherein the potential of the second electrode of the light emitting element is the third potential at the second timing,   wherein the second potential is higher than the first potential,   wherein the second potential is higher than the third potential, and   wherein the third potential is higher than the first potential.   
     
     
         7 . The method according to  claim 6 , wherein supplying the first potential to the third line begins before the first transistor is turned on and ends after the first transistor is turned off. 
     
     
         8 . The method according to  claim 6 , wherein a potential of the second line is a video signal potential at the first timing. 
     
     
         9 . The method according to  claim 6 ,
 wherein the first period is a writing period, and   wherein the second period is a display period.   
     
     
         10 . A method for driving a light emitting device comprising a first line, a second line, a third line, a first transistor, a second transistor, a capacitor and a light emitting element, wherein a gate of the first transistor is electrically connected to the first line, wherein one of a source and a drain of the first transistor is electrically connected to the second line, wherein the other of the source and the drain of the first transistor is electrically connected to a gate of the second transistor, wherein one of a source and a drain of the second transistor is electrically connected to a first electrode of the light emitting element, wherein the other of the source and the drain of the second transistor is electrically connected to the third line, wherein a first electrode of the capacitor is electrically connected to the gate of the second transistor and wherein a second electrode of the capacitor is electrically connected to the one of the source and the drain of the second transistor, the method comprising the steps of:
 supplying a first potential to the third line; and   supplying a second potential to the third line,   wherein a frame period comprises a first period and a second period after the first period,   wherein the first period comprises a first timing,   wherein the second period comprises a second timing,   wherein the first transistor is in an on-state at the first timing,   wherein a potential of the second line is a video signal potential at the first timing,   wherein a potential of the third line is the first potential at the first timing,   wherein the first transistor is in an off-state at the second timing,   wherein the potential of the third line is the second potential at the second timing, and   wherein the second potential is higher than the first potential.   
     
     
         11 . The method according to  claim 10 ,
 wherein the frame period further comprises a third timing before the first period, and   wherein a reverse bias is applied to the light emitting element at the third timing.   
     
     
         12 . The method according to  claim 10 ,
 wherein the first period is a writing period, and   wherein the second period is a display period.