Element substrate and light emitting device

Abstract

A light emitting device and an element substrate which are capable of suppressing variations in luminance intensity of a light emitting element among pixels due to characteristic variations of a driving transistor without suppressing off-current of a switching transistor low and increasing storage capacity of a capacitor. A gate potential of a driving transistor is connected to a first scan line or a second scan line, and the driving transistor operates in a saturation region. A current controlling transistor which operates in a linear region is connected in series to the driving transistor. A video signal which transmits a light emission or non-emission of a pixel is input to the gate of the current controlling transistor through a switching transistor.

1 . (canceled) 
     
     
         2 . A light emitting device comprising:
 a first transistor;   a second transistor;   a third transistor;   a fourth transistor;   a light emitting element;   a capacitor;   a power supply line;   a first scan line;   a second scan line; and   a wiring,   wherein one of source and drain of the first transistor is electrically connected to the light emitting element,   wherein another of source and drain of the first transistor is electrically connected to one of source and drain of the second transistor,   wherein another of source and drain of the second transistor is electrically connected to one electrode of the capacitor through the power supply line,   wherein another electrode of the capacitor is electrically connected to one of source and drain of the third transistor,   wherein another of source and drain of the third transistor is electrically connected to the wiring,   wherein the another electrode of the capacitor is electrically connected to one of source and drain of the fourth transistor,   wherein a gate of the third transistor is electrically connected to the first scan line,   wherein a gate of the fourth transistor is electrically connected to the second scan line, and   wherein the second transistor is a driving transistor of the light emitting element.   
     
     
         3 . The light emitting device according to  claim 2 , wherein the another electrode of the capacitor is electrically connected a gate of the first transistor. 
     
     
         4 . The light emitting device according to  claim 2 , wherein the wiring is a signal line. 
     
     
         5 . The light emitting device according to  claim 2 , wherein a gate of the second transistor is electrically connected to the second scan line. 
     
     
         6 . The light emitting device according to  claim 2 , wherein the another of source and drain of the fourth transistor is electrically connected to the power supply line. 
     
     
         7 . The light emitting device according to  claim 2 , wherein the light emitting device is incorporated in one selected from the group consisting of a display device, a mobile computer, a game machine, and a cellular phone. 
     
     
         8 . A light emitting device comprising:
 a first transistor;   a second transistor;   a third transistor;   a fourth transistor;   a light emitting element;   a capacitor;   a power supply line;   a first scan line;   a second scan line; and   a wiring,   wherein one of source and drain of the first transistor is electrically connected to the light emitting element,   wherein another of source and drain of the first transistor is electrically connected to one of source and drain of the second transistor,   wherein another of source and drain of the second transistor is electrically connected to one electrode of the capacitor through the power supply line,   wherein another electrode of the capacitor is electrically connected to one of source and drain of the third transistor,   wherein another of source and drain of the third transistor is electrically connected to the wiring,   wherein the another electrode of the capacitor is electrically connected to one of source and drain of the fourth transistor,   wherein a gate of the third transistor is electrically connected to the first scan line,   wherein a gate of the fourth transistor is electrically connected to the second scan line,   wherein the second transistor is a driving transistor of the light emitting element, and   wherein a semiconductor layer of the second transistor is curved so that a L/W (channel length/channel width) of the second transistor is larger than a L/W (channel length/channel width) of the first transistor.   
     
     
         9 . The light emitting device according to  claim 8 , wherein the another electrode of the capacitor is electrically connected a gate of the first transistor. 
     
     
         10 . The light emitting device according to  claim 8 , wherein the wiring is a signal line. 
     
     
         11 . The light emitting device according to  claim 8 , wherein a gate of the second transistor is electrically connected to the second scan line. 
     
     
         12 . The light emitting device according to  claim 8 , wherein the another of source and drain of the fourth transistor is electrically connected to the power supply line. 
     
     
         13 . The light emitting device according to  claim 8 , wherein the light emitting device is incorporated in one selected from the group consisting of a display device, a mobile computer, a game machine, and a cellular phone.