Semiconductor device and driving method thereof

Abstract

Brightness irregularities that develop in a light emitting device due to is persion among pixels in the threshold values of TFTs used for supplying electric current to light emitting devices become obstacles to improved image quality of the light emitting device. As an image signal input to a pixel from a source signal line, a desired electric potential is applied to a gate electrode of a TFT for supplying electric current to an EL device, through a TFT having its gate and drain connected to each other. A voltage equal to the TFT threshold value is produced between the source and the drain of the TFT 105 . An electric potential in which the image signal is offset by the amount of the threshold value is therefore applied to the gate electrode of the TFT. Further, TFTs are disposed in close proximity to each other within the pixel, so that dispersions in the TFT characteristics do not easily develop. A desired drain current can thus be supplied to the EL device even if there is dispersion in the threshold values of the TFTs among pixels, because this is offset by the threshold value of the TFT.

1 . (canceled) 
     
     
         2 . A semiconductor device comprising:
 a pixel comprising:
 a first transistor; 
 a second transistor; 
 a third transistor; 
 an electroluminescent device; and 
 a capacitor, 
   wherein a gate of the first transistor is directly connected to a first electrode of the capacitor,   wherein one of a source and a drain of the first transistor is electrically connected to the electroluminescent device,   wherein the other of the source and the drain of the first transistor is electrically connected to an electric current supply line,   wherein a second electrode of the capacitor is electrically connected to the one of the source and the drain of the first transistor,   wherein one of a source and a drain of the second transistor is directly connected to the gate of the first transistor,   wherein the other of the source and the drain of the second transistor is electrically connected to the other of the source and the drain of the first transistor,   wherein one of a source and a drain of the third transistor is directly connected to a source signal line, and   wherein the other of the source and the drain of the third transistor is electrically connected to the one of the source and the drain of the first transistor.   
     
     
         3 . The semiconductor device according to  claim 2 , further comprising a fourth transistor,
 wherein the other of the source and the drain of the first transistor is electrically connected to the electric current supply line via the fourth transistor.   
     
     
         4 . The semiconductor device according to  claim 2 , further comprising a fourth transistor,
 wherein one of a source and a drain of the fourth transistor is directly connected to the other of the source and the drain of the first transistor, and   wherein the other of the source and the drain of the fourth transistor is directly connected to the electric current supply line.   
     
     
         5 . The semiconductor device according to  claim 2 , further comprising a fifth transistor,
 wherein the one of the source and the drain of the first transistor is electrically connected to the electroluminescent device via the fifth transistor.   
     
     
         6 . The semiconductor device according to  claim 2 , further comprising a fifth transistor,
 wherein one of a source and a drain of the fifth transistor is directly connected to the one of the source and the drain of the first transistor, and   wherein the other of the source and the drain of the fifth transistor is directly connected to the electroluminescent device.   
     
     
         7 . The semiconductor device according to  claim 2 , further comprising a sixth transistor,
 wherein one of a source and a drain of the sixth transistor is directly connected to the second electrode of the capacitor.   
     
     
         8 . The semiconductor device according to  claim 7 , further comprising a sixth transistor,
 wherein the one of the source and the drain of the sixth transistor is directly connected to the electroluminescent device.   
     
     
         9 . The semiconductor device according to  claim 2 ,
 wherein each of the first transistor, the second transistor and the third transistor is an n-channel thin film transistor.