Display device and method for driving the same

Abstract

A semiconductor device having a configuration hardly generating variations in the current value due to a deteriorated EL element is to be provided. A capacitance element is disposed between the gate and the source of a driving TFT, video signals are inputted to the gate electrode, and then it is in the floating state. Suppose an EL element is deteriorated and the anode potential rises, that is, the source potential of the driving TFT rises, the potential of the gate electrode of the driving TFT, being in the floating state by coupling of the capacitance element, is to rise by the same amount. Accordingly, even when the anode potential rises due to the deteriorated EL element, the rise is added to the gate electrode potential as it is, and the gate-source voltage of the driving TFT is allowed to be constant.

1 . (canceled) 
     
     
         2 . A display device comprising:
 a pixel comprising a first transistor, a second transistor, a third transistor, a fourth transistor, a light-emitting element, and a capacitor,   wherein one of a source and a drain of the first transistor is electrically connected to a gate electrode of the second transistor and one electrode of the capacitor,   wherein one of a source and a drain of the second transistor is electrically connected to the light-emitting element,   wherein the other of the source and the drain of the second transistor is electrically connected to one of a source and a drain of the fourth transistor,   wherein one of a source and a drain of the third transistor is electrically connected to the light-emitting element,   wherein the other of the source and the drain of the third transistor is electrically connected to a wiring,   wherein the other of the source and the drain of the fourth transistor is electrically connected to a current supply line which is different from the wiring,   wherein the other of the source and the drain of the first transistor is electrically connected to a source signal line which is different from the wiring and the current supply line,   wherein a gate electrode of the first transistor is electrically connected to a first gate signal line,   wherein a gate electrode of the fourth transistor is electrically connected to a second gate signal line, and   wherein each of the first transistor, the second transistor, the third transistor, and the fourth transistor comprises an active layer comprising a single crystal.   
     
     
         3 . The display device according to  claim 2 , wherein the other electrode of the capacitor is electrically connected to the one of the source and the drain of the second transistor. 
     
     
         4 . The display device according to  claim 2 , wherein the wiring is a power line. 
     
     
         5 . The display device according to  claim 2 , wherein a gate electrode of the third transistor is electrically connected to the first gate signal line. 
     
     
         6 . The display device according to  claim 2 , wherein each of the first transistor, the second transistor, the third transistor, and the fourth transistor is a P-channel transistor. 
     
     
         7 . The display device according to  claim 2 , wherein the gate electrode of each of the first transistor, the second transistor, and the fourth transistor comprises a polycrystalline silicon film.