| abstract |
An object of the present invention is to suppress deterioration of a transistor. It has a first period and a second period. In the first period, the first transistor and the second transistor are alternately turned on and off, and the third transistor and the fourth transistor are turned off. In the second period, the first transistor and the second transistor are turned off, and the third transistor and the fourth transistor are alternately turned on and off. In this way, since the time for which the transistor is turned on can be shortened, deterioration of the characteristics of the transistor is suppressed. |