1. Field of the Invention
The present invention relates to a display device having light emitting elements and a driving method thereof.
2. Description of the Related Art
In recent years, display devices formed by using light emitting elements (self-luminous light emitting elements) are actively researched and developed. Such display devices are widely used as a display screen of a mobile phone, a monitor of a personal computer and the like by utilizing the advantages of high image quality, thin shape, lightweight and the like. In particular, since such display devices have features of high response speed, low voltage and low power consumption drive and the like that are suitable for displaying moving images, it is expected to have a wide scope of application including those for next-generation mobile phones or portable information terminals (PDAs).
Luminance of a light emitting element decays with the passage of time. For example, assuming that a light emitting element emits light at a predetermined luminance with a current I0 when a certain voltage V0 is applied, it can emit only a current I0′ after a certain period of time has passed even when the same voltage V0 is applied, therefore, predetermined luminance cannot be obtained. In addition, degradation of the light emitting element with the passage of time makes it difficult to obtain the same luminance even with a certain current supplied.
This is considered to be a result of the light emitting element generating heat by a voltage or current flowing thereto, which in turn changes the properties of the light emitting element on the boundary of the films or electrodes. Further, variations of the degradation level of each light emitting element cause a screen burn.
In order to suppress degradation of light emitting elements and improve reliability, there is a method of applying a reverse bias voltage that is the voltage in the opposite direction to a forward bias voltage by which a light emitting element emits light (see Patent Document 1).
[Patent Document 1] Japanese Patent Laid-Open No. 2001-117534
A pixel circuit having a light emitting element can adopt various configurations. It is an object of the invention to provide a circuitry and a driving method thereof in which a reverse bias voltage (hereinafter referred to as a reverse voltage) is applied to a light emitting element in order to control the degradation of the light emitting element and improve reliability for a display device comprising a pixel circuit.