1. Field of the Invention
The present invention relates to a display device inputted with video signals to display images, and particularly to a display device having a light emitting element. In addition, the invention relates to an electronic apparatus employing the display device.
2. Description of the Related Art
Described hereinafter is a display device in which a light emitting element is provided in each pixel and light emission of the light emitting element is controlled to display an image. The display device is constituted by a display and a peripheral circuitry for inputting signals to the display. FIG. 16 shows a configuration of a pixel portion of the display.
Source signal lines S1 to Sx, gate signal lines G1 to Gy, and power source lines V1 to Vx are arranged in a pixel portion 1603, and x columns and y rows (x and y are positive integers) of pixels are arranged therein. Each pixel 1700 includes a switching transistor 1701, a driving transistor 1702, a storage capacitor 1703, and a light emitting element 1704.
FIG. 17 shows an enlarged pixel of the pixel portion 1603 shown in FIG. 16.
A pixel is constituted by one source signal line S among the source signal lines S1 to Sx, one gate signal line G among the gate signal lines G1 to Gy, one power source line V among the power source lines V1 to Vx, the switching transistor 1701, the driving transistor 1702, the storage capacitor 1703, and the light emitting element 1704.
As for the switching transistor 1701, a gate electrode is connected to the gate signal line G, and one of a source electrode and a drain electrode is connected to the source signal line S while the other is connected to a gate electrode of the driving transistor 1702 and one electrode of the storage capacitor 1703. As for the driving transistor 1702, one of a source electrode and a drain electrode is connected to the power source line V while the other is connected to an anode or a cathode of the light emitting element 1704. As for the storage capacitor 1703, one of two electrodes is connected to the driving transistor 1702 and the switching transistor 1701 as described above while the other is connected to the power source line V.
An operation for light emission of the light emitting element 1704 in the above-described pixel is described below.
The gate signal line G is inputted with a signal and the switching transistor 1701 is turned ON. Then, through the source and drain electrodes of the switching transistor 1701, a signal from the source signal line S is inputted to the gate electrode of the driving transistor 1702. In addition, potential of the source signal line S is stored in the storage capacitor 1703. The signal inputted to the gate electrode of the driving transistor 1702 turns the driving transistor 1702 ON. The amount of current to be flown between the source and drain electrodes of the driving transistor 1702 depends on a potential difference between the gate electrode of the driving transistor 1702 and the power source line V. The current flowing between the source and drain electrodes of the driving transistor 1702 flows into the light emitting element 1704 through a pixel electrode thereof, resulting in light emission of the light emitting element 1704.
It is necessary to always flow a constant amount of current into the light emitting element 1704 during light emission, regardless of the deterioration of the light emitting element 1704. To flow a constant amount of current into the light emitting element 1704 regardless of a potential difference between the source and drain electrodes of the driving transistor 1702, it is preferable to design so that the driving transistor 1702 operates in the saturation region.
As described above, forward driving voltage for a light emitting element is always applied to a light emitting element of a conventional display.
However, it has been found that the deterioration of an I-V characteristic of a light emitting element can be suppressed by applying reverse driving voltage for a light emitting element to the light emitting element every certain period (see Non-Patent Document 1).
[Non-Patent Document 1]
D. Zou et al., “Improvement of Current-Voltage Characteristics in Organic Light Emitting Diodes by Application of Reversed-Bias Voltage”, Jpn. J. Appl. Phys. Vol. 37 (1998), pp. L1406-L1408, Part 2, No. 11B, 15 Nov. 1998