Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
2001-09-21
2004-08-24
Shalwala, Bipin (Department: 2673)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S090000, C345S098000
Reexamination Certificate
active
06781567
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a driving method for an organic electro-luminescence display device, a driving method for an electro-optical device suitable for use with a display device, such as an organic electro-luminescence display device, an electro-optical device, and an electronic apparatus provided with such an electro-optical device.
2. Description of Related Art
Attention is being given to organic electro-luminescence display devices using organic materials as luminescent materials of luminescent elements since they have a wide viewing angle, and will potentially meet market demands, i.e., demands for thinner, lighter, smaller, and lower power-consuming display devices.
Unlike conventional liquid crystal display devices, in organic electro-luminescence display devices, a luminescence state of the luminescent element must be controlled by a current. One such control method is the conductance control method (T. Shimoda, M. Kimura, et al., Proc. Asia Display 98, 217; M. Kimura, et al., IEEE Trans. Ele. Dev. 46, 2282 (1999); M. Kimura, et al., Proc. IDW 99, 171; and M. Kimura et al., Dig. AM-LCD 2000, to be published). In this method, the luminescence state of the luminescent element is controlled by a current value, which is an analog value, and more specifically, it is controlled by changing the potential applied to a gate electrode of a driving transistor that drives the luminescent element. When thin-film transistors having different current characteristics are used, however, the difference in the current characteristics of the individual transistors may sometimes directly result in non-uniformity in the luminescence state of the luminescent elements.
Accordingly, the area ratio gray-scale method (M. Kimura, et al., Proc. Euro Display '99 Late-News Papers, 71, Japanese Unexamined Patent Application Publication No. 9-233107, M. Kimura, et al., Proc. IDW 99,171, M. Kimura, et al, J. SID, to be published; and M. Kimura, et al., Dig. AM-LCD 2000 to be published) has been proposed. In the area ratio gray-scale method, unlike the above-mentioned conductance control method, the luminescence state of the luminescent elements is controlled without using a luminescence state at an intermediate luminance. More specifically, in this method, the gray-scale is displayed as follows. Pixels disposed in a matrix are divided into a plurality of sub-pixels, and it is determined whether the luminescent elements contained in the sub-pixels are either in a complete luminescence state or a complete non-luminescence state. Then, among the plurality of sub-pixels, the total area of the sub-pixels in the complete luminescence state is changed. In the area ratio gray-scale method, it is not necessary to set an intermediate current value corresponding to the luminescence state of the intermediate luminance. Accordingly, the influence of the current characteristics of the transistors that drives the luminescent elements can be reduced, thereby achieving a uniform image quality. In this method, however, the number of gray-scale levels is restricted by the number of sub-pixels. For a greater number of gray-scale levels, pixels must be divided into a greater number of sub-pixels, which makes the pixel structure complicated.
Accordingly, the time ratio gray-scale method (M. Kimura, et al., Proc. IDW 99, 171; M. Kimura, et al., Dig. AM-LCD 2000, to be published; M. Mizukami, et al., Dig. SID 2000, 912; and K. Inukai, et al., Dig. SID 2000,924) has been proposed. In the time ratio gray-scale method, the representation of the gray-scale is implemented by changing the period for which the luminescent elements in one frame are in the complete luminescence state. Accordingly, unlike the area ratio gray-scale method, it is not necessary to provide many sub-pixels for obtaining a greater number of gray-scale levels, and also, the time ratio gray-scale method can be used together with the area ratio gray-scale method. Thus, it is expected that the time ratio gray-scale method will be a promising method for digitally displaying a gray-scale.
SUMMARY OF THE INVENTION
However, in the SES (Simultaneous-Erasing-Scan) time ratio gray-scale method, which is reported in “K. Inukai, et al., Dig. SID 2000,924”, in addition to the scanning lines, reset lines are required, and thus, the luminescence area is disadvantageously reduced.
Accordingly, a first object of the present invention is to provide a method for implementing the representation of a gray-scale of an electro-optical device without reset lines, and in particular, to provide a method for implementing the representation of the gray-scale of an electro-optical device, such as an organic electro-luminescence display device, according to the time ratio gray-scale method. A second object of the present invention is to provide an electro-optical device that is driven by the above-described driving method.
In order to achieve the first object, a first driving method for an electro-optical device according to the present invention is a driving method for an electro-optical device which includes, at an intersection of a scanning line and a data line, an electro-optical element, a driving transistor that drives the electro-optical element, a switching transistor that controls the driving transistor, and a reset transistor that resets the driving transistor to a non-conducting state. The driving method includes: a setting step of supplying an on-signal to cause the switching transistor to be in an on-state to the switching transistor via the scanning line, and of supplying a set signal to select a conducting state or a non-conducting state of the driving transistor to the driving transistor via the data line and the switching transistor in accordance with a period for which the on-signal is supplied; and a resetting step of supplying an on-signal to cause the reset transistor to be in an on-state to the reset transistor via the scanning line so as to reset the driving transistor to the non-conducting state. Accordingly, by supplying the on-signal for the switching transistor and the on-signal for the reset transistor via the same scanning line, the luminescence period can suitably be set without a reset line. In this specification, the electro-optical element and the electro-optical device respectively indicate an element and a device in which the luminescence state or the optical characteristic is electrically controlled. Specific examples of the electro-optical device include display devices, such as luminescence display devices, liquid crystal display devices, and electrophoretic display devices.
Throughout the specification, the “step of supplying an on-signal to the switching transistor via the scanning line, and of supplying a set signal to select a conducting state or a non-conducting state of the driving transistor to the driving transistor via the data line and the switching transistor in accordance with the on-signal” is defined as the “setting step”. The “step of resetting the driving transistor to the non-conducting state by supplying an on-signal to cause the reset transistor to be in the on-state to the reset transistor via the scanning line” is defined as the “resetting step”.
According to a second driving method for an electro-optical device of the present invention, in the above-described driving method for an electro-optical device, the electro-optical device may further include a power line that supplies a current to the electro-optical element via the driving transistor, and one end of the reset transistor may be connected to the power line.
According to a third driving method for an electro-optical device of the present invention, the conductivity type of the switching transistor and the conductivity type of the reset transistor may be different from each other. More specifically, for example, if the switching transistor is n-type, the reset transistor is p-type. If the switching transistor is p-type, the reset transistor is n-type. Accordingly, by suitably selecting a high-potential signal
Lewis David L.
Seiko Epson Corporation
Shalwala Bipin
LandOfFree
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