The invention relates to an organic light emitting diode (OLED) display, an information device having an OLED display, and a method for displaying an image in an OLED display.
OLED displays require no backlight, and are therefore optimum for thin formation, with no limitation of viewing angle. Thus, OLED displays have become popular substitutes for cathode ray tube (CRT) and liquid crystal display (LCD) devices.
One problem using organic light emitting elements is Mura defect, which is caused mainly by inconsistent luminance of the organic light emitting elements. Luminance of an organic light emitting element is determined in a manufacturing process and degrades with time. The rate of luminance decay of an organic light emitting element depends especially on characteristics of the organic light emitting element, conditions in a manufacturing process, how the organic light emitting element is driven, and other conditions.
Mura defects can be aggravated in full-color OLED display panels that emit red, green, and blue light. The organic light emitting elements of varying colors have different rates of luminance decay. The differences in luminance between the organic light emitting elements of a plurality of colors typically become more apparent with time.
In addition to Mura defects, an OLED display (particularly, the Electro Luminescent (EL) materials) will age and become less efficient at emitting light, reducing the lifetime of the display. The aging of the OLEDs is related to the cumulative current passed through the OLED resulting in reduced performance, also the aging of the OLED material results in an increase in the apparent resistance of the OLED that causes a decrease in the current passing through the OLED at a given voltage. The decrease in current is directly related to the decrease in luminance of the OLED at a given voltage. In addition to the OLED resistance changing with use, the light emitting efficiency of the organic materials is reduced. The different materials may age at different rates, causing “differential color aging” and thus the “shift of white point”. Moreover, each individual pixel may age at different rate than others, resulting in display non-uniformity or so-called “image sticking”.
Conventionally, the Mura defects and the aging of the OLEDs are addressed in separate ways, which make the circuit design complicated and increases the production cost. Therefore, it is desired to have an OLED display and a method for displaying an image in an OLED display, which can compensate the “non-uniformity” resulted from either the Mura defects or the material aging.
The present invention is directed to an OLED display pre-storing a compensation table, and is also directed to a method for displaying an image in the OLED display. In one aspect of the present invention, the current sensor senses a current of at least one sub-pixel among the plurality of sub-pixels, and the compensation table is updated according to the sensed current. Later the processor receives image data and generates compensated image data based on the image data and the updated compensation table. Then the display panel displays the compensated image data.
The foregoing and other features of the invention will be apparent from the following more particular description of embodiment of the invention.
The present invention is illustrated by way of example and not intended to be limited by the figures of the accompanying drawing, in which like notations indicate similar elements.
The present invention is useful for both top-emitting OLED display devices (those that emit light through a cover placed above a substrate on which the OLED is constructed) and bottom-emitting OLED display devices (those that emit light through the substrate on which the OLED is constructed). Moreover, this invention is advantageously practiced with, but not limited to, both top-emitting and bottom-emitting OLED active matrix devices.
As shown in
The memory 103, which may be embodied as a flash memory, a SRAM, or a DRAM, is provided for storing and maintaining a compensation table 105. Initially, the compensation table 105 is established based on the characteristic of each sub-pixel 102 and the average luminance of the all sub-pixels 102. With a given test signal provided to each sub-pixel 102, the characteristics of each sub-pixel 102 are determined according to the luminance, or the currents of each sub-pixel 102. For example, the electric characteristic of each sub-pixel 102 can be measured by a thin film transistor (not shown) connected to each sub-pixel 102, or the optical characteristic can be measured by a photo sensor (not shown) provided to each sub-pixel 102. Due to the manufacturing process and other factors known to those skilled in the art, each sub-pixel may not have uniform characteristics, and thus results in different emitting performances. Then by mapping the characteristics of each sub-pixel 102 with regard to the average luminance of all sub-pixels 102, the compensation parameter for each sub-pixel 102 are estimated, and the compensation table 105 including the estimated compensation parameter for each sub-pixel 102 is further written into and kept in the memory 103. Later when the information device 1 has an image to display, the processing circuit 110 will consult the compensation table 105 to drive each sub-pixel 102 with different voltages in order to display the image correctly, whereby the Mura defect is eliminated. Moreover, those skilled in the art can understand that the compensation table 105 can be established in other ways, and all of them are covered by the present invention.
The processing circuit 110, which can be embodied as an Application Specific Integrated Circuit (ASIC), includes a current sensor 112, and a processor 114 integrated thereon. The processing circuit 110 shown in
The exemplary predetermined relationships are shown as the curves in
In another embodiment, each time when the current sensor 112 is turned on, it senses the currents of each individual sub-pixel 102 of the display panel 101; then following a procedure similar to the one described above, the compensation parameters for each sub-pixel 102 in the compensation table 105 are adjusted according to the aforementioned predetermined relationships. The updating of the compensation table 105 is performed for all sub-pixels 102, but it may take longer time to complete. In yet another embodiment that is more efficient, the current sensor 112 is provided for sensing a sum of currents of a group of pixels 102 by sensing the sum of currents at cathodes of the group of sub-pixels 102, as shown in
In still another embodiment, the current sensor 112 sense only the currents (or a sum of the currents) of sub-pixels 102 that are located in a predetermined area of display panel 101, and only the compensation parameters for those sub-pixels 102 in the compensation table 105 are updated, while compensation parameters for other sub-pixels 102 are left intact. The predetermined area is the area where the sub-pixels thereon emit most often, for example, the area where the current date and time are presented.
To avoid the conflict with the normal operation of the display panel 10, the current sensor 112 is activated during the “Idle” mode or the “Screensaving” mode, or even when the information device 1 is charging. In another embodiment, the current sensor 112 is activated according to a user setting. For example, the user inputs a command by a special key (not shown) on the information device 1 to activate the current sensor 112 to sense the current of the sub-pixel(s) 102 and then to update the compensation table 105. Alternatively, the user, via an interface (e.g., a selecting menu, not shown in
Based on the provided the information device 1 and the OLED display 10, the present invention further discloses a method for displaying an image.
The step 405 is to sense, by the current sensor 112, a current of at least one sub-pixel 102 on the display panel 101, or in another embodiment, to sense the currents of each individual sub-pixel 102 of the display panel 101, or in yet another embodiment, to sense a sum of currents of a group of pixels 102. In the step 407, the compensation table in the memory 103 is updated according to the sensed current and the “current-compensation parameter” curves shown in
The step 505 is to sense, by the current sensor 112, the currents of each individual sub-pixel located within the determined area in the step 503, or in another embodiment, a sum of currents of all sub-pixel 102 located within selected area. In the step 507, the compensation table in the memory 103 is updated according to the current(s) sensed in the step 505, and the predetermined relationship(s), similar to curves shown in
By the embodiments presented above, the present invention provides an OLED display, an information device having an OLED display, and a method for displaying an image in an OLED display, which can compensate the “non-uniformity” resulted from either the Mura defects or the material aging. Meanwhile, the aforementioned “non-uniformity” for a predetermined area of the display can be compensated. Furthermore, the present invention is able to compensate the aforementioned “non-uniformity” according to a user setting, particularly after the OLED display or the information device is delivered to the consumer.
While this invention has been described with reference to the illustrative embodiments, these descriptions should not be construed in a limiting sense. Various modifications of the illustrative embodiment, as well as other embodiments of the invention, will be apparent upon reference to these descriptions. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as falling within the true scope of the invention and its legal equivalents.
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Number | Date | Country | |
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20090174628 A1 | Jul 2009 | US |