Patent Grant
8013817
The present invention relates to flat panel displays, specifically flat panel displays having segmented light-emitting elements to provide improved spatial uniformity.
Flat panel, color displays for displaying information, including images, text, and graphics are widely used. These displays may employ any number of known technologies, including liquid crystal light modulators, plasma emission, electro-luminescence (including organic light-emitting diodes), and field emission. Such displays include entertainment devices such as televisions, monitors for interacting with computers, and displays employed in hand-held electronic devices such as cell phones, game consoles, and personal digital assistants. In these displays, the resolution of the display is always a critical element in the performance and usefulness of the display. The resolution of the display specifies the quantity of information that can be usefully shown on the display and the quantity of information directly impacts the usefulness of the electronic devices that employ the display.
However, the term “resolution” is often used or misused to represent any number of quantities. Common misuses of the term include referring to the number of light-emitting elements or to the number of full-color groupings of light-emitting elements (typically referred to as pixels) as the “resolution” of the display. This number of light-emitting elements is more appropriately referred to as the addressability of the display. Within this document, we will use the term “addressability” to refer to the number of independently-addressable light-emitting elements per unit area of the display device. A more appropriate definition of resolution is to define the size of the smallest element that can be displayed with fidelity on the display. One method of measuring this quantity is to display the narrowest possible, neutral (e.g., white) horizontal or vertical line on a display and to measure the width of this line or to display an alternating array of neutral and black lines on a display and to measure the period of this alternating pattern. Note that using these definitions, as the number of light-emitting elements increases within a given display area, the addressability of the display will increase while the resolution, using this definition, generally decreases. Therefore, counter to the common use of the term “resolution”, the quality of the display is generally improved as the resolution becomes finer in pitch or smaller.
Addressability in most flat-panel displays, especially active-matrix displays, is limited by the need to provide signal busses and electronic control elements in the display. Further in many flat panel displays, including Liquid Crystal Displays (LCDs) and bottom-emitting Electro-Luminescent (EL) displays, the electronic control elements are required to share the area that is required for light emission or transmission. In these technologies, the more such busses and control elements that are needed, the less area in the display is available for light emission. Depending upon the technology, reduction of the area available for light emission can reduce the efficiency of light output, as is the case for LCDs, or reduce the brightness and/or lifetime of the display device, as is the case for EL displays. Regardless of whether the area required for patterning busses and control elements competes with the light-emitting area of the display, the decrease in buss and control element size that occur with increases in addressability for a given display generally require more accurate, and therefore more complex, manufacturing processes and can result in greater number of defective panels, decreasing yield rate and increasing the cost of marketable displays. Therefore, from a cost and manufacturing complexity point of view, it is generally advantageous to be able to provide a display with lower addressability. This desire is, of course, in conflict with the need to provide higher apparent resolution. Therefore, it would be desirable to provide a display that has relatively low addressability but that also provides high apparent resolution.
It has been known for many years that the human eye is more sensitive to the spatial frequency of luminance in a scene than to color. In fact, current understanding of the visual system includes the fact that processing is performed within or near the retina of the human eye that converts the signal that is generated by the photoreceptors into a luminance signal, a red/green difference signal and a blue/yellow difference signal. Each of these three signals have a different resolution with the luminance channel having the highest spatial frequency cutoff followed by the red/green spatial frequency cutoff and finally the blue/yellow spatial frequency cutoff. In fact, the cutoff for the luminance channel is nearly twice the spatial frequency cutoff for the red/green difference signal and nearly four times the spatial frequency cutoff of the blue/yellow difference signal.
This difference in sensitivity is well appreciated within the imaging industry and has been employed to provide display devices with high apparent resolution for a reduced addressability. In one example, Takashi et al. in U.S. Pat. No. 5,113,274, entitled “Matrix-type color liquid crystal display device”, proposed the use of displays having two green for every red and blue light-emitting element. While such an array of light-emitting elements can perform well for displays with a very high addressability, it is important that the red light-emitting elements typically provide approximately 30 percent of the luminance. Therefore, under certain conditions, such as when displaying flat fields of red, it is possible to see artifacts (e.g., a red and black checkerboard pattern in areas that are intended to be perceived as a flat field red) that occur because of the scarcity of the red light-emitting elements within the array. Therefore, it is important to understand that in displays it is not only the size or the frequency of light-emitting elements that are important to understand the quality of the display device but also the space between the light-emitting elements. In fact, anytime that the distance between any two light-emitting elements of the same color subtends a visual angle greater than 1 minute of arc, it will be possible to see a checkerboard pattern when attempting to display a flat field of color.
It may be additionally desirable to include additional high luminance light-emitting elements. For example, within the field of Organic Light Emitting Diodes (OLEDs), it is known to introduce more than three light-emitting elements where the additional light-emitting elements have higher luminance efficiency, resulting in a display having higher luminance efficiency. Such displays have been discussed by Miller et al. in U.S. Patent Application Publication 2004/0113875, entitled “Color OLED display with improved power efficiency”. When applying four or more different colors of subpixels it is then further known to utilize patterns of light-emitting elements having a higher addressability of high luminance white and green light-emitting elements than arrays of low luminance red and blue light-emitting elements as discussed by Miller et al. in U.S. Patent Application 2005/0270444, entitled “Color display with enhanced pixel pattern”. Unfortunately, such an arrangement of light-emitting elements can result in the same undesirable checkerboard pattern in the color channels with lower addressability.
It is also known to provide displays having more than one color of high luminance light-emitting element and to use each of these high luminance light-emitting elements to create the high frequency luminance channel. For example, U.S. Patent Application 2005/0225574 and U.S. Patent Application 2005/0225575, each entitled “Novel subpixel layouts and arrangements for high brightness displays” provide various arrangements of light-emitting elements having two colors of high luminance light-emitting elements, such as the white and green light-emitting elements, and to arrange these light-emitting elements such that each row in the arrangement contains all colors of light-emitting elements, making it possible to produce a line of any color using only one row of light-emitting elements. Similarly, every pair of columns within the arrangement discussed within this disclosure contains all colors of light-emitting elements within the display, making it possible to produce a line of any color using only two columns of light-emitting elements. Therefore, when the LCD is driven correctly, it can be argued that the vertical resolution of the device is equal to the inverse of the height of one row of light-emitting elements and the horizontal resolution of the device is equal to the inverse of the width of two columns of light-emitting elements, even though it realistically requires more light-emitting elements than the two light-emitting elements at the intersection of such horizontal and vertical lines to produce a full-color image. However, since each pair of light-emitting elements at the junction of such horizontal and vertical lines contains one high luminance (i.e., white or green) light-emitting element, each pair of light-emitting elements provides a relatively accurate luminance signal within each pair of light-emitting elements, providing a high-resolution luminance signal. It is important to note that in arrangements of light-emitting elements such as these, as well as those discussed by U.S. Pat. No. 5,113,274, the high-luminance light-emitting elements can provide a luminance image with higher addressability than the addressability of any individual color of light-emitting element. As was the case with Takashi and Miller, displays utilizing this pixel pattern will exhibit a checkerboard pattern when a flat field, single color luminance pattern is input.
Although the reduced addressability that can be attained using pixel patterns such as U.S. Pat. No. 5,113,274, U.S. Patent Application 2005/0270444, U.S. Patent Application 2005/0225574 or U.S. Patent Application 2005/0225575 generally reduce the complexity of manufacturing the final display, these patterns also lack uniformity when displaying flat fields of color for any display in which the gap between any two color subpixels of any one color subtends an angle greater than 1 minute of arc on the user's retina. This artifact limits the use of such patterns to displays with an addressability of around 300 full color pixels per inch or greater. Displays with lower resolution will provide objectionable levels of the checkerboard artifact when viewed from some typical viewing distance. This is particularly troubling when attempting to apply these techniques in larger displays which are generally designed to have a lower addressability because they are typically viewed from a larger viewing distance. However because these displays can be viewed from near viewing distances and often are viewed from near viewing distances by individuals making purchasing decisions on show room floors, the artifacts that occur in images generated on such arrangements of light-emitting elements makes the use of such pixel patterns on larger displays impractical.
Artifact reduction using arrangements of light-emitting elements such as the “RGB delta” pattern has been taught, for example by Noguchi et al. in U.S. Pat. No. 4,969,718, that are enabled by splitting the subpixel electrodes into equal halves. However in this case the split is done solely to solve electrical problems associated with the RGB delta pattern, and the split electrodes drive identical colors and remain juxtaposed.
It is also known in the art to correct for image degradation (e.g., avoid flicker in LCD displays) by localizing the degradation on dark-colored, or low luminance subpixels, as taught in U.S. Patent Application 2005/0083277A1. It is taught therein that successive pairs of blue columns may share the same column driver through an interconnect, however the row selection mechanisms are independent, and the TFT's of the blue subpixels are remapped to avoid sharing of exact data values.
There is therefore a need to provide an enhanced arrangement of light-emitting elements, such as the ones described within this background, that require a minimum number of drive circuits and that enable the use of even lower addressabilities on full color displays. Specifically, it is desired to provide such an enhanced arrangement of light-emitting elements in displays having an addressability of less than 300 pixels per inch without creating the perception of non-uniformity within areas of an image that are intended to have a uniform color.
In accordance with one embodiment, the invention is directed towards a display with improved visual uniformity, comprised of an array of independently-addressable light-emitting elements, including at least a first independently-addressable light-emitting element for producing a first color of light and a second independently-addressable light-emitting element for producing a second color of light; wherein at least the first independently-addressable light-emitting element is subdivided into at least two spatially separated commonly-addressed light-emitting areas and wherein at least a portion of the second independently-addressable light-emitting element is positioned between the spatially separated commonly-addressed light-emitting areas of the first independently-addressable light-emitting element.
As shown in
To fully appreciate the present invention, it is necessary to define low and high luminance light-emitting elements. Within the present invention, the term “high luminance light-emitting element” is defined as a light-emitting element that has a peak output luminance value that is 40 percent or greater of the peak white luminance of the display device while a “low luminance light-emitting element” is a light-emitting element with a peak output luminance value less than 40 percent of the peak white luminance of the display device. Within a display comprised of at least red, green, and blue light-emitting elements, the red and blue light-emitting elements will typically be low luminance light-emitting elements while the green light-emitting element will be a high luminance light-emitting element. In displays further comprised of broadband or multi-band light-emitting elements, such as white, yellow, or cyan these broadband or multi-band light-emitting elements will be high-luminance light-emitting elements.
As described above, at least the first independently-addressable light-emitting element is subdivided into at least two spatially separated commonly-addressed light-emitting areas. For purposes of the invention, such spatially separated commonly-addressed light-emitting areas of a single independently addressable light-emitting element may conveniently be referred to as commonly addressed “portions” of the light emitting element, or as commonly addressed “sub-elements” of the independently addressable light-emitting element.
As used within this disclosure, the phrase “commonly addressed” refers to an arrangement in which two light emitting areas of a light emitting element are electrically connected in a manner such that they are not independently controllable. That is, the commonly addressed light emitting areas share the same select and drive lines, so that both necessarily receive the same input or driving signal.
As used within this disclosure, the phrase “positioned between” refers to a physical arrangement in which at least a portion of a second light-emitting element is interspersed with at least two spatially separated, commonly addressed light-emitting areas of a first light-emitting element, such that a line drawn between at least one point in one area of the first element and at least one point in another area of the first element intersects a portion of the second element. Because the patterns of the present invention often involve the arrangement of first and second elements within a rectilinear grid, often with inactive area for providing electronics, it is often impractical to place an element such that the centroid of a portion of the second element is geometrically between the center of mass of two portions of the first element. Therefore, the term “positioned between” will include arrangements in which multiple portions of the first element are located in separate rows or columns and a portion of the second element is located in the same row or column as one of the portions of the first element, but also in a row or column that is between the separate rows or columns which contain the portions of the first light-emitting element.
As shown in
Ideally, the formation of light-emitting elements, which are composed of multiple sub-elements, will insure that the largest distance between two light-emitting regions (i.e., sub-elements or single light-emitting regions which comprise a light-emitting element) emitting light of a single color will be less than 1 minute of arc when the display is viewed from any reasonable viewing distance. This requirement insures that when a flat field of an individual color is shown on the display, the display will appear to be uniform in luminance rather than exhibiting spatial artifacts, such as a visible checkerboard pattern. Since any display may reasonably be viewed from distances of 16 inches or less, the invention will be preferably applied in displays having an addressability of 300 pixels per inch or less and more preferably in displays having an addressability of 200 pixels per inch or less. It might be noted that at these resolutions and a viewing distance of 16 inches, the visual angle of a pixel of a 300 pixel per inch display is just under 0.8 minutes of arc and the visual angle of a pixel on a 200 pixel per inch display is approximately 1.1 minutes of arc.
In another embodiment shown in
As shown in
Within this embodiment, the commonly-addressed sub-elements may be electrically connected to form each independently-addressable light-emitting element. The connecting lines 30, 32, 34, 36 represent electrical connections for connecting each of the commonly-addressed sub-elements together. Generally, when the present invention is implemented within an active-matrix display, it will be preferred that an active matrix circuit will be provided to supply power to each independently-addressable light-emitting element and this same circuit will be connected to each of the commonly addressed sub-elements directly or that an electrical connection may be formed between the two sub-elements to allow power to be provided from one circuit to the commonly-addressed sub-elements within each light-emitting element. As stated earlier, the independently-addressable light-emitting elements of
A full color display employing the array of four light-emitting elements 22, 24, 26, 28 in
When rendering information on displays having commonly-addressed sub-elements as shown in the previous patterns, the apparent uniformity of the display will be significantly improved. However, by increasing the extent of the elements, it is possible that when presenting images on such displays, the apparent sharpness of the display may, under certain conditions, be reduced slightly. This loss of apparent sharpness may be overcome when spatially separated commonly-addressed light emitting areas are arranged to be aligned along two or more dimensions of the display. That is, the loss of sharpness can be reduced when the spatially separated commonly-addressed light emitting areas of at least one of the independently-addressable light emitting element lie substantially along a first dimension, and the spatially separated commonly-addressed light emitting areas of at least one other independently-addressable light emitting element lie substantially along a second dimension of the display. One embodiment of such arrangement of light-emitting elements is depicted in
As shown in
It should be further noted, that in such a display, it is preferable that the incoming data be processed to be sensitive to the presence and directions of edges within the images that are to be displayed. Specifically, the processing method should determine the location of edges within the input data. When an edge is detected, its direction should be determined and the incoming data should be processed to form the final image such that the independently-addressable light-emitting elements whose separated commonly-addressed light emitting areas lie along a direction that is most similar to the direction of the edge within the incoming data are preferentially driven to higher drive values than independently-addressable light-emitting elements whose separated commonly-addressed light emitting areas lie along a different direction.
In another embodiment shown in
As illustrated by this embodiment, several commonly-addressed sub-elements may be used to compose a single independently-addressable light-emitting element. The fact that each of these independently-addressable light-emitting elements may require only one circuit to drive the entire group of sub-elements which comprise this light-emitting element relaxes the constraint on the number of individual light-emitting sub-elements within a display, as it is often the size of the circuitry required to drive any sub-element which constrains the number of sub-elements. For this reason, it is important to discuss an active matrix embodiment of this invention in more detail. The basic concept of the present disclosure may be applied using any display technology, including displays that actively produce light. Such displays may include technologies that modulate light from a large area light source, including technologies such as liquid crystal displays. However, this invention will preferably be provided in emissive displays such as electroluminescent displays.
Within this disclosure, relevant electroluminescent display technologies include those employing stacks of organic materials, typically referred to as Organic Light Emitting Diode or OLED displays. The structure of an OLED typically comprises, in sequence, an anode, an organic electroluminescent (EL) medium, and a cathode, which are deposited upon a substrate. The organic EL medium disposed between the anode and the cathode is commonly comprised of an organic hole-transporting layer (HTL) and an organic electron-transporting layer (ETL). Holes and electrons recombine and emit light in the ETL near the interface of HTL/ETL. Tang et al., “Organic electroluminescent diodes”, Applied Physics Letters, 51, 913 (1987), and U.S. Pat. No. 4,769,292, demonstrated highly efficient OLEDs using such a layer structure. Since then, numerous OLEDs with alternative layer structures have been disclosed. For example, there are three-layer OLEDs that contain an organic light-emitting layer (LEL) between the HTL and the ETL, such as that disclosed by Adachi et al., “Electroluminescence in Organic Films with Three-Layer Structure”, Japanese Journal of Applied Physics, 27, L269 (1988), and by Tang et al., “Electroluminescence of doped organic thin films”, Journal of Applied Physics, 65, 3610 (1989). The LEL commonly includes a host material doped with a guest material wherein the layer structures are denoted as HTL/LEL/ETL. Further, there are other multi-layer OLEDs that contain a hole-injecting layer (HIL), and/or an electron-injecting layer (EIL), and/or a hole-blocking layer, and/or an electron-blocking layer in the devices. While the subsequent embodiments will be provided with respect to OLED display, it will be well understood by those skilled in the art that this same invention may readily be applied to EL displays which include coatable inorganic materials or combinations of organic and inorganic materials, which may be coated onto an active or passive matrix backplane. One such display technology employs a light-emitting layer formed from quantum dots as described in co-pending U.S. Ser. No. 11/226,622 filed Sep. 14, 2005, entitled “Quantum Dot Light Emitting Layer”, the disclosure of which is herein incorporated by reference.
Herein, a particular embodiment employing an active-matrix, top-emitting organic light emitting diode (OLED) display will be provided, the structure of which is shown in
In this embodiment, it should be noted that in addition to providing a layer that allows uniform coating of the organic electro-luminescent materials 112 and the second electrode 114, the inter-pixel dielectric 110 also prevents contact of the connector segments 108 with the electro-luminescent materials 112 or the second electrode 114 such that light emission will not occur in the area of the connector segments 108. Therefore, while light emission 116 will occur over the area of each segment of the first electrode 106, light will not be emitted in the areas that are defined by the connector segments 108.
A representation of a portion 120 of the top view of the layer forming the first electrode 106 and connector segment layer 108 is shown in
Note that within this embodiment, the display may be a color display having three or more differently colored light-emitting elements. In one embodiment, different organic electro-luminescent materials may be deposited on the electrode segments that produce the different independently addressable light-emitting elements. However, in another embodiment, an encapsulating glass may be placed above the second light-emitting layer to provide a transparent protective layer. Further, color change materials may be deposited on top of the electrode or color filters may be deposited on the inside of the encapsulating glass to provide a full color display without patterning organic electro-luminescent materials within the display structure. Note that regardless of where the color filter or color change materials are placed, different materials will generally be aligned such that the light that is emitted by the various sub-elements 122a, 122b that form an independently-addressable light-emitting element will be affected to provide the user with the same color of light.
It is also possible to provide passive matrix embodiments of the present invention. Typical passive matrix displays are comprised of a first electrode that is typically formed from horizontal lines of a material to form electrode rows. The active materials, i.e., emissive or modulating, are then placed over this first layer and a second electrode layer is formed as vertical lines of material to form electrode columns. An independently addressable light-emitting element is then formed at the intersection of a row and column electrode such that when an electric field is created between them, the light-emitting element produces or modulates light.
Within the current invention, at least a first independently-addressable light-emitting element is subdivided into at least two commonly-addressed sub-elements and a portion of the second independently-addressable light-emitting element is positioned between the commonly-addressed sub-elements of the first independently-addressable light-emitting element. Within a passive matrix embodiment, this may be accomplished by creating a row or column electrode that intersects the remaining electrode at two locations rather than one.
One such embodiment of a pair of row electrodes 152, 154 and areas of the light-emitting elements defined by the intersection of these row electrodes 152, 154 and column electrodes 160, 162, 164, 166 is shown in
When different organic electro-luminescent materials are deposited at the light-emitting element 158 than is deposited at the light-emitting element 156, or when a color filter or color change material is deposited such that it influences the color of light for one of these light-emitting elements differently than for the other, it is possible to obtain a display with improved visual uniformity. This display includes at least a first independently-addressable light-emitting element 156 for producing a first color of light and a second independently-addressable light-emitting element 158 for producing a second color of light; wherein at least the first independently-addressable light-emitting element 156 is subdivided into at least two commonly-addressed sub-elements 156a, 156b and wherein at least a portion of the second independently-addressable light-emitting element 158 is positioned between the commonly-addressed sub-elements of the first independently-addressable light-emitting element.
The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.
| Number | Name | Date | Kind |
|---|---|---|---|
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| 5113274 | Takahashi et al. | May 1992 | A |
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| Number | Date | Country |
|---|---|---|
| 03052725 | Jun 2003 | WO |
| 2004027503 | Apr 2004 | WO |
| 2005001805 | Jan 2005 | WO |
| 2005059875 | Jun 2005 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20080158107 A1 | Jul 2008 | US |
