OLED-BASED DISPLAYS AND METHODS WITH PIXEL COMPENSATION - Patent application

Abstract

An OLED display system is provided with visual performance pixel compensation for brightness loss, including display pixels, each display pixel having an OLED subpixel and pixel drive circuitry, a sensing system having a sensor and analog-to-digital conversion circuitry connected to each of the sensors, and a processor providing image data drive signals to each of the display pixels, receiving a sensor signal from the ADC circuitry for each sensor, estimating a state of degradation of at least one of the display pixels, determining drive signal compensation for each display pixel having the estimated state of degradation, and compensating the image data drive signal to each display pixel having the estimated state of degradation. A method for compensating pixels for an image in a display is also provided.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63 / 209,215, filed June 10, 2021, entitled OLED-Based Display Having Pixel Compensation and Method, which is pending, the complete specification of which is hereby incorporated by reference in its entirety.

[0002] The present invention relates to image display technology, and more particularly to visual performance compensation of organic light emitting diode (OLED) pixels in OLED-based displays. [Background technology]

[0003] An organic light-emitting diode (OLED) display includes an array of pixels, each of which typically contains at least one OLED to provide light. Each OLED includes a light-emitting layer (or multiple sublayers) of luminescent organic material disposed between a cathode and an anode. In response to electrical signals applied to the cathode and anode, the luminescent organic material emits light. By applying appropriate drive signals to the pixels, a desired image is generated by the display.

[0004] As is well known to those skilled in the art, as an OLED element receives increased usage time, it undergoes degradation that manifests as a loss of brightness. As a result, variations in the brightness of OLED-based pixels across a display occur over time due to differences in the amount of stress each is exposed to over time, as well as the duration of accumulation of that stress. For example, in some cases, some OLEDs within a display are under more stress than others due to fixed symbologies, patterns, or icons. Unfortunately, the location and severity of degradation within a pixel cannot be identified without sensing each individual pixel.

[0005] Compensating for pixel brightness degradation in OLED displays, however, is difficult due to inherent signal characteristics, such as small electrical amplitudes in the nanoampere range (nA) in typical pixel drive circuits. Further complicating matters, the amount of space available in the pixel area is limited—especially when high-density displays, such as microdisplays (e.g., microdisplays with more than thousands of dots per inch), are used in near-eye applications such as augmented reality (AR) and virtual reality (VR) devices. Typically, these pixel areas are already space-constrained due to the high density of electrical components (e.g., transistors, capacitors, etc.) they require. As a result, it is difficult, if not impossible, to add special components for pixel compensation without negatively impacting overall signal integrity or manufacturing yield.

[0006] Conventional approaches for visual performance compensation utilize sensing units integrated into a display backplane in an area outside the active pixel area (i.e., the display area) of the display. One illustrative approach involves placing a reference pixel (or two or more) on the substrate of the active pixel array just outside the display area. The voltage change across the reference pixel is measured and used to compensate pixels within the display area according to the measured change. Such an approach is described, for example, in U.S. Pat. No. 7,321,348 (Cok et al.), which is incorporated herein by reference in its entirety.

[0007] Another exemplary prior art compensation approach involves measuring the initial state of each active pixel in the display area, measuring its current value via a feedback loop on the system's backplane, and storing it in memory. Resistance changes corresponding to OLED degradation can be determined by observing the current feedback and used to set compensation levels for each OLED. Such an approach is described, for example, in U.S. Patent Application Publication No. 2005 / 0110420 (Arnold et al.), which is incorporated herein by reference in its entirety.

[0008] Unfortunately, such prior art compensation techniques are inadequate for many applications and significantly increase the cost and complexity of the display and its backplane technology.

[0009] The need for providing visual performance compensation in an OLED-based display in a practical, low-cost manner remains unmet in the prior art. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 7,321,348 [Patent Document 2] US Patent Application Publication No. 2005 / 0110420 Summary of the Invention [Problem to be solved by the invention]

[0011] The present disclosure is directed to visual performance compensation of OLED-based displays that does not affect the active pixel area in the backplane of the display. The compensation is achieved using a sensing device that is external to the backplane and a compensation method to detect degradation and the extent to which it has occurred. As a result, the teachings herein enable improved visual performance compensation without the use of backplane silicon area. [Means for solving the problem]

[0012] One exemplary embodiment includes a plurality of sensor devices positioned near an OLED light-emitting area, the sensors configured to detect brightness from the light-emitting window. An initial brightness is determined for each pixel, after which a set of fixed pattern images is projected by the display. The sensors detect brightness differences among the pixels, allowing identification of pixels whose brightness has decreased from their initial value. Compensation is applied to the degraded pixels by an input processing unit in the next on / off sequence.

[0013] In some embodiments, a test image including the output of multiple pixels is generated by the display. The method begins by determining the number of non-degraded pixels that exceed a threshold brightness and turn on the sensor. The sensor output, which can be an electrical parameter such as voltage, is recorded for the threshold brightness. The number of pixels and the corresponding output are then recorded in the sensor's active area. Typically, degraded pixels are located on a symbology or icon and experience the same aging stress, while normal pixels are not on the symbology. The method continues by first collecting an equal number of degraded pixels and adding one degraded pixel at a time until the threshold brightness is reached. The number of degraded pixels is then recorded. If the number of degraded pixels is not enough to achieve the threshold brightness, good pixels are added until the threshold brightness is reached. If good pixels are mixed with degraded ones in the test image, a proportional method can be used to determine the sensor output only from the degraded pixels. The difference between the reference and degraded pixels is determined, and the difference is divided by the number of degraded pixels. As a result, the relative level of degradation for each pixel is estimated. The level of degradation and the location of the degraded pixels are then sent to an input processing unit for adjustment (i.e., compensation) of each pixel's input level.

[0014] In some cases, the test image comprises the output of a single pixel.

[0015] The choice of whether to use one pixel or two or more pixels in the test image is typically based on the sensitivity of one or more photodetectors. Methods according to the present disclosure have the flexibility to mitigate sensitivity differences. If degradation of a single pixel is detected by the sensor, the test image can consist of a single pixel.

[0016] In a first illustrative embodiment of the present invention, an organic light-emitting diode (OLED) display system with visual performance pixel compensation for brightness loss is provided. The display system includes a plurality of display pixels, each display pixel comprising a plurality of OLED subpixels and pixel drive circuitry; and a sensing system including a plurality of sensors and analog-to-digital conversion (ADC) circuitry operatively connected to each of the sensors, the ADC circuitry providing a sensor signal for each of the sensors. A processor is provided to provide image data drive signals to each of the display pixels, receive the sensor signals from the ADC circuitry for each sensor, estimate a state of degradation of at least one of the display pixels, determine drive signal compensation for each display pixel having the estimated state of degradation, and compensate the image data drive signal to each display pixel having the estimated state of degradation based on the drive signal compensation for each display pixel having the estimated state of degradation.

[0017] The processor may include hardware local to the display system. The processor may include firmware local to the display system. The sensors may be optical sensors such as photodetectors. The sensors may be arranged around a perimeter defined by the display pixels. An area outside the perimeter defined by the display pixels may be a backplane, and the sensors are on the backplane. Each of the sensors may be oriented orthogonal to a plane of a substrate of the plurality of pixels. The image data signals may provide a test image.

[0018] In a second illustrative embodiment of the present invention, a method for compensating at least one pixel for an image in a display is provided. The method includes the steps of: storing a pixel map for a display area of ​​the display, the pixel map having a plurality of non-degraded pixels and at least one degraded pixel; projecting at least one fixed pattern onto the display area; and determining the number of non-degraded pixels (N) required to turn on a sensing system. O ), where the number of non-degraded pixels have luminescence above a threshold luminescence sufficient to turn on the sensing system; setting a count value (i) to zero; generating a symbol S by energizing a number of degraded pixels equal to i; and measuring the luminescence output of the sensing system to determine if the sensing system is on. If the sensing system is not turned on, the method continues with the steps of adding 1 to i and regenerating S by energizing one additional degraded pixel. If the sensing system is turned on, the method continues with the steps of adding 1 to i and regenerating S by energizing one additional degraded pixel. O and S, updating the pixel map based on the current value of S and the degradation level, and generating image data for forming a compensated image on the display.

[0019] The sensor output may be a voltage. The deterioration level is calculated by the formula (i / N O ) × 100%.

[0020] One fixed pattern may include a single pixel test pattern.

[0021] In a third illustrative embodiment of the present invention, a method for compensating at least one pixel for an image in a display is provided. The method includes the steps of: storing a pixel map for a display area of ​​the display, the pixel map having a plurality of non-degraded pixels and at least one degraded pixel; projecting at least one fixed pattern onto the display area; and determining the number of non-degraded pixels (N) required to turn on a sensing system. O The method includes determining a count value (i) of a number of non-degraded pixels having luminescence above a threshold luminescence sufficient to turn on the sensing system, and determining the number of degraded pixels (N1) present in the stored pixel map. The method continues with setting a count value (i) to zero and generating a symbol S by energizing an initial number of degraded pixels. The method then continues with measuring the luminescence output of the sensing system to determine if the sensing system is on. If the sensing system is not turned on in the above step, the count value i is incremented by 1, S is regenerated by energizing one additional degraded pixel, and the method returns to the measuring step. If the sensing system is turned on, the method continues with setting a count value (i) to zero and generating a symbol S by energizing one additional degraded pixel, and the method returns to the measuring step. O and determining a degradation level based on the current values ​​of S. Finally, the method continues with updating the pixel map based on S and the degradation level, and generating image data for forming a compensated image on the display.

[0022] The sensor output may be a voltage. The deterioration level is calculated by the formula ((N1-(N o -i)) / (N0-i))×100%. The fixed pattern may be a single pixel test pattern. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a schematic illustration of salient features of an image rendering system in accordance with an illustrative embodiment of the present invention; [Figure 2] 2 is a schematic diagram of a more detailed perspective view of a portion of the display of FIG. 1; [Figure 3] 1 is a flowchart of a first exemplary method for compensating one or more pixels in a display according to this invention. [Figure 4] 10 is a flowchart of a second illustrative method for compensating one or more pixels in a display according to this invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The following is merely illustrative of the principles of the present disclosure, and it will thus be recognized that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the present disclosure and are included within its spirit and scope.

[0025] Furthermore, all examples and conditional language recited herein are expressly intended to be solely for instructional purposes, primarily to aid the reader in understanding the principles of the present disclosure and the concepts contributed by the inventors to furthering the art, and should not be construed as being limited to such specifically recited examples and conditions.

[0026] Moreover, all statements herein reciting specific examples, as well as principles, aspects, and embodiments of the present disclosure, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include not only currently known equivalents, but also equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.

[0027] Thus, for example, those skilled in the art will recognize that any block diagrams herein represent conceptual views of illustrative circuitry embodying the principles of the present disclosure. Similarly, any flowcharts, flow diagrams, state transition diagrams, pseudocode, etc., may be substantially represented on a computer-readable medium and represent various processes that may be executed by a computer or processor, whether or not such a computer or processor is explicitly illustrated.

[0028] The functionality of the various elements illustrated in the figures, including any functional block that may be labeled as a "processor," may be provided through the use of dedicated hardware as well as hardware capable of executing software, in association with appropriate software. When provided by a processor, the functionality may be provided by a single dedicated processor, by a single shared processor, or by multiple individual processors, some of which may be shared. Moreover, explicit use of the terms "processor" or "controller" should not be construed to refer exclusively to hardware capable of executing software, but may implicitly include, without limitation, digital signal processor (DSP) hardware, network processors, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), read-only memory (ROM) for storing software, random access memory (RAM), and non-volatile storage. Other hardware, both conventional and / or customized, may also be included.

[0029] Software modules, or simply modules that are meant to be software, may be represented herein as any combination of flowchart elements or other elements that represent process steps and / or the performance of textual descriptions. Such modules may be executed by explicitly or implicitly illustrated hardware.

[0030] Unless otherwise expressly specified herein, the figures comprising the drawings are not drawn to scale.

[0031] 1 shows a schematic diagram of salient features of an image rendering system according to the present disclosure. A display 100 includes a display system 102, a sensing system 104, and a processor 106.

[0032] Display system 102 includes a plurality of display pixels, each of which includes a plurality of OLED-based sub-pixels, pixel drive circuitry and associated system electronics.

[0033] The sensing system 104 includes a plurality of sensors and analog-to-digital conversion (ADC) circuitry operatively coupled to the sensors.

[0034] Processor 106 is preferably an external processor configured to at least partially perform the following: provide image data to display system 102, receive sensor signals from ADC circuitry, execute programs and store data, run software routines to estimate the health (i.e., state of degradation) of one or more OLEDs in display area 202, determine appropriate drive signal compensation for the OLEDs, and compensate the image data accordingly to provide compensated drive signals to their corresponding display pixels. In the illustrated example, processor 106 is incorporated into an image processing system typically used to drive conventional displays. In some embodiments, however, processor 106 includes hardware and / or firmware that is local to the display system and / or sensing system. In some embodiments, methods for determining the needed compensation are preferably incorporated into the display's firmware.

[0035] FIG. 2 shows a schematic perspective view of a portion of display 100 in more detail.

[0036] Display system 102 includes a display area 202, which is the area of ​​the display where images are generated by light emission from multiple OLED-based pixels. Display area 202 (also referred to as the "active OLED pixel area") comprises multiple display pixels, each of which includes at least one OLED and its associated pixel drive circuitry, as well as any other associated electronic circuitry.

[0037] A plurality of OLEDs and their associated drive circuitry are mounted on a substrate 208, which defines the backplane of the display area 202. The display area is covered by a cover glass 210, and the substrate 208 is mounted on the surface of a carrier board 212.

[0038] The sensing system 104 includes a sensor 204 and analog-to-digital conversion (ADC) circuitry 206 .

[0039] The sensors 204 are conventional light sensors positioned around the perimeter of the viewing area 202. In the illustrated example, each of the sensors 204 is a conventional photodetector; however, any suitable sensor can be used in the sensing system 104 without departing from the scope of this disclosure. The sensors 204 are positioned such that their respective substrates are oriented orthogonal to the plane of the substrate 208, such that they receive light from the OLEDs at the edge of the cover glass 210. In some embodiments, the cover glass 210 includes optical elements (e.g., diffractive optical elements, holograms, prisms, tilted mirrors, etc.) to improve the ability of the sensors 204 to sense the luminescence of one or more of the OLEDs of the display pixels. The sensors 204 may be external photoelectric (OE) sensors that convert light intensity into an electrical signal. The sensor locations are at the edges of the cover glass 210.

[0040] The ADC circuitry 206 comprises one or more conventional analog-to-digital converter circuits and associated additional components suitable for converting the output of the sensor 204 into a digital signal usable by the processor 106 .

[0041] As will be apparent to those skilled in the art upon reading this specification, the luminance intensity of a single pixel (or subpixel) in a display may be too small to be measured by some sensors. However, it is an aspect of the present disclosure that test images can be generated by the display and used to determine which, if any, OLEDs in the display require compensation and how to compensate them. It should be noted that in some cases, if the sensitivity of one or more sensors is sufficient, such images can be limited to the output of only one pixel. Furthermore, the methods disclosed herein enable a learning process in which the number of pixels required for a test image can be empirically determined over time.

[0042] 3 illustrates the operations of a first method for compensating one or more pixels in a display according to the present disclosure. Method 300 begins at operation 301, where a pixel map for display area 202 is stored by processor 106 and a count value i is set to zero. The value of i represents the number of additional degraded pixels that must be added to symbol S1 to turn on sensing system 104, as described below.

[0043] In operation 302, the number of good (non-degraded) pixels N required to turn on the sensing system 104 based on its threshold brightness is determined. o is determined. Along with this value, the corresponding output of the sensor system 104 is then stored. In the illustrated example, the output of the sensor system 104 is a voltage; however, in some embodiments, it is a different electrical parameter.

[0044] In operation 303, the same number (i.e., N o ) to generate symbol S1. Typically, symbol S1 is designed such that it does not contain any non-degraded pixels and the degraded pixels it does contain are subjected to the same aging stress.

[0045] In operation 304, the output of the sensing system 104 is measured to determine if it has been turned on.

[0046] If the sensing system 104 does not turn on in response to symbol S1, the method 300 continues with operation 305A, where the symbol is increased by energizing one additional degraded pixel, the value of i is incremented, and the method returns to operation 304.

[0047] If the sensing system 104 is turned on, the method 300 continues with operation 305B, where the degradation level DL1 for the pixels included in the symbol S1 is set to N o and the value of i. In the illustrated example, the degradation level is determined as:

[0048]

number

[0049] For example, if 300 non-degraded pixels are required to turn on the sensing system 104, and symbol S1 requires 360 degraded pixels to be energized to turn on the sensing system, then N o = 300 and i = 60, giving DL1 as 20%.

[0050] In operation 306, the pixel map is updated based on S1 and DL1.

[0051] In operation 307, the updated pixel map is used to generate image data for forming a compensated image on the display.

[0052] In some embodiments of the present invention, the test image (i.e., symbol) contains both degraded and non-degraded pixels. In such cases, a proportional method can be used to compensate the display elements primarily or exclusively based on the degraded pixels. In such an approach, the difference between the reference and degraded pixels is determined and then divided by the number of degraded pixels to give the relative level of degradation for each pixel.

[0053] 4 illustrates the operations of a second method for compensating one or more pixels in a display according to the present disclosure. Method 400 begins at operation 401, where a pixel map for display area 202 is stored by processor 106 and a count value i is set to zero.

[0054] In operation 402, the number of good (non-degraded) pixels N required to turn on the sensing system 104 based on its threshold brightness is determined. o is determined. This value, along with the corresponding output of the sensor system 104, is then stored.

[0055] In operation 403, symbol S2 is generated using N1 degraded pixels and the value of variable i is set to zero, in this example the value of i represents the number of non-degraded pixels that must be added to symbol S2 to turn on sensing system 104, as described below.

[0056] In operation 404, the output of the sensing system 104 is measured to determine if it has been turned on.

[0057] If the sensing system 104 does not turn on in response to symbol S2, the method 400 continues with operation 405A, where symbol S2 is increased by energizing one additional non-degraded pixel, the value of i is incremented, and the method returns to operation 404.

[0058] Once the sensing system 104 is turned on, the method 400 continues with operation 405B, where a degradation level DL2 for the pixels included in symbol S2 is determined. In the illustrated example, the degradation level is determined as:

[0059]

number

[0060] For example, if 300 non-degraded pixels are required to turn on the sensing system 104, and symbol S2 initially contains 250 degraded pixels, but requires an additional 70 non-degraded pixels to be energized to turn on the sensing system, then N o = 300, N1 = 250 and i = 70, giving DL2 as 8.7%.

[0061] In operation 406, the pixel map is updated based on S2 and DL2.

[0062] In operation 407, the updated pixel map is used to generate image data for forming a compensated image on the display.

[0063] It is an aspect of the present invention that providing luminescence sensing outside of the display area 202 provides significant advantages over the prior art, such as: i. Avoid additional components on the display backplane, or ii. A wide range of sensors are suitable for use; or iii. Any practical electrical signal level can be used for the pixel drive circuitry; or iv. Independent of the topology of the pixel drive circuitry in the OLED light-emitting stack or backplane; or v. The method is a learning process and is flexible with respect to the number of pixels to be compensated and the time at which the compensation is determined; or vi. Adding or removing sensing capabilities can be implemented at any time; or vii. The compensation capability is external to the normal backplane configuration, so that it can be added to an existing display system; or viii. Any combination of i, ii, iii, iv, v, vi and vii.

[0064] Additional advantages may include: i. Does not occupy backplane silicon as implementation can be done externally ii. The test image pattern can be changed at any time iii. the present invention is independent of the topology of the pixel driving circuitry in the OLED light-emitting stack or backplane; and iv. Implementations of the present invention can be added and removed at any time.

[0065] It should be understood that this disclosure teaches only one example of an exemplary embodiment, and that many variations of the invention can be readily devised by those skilled in the art after reading this disclosure, and that the scope of the present invention will be defined by the claims that follow. [Explanation of symbols]

[0066] 100 displays 102 Display System 104 Sensing System 106 processors 202 Display area 204 Sensors 206 Analog-to-Digital Conversion (ADC) Circuit Network 208 PCB 210 Cover Glass 212 Carrier Board

Claims

1. 1. An organic light emitting diode (OLED) display system having visual performance pixel compensation for brightness loss, comprising: (a) a plurality of display pixels, each display pixel comprising a plurality of OLED subpixels and pixel drive circuitry; (b) a sensing system comprising a plurality of sensors and analog-to-digital conversion (ADC) circuitry operatively connected to each of the sensors, the ADC circuitry providing a sensor signal for each of the sensors; (c) a processor, the processor comprising: (i) providing image data drive signals to each of said display pixels; (ii) receiving the sensor signal from the ADC circuitry for each sensor; (iii) The following steps: (A) The number of non-degraded pixels required to turn on the sensing system (N Ｏ ), wherein the number of non-degraded pixels has luminescence above a threshold luminescence sufficient to turn on the sensing system; (B) setting a count value (i) to zero; (C) generating a symbol S by energizing a number of degraded pixels equal to i; (D) measuring the luminescence output of the sensing system to determine if the sensing system is on; (E) if the sensing system was not turned on in step (D), regenerating S by adding 1 to i and energizing one additional degraded pixel; (F) If the sensing system is turned on in step (E), Ｏ determining a degradation level based on S; estimating a state of degradation of at least one of said display pixels by (iv) determining a drive signal compensation for each display pixel having an estimated state of degradation; (v) compensating the image data drive signal to each display pixel having an estimated state of degradation based on the drive signal compensation for each display pixel having an estimated state of degradation; An OLED display system, wherein the processor includes hardware local to the display system.

2. The OLED display system of claim 1 wherein the processor includes firmware local to the display system.

3. 10. The OLED display system of claim 1, wherein the plurality of sensors are optical sensors.

4. 4. The OLED display system of claim 3, wherein the light sensor is a photodetector.

5. 10. The OLED display system of claim 1, wherein each of the plurality of sensors is disposed around a perimeter defined by the display pixels.

6. 6. The OLED display system of claim 5, wherein an area outside the perimeter defined by the display pixels is a backplane, and the plurality of sensors are on the backplane.

7. 10. The OLED display system of claim 1, wherein each of the plurality of sensors is oriented orthogonal to a plane of a substrate of the plurality of display pixels.

8. 10. The OLED display system of claim 1, wherein the processor provides the image data drive signals to provide a test image.

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