Facebook Patent | Error Correction For Display Device

Patent: Error Correction For Display Device

Publication Number: 20200051483

Publication Date: 20200213

Applicants: Facebook

Abstract

A display device has an image processing unit that determines an error for a pixel location that is based on the difference between an input color dataset and an output color dataset. The error is fed back to the image processing unit to propagate and spread across other neighboring pixel locations. In generating the output color dataset, an error-modified dataset that includes the input dataset and the error may first be generated. The error-modified dataset is examined to ensure the color values fall within the display gamut. The color dataset is also quantized and dithered to make the output dataset having a bit depth that is compatible with what the light emitters can support. Lookup tables and transformation matrices may also be used to account for any potential color shifts of the light emitters due to different driving conditions such as driving currents.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. Provisional Application No. 62/715,721, filed Aug. 7, 2018, which is incorporated by reference in its entirety.

BACKGROUND

[0002] This disclosure relates to structure and operation of a display device and more specifically to error propagation and correction in an image processing unit of a display device.

[0003] A virtual reality (VR) or augmented-reality (AR) system often includes a head-mounted display or a near-eye display for users to immerse in the simulated environment. The image quality generated by the display device directly affects the users’ perception of the simulated reality and the enjoyment of the VR or AR system. Since the display device is often head mounted or portable, the display device is subject to different types of limitations such as size, distance, and power. The limitations may affect the precisions of the display in rendering images, which may result in various visual artifacts, thus negatively impacting the user experience with the VR or AR system.

SUMMARY

[0004] Embodiments described herein generally relate to error correction processes for display devices by determining an error at a pixel location and use the determined error to dither color values of neighboring pixel locations so that the neighboring pixel locations may collaboratively compensate for the error. A display device may include a display panel with light emitters that may not be able to perfectly produce the precise color value that is specified by an image source. The color values intended to be displayed and the actual color values that is displayed may vary. Those variations, however small, may affect the overall image quality and the perceived color depth of the display device. An image processing unit of the display device determines the error at a pixel location resulted from those variations and perform dithering of color datasets of neighboring pixel locations to compensate for the error.

[0005] In accordance with an embodiment, a display device may process color datasets sequentially based on pixel locations. The image processing unit of the display device receives a first input color dataset. The first input color dataset may represent a color value intended to be displayed at a first pixel location. The display device generates, from the first input color dataset, a first output color dataset for driving a first set of light emitters that emit light for the first pixel location. The output color dataset may not be exactly the same as input color dataset. The display device determines the error resulting from a difference between the first input color dataset and the first output color dataset, and generates an error correction dataset accordingly.

[0006] In one embodiment, the error correction dataset may be generated by passing the error values to an image kernel that is designed to spread the error values to one or more pixel locations neighboring the first pixel location.

[0007] In one embodiment, the determined error correction dataset is fed back to the input side of the image processing unit to change other incoming input color values. When the image processing unit receives a second input color dataset for a second pixel location, the display device dithers the second input color dataset using some of the values in the error correction dataset to generate a dithered color dataset. The dithering may include one or more sub-steps that modify the input color values based on the error correction values, ensure the color values fall within a display gamut of the display device, and quantize the color values. The display device generates a second output color dataset for driving a second set of light emitters that emit light for the second pixel location. The second pixel location may neighbor the first pixel location so that the error at the first pixel location is compensated by the adjustment in the second pixel location. The error determination and compensation process may be repeated for other pixel locations to improve the image quality of the display device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is a perspective view of a near-eye-display (NED), in accordance with an embodiment.

[0009] FIG. 2 is a cross-section of an eyewear of the NED illustrated in FIG. 1, in accordance with an embodiment.

[0010] FIG. 3A is a perspective view of a display device, in accordance with an embodiment.

[0011] FIG. 3B is a block diagram of a display device, in accordance with an embodiment.

[0012] FIGS. 4A, 4B, and 4C are conceptual diagrams representing different arrangements of light emitters, in accordance with some embodiments.

[0013] FIGS. 4D and 4E are schematic cross-sectional diagrams of light emitters, in accordance with some embodiments.

[0014] FIG. 5A is a diagram illustrating a scanning operation of a display device using a mirror to project light from a light source to an image field, in accordance with an embodiment.

[0015] FIG. 5B is a diagram illustrating a waveguide configuration, in accordance with an embodiment.

[0016] FIG. 5C is a top view of display device, in accordance with an embodiment.

[0017] FIG. 6A is a waveform diagram illustrating the analog modulation of driving signals for a display panel, in accordance with an embodiment.

[0018] FIG. 6B is a waveform diagram illustrating the digital modulation of driving signals for a display panel, in accordance with an embodiment.

[0019] FIG. 6C is a waveform diagram illustrating the hybrid modulation of driving signals for a display panel, in accordance with an embodiment.

[0020] FIGS. 7A, 7B, and 7C are conceptual diagrams illustrating example color gamut regions in chromaticity diagrams.

[0021] FIG. 8 is a block diagram depicting an image processing unit, in accordance with some embodiments.

[0022] FIG. 9 is a schematic block diagram an image processing unit of a display device, in accordance with an embodiment.

[0023] FIG. 10 is a schematic block diagram an image processing unit of a display device, in accordance with an embodiment.

[0024] FIG. 11 is a schematic block diagram an image processing unit of a display device, in accordance with an embodiment.

[0025] FIG. 12 is an image of an example blue noise mask pattern, in accordance with an embodiment.

[0026] FIG. 13 is a flowchart depicting a process of operating a display device, in accordance with an embodiment.

[0027] The figures depict embodiments of the present disclosure for purposes of illustration only.

DETAILED DESCRIPTION

[0028] Embodiments relate to display devices that perform operations for compensating for the error at a pixel location through adjustment of color values at neighboring pixel locations. Owing to various practical conditions and operating constraints, the light emitters of a display device may not be able to render the precise color at a pixel location. The cumulative effect of errors at different individual pixel locations may cause visual artifacts that are perceivable by users and may render the overall color representation of the display device imprecise. One or more dithering techniques are used across one or more neighboring pixel locations to compensate for the error at a given pixel location. By doing so, the overall image quality produced by the display device is improved.

[0029] Embodiments of the invention may include or be implemented in conjunction with an artificial reality system. Artificial reality is a form of reality that has been adjusted in some manner before presentation to a user, which may include, e.g., a virtual reality (VR), an augmented reality (AR), a mixed reality (MR), a hybrid reality, or some combination and/or derivatives thereof. Artificial reality content may include completely generated content or generated content combined with captured (e.g., real-world) content. The artificial reality content may include video, audio, haptic feedback, or some combination thereof, and any of which may be presented in a single channel or in multiple channels (such as stereo video that produces a three-dimensional effect to the viewer). Additionally, in some embodiments, artificial reality may also be associated with applications, products, accessories, services, or some combination thereof, that are used to, e.g., create content in an artificial reality and/or are otherwise used in (e.g., perform activities in) an artificial reality. The artificial reality system that provides the artificial reality content may be implemented on various platforms, including a head-mounted display (HMD) connected to a host computer system, a standalone HMD, a mobile device or computing system, or any other hardware platform capable of providing artificial reality content to one or more viewers.

Near-Eye Display

[0030] Figure (FIG.) 1 is a diagram of a near-eye display (NED) 100, in accordance with an embodiment. The NED 100 presents media to a user. Examples of media presented by the NED 100 include one or more images, video, audio, or some combination thereof. In some embodiments, audio is presented via an external device (e.g., speakers and/or headphones) that receives audio information from the NED 100, a console (not shown), or both, and presents audio data based on the audio information. The NED 100 may operate as a VR NED. However, in some embodiments, the NED 100 may be modified to also operate as an augmented reality (AR) NED, a mixed reality (MR) NED, or some combination thereof. For example, in some embodiments, the NED 100 may augment views of a physical, real-world environment with computer-generated elements (e.g., images, video, sound, etc.).

[0031] The NED 100 shown in FIG. 1 includes a frame 105 and a display 110. The frame 105 includes one or more optical elements which together display media to users. The display 110 is configured for users to see the content presented by the NED 100. As discussed below in conjunction with FIG. 2, the display 110 includes at least a source assembly to generate an image light to present media to an eye of the user. The source assembly includes, e.g., a light source, an optics system, or some combination thereof.

[0032] FIG. 1 is only an example of a VR system. However, in alternate embodiments, FIG. 1 may also be referred to as a Head-Mounted-Display (HMD).

[0033] FIG. 2 is a cross section of the NED 100 illustrated in FIG. 1, in accordance with an embodiment. The cross section illustrates at least one waveguide assembly 210. An exit pupil is a location where the eye 220 is positioned in an eyebox region 230 when the user wears the NED 100. In some embodiments, the frame 105 may represent a frame of eye-wear glasses. For purposes of illustration, FIG. 2 shows the cross section associated with a single eye 220 and a single waveguide assembly 210, but in alternative embodiments not shown, another waveguide assembly which is separate from the waveguide assembly 210 shown in FIG. 2, provides image light to another eye 220 of the user.

[0034] The waveguide assembly 210, as illustrated below in FIG. 2, directs the image light to the eye 220 through the exit pupil. The waveguide assembly 210 may be composed of one or more materials (e.g., plastic, glass, etc.) with one or more refractive indices that effectively minimize the weight and widen a field of view (hereinafter abbreviated as FOV) of the NED 100. In alternate configurations, the NED 100 includes one or more optical elements between the waveguide assembly 210 and the eye 220. The optical elements may act (e.g., correct aberrations in image light emitted from the waveguide assembly 210) to magnify image light emitted from the waveguide assembly 210, some other optical adjustment of image light emitted from the waveguide assembly 210, or some combination thereof. The example for optical elements may include an aperture, a Fresnel lens, a convex lens, a concave lens, a filter, or any other suitable optical element that affects image light. In one embodiment, the waveguide assembly 210 may produce and direct many pupil replications to the eyebox region 230, in a manner that will be discussed in further detail below in association with FIG. 5B.

[0035] FIG. 3A illustrates a perspective view of a display device 300, in accordance with an embodiment. In some embodiments, the display device 300 is a component (e.g., the waveguide assembly 210 or part of the waveguide assembly 210) of the NED 100. In alternative embodiments, the display device 300 is part of some other NEDs, or another system that directs display image light to a particular location. Depending on embodiments and implementations, the display device 300 may also be referred to as a waveguide display and/or a scanning display. However, in other embodiment, the display device 300 does not include a scanning mirror. For example, the display device 300 can include matrices of light emitters that project light on an image field through a waveguide but without a scanning mirror. In another embodiment, the image emitted by the two-dimensional matrix of light emitters may be magnified by an optical assembly (e.g., lens) before the light arrives a waveguide or a screen.

[0036] For a particular embodiment that uses a waveguide and an optical system, the display device 300 may include a source assembly 310, an output waveguide 320, and a controller 330. The display device 300 may provide images for both eyes or for a single eye. For purposes of illustration, FIG. 3A shows the display device 300 associated with a single eye 220. Another display device (not shown), separated (or partially separated) from the display device 300, provides image light to another eye of the user. In a partially separated system, one or more components may be shared between display devices for each eye.

[0037] The source assembly 310 generates image light 355. The source assembly 310 includes a light source 340 and an optics system 345. The light source 340 is an optical component that generates image light using a plurality of light emitters arranged in a matrix. Each light emitter may emit monochromatic light. The light source 340 generates image light including, but not restricted to, Red image light, Blue image light, Green image light, infra-red image light, etc. While RGB is often discussed in this disclosure, embodiments described herein are not limited to using red, blue and green as primary colors. Other colors are also possible to be used as the primary colors of the display device. Also, a display device in accordance with an embodiment may use more than three primary colors.

[0038] The optics system 345 performs a set of optical processes, including, but not restricted to, focusing, combining, conditioning, and scanning processes on the image light generated by the light source 340. In some embodiments, the optics system 345 includes a combining assembly, a light conditioning assembly, and a scanning mirror assembly, as described below in detail in conjunction with FIG. 3B. The source assembly 310 generates and outputs an image light 355 to a coupling element 350 of the output waveguide 320.

[0039] The output waveguide 320 is an optical waveguide that outputs image light to an eye 220 of a user. The output waveguide 320 receives the image light 355 at one or more coupling elements 350, and guides the received input image light to one or more decoupling elements 360. The coupling element 350 may be, e.g., a diffraction grating, a holographic grating, some other element that couples the image light 355 into the output waveguide 320, or some combination thereof. For example, in embodiments where the coupling element 350 is diffraction grating, the pitch of the diffraction grating is chosen such that total internal reflection occurs, and the image light 355 propagates internally toward the decoupling element 360. The pitch of the diffraction grating may be in the range of 300 nm to 600 nm.

[0040] The decoupling element 360 decouples the total internally reflected image light from the output waveguide 320. The decoupling element 360 may be, e.g., a diffraction grating, a holographic grating, some other element that decouples image light out of the output waveguide 320, or some combination thereof. For example, in embodiments where the decoupling element 360 is a diffraction grating, the pitch of the diffraction grating is chosen to cause incident image light to exit the output waveguide 320. An orientation and position of the image light exiting from the output waveguide 320 are controlled by changing an orientation and position of the image light 355 entering the coupling element 350. The pitch of the diffraction grating may be in the range of 300 nm to 600 nm.

[0041] The output waveguide 320 may be composed of one or more materials that facilitate total internal reflection of the image light 355. The output waveguide 320 may be composed of e.g., silicon, plastic, glass, or polymers, or some combination thereof. The output waveguide 320 has a relatively small form factor. For example, the output waveguide 320 may be approximately 50 mm wide along X-dimension, 30 mm long along Y-dimension and 0.5-1 mm thick along Z-dimension.

[0042] The controller 330 controls the image rendering operations of the source assembly 310. The controller 330 determines instructions for the source assembly 310 based at least on the one or more display instructions. Display instructions are instructions to render one or more images. In some embodiments, display instructions may simply be an image file (e.g., bitmap). The display instructions may be received from, e.g., a console of a VR system (not shown here). Scanning instructions are instructions used by the source assembly 310 to generate image light 355. The scanning instructions may include, e.g., a type of a source of image light (e.g., monochromatic, polychromatic), a scanning rate, an orientation of a scanning apparatus, one or more illumination parameters, or some combination thereof. The controller 330 includes a combination of hardware, software, and/or firmware not shown here so as not to obscure other aspects of the disclosure.

[0043] FIG. 3B is a block diagram illustrating an example source assembly 310, in accordance with an embodiment. The source assembly 310 includes the light source 340 that emits light that is processed optically by the optics system 345 to generate image light 335 that will be projected on an image field (not shown). The light source 340 is driven by the driving circuit 370 based on the data sent from a controller 330 or an image processing unit 375. In one embodiment, the driving circuit 370 is the circuit panel that connects to and mechanically holds various light emitters of the light source 340. The driving circuit 370 and the light source 340 combined may sometimes be referred to as a display panel 380 or an LED panel (if some forms of LEDs are used as the light emitters).

[0044] The light source 340 may generate a spatially coherent or a partially spatially coherent image light. The light source 340 may include multiple light emitters. The light emitters can be vertical cavity surface emitting laser (VCSEL) devices, light emitting diodes (LEDs), microLEDs, tunable lasers, and/or some other light-emitting devices. In one embodiment, the light source 340 includes a matrix of light emitters. In another embodiment, the light source 340 includes multiple sets of light emitters with each set grouped by color and arranged in a matrix form. The light source 340 emits light in a visible band (e.g., from about 390 nm to 700 nm). The light source 340 emits light in accordance with one or more illumination parameters that are set by the controller 330 and potentially adjusted by image processing unit 375 and driving circuit 370. An illumination parameter is an instruction used by the light source 340 to generate light. An illumination parameter may include, e.g., source wavelength, pulse rate, pulse amplitude, beam type (continuous or pulsed), other parameter(s) that affect the emitted light, or some combination thereof. The light source 340 emits source light 385. In some embodiments, the source light 385 includes multiple beams of Red light, Green light, and Blue light, or some combination thereof.

[0045] The optics system 345 may include one or more optical components that optically adjust and potentially re-direct the light from the light source 340. One form of example adjustment of light may include conditioning the light. Conditioning the light from the light source 340 may include, e.g., expanding, collimating, correcting for one or more optical errors (e.g., field curvature, chromatic aberration, etc.), some other adjustment of the light, or some combination thereof. The optical components of the optics system 345 may include, e.g., lenses, mirrors, apertures, gratings, or some combination thereof. Light emitted from the optics system 345 is referred to as an image light 355.

[0046] The optics system 345 may redirect image light via its one or more reflective and/or refractive portions so that the image light 355 is projected at a particular orientation toward the output waveguide 320 (shown in FIG. 3A). Where the image light is redirected toward is based on specific orientations of the one or more reflective and/or refractive portions. In some embodiments, the optics system 345 includes a single scanning mirror that scans in at least two dimensions. In other embodiments, the optics system 345 may include a plurality of scanning mirrors that each scan in orthogonal directions to each other. The optics system 345 may perform a raster scan (horizontally, or vertically), a biresonant scan, or some combination thereof. In some embodiments, the optics system 345 may perform a controlled vibration along the horizontal and/or vertical directions with a specific frequency of oscillation to scan along two dimensions and generate a two-dimensional projected line image of the media presented to user’s eyes. In other embodiments, the optics system 345 may also include a lens that serves similar or same function as one or more scanning mirror.

[0047] In some embodiments, the optics system 345 includes a galvanometer mirror. For example, the galvanometer mirror may represent any electromechanical instrument that indicates that it has sensed an electric current by deflecting a beam of image light with one or more mirrors. The galvanometer mirror may scan in at least one orthogonal dimension to generate the image light 355. The image light 355 from the galvanometer mirror represents a two-dimensional line image of the media presented to the user’s eyes.

[0048] In some embodiments, the source assembly 310 does not include an optics system. The light emitted by the light source 340 is projected directly to the waveguide 320 (shown in FIG. 3A).

[0049] The controller 330 controls the operations of light source 340 and, in some cases, the optics system 345. In some embodiments, the controller 330 may be the graphics processing unit (GPU) of a display device. In other embodiments, the controller 330 may be other kinds of processors. The operations performed by the controller 330 includes taking content for display, and dividing the content into discrete sections. The controller 330 instructs the light source 340 to sequentially present the discrete sections using light emitters corresponding to a respective row in an image ultimately displayed to the user. The controller 330 instructs the optics system 345 to perform different adjustment of the light. For example, the controller 330 controls the optics system 345 to scan the presented discrete sections to different areas of a coupling element of the output waveguide 320 (shown in FIG. 3A). Accordingly, at the exit pupil of the output waveguide 320, each discrete portion is presented in a different location. While each discrete section is presented at different times, the presentation and scanning of the discrete sections occur fast enough such that a user’s eye integrates the different sections into a single image or series of images. The controller 330 may also provide scanning instructions to the light source 340 that include an address corresponding to an individual source element of the light source 340 and/or an electrical bias applied to the individual source element.

[0050] The image processing unit 375 may be a general-purpose processor and/or one or more application-specific circuits that are dedicated to performing the features described herein. In one embodiment, a general-purpose processor may be coupled to a memory to execute software instructions that cause the processor to perform certain processes described herein. In another embodiment, the image processing unit 375 may be one or more circuits that are dedicated to performing certain features. While in FIG. 3B the image processing unit 375 is shown as a stand-alone unit that is separate from the controller 330 and the driving circuit 370, in other embodiments the image processing unit 375 may be a sub-unit of the controller 330 or the driving circuit 370. In other words, in those embodiments, the controller 330 or the driving circuit 370 performs various image processing procedures of the image processing unit 375. The image processing unit 375 may also be referred to as an image processing circuit.

Light Emitters

[0051] FIGS. 4A through 4E are conceptual diagrams that illustrate different light emitters’ structure and arrangement, in accordance with various embodiments.

[0052] FIGS. 4A, 4B, and 4C are top views of matrix arrangement of light emitters’ that may be included in the light source 340 of FIGS. 3A and 3B, in accordance to some embodiments. The configuration 400A shown in FIG. 4A is a linear configuration of the light emitter arrays 402A-C of FIG. 4A along the axis A1. This particular linear configuration may be arranged according to a longer side of the rectangular light emitter arrays 402. While the light emitter arrays 402 may have a square configuration of light emitters in some embodiments, other embodiments may include a rectangular configuration of light emitters. The light emitter arrays 402A-C each include multiple rows and columns of light emitters. Each light emitter array 402A-C may include light emitters of a single color. For example, light emitter array 402A may include red light emitters, light emitter array 402B may include green light emitters, and light emitter array 402C may include blue light emitters. In other embodiments, the light emitter arrays 402A-C may have other configurations (e.g., oval, circular, or otherwise rounded in some fashion) while defining a first dimension (e.g., a width) and a second dimension (e.g., length) orthogonal to the first direction, with one dimension being either equal or unequal to each other. In FIG. 4B, the light emitter arrays 402A-C may be disposed in a linear configuration 400B according to a shorter side of the rectangular light emitter arrays 402, along an axis A2. FIG. 4C shows a triangular configuration of the light emitter arrays 402A-C in which the centers of the light emitter arrays 402 form a non-linear (e.g., triangular) shape or configuration. Some embodiments of the configuration 400C of FIG. 4C may further include a white-light emitter array 402D, such that the light emitter arrays 402 are in a rectangular or square configuration. The light emitter arrays 402 may have a two-dimensional light emitter configuration with more than 1000 by 1000 light emitters, in some embodiments. Various other configurations are also within the scope of the present disclosure.

[0053] While the matrix arrangements of light emitters shown in FIGS. 4A-4C are arranged in perpendicular rows and columns, in other embodiments the matrix arrangements may be arranged other forms. For example, some of the light emitters may be aligned diagonally or in other arrangements, regular or irregular, symmetrical or asymmetrical. Also, the terms rows and columns may describe two relative spatial relationships of elements. While, for the purpose of simplicity, a column described herein is normally associated with a vertical line of elements, it should be understood that a column does not have to be arranged vertically (or longitudinally). Likewise, a row does not have to be arranged horizontally (or laterally). A row and a column may also sometimes describe an arrangement that is non-linear. Rows and columns also do not necessarily imply any parallel or perpendicular arrangement. Sometimes a row or a column may be referred to as a line. Also, in some embodiments, the light emitters may not be arranged in a matrix configuration. For example, in some display devices that include a rotating mirror that will be discussed in further details in FIG. 5A, there may be a single line of light emitters for each color. In other embodiments, there may be two or three lines of light emitters for each color.

[0054] FIGS. 4D and 4E are schematic cross-sectional diagrams of an example of light emitters 410 that may be used as an individual light emitter in the light emitter arrays 402 of FIGS. 4A-C, in accordance with some embodiments. In one embodiment, the light emitter 410 may be microLED 460A. In other embodiments, other types of light emitters may be used and do not need to be microLED. FIG. 4D shows a schematic cross-section of a microLED 460A. A “microLED” may be a particular type of LED having a small active light emitting area (e.g., less than 2,000 .mu.m.sup.2 in some embodiments, less than 20 .mu.m.sup.2 or less than 10 .mu.m.sup.2 in other embodiments). In some embodiments, the emissive surface of the microLED 460A may have a diameter of less than approximately 5 .mu.m, although smaller (e.g., 2 .mu.m) or larger diameters for the emissive surface may be utilized in other embodiments. The microLED 460A may also have collimated or non-Lambertian light output, in some examples, which may increase the brightness level of light emitted from a small active light-emitting area.

[0055] The microLED 460A may include, among other components, an LED substrate 412 with a semiconductor epitaxial layer 414 disposed on the substrate 412, a dielectric layer 424 and a p-contact 429 disposed on the epitaxial layer 414, a metal reflector layer 426 disposed on the dielectric layer 424 and p-contact 429, and an n-contact 428 disposed on the epitaxial layer 414. The epitaxial layer 414 may be shaped into a mesa 416. An active light-emitting area 418 may be formed in the structure of the mesa 416 by way of a p-doped region 427 of the epitaxial layer 414.

[0056] The substrate 412 may include transparent materials such as sapphire or glass. In one embodiment, the substrate 412 may include silicon, silicon oxide, silicon dioxide, aluminum oxide, sapphire, an alloy of silicon and germanium, indium phosphide (InP), and the like. In some embodiments, the substrate 412 may include a semiconductor material (e.g., monocrystalline silicon, germanium, silicon germanium (SiGe), and/or a III–V based material (e.g., gallium arsenide), or any combination thereof. In various embodiments, the substrate 412 can include a polymer-based substrate, glass, or any other bendable substrate including two-dimensional materials (e.g., graphene and molybdenum disulfide), organic materials (e.g., pentacene), transparent oxides (e.g., indium gallium zinc oxide (IGZO)), polycrystalline III-V materials, polycrystalline germanium, polycrystalline silicon, amorphous III-V materials, amorphous germanium, amorphous silicon, or any combination thereof. In some embodiments, the substrate 412 may include a III-V compound semiconductor of the same type as the active LED (e.g., gallium nitride). In other examples, the substrate 412 may include a material having a lattice constant close to that of the epitaxial layer 414.

[0057] The epitaxial layer 414 may include gallium nitride (GaN) or gallium arsenide (GaAs). The active layer 418 may include indium gallium nitride (InGaN). The type and structure of semiconductor material used may vary to produce microLEDs that emit specific colors. In one embodiment, the semiconductor materials used can include a III-V semiconductor material. III-V semiconductor material layers can include those materials that are formed by combining group III elements (Al, Ga, In, etc.) with group V elements (N, P, As, Sb, etc.). The p-contact 429 and n-contact 428 may be contact layers formed from indium tin oxide (ITO) or another conductive material that can be transparent at the desired thickness or arrayed in a grid-like pattern to provide for both good optical transmission/transparency and electrical contact, which may result in the microLED 460A also being transparent or substantially transparent. In such examples, the metal reflector layer 426 may be omitted. In other embodiments, the p-contact 429 and the n-contact 428 may include contact layers formed from conductive material (e.g., metals) that may not be optically transmissive or transparent, depending on pixel design.

[0058] In some implementations, alternatives to ITO can be used, including wider-spectrum transparent conductive oxides (TCOs), conductive polymers, metal grids, carbon nanotubes (CNT), graphene, nanowire meshes, and thin-metal films. Additional TCOs can include doped binary compounds, such as aluminum-doped zinc-oxide (AZO) and indium-doped cadmium-oxide. Additional TCOs may include barium stannate and metal oxides, such as strontium vanadate and calcium vanadate. In some implementations, conductive polymers can be used. For example, a poly(3,4-ethylenedioxythiophene) PEDOT: poly(styrene sulfonate) PSS layer can be used. In another example, a poly(4,4-dioctyl cyclopentadithiophene) material doped with iodine or 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) can be used. The example polymers and similar materials can be spin-coated in some example embodiments.

[0059] In some embodiments, the p-contact 429 may be of a material that forms an ohmic contact with the p-doped region 427 of the mesa 416. Examiner of such materials may include, but are not limited to, palladium, nickel oxide deposited as a NiAu multilayer coating with subsequent oxidation and annealing, silver, nickel oxide/silver, gold/zinc, platinum gold, or other combinations that form ohmic contacts with p-doped III-V semiconductor material.

[0060] The mesa 416 of the epitaxial layer 414 may have a truncated top on a side opposed to a substrate light emissive surface 420 of the substrate 412. The mesa 416 may also have a parabolic or near-parabolic shape to form a reflective enclosure or parabolic reflector for light generated within the microLED 460A. However, while FIG. 4D depicts a parabolic or near-parabolic shape for the mesa 416, other shapes for the mesa 416 are possible in other embodiments. The arrows indicate how light 422 emitted from the active layer 418 may be reflected off the internal walls of the mesa 416 toward the light emissive surface 420 at an angle sufficient for the light to escape the microLED 460A (i.e., outside an angle of total internal reflection). The p-contact 429 and the n-contact 428 may electrically connect the microLED 460A to a substrate.

[0061] The parabolic-shaped structure of the microLED 460A may result in an increase in the extraction efficiency of the microLED 460A into low illumination angles when compared to unshaped or standard LEDs. Standard LED dies may generally provide an emission full width at half maximum (FWHM) angle of 120.degree.. In comparison, the microLED 460A can be designed to provide controlled emission angle FWHM of less than standard LED dies, such as around 41.degree.. This increased efficiency and collimated output of the microLED 460A can enable improvement in overall power efficiency of the NED, which can be important for thermal management and/or battery life.

[0062] The microLED 460A may include a circular cross-section when cut along a horizontal plane, as shown in FIG. 4D. However, the microLED 460A cross-section may be non-circular in other examples. The microLED 460A may have a parabolic structure etched directly onto the LED die during the wafer processing steps. The parabolic structure may include the active light-emitting area 418 of the microLED 460A to generate light, and the parabolic structure may reflect a portion of the generated light to form the quasi-collimated light 422 emitted from the substrate light emissive surface 420. In some examples, the optical size of the microLED 460A may be smaller than or equal to the active light-emitting area 418. In other embodiments, the optical size of the microLED 460A may be larger than the active light-emitting area 418, such as through a refractive or reflective approach, to improve usable brightness of the microLED 460A, including any chief ray angle (CRA) offsets to be produced by the light emitter array 402.

[0063] FIG. 4E depicts a microLED 460B that is similar in many respects to the microLED 460A of FIG. 4D. The microLED 460B may further include a microlens 450, which may be formed over the parabolic structure. In some embodiments, the microlens 450 may be formed by applying a polymer coating over the microLED 460A, patterning the coating, and reflowing the coating to achieve the desired lens curvature. The microlens 450 may be disposed over an emissive surface to alter a chief ray angle of the microLED 460B. In another embodiment, the microlens 450 may be formed by depositing a microlens material above the microLED 460A (for example, by a spin-on method or a deposition process). For example, a microlens template (not shown) having a curved upper surface can be patterned above the microlens material. In some embodiments, the microlens template may include a photoresist material exposed using a distributing exposing light dose (e.g., for a negative photoresist, more light is exposed at a bottom of the curvature and less light is exposed at a top of the curvature), developed, and baked to form a rounding shape. The microlens 450 can then be formed by selectively etching the microlens material according to the microlens template. In some embodiments, the shape of the microlens 450 may be formed by etching into the substrate 412. In other embodiments, other types of light-shaping or light-distributing elements, such as an annular lens, Fresnel lens, or photonic crystal structures, may be used instead of microlenses.

In some embodiments, microLED arrangements other than those specifically discussed above in conjunction with FIGS. 4D and 4E may be employed as a microLED in light emitter array 402. For example, the microLED may include isolated pillars of epitaxially grown light-emitting material surrounded by a metal reflector. The pixels of the light emitter array 402 may also include clusters of small pillars (e.g., nanowires) of epitaxially grown material that may or may not be surrounded by reflecting material or absorbing material to prevent optical crosstalk. In some examples, the microLED pixels may be individual metal p-contacts on a planar, epitaxially grown LED device, in which the individual pixels may be electrically isolated using passivation means, such as plasma treatment, ion-implantation, or the like. Such devices may be fabricated with light extraction enhancement methods, such as microlenses, diffractive structures, or photonic crystals. Other processes for fabricating the microLEDs of the dimensions noted above other than those specifically disclosed herein may be employed in other embodiments.

Formation of an Image

[0064] FIGS. 5A and 5B illustrate how images and pupil replications are formed in a display device based on different structural arrangement of light emitters, in accordance with different embodiments. An image field is an area that receives the light emitted by the light source and forms an image. For example, an image field may correspond to a portion of the coupling element 350 or a portion of the decoupling element 360 in FIG. 3A. In some cases, an image field is not an actual physical structure but is an area to which the image light is projected and which the image is formed. In one embodiment, the image field is a surface of the coupling element 350 and the image formed on the image field is magnified as light travels through the output waveguide 320. In another embodiment, an image field is formed after light passing through the waveguide which combines the light of different colors to form the image field. In some embodiments, the image field may be projected directly into the user’s eyes.

[0065] FIG. 5A is a diagram illustrating a scanning operation of a display device 500 using a scanning mirror 520 to project light from a light source 340 to an image field 530, in accordance with an embodiment. The display device 500 may correspond to the near-eye display 100 or another scan-type display device. The light source 340 may correspond to the light source 340 shown in FIG. 3B, or may be used in other display devices. The light source 340 includes multiple rows and columns of light emitters 410, as represented by the dots in inset 515. In one embodiment, the light source 340 may include a single line of light emitters 410 for each color. In other embodiments, the light source 340 may include more than one lines of light emitters 410 for each color. The light 502 emitted by the light source 340 may be a set of collimated beams of light. For example, the light 502 in FIG. 5 shows multiple beams that are emitted by a column of light emitters 410. Before reaching the mirror 520, the light 502 may be conditioned by different optical devices such as the conditioning assembly 430 (shown in FIG. 3B but not shown in FIG. 5). The mirror 520 reflects and projects the light 502 from the light source 340 to the image field 530. The mirror 520 rotates about an axis 522. The mirror 520 may be a microelectromechanical system (MEMS) mirror or any other suitable mirror. The mirror 520 may be an embodiment of the optics system 345 in FIG. 3B or a part of the optics system 345. As the mirror 520 rotates, the light 502 is directed to a different part of the image field 530, as illustrated by the reflected part of the light 504 in solid lines and the reflected part of the light 504 in dash lines.

[0066] At a particular orientation of the mirror 520 (i.e., a particular rotational angle), the light emitters 410 illuminate a portion of the image field 530 (e.g., a particular subset of multiple pixel locations 532 on the image field 530). In one embodiment, the light emitters 410 are arranged and spaced such that a light beam from each light emitter 410 is projected on a corresponding pixel location 532. In another embodiment, small light emitters such as microLEDs are used for light emitters 410 so that light beams from a subset of multiple light emitters are together projected at the same pixel location 532. In other words, a subset of multiple light emitters 410 collectively illuminates a single pixel location 532 at a time.

[0067] The image field 530 may also be referred to as a scan field because, when the light 502 is projected to an area of the image field 530, the area of the image field 530 is being illuminated by the light 502. The image field 530 may be spatially defined by a matrix of pixel locations 532 (represented by the blocks in inset 534) in rows and columns. A pixel location here refers to a single pixel. The pixel locations 532 (or simply the pixels) in the image field 530 sometimes may not actually be additional physical structure. Instead, the pixel locations 532 may be spatial regions that divide the image field 530. Also, the sizes and locations of the pixel locations 532 may depend on the projection of the light 502 from the light source 340. For example, at a given angle of rotation of the mirror 520, light beams emitted from the light source 340 may fall on an area of the image field 530. As such, the sizes and locations of pixel locations 532 of the image field 530 may be defined based on the location of each light beam. In some cases, a pixel location 532 may be subdivided spatially into subpixels (not shown). For example, a pixel location 532 may include a Red subpixel, a Green subpixel, and a Blue subpixel. The Red subpixel corresponds to a location at which one or more Red light beams are projected, etc. When subpixels are present, the color of a pixel 532 is based on the temporal and/or spatial average of the subpixels.

[0068] The number of rows and columns of light emitters 410 of the light source 340 may or may not be the same as the number of rows and columns of the pixel locations 532 in the image field 530. In one embodiment, the number of light emitters 410 in a row is equal to the number of pixel locations 532 in a row of the image field 530 while the number of light emitters 410 in a column is two or more but fewer than the number of pixel locations 532 in a column of the image field 530. Put differently, in such embodiment, the light source 340 has the same number of columns of light emitters 410 as the number of columns of pixel locations 532 in the image field 530 but has fewer rows than the image field 530. For example, in one specific embodiment, the light source 340 has about 1280 columns of light emitters 410, which is the same as the number of columns of pixel locations 532 of the image field 530, but only a handful of light emitters 410. The light source 340 may have a first length L1, which is measured from the first row to the last row of light emitters 410. The image field 530 has a second length L2, which is measured from row 1 to row p of the scan field 530. In one embodiment, L2 is greater than L1 (e.g., L2 is 50 to 10,000 times greater than L).

[0069] Since the number of rows of pixel locations 532 is larger than the number of rows of light emitters 410 in some embodiments, the display device 500 uses the mirror 520 to project the light 502 to different rows of pixels at different times. As the mirror 520 rotates and the light 502 scans through the image field 530 quickly, an image is formed on the image field 530. In some embodiments, the light source 340 also has a smaller number of columns than the image field 530. The mirror 520 can rotate in two dimensions to fill the image field 530 with light (e.g., a raster-type scanning down rows then moving to new columns in the image field 530).

[0070] The display device may operate in predefined display periods. A display period may correspond to a duration of time in which an image is formed. For example, a display period may be associated with the frame rate (e.g., a reciprocal of the frame rate). In the particular embodiment of display device 500 that includes a rotating mirror, the display period may also be referred to as a scanning period. A complete cycle of rotation of the mirror 520 may be referred to as a scanning period. A scanning period herein refers to a predetermined cycle time during which the entire image field 530 is completely scanned. The scanning of the image field 530 is controlled by the mirror 520. The light generation of the display device 500 may be synchronized with the rotation of the mirror 520. For example, in one embodiment, the movement of the mirror 520 from an initial position that projects light to row 1 of the image field 530, to the last position that projects light to row p of the image field 530, and then back to the initial position is equal to a scanning period. The scanning period may also be related to the frame rate of the display device 500. By completing a scanning period, an image (e.g., a frame) is formed on the image field 530 per scanning period. Hence, the frame rate may correspond to the number of scanning periods in a second.

[0071] As the mirror 520 rotates, light scans through the image field and images are formed. The actual color value and light intensity (brightness) of a given pixel location 532 may be an average of the color various light beams illuminating the pixel location during the scanning period. After completing a scanning period, the mirror 520 reverts back to the initial position to project light onto the first few rows of the image field 530 again, except that a new set of driving signals may be fed to the light emitters 410. The same process may be repeated as the mirror 520 rotates in cycles. As such, different images are formed in the scanning field 530 in different frames.

[0072] FIG. 5B is a conceptual diagram illustrating a waveguide configuration to form an image and replications of images that may be referred to as pupil replications, in accordance with an embodiment. In this embodiment, the light source of the display device may be separated into three different light emitter arrays 402, such as based on the configurations shown in FIGS. 4A and 4B. The primary colors may be red, green, and blue or another combination of other suitable primary colors. In one embodiment, the number of light emitters in each light emitter array 402 may be equal to the number of pixel locations an image field (not shown in FIG. 5B). As such, contrary to the embodiment shown in FIG. 5A that uses a scanning operation, each light emitter may be dedicated to generating images at a pixel location of the image field. In another embodiment, the configuration shown in FIGS. 5A and 5B may be combined. For example, the configuration shown in FIG. 5B may be located downstream of the configuration shown in FIG. 5A so that the image formed by the scanning operation in FIG. 5A may further be replicated to generate multiple replications.

[0073] The embodiments depicted in FIG. 5B may provide for the projection of many image replications (e.g., pupil replications) or decoupling a single image projection at a single point. Accordingly, additional embodiments of disclosed NEDs may provide for a single decoupling element. Outputting a single image toward the eyebox 230 may preserve the intensity of the coupled image light. Some embodiments that provide for decoupling at a single point may further provide for steering of the output image light. Such pupil-steering NEDs may further include systems for eye tracking to monitor a user’s gaze. Some embodiments of the waveguide configurations that provide for pupil replication, as described herein, may provide for one-dimensional replication, while other embodiments may provide for two-dimensional replication. For simplicity, one-dimensional pupil replication is shown in FIG. 5B. Two-dimensional pupil replication may include directing light into and outside the plane of FIG. 5B. FIG. 5B is presented in a simplified format. The detected gaze of the user may be used to adjust the position and/or orientation of the light emitter arrays 402 individually or the light source 340 as a whole and/or to adjust the position and/or orientation of the waveguide configuration.

[0074] In FIG. 5B, a waveguide configuration 540 is disposed in cooperation with a light source 340, which may include one or more monochromatic light emitter arrays 402 secured to a support structure 564 (e.g., a printed circuit board or another structure). The support structure 564 may be coupled to the frame 105 of FIG. 1. The waveguide configuration 540 may be separated from the light source 340 by an air gap having a distance D1. The distance D1 may be in a range from approximately 50 .mu.m to approximately 500 .mu.m in some examples. The monochromatic image or images projected from the light source 340 may pass through the air gap toward the waveguide configuration 540. Any of the light source embodiments described herein may be utilized as the light source 340.

[0075] The waveguide configuration may include a waveguide 542, which may be formed from a glass or plastic material. The waveguide 542 may include a coupling area 544 and a decoupling area formed by decoupling elements 546A on a top surface 548A and decoupling elements 546B on a bottom surface 548B in some embodiments. The area within the waveguide 542 in between the decoupling elements 546A and 546B may be considered a propagation area 550, in which light images received from the light source 340 and coupled into the waveguide 542 by coupling elements included in the coupling area 544 may propagate laterally within the waveguide 542.

[0076] The coupling area 544 may include a coupling element 552 configured and dimensioned to couple light of a predetermined wavelength, e.g., red, green, or blue light. When a white light emitter array is included in the light source 340, the portion of the white light that falls in the predetermined wavelength may be coupled by each of the coupling elements 552. In some embodiments, the coupling elements 552 may be gratings, such as Bragg gratings, dimensioned to couple a predetermined wavelength of light. In some examples, the gratings of each coupling element 552 may exhibit a separation distance between gratings associated with the predetermined wavelength of light that the particular coupling element 552 is to couple into the waveguide 542, resulting in different grating separation distances for each coupling element 552. Accordingly, each coupling element 552 may couple a limited portion of the white light from the white light emitter array when included. In other examples, the grating separation distance may be the same for each coupling element 552. In some examples, coupling element 552 may be or include a multiplexed coupler.

[0077] As shown in FIG. 5B, a red image 560A, a blue image 560B, and a green image 560C may be coupled by the coupling elements of the coupling area 544 into the propagation area 550 and may begin traversing laterally within the waveguide 542. In one embodiment, the red image 560A, the blue image 560B, and the green image 560C, each represented by a different dash line in FIG. 5B, may converge to form an overall image that is represented by a solid line. For simplicity, FIG. 5B may show an image by a single arrow, but each arrow may represent an image field where the image is formed. In another embodiment, red image 560A, the blue image 560B, and the green image 560C, may correspond to different spatial locations.

[0078] A portion of the light may be projected out of the waveguide 542 after the light contacts the decoupling element 546A for one-dimensional pupil replication, and after the light contacts both the decoupling element 546A and the decoupling element 546B for two-dimensional pupil replication. In two-dimensional pupil replication embodiments, the light may be projected out of the waveguide 542 at locations where the pattern of the decoupling element 546A intersects the pattern of the decoupling element 546B.

[0079] The portion of light that is not projected out of the waveguide 542 by the decoupling element 546A may be reflected off the decoupling element 546B. The decoupling element 546B may reflect all incident light back toward the decoupling element 546A, as depicted. Accordingly, the waveguide 542 may combine the red image 560A, the blue image 560B, and the green image 560C into a polychromatic image instance, which may be referred to as a pupil replication 562. The polychromatic pupil replication 562 may be projected toward the eyebox 230 of FIG. 2 and to the eye 220, which may interpret the pupil replication 562 as a full-color image (e.g., an image including colors in addition to red, green, and blue). The waveguide 542 may produce tens or hundreds of pupil replications 562 or may produce a single replication 562.

[0080] In some embodiments, the waveguide configuration may differ from the configuration shown in FIG. 5B. For example, the coupling area may be different. Rather than including gratings as coupling element 552, an alternate embodiment may include a prism that reflects and refracts received image light, directing it toward the decoupling element 706A. Also, while FIG. 5B generally shows the light source 340 having multiple light emitters arrays 402 coupled to the same support structure 564, other embodiments may employ a light source 340 with separate monochromatic emitters arrays 402 located at disparate locations about the waveguide configuration (e.g., one or more emitters arrays 402 located near a top surface of the waveguide configuration and one or more emitters arrays 402 located near a bottom surface of the waveguide configuration).

[0081] Also, although only three light emitter arrays are shown in FIG. 5B, an embodiment may include more or fewer light emitter arrays. For example, in one embodiment, a display device may include two red arrays, two green arrays, and two blue arrays. In one case, the extra set of emitter panels provides redundant light emitters for the same pixel location. In another case, one set of red, green, and blue panels is responsible for generating light corresponding to the most significant bits of a color dataset for a pixel location while another set of panels is responsible for generating light corresponding the least significant bits of the color dataset. The separation of most and least significant bits of a color dataset will be discussed in further detail below in FIG. 6.

[0082] While FIGS. 5A and 5B show different ways an image may be formed in a display device, the configurations shown in FIGS. 5A and 5B are not mutually exclusive. For example, in one embodiment, a display device may use both a rotating mirror and a waveguide to form an image and also to form multiple pupil replications.

[0083] FIG. 5C is a top view of a display system (e.g., an NED), in accordance with an embodiment. The NED 570 in FIG. 9A may include a pair of waveguide configurations. Each waveguide configuration projects images to an eye of a user. In some embodiments not shown in FIG. 5C, a single waveguide configuration that is sufficiently wide to project images to both eyes may be used. The waveguide configurations 590A and 590B may each include a decoupling area 592A or 592B. In order to provide images to an eye of the user through the waveguide configuration 590, multiple coupling areas 594 may be provided in a top surface of the waveguide of the waveguide configuration 590. The coupling areas 594A and 594B may include multiple coupling elements to interface with light images provided by a light emitter array set 596A and a light emitter array set 596B, respectively. Each of the light emitter array sets 596 may include a plurality of monochromatic light emitter arrays, as described herein. As shown, the light emitter array sets 596 may each include a red light emitter array, a green light emitter array, and a blue light emitter array. As described herein, some light emitter array sets may further include a white light emitter array or a light emitter array emitting some other color or combination of colors.

[0084] The right eye waveguide 590A may include one or more coupling areas 594A, 594B, 594C, and 594D (all or a portion of which may be referred to collectively as coupling areas 594) and a corresponding number of light emitter array sets 596A, 596B, 596C, and 596D (all or a portion of which may be referred to collectively as the light emitter array sets 596). Accordingly, while the depicted embodiment of the right eye waveguide 590A may include two coupling areas 594 and two light emitter array sets 596, other embodiments may include more or fewer. In some embodiments, the individual light emitter arrays of a light emitter array set may be disposed at different locations around a decoupling area. For example, the light emitter array set 596A may include a red light emitter array disposed along a left side of the decoupling area 592A, a green light emitter array disposed along the top side of the decoupling area 592A, and a blue light emitter array disposed along the right side of the decoupling area 592A. Accordingly, light emitter arrays of a light emitter array set may be disposed all together, in pairs, or individually, relative to a decoupling area.

[0085] The left eye waveguide 590B may include the same number and configuration of coupling areas 594 and light emitter array sets 596 as the right eye waveguide 590A, in some embodiments. In other embodiments, the left eye waveguide 590B and the right eye waveguide 590A may include different numbers and configurations (e.g., positions and orientations) of coupling areas 594 and light emitter array sets 596. Included in the depiction of the left waveguide 590A and the right waveguide 590B are different possible arrangements of pupil replication areas of the individual light emitter arrays included in one light emitter array set 596. In one embodiment, the pupil replication areas formed from different color light emitters may occupy different areas, as shown in the left waveguide 590A. For example, a red light emitter array of the light emitter array set 596 may produce pupil replications of a red image within the limited area 598A. A green light emitter array may produce pupil replications of a green image within the limited area 598B. A blue light emitter array may produce pupil replications of a blue image within the limited area 598C. Because the limited areas 598 may be different from one monochromatic light emitter array to another, only the overlapping portions of the limited areas 598 may be able to provide full-color pupil replication, projected toward the eyebox 230. In another embodiment, the pupil replication areas formed from different color light emitters may occupy the same space, as represented by a single solid-lined circle 598 in the right waveguide 590B.

[0086] In one embodiment, waveguide portions 590A and 590B may be connected by a bridge waveguide (not shown). The bridge waveguide may permit light from the light emitter array set 596A to propagate from the waveguide portion 590A into the waveguide portion 590B. Similarly, the bridge waveguide may permit light emitted from the light emitter array set 596B to propagate from the waveguide portion 590B into the waveguide portion 590A. In some embodiments, the bridge waveguide portion may not include any decoupling elements, such that all light totally internally reflects within the waveguide portion. In other embodiments, the bridge waveguide portion 590C may include a decoupling area. In some embodiments, the bridge waveguide may be used to obtain light from both waveguide portions 590A and 590B and couple the obtained light to a detector (e.g. a photodetector), such as to detect image misalignment between the waveguide portions 590A and 590B.

Driving Circuit Signal Modulations

[0087] The driving circuit 370 modulates color dataset signals that are outputted from the image processing unit 375 and provides different driving currents to individual light emitters of the light source 340. In various embodiments, different modulation schemes may be used to drive the light emitters.

[0088] In one embodiment, the driving circuit 370 drives the light emitters using a modulation scheme that may be referred to as an “analog” modulation scheme in this disclosure. FIG. 6A is an illustrative diagram of the analog modulation scheme, in accordance with an embodiment. In the analog modulation scheme, the driving circuit 370 provides different levels of current to the light emitter, depending on the color value. The intensity of a light emitter can be adjusted based on the level of current provided to the light emitter. The current provided to the light emitter may be quantized into a pre-defined number of levels, such as 128 different levels, or, in some embodiments, may not be quantized. When the driving circuit 370 receives a color value, the driving circuit 370 adjusts the current provided to the light emitter to control the light intensity. For example, the overall color of a pixel location may be expressed as a color dataset that includes R, G, and B values. For the red light emitter, the driving circuit 370 provides a driving current based on the value of the R value. The higher the R value, the higher the current level is provided to the red light emitter, and vice versa. In total, the pixel location displays an additive color that is the sum of the R, G, and B values.

[0089] In another embodiment, the driving circuit 370 drives the light emitters using a modulation scheme that may be referred to as a “digital” modulation scheme in this disclosure. FIG. 6B is an illustrative diagram of the digital modulation scheme, in accordance with an embodiment. In the digital modulation scheme, the driving circuit 370 provides pulse width modulated (PWM) currents to drive the light emitters. The current level of the pulses is constant in a digital modulation scheme. The duty cycle of the driving current depends on the color value provided to the driving circuit. For example, when a color value for a light emitter is high, the duty cycle of the PWM driving current is also high compared to a driving current that corresponds to a low color value. In one case, the change in duty cycle can be managed through the number of potentially on intervals that are actually turned on. In a display period (e.g., a frame), there may be 128 pulses sent to the light emitters. For a color value that corresponds to 42/128 of the intensity, 42 out of the 128 pulses (potential-on intervals) are on in the period. As such, from the perspective of a human user, the pixel location has an intensity of that color 42/128 of the maximum intensity.

[0090] In yet another embodiment, the driving circuit 370 drives the light emitters using a modulation scheme that may be referred to as a hybrid modulation scheme. In the hybrid modulation scheme, for each primary color, at least two light emitters are used to generate the color value at a pixel location. The first light emitter is provided with a PWM current at a high current level while the second light emitter is provided with a PWM current at a low current level. The hybrid modulation scheme includes some features from the analog modulation and other features from the digital modulation. The details of the hybrid modulation scheme are explained in FIG. 6C.

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