Patent Description:
Generally, a full color high-resolution display can be realized by fabricating separate mono color displays for the three separate colors, namely red, green and blue, with different compound semiconductors and by overlaying the separate displays with an optical combiner. Such a technique can be effectively implemented for projection display systems, augmented reality display systems, virtual reality display systems and the like.

For example, the document <CIT> discloses a projection display system with separate light emitting diode display panels, where the corresponding emissions are combined on a beam combiner. In this context, the beam combiner includes one or more dichroic mirrors and one or more prisms. However, the foregoing arrangement is limited by size constraints, e.g., the size of the beam combiner, especially for augmented reality glasses. Moreover, in practice, there will be misalignment due to process and equipment limitations, especially between <NUM>-<NUM> micrometers in the packaging and placement process of the separate displays with the combiner. This will have a significant impact on the image quality and color mixing.

<CIT> discloses a display apparatus that includes an LED display unit comprising a plurality of LED display panels outputting light images.

<CIT> discloses a transparent display that combines Substrate Guided Optics (SGO) and Switchable Bragg Gratings (SBGs).

<CIT> discloses a scanning image display system that scans multiple incoming light beams at the same time and combines the individual fields of view into a larger composite field of view.

<CIT> discloses a display device that comprises one or more light emitters and a first waveguide disposed with respect to said one or more light emitters to receive light from said one or more light emitters.

<CIT> discloses an apparatus including (<NUM>) a plurality of monochromatic emitter arrays, where each of the plurality of monochromatic emitter arrays has a plurality of emitters disposed in a two-dimensional configuration and emits a monochromatic image of a corresponding color, (<NUM>) a waveguide configuration that includes (a) a top surface, (b) a bottom surface disposed opposite the top surface, (c) a coupling area that receives the monochromatic images, and (d) a decoupling area that projects a plurality of instances of a polychromatic image including a combination of the monochromatic images toward an eyebox through the bottom surface, and (<NUM>) an actuator system that produces lateral shifting of the plurality of instances of the polychromatic image between at least two positions relative to the waveguide configuration. In paragraph [<NUM>] it discloses a calibration and/or alignment system employed to align the multiple monochromatic images (e.g., via mechanical movement of one or more of the monochromatic emitter arrays or software movement of one or more of the monochromatic images by one or more pixels as emitted from their associated monochromatic emitter arrays) to produce a desired or intended, properly aligned polychromatic image.

Accordingly, the object of the invention is to provide methods for calibrating the said display systems, which can address the aforementioned limitations.

The object is solved by the features of the first and second independent claims. The dependent claims contain further developments.

According to an aspect not forming part of the claimed invention, a display system is provided. The display system comprises a first display die configured to emit light of a first color, a second display die configured to emit light of a second color and a third display die configured to emit light of a third color. In addition, the display system further comprises a lens system and an optical waveguide system, wherein the optical waveguide system comprises a first grating portion configured to couple in an incident light to the optical waveguide system and a second grating portion configured to couple out a transmitting light from the optical waveguide system.

Furthermore, the first display die, the second display die and the third display die are arranged in one package. Moreover, the lens system is arranged in between the package and the optical waveguide system, configured to collimate the light of first color, the light of second color and the light of third color onto the first grating portion of the optical waveguide system. Therefore, a display system is provided with a focal implementation for near eye displays, e.g., augmented reality glasses. Three separate display dies emit images with respective colors, i.e., red, green and blue, and are collimated with a common lens system. The collimated beams traverse through a waveguide system (total internal reflection) with localized grating portions acting as in and out couplers for the beams.

Preferably, the first grating portion is configured to couple in the light of first color, the light of second color and the light of third color to the optical waveguide system and the second grating portion is configured to couple out the light of first color, the light of second color and the light of third color from the optical waveguide system. Thus, the three mono color beams emitted from the three separate displays are collimated by the lens system and are coupled into the waveguide system by the first grating portion. When the beams hit the second grating portion, the beams are diffracted out of the waveguide system.

Preferably and advantageously, the optical waveguide system comprises at least three separate waveguides corresponding to the light of first color, the light of second color and the light of third color, whereby each separate waveguide comprises a first grating portion and a second grating portion in order to couple in and couple out the respective light. In a more preferred implementation, the structure of the first grating portion and the structure of the second grating portion are the same for each waveguide. Especially, the grating angle and grating spacing for the first and second grating portions of a waveguide are identical. In addition, the second grating portions of the separate waveguides for coupling out the respective light are preferably overlaid at the same location with respect to each other. However, the first grating portions of the separate waveguides for coupling in the respective light can be arranged either in an overlaying fashion or in respective separate locations, which correspond to the incidence locations for the collimated beam of lights on the waveguides.

Advantageously, the first display die, the second display die and the third display die are light emitting dies, preferably comprising arrays of microscopic light emitting diodes forming the individual pixel elements. In this context, the first display die, the second display die and the third display die comprise a driver circuit array including a plurality of pixel driver circuits, each being coupled to the individual pixel elements. This allows for micro-level fabrication of display emitter that can achieve a targeted pixel pitch between <NUM>-<NUM> micrometers for micro-LED displays on CMOS, especially for augmented or virtual reality applications.

According to another aspect not forming part of the claimed invention, another display system is provided. The display system comprises a first display die configured to emit light of a first color, a second display die configured to emit light of a second color and a third display die configured to emit light of a third color. The display system further comprises a first lens, a second lens and a third lens. Additionally, the display system comprises an optical waveguide system comprising a first grating portion configured to couple in an incident light to the optical waveguide system and a second grating portion configured to couple out a transmitting light from the optical waveguide system.

Furthermore, the first display die, the second display die and the third display die are arranged in three separate packages. Moreover, the first lens, the second lens and the third lens are arranged in between the packages and the optical waveguide system, whereby the first lens is configured to collimate the light of first color, the second lens is configured to collimate the light of second color and the third lens is configured to collimate the light of third color onto the first grating portion of the optical waveguide system.

Therefore, a display system is provided with a focal implementation for near eye displays, e.g., augmented reality glasses. Three separate display dies emit images with respective colors, i.e., red, green and blue, and are collimated with a respective lens. Moreover, the dies are arranged on three separate packages. This advantageously allows for a relaxed arrangement for the dies with respect to the waveguide system, especially regarding the spatial placement of the dies. The collimated beams traverse through the waveguide system with localized grating portions acting as in and out couplers for the beams.

Preferably, the first grating portion is configured to couple in the light of first color, the light of second color and the light of third color to the optical waveguide system and the second grating portion is configured to couple out the light of first color, the light of second color and the light of third color from the optical waveguide system. Thus, the three mono color beams emitted from the three separate displays are collimated by the respective lenses and are coupled into the waveguide system by the first grating portion. When the beams hit the second grating portion, the beams are diffracted out of the waveguide system.

Preferably and advantageously, the optical waveguide system comprises at least three separate waveguides corresponding to the light of first color, the light of second color and the light of third color, whereby each separate waveguide comprises a first grating portion and a second grating portion in order to couple in and couple out the respective light. This allows for an effective beam combination that can be realized on augmented or virtual reality glasses.

According to the invention, a method for calibrating a display system with a first display die configured to emit light of a first color, a second display die configured to emit light of a second color and a third display die configured to emit light of a third color with a driver circuit array is provided. The display dies being assembled onto an optical waveguide system with a lens system and a camera is placed in the eye box position.

The method comprises the step of optically measuring offsets corresponding to optical misalignments with respect to the optical waveguide system along at least two axes between the first display die, the second display die and the third display die by applying calibration images. The method further comprises the step of cropping an actual content to be displayed on the first display die, the second display die and the third display die by a scale based on the measured offsets, thereby generating respective modified contents.

Moreover, the method comprises the step of offsetting the modified contents corresponding to the measured offsets. Therefore, a calibration method is provided, especially concerning the integration of a micro-LED display onto an optical waveguide for augmented reality glasses. Advantageously, the calibration method can be realized as a pure software implementation in the external graphic and computation hardware without any significant alteration in the driver circuit or display design.

Preferably, the method comprises the step of optically measuring transversal and rotational offsets between the first display die, the second display die and the third display die. Furthermore, the method comprises the step of offsetting the modified contents corresponding to the measured transversal and rotational offsets. This allows for a comprehensive calibration of misalignments between the separate display dies, especially after the assembly process.

According to the invention, another method for calibrating a display system with a first display die configured to emit light of a first color, a second display die configured to emit light of a second color and a third display die configured to emit light of a third color with a driver circuit array is provided. The display dies being assembled onto an optical waveguide system with a lens system and a camera is placed in the eye box position.

The method comprises the step of adding additional addressable pixels along at least two axes on the first display die, the second display die and the third display die. The method further comprises the step of optically measuring offsets corresponding to optical misalignments with respect to the optical waveguide system along at least two axes between the first display die, the second display die and the third display die by applying calibration images.

Moreover, the method comprises the step of shifting an actual content to be displayed on the first display die, the second display die and the third display die corresponding to the measured offsets. Therefore, a calibration method is provided, especially concerning the integration of a micro-LED display onto an optical waveguide for augmented reality glasses. Advantageously, the calibration method can be performed within the display module comprising the separate display dies.

Preferably, the method comprises the step of optically measuring transversal and rotational offsets between the first display die, the second display die and the third display die. Furthermore, the method comprises the step of offsetting the actual content corresponding to the measured transversal and rotational offsets. This allows for a comprehensive calibration of misalignments between the separate display dies, especially after the assembly process.

Preferably, the method comprises the step of modifying the driver circuit array with respect to the additional addressable pixels along the two axes on the first display die, the second display die and the third display die. In addition, the method further comprises the step of controlling the driver circuit array in order to shift the actual content to be displayed on the first display die, the second display die and the third display die corresponding to the measured offsets.

In the following, parts of the description and drawings referring to embodiments, which are not covered by the claims, are not presented as embodiments of the invention, but as examples useful for understanding the invention. In the drawings:.

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings. However, the following embodiments of the present invention may be variously modified and the range of the present invention is not limited by the following embodiments.

In <FIG>, the general working principle of an augmented reality optics is illustrated. The arrangement <NUM> typically comprises an emitter <NUM> that emits an image to be projected. Such an emitter can be realized in the form of organic light emitting diode, quantum light emitting diode, micro-light emitting diode and the like. In addition, liquid crystal on silicon (LCOS) with LED light illumination, digital light processing (DLP) with LED light illumination and Laser scanning are examples of reflective displays with an illumination source operating in color sequences. The beam emitted from the emitter <NUM> is collimated via a lens <NUM> onto a glass plate <NUM>, effectively splitting the incident beam via beam splitters <NUM>.

As such, at each incident region, the glass plate <NUM> acts in both transmit mode and reflect mode. The beam <NUM> within the glass plate <NUM> traverses in a slanted fashion due to total internal reflection and is eventually split out from the plate <NUM> via beam splitters <NUM>. A viewer <NUM> in line with the split out beam therefore can see the virtual image <NUM> of the actual image that is being emitted by the emitter <NUM>.

In <FIG>, the system <NUM> is illustrated. In <FIG>, the display system <NUM> is implemented for augmented reality glasses, where three separate display dies <NUM>,<NUM>,<NUM> are integrated on an optical waveguide system <NUM> acting as a beam combiner. In <FIG>, it can be seen that the three separate display dies <NUM>,<NUM>,<NUM> emit light of respective colors <NUM>,<NUM>,<NUM>. For instance, the first display die <NUM> may emit light of red color <NUM>, the second display die <NUM> may emit light of blue color <NUM>, and the third display die <NUM> may emit light of green color <NUM>.

The system <NUM> comprises a lens system <NUM>, which can be implemented as a common lens system for the three separate display dies <NUM>,<NUM>,<NUM> or as an array of multiple lenses respective to each display die <NUM>,<NUM>,<NUM>. In either case, the lens system <NUM> collimates the lights onto the optical waveguide system <NUM>. In particular, the optical waveguide system <NUM> has a first grating portion <NUM> that acts as an in-coupler and a second grating portion <NUM> that acts as an out-coupler for the incident and transmitted light, respectively.

As can be seen in <FIG>, the optical waveguide system <NUM> is shown as three separate waveguides <NUM>,<NUM>,<NUM> for each color <NUM>,<NUM>,<NUM> attached above each other. Each separate waveguide <NUM>,<NUM>,<NUM> has a separate in-coupling area <NUM>,<NUM>,<NUM> and a separate out-coupling area <NUM>,<NUM>,<NUM> for each color <NUM>,<NUM>,<NUM>. The waveguide grating can be based on a surface grating, for instance, a surface relief grating in order tc achieve beam diffraction for the incident and transmitted light.

It is also conceivable that the optical waveguide system <NUM> may comprise only two separate waveguides for two colors and the third color can be split or combined with one of the two. For instance, the two separate waveguides can be implemented for the red color and the blue color. The green color can be either split between both waveguides or combined with one of the two. It is further conceivable that the optical waveguide system <NUM> may comprise only one waveguide, for instance, by means of volumetric holographic gratings provided by holographic optical elements or via surface microstructures at the coupling portions on the waveguide, thereby forming a single diffractive waveguide for all three colors <NUM>,<NUM>,<NUM>.

In <FIG>, an exemplary arrangement of the display dies <NUM>,<NUM>,<NUM> on a single package is illustrated. In particular, the display dies <NUM>,<NUM>,<NUM> are arranged on a rigid package that facilitates the implementation of a single collimating lens <NUM> as explained above. Preferably, each display die <NUM>,<NUM>,<NUM> comprises arrays of microscopic light emitting diodes forming the individual pixel elements. As such, each display die <NUM>,<NUM>,<NUM> has a respective emission area <NUM>,<NUM>,<NUM> that comprises the individual pixel elements.

In addition, each display die <NUM>,<NUM>,<NUM> comprises driver circuitry <NUM>,<NUM> including a plurality of pixel driver circuits, preferably distributed along two axes. Particularly, the driver array <NUM> that is distributed along the horizontal axis with respect to the die position may act as source driver and the driver array <NUM> that is distributed along the vertical axis with respect to the die position may act as gate driver for the respective pixel elements. The package is preferably realized on a PCB <NUM> where the separate dies <NUM>,<NUM>,<NUM> are arranged in close proximity.

Preferably, the three display dies <NUM>,<NUM>,<NUM> are fabricated with different compound semiconductors. For instance, the display die <NUM> corresponding to red color <NUM> may be fabricated with Aluminum Gallium Indium Phosphide (AlGaInP), the display die <NUM> corresponding to blue color <NUM> as well as the display die <NUM> corresponding to green color <NUM> may be fabricated with Indium Gallium Nitride (InGaN). The package includes a non-volatile memory <NUM>, e.g., a flash memory that can be used to store calibration data and images. Especially, the flash memory <NUM> stores optical and electrical calibration data for each pixel and may store additional pixel offset data generated by the proposed offset calibration schemes as described later, if required. A connector <NUM>, e.g., a flex-connector is also provided in order to communicate with, respectively, the display dies <NUM>,<NUM>,<NUM> and the PCB package <NUM>.

It is advantageous that the three separate display dies <NUM>,<NUM>,<NUM> (in short: RGB dies) are combined in one package and the respective light <NUM>,<NUM>,<NUM> (in short: RGB light) is collimated with the lens system <NUM> and coupled into the optical waveguide system <NUM>. At a respective out-coupling portion, the respective light <NUM>,<NUM>,<NUM> is coupled out within the field of view of an observer <NUM>. Any mutual misalignment between the RGB dies <NUM>,<NUM>,<NUM> typically arises from the packing into one package. Standard flip-chip technology allows a die placement with an accuracy of <NUM> micrometers bondpad pitch on a printed circuit board (PCB) or within a package. Advanced products using die-to-wafer flip-chip bonding may achieve a bonding accuracy to a bondpad pitch down to <NUM>-<NUM> micrometers in production. If an assumption is made for a target pitch of a micro-LED display of about <NUM> micrometers, a misplacement of <NUM>-<NUM> pixels of the RGB light can be anticipated as it couples out of the waveguide.

In <FIG>, a first exemplary system <NUM> is illustrated. The system <NUM> differs from the system <NUM> of <FIG> in that additional measures have been taken into consideration in the system <NUM> so that the separate display dies <NUM>,<NUM>,<NUM> can be placed with higher flexibility across the optical waveguide system <NUM> to allow a better form-factor. Particularly, it can be seen from <FIG> that the system <NUM> comprises three separate lenses, namely a first lens <NUM>, a second lens <NUM> and a third lens <NUM>, instead of a common single lens <NUM> as illustrated in <FIG> for beam collimation.

As such, the light of first color <NUM> emitted from the first display die <NUM> is collimated by the first lens <NUM> onto the first grating portion <NUM> of a waveguide <NUM> of the optical waveguide system <NUM>. Similarly, the light of second color <NUM> emitted from the second display die <NUM> is collimated by the second lens <NUM> onto the first grating portion <NUM> of a waveguide <NUM> of the optical waveguide system <NUM>. Further, the light of third color <NUM> emitted from the third display die <NUM> is collimated by the third lens <NUM> onto the first grating portion <NUM> of a waveguide <NUM> of the optical waveguide system <NUM>.

Advantageously, the separate display dies <NUM>,<NUM>,<NUM> are arranged in separate packages. Thus, each display die <NUM>,<NUM>,<NUM> can be separately placed with an own lens <NUM>,<NUM>,<NUM> onto the optical waveguide system <NUM>. Due to the compact size of the lenses <NUM>,<NUM>,<NUM> compared with the common lens system <NUM> of <FIG>, the display dies <NUM>,<NUM>,<NUM> can be placed across the optical waveguide system <NUM> with a greater flexibility.

In <FIG>, a second exemplary system <NUM> is illustrated. The system <NUM> differs from the system <NUM> of <FIG> in that the first display die <NUM>, the second display die <NUM> and the third display die <NUM> are adapted to emit the light of first color <NUM>, the light of second color <NUM> and the light of third color <NUM> respectively, which are already collimated. As such, the first display die <NUM> corresponds to the first display die <NUM> and the respective first lens <NUM>. Similarly, the second display die <NUM> corresponds to the second display die <NUM> and the respective second lens <NUM>. Further, the third display die <NUM> corresponds to the third display die <NUM> and the respective third lens <NUM>.

The combined effect of light emission and collimation (whereby every pixel is collimated but not necessarily all pixels emit with the same emission angle) can be achieved by integrating a wafer level lens onto the packaging of the separate display dies <NUM>,<NUM>,<NUM>. It is also conceivable that the first display die <NUM>, the second display die <NUM> and the third display die <NUM> can be realized in the form of a display that already emits collimated light, i.e., light emission with the same emission angle, in order to achieve the collimation effect. It is further conceivable that the first display die <NUM>, the second display die <NUM> and the third display die <NUM> may comprise arrays of microscopic light emitting diodes with a resonant cavity in order to achieve the collimation effect.

In <FIG>, an exemplary arrangement of the display dies <NUM>,<NUM>,<NUM> on separate packages is illustrated. Although the display dies <NUM>,<NUM>,<NUM> are referred to herein as the display dies <NUM>,<NUM>,<NUM> of <FIG>, it is to be understood that the said arrangement is also compatible with the display dies <NUM>,<NUM>,<NUM> of <FIG>. Similar to <FIG>, the first display die <NUM>, the second display die <NUM> and the third display die <NUM> comprise arrays of microscopic light emitting diodes forming the individual pixel elements. As such, each display die <NUM>,<NUM>,<NUM> has a respective emission area <NUM>,<NUM>,<NUM> that comprises the individual pixel elements.

In addition, each display die <NUM>,<NUM>,<NUM> comprises driver circuitry <NUM>,<NUM> including a plurality of pixel driver circuits, preferably distributed along two axes. Particularly, the driver array <NUM> that is distributed along the horizontal axis with respect to the die position may act as source driver and the driver array <NUM> that is distributed along the vertical axis with respect to the die position may act as gate driver for the respective pixel elements.

As it can be seen in <FIG>, the first display die <NUM> is arranged on a first PCB package <NUM>, the second display die <NUM> is arranged on a second PCB package <NUM> and the third display die <NUM> is arranged on a third PCB package <NUM>. Thus, the separate display dies <NUM>,<NUM>,<NUM> are arranged on separate packages <NUM>,<NUM>,<NUM> in order to facilitate the implementation of three separate respective lenses <NUM>,<NUM>,<NUM>, thereby allowing a much more relaxed positioning of the display dies <NUM>,<NUM>,<NUM> as explained above. The separate display dies <NUM>,<NUM>,<NUM> are interconnected via a connector <NUM>, e.g., a flex-connector, which further connects the display dies <NUM>,<NUM>,<NUM> to a power source, an external graphic processor or/and an additional non-volatile memory <NUM> containing calibration data, e.g., a flash memory.

As mentioned above, the integration of separate display dies <NUM>,<NUM>,<NUM> onto an optical waveguide system <NUM> would raise misalignments due to process and equipment limitations, especially between <NUM>-<NUM> micrometers in the packaging and placement process of the display dies <NUM>,<NUM>,<NUM> with the waveguide system <NUM>. In order to calibrate those misalignments away after the assembly process, the invention proposes two calibration methods based on depth system design modifications. In both cases, the misalignments or offsets are measured optically after the assembly process and are stored in the memory, e.g., the flash memory <NUM>, as calibration data.

In <FIG>, exemplary calibration sequences are illustrated in order to determine misalignments or offsets. It is to be noted that the calibration sequences are applicable for all display systems <NUM>,<NUM>,<NUM> described along <FIG>, <FIG> and <FIG> respectively. In order to initiate the sequences, the separate display dies <NUM>,<NUM>,<NUM> are assembled onto the optical waveguide system <NUM> along with the lens system <NUM> or separate respective lenses <NUM>,<NUM>,<NUM>, and a high-resolution camera is placed in the eye box position <NUM>.

Thus, in a first step S71, the optical waveguide system <NUM> with lens system <NUM> or lenses <NUM>,<NUM>,<NUM> and the separate display dies <NUM>,<NUM>,<NUM> are assembled. In a second step S72, the high-definition camera is focused in the field of view of the optical waveguide system <NUM>. In a third step S73, a calibration image or pattern is applied for the display die <NUM>, i.e., the second display die <NUM>, which is adapted to emit the image in blue color <NUM>. The image is then centered with respect to the dimension of the second display die <NUM>. The optically measured offset along the horizontal axis X and along the vertical axis Y of the second display die <NUM> is stored as well as the relative transversal and rotational offsets in the flash memory <NUM>.

In a subsequent fourth step S74, the calibration image is further applied for the display die <NUM>, i.e., the third display die <NUM>, which is adapted to emit the image in green color <NUM>, and is overlaid onto the second display die <NUM> of the previous step S73. The green image is shifted along the horizontal axis x and the vertical axis y with respect to the third display die <NUM> until the green image overlaps with the blue image. Then, the green image is switched off, and the optically measured offset along the horizontal axis X and along the vertical axis Y of the second display die <NUM> is stored as well as the relative transversal and rotational offsets in the flash memory <NUM>.

Finally, in a fifth step S75, the calibration image is further applied for the display die <NUM>, i.e., the first display die <NUM>, which is adapted to emit the image in red color <NUM>, and is overlaid onto the second display die <NUM> of the step S73. The red image is shifted along the horizontal axis x and the vertical axis y with respect to the first display die <NUM> until the red image overlaps with the blue image. Then, the optically measured offset along the horizontal axis X and along the vertical axis Y of the second display die <NUM> is stored as well as the relative transversal and rotational offsets in the flash memory <NUM>.

In <FIG>, exemplary calibration patterns or images are illustrated in order to determine misalignments. At the top left of <FIG>, a calibration pattern <NUM> of a hollow square is shown, which is aligned at the center of the display dimensions. At the top right of <FIG>, a calibration pattern <NUM> of two parallel vertical lines is shown, which are aligned at the center with respect to the horizontal dimension of the display. Furthermore, at the bottom left of <FIG>, a calibration pattern <NUM> of a diagonal line is shown, which is aligned at the center with respect to the horizontal dimension of the display, starting from the left top corner to the right bottom corner of the display. Finally, at the bottom right of <FIG>, a calibration pattern <NUM> of two parallel horizontal lines is shown, which are aligned at the center with respect to the vertical dimension of the display.

In <FIG>, an exemplary embodiment of the method according to the invention is illustrated. In a first step S91, offsets along at least two axes between the first display die, the second display die and the third display die are optically measured by applying calibration images. In a second step S92, an actual content to be displayed on the first display die, the second display die and the third display die is cropped by a scale based on the measured offsets, thereby generating respective modified contents. Finally, in a third step S93, the modified contents are offset corresponding to the measured offsets.

In <FIG>, an exemplary active matrix addressing of display according to the invention is illustrated. The main advantage of this calibration method is that no change in the driver or display design is required and all calibration is done as a pure software implementation in the external graphic (GPU) and computation (CPU) hardware. Generally, the data stream from the GPU is in a standard video stream format, e.g., Mobile Industry Processor Interface (MIPI), High-Definition Multimedia Interface (HDMI), and so on. These are configured for a defined frame output format, e.g., a Full High-Definition (FHD) 1920x1280x3, a VGA, 4K2K, etc. with a defined frame rate, e.g., <NUM> frames per second, <NUM> frames per second, and so on, and a defined grey level depth per color, e.g., <NUM> bit, <NUM> bit, <NUM> bit, and the like.

In order to calibrate the output of three separate display dies <NUM>,<NUM>,<NUM> (i.e., RGB dies), which are overlapping pixel by pixel, the calibration method foresees the reduction of frame size (i.e., cut away) of the actual content to be shown and offsetting the misalignment in the software. For instance, <FIG> shows a display <NUM> with the frame size 10x10 pixels, i.e., a horizontal dimension Xpix of <NUM> pixels and a vertical dimension Ypix of <NUM> pixels. <FIG> further shows the driver circuitry, especially the source driver <NUM> and the gate driver <NUM> to drive each respective pixel element of the display <NUM>.

For this example, it is considered that the measured misalignment, e.g., obtained from the calibration sequence described in <FIG>, is <NUM> pixels along the vertical axis, i.e., dX, and is <NUM> pixels along the horizontal axis, i.e., dY. In order to calibrate the misalignments away, the actual shown content is cropped to 5x5 pixels whereby all other pixels are set off. This results in the modified content <NUM>, having a horizontal dimension Xcon of <NUM> pixels and a vertical dimension Ycon of <NUM> pixels. For every frame that is sent from the GPU to the display <NUM>, the computation is performed to satisfy that the actual content is cropped and the modified content <NUM> is offset by a dX,dY value for every color corresponding to the actual measured offset between the RGB dies <NUM>,<NUM>,<NUM>.

In <FIG>, a further exemplary embodiment of the method according to the invention is illustrated. In a first step S111, offsets along at least two axes between the first display die, the second display die and the third display die are optically measured by applying calibration images. In a second step S112, additional addressable pixels are added along the two axes on the first display die, the second display die and the third display die based on the measured offsets. Finally, in a third step S113, an actual content to be displayed on the first display die, the second display die and the third display die is shifted corresponding to the measured offsets.

In <FIG>, an exemplary active matrix addressing of display according to the invention is illustrated. The calibration method requires changes in display and display driver design and all calibration is done within the display module itself. It is assumed that the standard frame size of the intended data format is 10x10 pixels, i.e., the horizontal dimension Xcon of the actual content <NUM> is <NUM> pixels and the vertical dimension Ycon of the actual content <NUM> is <NUM> pixels. The source driver <NUM> and the gate driver <NUM> are present in order to address their respective pixel elements.

For this example, it is considered that the measured misalignment, e.g., obtained from the calibration sequence described along <FIG>, is <NUM> pixels along the vertical axis, i.e., dX, and is <NUM> pixels along the horizontal axis, i.e., dY. In order to calibrate the misalignments away, <NUM> additional pixels are added along the horizontal axis X and the vertical axis Y of the display <NUM>, that result in an extended display <NUM> with a horizontal dimension of:<MAT> and a vertical dimension of:<MAT>.

Therefore, it is required to add a modified gate driver and a modified source driver respect to the Xpix_ext and Ypix_ext for the larger size display <NUM>. Since the actual content <NUM> is smaller, it is undesirable to drive and update the full display. Hence, only the section that contains the actual data content <NUM> is driven and updated in order to avoid additional flicker caused by the drive circuits <NUM>, <NUM>.

In order to modify the source driver <NUM> and the gate driver <NUM>, respective specific multiplexers <NUM>,<NUM> are implemented. Particularly, the multiplexer <NUM> implemented to the source driver <NUM> simply shifts which pixels get which data content. On the gate driver <NUM> side, the multiplexer <NUM> is configured to shift the reset signal to the first shift register that gets actually activated and comprises a separate counter to reset after the horizontal pixel lines, e.g., <NUM> pixels, are addressed.

The calibration method of <FIG> is more cost-effective than the method of <FIG>. However, the calibration method of <FIG> is more effective with respect to performance and image rendering than the method of <FIG>. Nonetheless, both calibration methods relax the requirements for the placement and bonding accuracy of the RGB dies with respect to each other and the waveguide to more realistic values that can be implemented in production.

Various embodiments of the present invention may be implemented by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, or the like.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Numerous changes to the disclosed embodiments can be made in accordance with the disclosure herein without departing from the scope of the invention. Thus, the scope of the present invention should not be limited by any of the above described embodiments. Rather, the scope of the invention should be defined in accordance with the following claims.

Claim 1:
A method for calibrating a display system with a first display die (<NUM>) configured to emit light of a first color, a second display die (<NUM>) configured to emit light of a second color, a third display die (<NUM>) configured to emit light of a third color, and a driver circuit array (<NUM>,<NUM>), the display dies (<NUM>, <NUM>, <NUM>) being assembled onto an optical waveguide system (<NUM>) with a lens system (<NUM>) and a camera being placed in an eye box position (<NUM>), the method comprising the steps of:
optically measuring offsets corresponding to optical misalignments with respect to the optical waveguide system (<NUM>) along at least two axes for the first display die (<NUM>), the second display die (<NUM>) and the third display die (<NUM>) by applying calibration images,
cropping an actual content to be displayed on the first display die (<NUM>), the second display die (<NUM>) and the third display die (<NUM>) by a scale based on the measured offsets, thereby generating respective modified contents, and
offsetting the modified contents corresponding to the measured offsets.