PATENT DOCUMENT

Publication Number: US-11804197-B1
Application Number: US-202117459731-A
Country: US
Kind Code: B1

Title: Optical systems having overdriven fLCOS display panels

Abstract:
A display may include illumination optics, a ferroelectric liquid crystal on silicon (fLCOS) panel, and a waveguide. The display may include a temperature sensor that gathers temperature sensor data. Control circuitry may select a non-square wave drive voltage waveform based on the gathered temperature sensor data and/or based on frame history information for the fLCOS display panel. The control circuitry may control the fLCOS panel to produce image light by driving the fLCOS panel using the selected non-square wave drive voltage waveform. The non-square wave drive voltage waveform may be an overdrive waveform or an underdrive waveform. This may serve to optimize the reflectance of the fLCOS display panel and thus the optical performance of the display module regardless of operating temperature and frame history.

Claims:
What is claimed is: 
     
       1. An electronic device comprising:
 a light source configured to produce illumination; 
 a reflective panel configured to produce light based on the illumination and image data; 
 a waveguide configured to propagate the light via total internal reflection; and 
 a temperature sensor configured to gather temperature sensor data, wherein the reflective panel is configured to produce the light using a non-square wave drive voltage waveform that has a first shape when the temperature sensor data is at a first level and that has a second shape that is different from the first shape when the temperature sensor data is at a second level. 
 
     
     
       2. The electronic device of  claim 1 , wherein the non-square wave drive voltage waveform is selected based on an estimated temperature of the reflective panel identified based on the temperature sensor data. 
     
     
       3. The electronic device of  claim 1 , further comprising an additional temperature sensor configured to gather additional temperature sensor data, wherein the non-square wave drive voltage waveform is selected based on the additional temperature sensor data. 
     
     
       4. The electronic device of  claim 1 , wherein the reflective panel is configured to be overdriven using the selected non-square wave drive voltage waveform. 
     
     
       5. The electronic device of  claim 1 , wherein the reflective panel is configured to be underdriven using the selected non-square wave drive voltage waveform. 
     
     
       6. The electronic device of  claim 1 , wherein the non-square wave drive voltage waveform is selected from a set of predetermined non-square wave drive voltage waveforms stored on the electronic device. 
     
     
       7. The electronic device of  claim 1 , wherein the non-square wave drive voltage waveform is selected based at least in part on frame history information for the reflective panel. 
     
     
       8. The electronic device of  claim 1 , wherein the non-square wave drive voltage waveform has a peak voltage level that is greater than or equal to 1.8V. 
     
     
       9. An electronic device comprising:
 a light source configured to produce illumination; 
 a reflective panel configured to produce light by modulating the illumination using image data; and 
 a waveguide configured to propagate the light via total internal reflection, wherein the reflective panel is configured to produce the light using a non-square wave drive voltage waveform that is based on frame history information associated with the image data. 
 
     
     
       10. The electronic device of  claim 9 , wherein the reflective panel is configured to produce the light using a first non-square wave drive voltage waveform when the frame history information identifies that a previous image frame displayed by the reflective panel was on for a first percentage of a corresponding illumination time and wherein the reflective panel is configured to produce the light using a second non-square drive voltage waveform when the frame history information identifies that the previous image frame displayed by the reflective panel was on for a second percentage of the illumination time that is different from the first percentage of the illumination time. 
     
     
       11. The electronic device of  claim 9 , wherein the reflective panel is configured to be overdriven using the non-square wave drive voltage waveform. 
     
     
       12. The electronic device of  claim 9 , wherein the reflective panel is configured to be underdriven using the non-square wave drive voltage waveform. 
     
     
       13. The electronic device of  claim 9 , wherein the non-square wave drive voltage waveform is selected from a set of predetermined non-square wave drive voltage waveforms stored on the electronic device. 
     
     
       14. The electronic device of  claim 13 , wherein the set of predetermined non-square wave drive voltage waveforms are stored in a look-up table on the electronic device. 
     
     
       15. The electronic device of  claim 9 , wherein the non-square wave drive voltage waveform has a peak voltage level that is greater than or equal to 1.8V. 
     
     
       16. The electronic device of  claim 9 , wherein the reflective panel is configured to produce additional light using a square wave drive voltage waveform. 
     
     
       17. The electronic device of  claim 16 , wherein the reflective panel exhibits greater reflectance when driven by the selected non-square wave drive voltage waveform than when driven by the square wave drive voltage waveform. 
     
     
       18. An electronic device comprising:
 a light source configured to produce illumination; 
 a reflective panel configured to produce light by modulating the illumination using image data; 
 a waveguide configured to propagate the light via total internal reflection; and 
 a temperature sensor configured to gather temperature sensor data, wherein the reflective panel has a dark gap that is adjusted by driving the reflective panel with a first overdrive waveform when the temperature sensor data has a first level and by driving the reflective panel with a second overdrive waveform that is different from the first overdrive waveform when the temperature sensor data has a second level that is different from the first level.

Description:
This application claims the benefit of U.S. Provisional Patent Application No. 63/072,009, filed Aug. 28, 2020, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to optical systems and, more particularly, to optical systems for displays. 
     Electronic devices may include displays that present images to a user&#39;s eyes. For example, devices such as virtual reality and augmented reality headsets may include displays with optical elements that allow users to view the displays. 
     It can be challenging to design devices such as these. If care is not taken, the components used in displaying content may be unsightly and bulky, can consume excessive power, and may not exhibit desired levels of optical performance. 
     SUMMARY 
     An electronic device such as a head-mounted device may have one or more near-eye displays that produce images for a user. The head-mounted device may be a pair of virtual reality glasses or may be an augmented reality headset that allows a viewer to view both computer-generated images and real-world objects in the viewer&#39;s surrounding environment. 
     The display may include a display module and a waveguide. The display module may include a spatial light modulator such as a ferroelectric liquid crystal on silicon (fLCOS) display panel and illumination optics. The illumination optics may include light sources such as light emitting diodes (LEDs) that produce illumination light. The illumination light may be provided with a linear polarization and may be transmitted to the fLCOS display panel. The fLCOS display panel may modulate image data (e.g., image frames) onto the illumination light to produce image light. The waveguide may direct the image light towards an eye box. 
     The display may include a temperature sensor that gathers temperature sensor data. Control circuitry may select a non-square wave drive voltage waveform based on the gathered temperature sensor data and/or based on frame history information for the fLCOS display panel. The control circuitry may control the fLCOS panel to produce the image light by driving the fLCOS panel using the selected non-square wave drive voltage waveform. The non-square wave drive voltage waveform may be an overdrive waveform or an underdrive waveform. This may serve to optimize the reflectance of the fLCOS display panel and thus the optical performance of the display module regardless of operating temperature and frame history. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram of an illustrative system having a display in accordance with some embodiments. 
         FIG.  2    is a top view of an illustrative optical system for a display having a display module that provides image light to a waveguide in accordance with some embodiments. 
         FIG.  3    is a top view of an illustrative display module having a ferroelectric liquid crystal on silicon (fLCOS) display panel in accordance with some embodiments. 
         FIG.  4    is a timing diagram of illustrative driving voltages that may be used to drive an fLCOS display panel in accordance with some embodiments. 
         FIG.  5    is a timing diagram showing how an illustrative fLCOS display panel may be overdriven by a non-square wave driving voltage waveform in accordance with some embodiments. 
         FIG.  6    is a flow chart of illustrative steps that may be involved in overdriving an fLCOS display panel based on temperature sensor measurements in accordance with some embodiments. 
         FIG.  7    is a flow chart of illustrative steps that may be involved in overdriving an fLCOS display panel based on frame history information in accordance with some embodiments. 
         FIG.  8    is a plot of fLCOS performance (response time as a function of temperature) that shows how overdriving an fLCOS display panel based on temperature sensor measurements may minimize fLCOS response time in accordance with some embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     An illustrative system having a device with one or more near-eye display systems is shown in  FIG.  1   . System  10  may be a head-mounted device having one or more displays such as near-eye displays  14  mounted within support structure (housing)  20 . Support structure  20  may have the shape of a pair of eyeglasses (e.g., supporting frames), may form a housing having a helmet shape, or may have other configurations to help in mounting and securing the components of near-eye displays  14  on the head or near the eye of a user. Near-eye displays  14  may include one or more display modules such as display modules  14 A and one or more optical systems such as optical systems  14 B. Display modules  14 A may be mounted in a support structure such as support structure  20 . Each display module  14 A may emit light  22  (sometimes referred to herein as image light  22 ) that is redirected towards a user&#39;s eyes at eye box  24  using an associated one of optical systems  14 B. 
     The operation of system  10  may be controlled using control circuitry  16 . Control circuitry  16  may include storage and processing circuitry for controlling the operation of system  10 . Circuitry  16  may include storage such as hard disk drive storage, nonvolatile memory (e.g., electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Processing circuitry in control circuitry  16  may be based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio chips, graphics processing units, application specific integrated circuits, and other integrated circuits. Software code (instructions) may be stored on storage in circuitry  16  and run on processing circuitry in circuitry  16  to implement operations for system  10  (e.g., data gathering operations, operations involving the adjustment of components using control signals, image rendering operations to produce image content to be displayed for a user, etc.). 
     System  10  may include input-output circuitry such as input-output devices  12 . Input-output devices  12  may be used to allow data to be received by system  10  from external equipment (e.g., a tethered computer, a portable device such as a handheld device or laptop computer, or other electrical equipment) and to allow a user to provide head-mounted device  10  with user input. Input-output devices  12  may also be used to gather information on the environment in which system  10  (e.g., head-mounted device  10 ) is operating. Output components in devices  12  may allow system  10  to provide a user with output and may be used to communicate with external electrical equipment. Input-output devices  12  may include sensors and other components  18  (e.g., image sensors for gathering images of real-world object that are digitally merged with virtual objects on a display in system  10 , accelerometers, depth sensors, light sensors, haptic output devices, speakers, batteries, wireless communications circuits for communicating between system  10  and external electronic equipment, etc.). In one suitable arrangement that is sometimes described herein as an example, the sensors in components  18  may include one or more temperature (T) sensors  19 . Temperature sensor(s)  19  may gather temperature sensor data (e.g., temperature values) from one or more locations in system  10 . If desired, control circuitry  16  may use the gathered temperature sensor data in controlling the operation of display module  14 A. 
     Display modules  14 A (sometimes referred to herein as display engines  14 A, light engines  14 A, or projectors  14 A) may include reflective displays (e.g., displays with a light source that produces illumination light that reflects off of a reflective display panel to produce image light such as liquid crystal on silicon (LCOS) displays (e.g., ferroelectric liquid crystal on silicon (fLCOS) displays), digital-micromirror device (DMD) displays, or other spatial light modulators), emissive displays (e.g., micro-light-emitting diode (uLED) displays, organic light-emitting diode (OLED) displays, laser-based displays, etc.), or displays of other types. An arrangement in which display module  14 A includes an fLCOS display is sometimes described herein as an example. Light sources in display modules  14 A may include uLEDs, OLEDs, LEDs, lasers, combinations of these, or any other desired light-emitting components. 
     Optical systems  14 B may form lenses that allow a viewer (see, e.g., a viewer&#39;s eyes at eye box  24 ) to view images on display(s)  14 . There may be two optical systems  14 B (e.g., for forming left and right lenses) associated with respective left and right eyes of the user. A single display  14  may produce images for both eyes or a pair of displays  14  may be used to display images. In configurations with multiple displays (e.g., left and right eye displays), the focal length and positions of the lenses formed by components in optical system  14 B may be selected so that any gap present between the displays will not be visible to a user (e.g., so that the images of the left and right displays overlap or merge seamlessly). 
     If desired, optical system  14 B may contain components (e.g., an optical combiner, etc.) to allow real-world image light from real-world images or objects  25  to be combined optically with virtual (computer-generated) images such as virtual images in image light  22 . In this type of system, which is sometimes referred to as an augmented reality system, a user of system  10  may view both real-world content and computer-generated content that is overlaid on top of the real-world content. Camera-based augmented reality systems may also be used in device  10  (e.g., in an arrangement in which a camera captures real-world images of object  25  and this content is digitally merged with virtual content at optical system  14 B). 
     System  10  may, if desired, include wireless circuitry and/or other circuitry to support communications with a computer or other external equipment (e.g., a computer that supplies display  14  with image content). During operation, control circuitry  16  may supply image content to display  14 . The content may be remotely received (e.g., from a computer or other content source coupled to system  10 ) and/or may be generated by control circuitry  16  (e.g., text, other computer-generated content, etc.). The content that is supplied to display  14  by control circuitry  16  may be viewed by a viewer at eye box  24 . 
       FIG.  2    is a top view of an illustrative display  14  that may be used in system  10  of  FIG.  1   . As shown in  FIG.  2   , display  14  may include one or more display modules such as display module  14 A and an optical system such as optical system  14 B. Optical system  14 B may include optical elements such as one or more waveguides  26 . Waveguide  26  may include one or more stacked substrates (e.g., stacked planar and/or curved layers sometimes referred to herein as waveguide substrates) of optically transparent material such as plastic, polymer, glass, etc. 
     If desired, waveguide  26  may also include one or more layers of holographic recording media (sometimes referred to herein as holographic media, grating media, or diffraction grating media) on which one or more diffractive gratings are recorded (e.g., holographic phase gratings, sometimes referred to herein as holograms). A holographic recording may be stored as an optical interference pattern (e.g., alternating regions of different indices of refraction) within a photosensitive optical material such as the holographic media. The optical interference pattern may create a holographic phase grating that, when illuminated with a given light source, diffracts light to create a three-dimensional reconstruction of the holographic recording. The holographic phase grating may be a non-switchable diffractive grating that is encoded with a permanent interference pattern or may be a switchable diffractive grating in which the diffracted light can be modulated by controlling an electric field applied to the holographic recording medium. Multiple holographic phase gratings (holograms) may be recorded within (e.g., superimposed within) the same volume of holographic medium if desired. The holographic phase gratings may be, for example, volume holograms or thin-film holograms in the grating medium. The grating media may include photopolymers, gelatin such as dichromated gelatin, silver halides, holographic polymer dispersed liquid crystal, or other suitable holographic media. 
     Diffractive gratings on waveguide  26  may include holographic phase gratings such as volume holograms or thin-film holograms, meta-gratings, or any other desired diffractive grating structures. The diffractive gratings on waveguide  26  may also include surface relief gratings formed on one or more surfaces of the substrates in waveguides  26 , gratings formed from patterns of metal structures, etc. The diffractive gratings may, for example, include multiple multiplexed gratings (e.g., holograms) that at least partially overlap within the same volume of grating medium (e.g., for diffracting different colors of light and/or light from a range of different input angles at one or more corresponding output angles). 
     Optical system  14 B may include collimating optics such as collimating lens  34 . Collimating lens  34  may include one or more lens elements that help direct image light  22  towards waveguide  26 . Collimating lens  34  is shown external to display module  14 A in  FIG.  2    for the sake of clarity. In general, collimating lens  34  may be formed entirely external to display module  14 A, entirely within display module  14 A, or one or more lens elements in collimating lens  34  may be formed in display module  14 A (e.g., collimating lens  34  may include both lens elements that are internal to display module  14 A and lens elements that are external to display module  14 A). Collimating lens  34  may be omitted if desired. If desired, display module(s)  14 A may be mounted within support structure  20  of  FIG.  1    while optical system  14 B may be mounted between portions of support structure  20  (e.g., to form a lens that aligns with eye box  24 ). Other mounting arrangements may be used, if desired. 
     As shown in  FIG.  2   , control circuitry  16  may control display module  14 A to generate image light  22  associated with image content (data) to be displayed to (at) eye box  24 . In the example of  FIG.  2   , display module  14 A includes illumination optics  36  and a spatial light modulator such as fLCOS display panel  40  (sometimes referred to herein simply as fLCOS panel  40 ). 
     Control circuitry  16  may be coupled to illumination optics  36  over control path(s)  42 . Control circuitry  16  may be coupled to fLCOS panel  40  over control path(s)  44 . Control circuitry  16  may provide control signals to illumination optics  36  over control path(s)  42  that control illumination optics  36  to produce illumination light  38  (sometimes referred to herein as illumination  38 ). The control signals may, for example, control illumination optics  36  to produce illumination light  38  using a corresponding illumination sequence. The illumination sequence may involve sequentially illuminating light sources of different colors in illumination optics  36 . In one suitable arrangement that is sometimes described herein as an example, the illumination sequence may be a green-heavy illumination sequence. 
     Illumination optics  36  may illuminate fLCOS display panel  40  using illumination light  38 . Control circuitry  16  may provide control signals to fLCOS display panel  40  over control path(s)  44  that control fLCOS display panel  40  to modulate illumination light  38  to produce image light  22 . For example, control circuitry  16  may provide image data such as image frames to fLCOS display panel  40 . The image light  22  produced by fLCOS display panel  40  may include the image frames identified by the image data. Control circuitry  16  may, for example, control fLCOS display panel  40  to provide fLCOS drive voltage waveforms to electrodes in the display panel. The fLCOS drive voltage waveforms may be overdriven or underdriven to optimize the performance of display module  14 A, if desired. While an arrangement in which display module  14 A includes fLCOS display panel  40  is described herein as an example, in general, display module  14 A may include any other desired type of reflective display panel (e.g., a DMD panel), an emissive display panel, etc. 
     Image light  22  may be collimated using collimating lens  34  (sometimes referred to herein as collimating optics  34 ). Optical system  14 B may be used to present image light  22  output from display module  14 A to eye box  24 . Optical system  14 B may include one or more optical couplers such as input coupler  28 , cross-coupler  32 , and output coupler  30 . In the example of  FIG.  2   , input coupler  28 , cross-coupler  32 , and output coupler  30  are formed at or on waveguide  26 . Input coupler  28 , cross-coupler  32 , and/or output coupler  30  may be completely embedded within the substrate layers of waveguide  26 , may be partially embedded within the substrate layers of waveguide  26 , may be mounted to waveguide  26  (e.g., mounted to an exterior surface of waveguide  26 ), etc. 
     The example of  FIG.  2    is merely illustrative. One or more of these couplers (e.g., cross-coupler  32 ) may be omitted. Optical system  14 B may include multiple waveguides that are laterally and/or vertically stacked with respect to each other. Each waveguide may include one, two, all, or none of couplers  28 ,  32 , and  30 . Waveguide  26  may be at least partially curved or bent if desired. 
     Waveguide  26  may guide image light  22  down its length via total internal reflection. Input coupler  28  may be configured to couple image light  22  from display module(s)  14 A into waveguide  26  (e.g., at an angle such that the image light can propagate down waveguide  26  via total internal reflection), whereas output coupler  30  may be configured to couple image light  22  from within waveguide  26  to the exterior of waveguide  26  and towards eye box  24 . Input coupler  28  may include a reflective or transmissive input coupling prism if desired. As an example, display module(s)  14 A may emit image light  22  in the +Y direction towards optical system  14 B. 
     When image light  22  strikes input coupler  28 , input coupler  28  may redirect image light  22  so that the light propagates within waveguide  26  via total internal reflection towards output coupler  30  (e.g., in the +X direction). When image light  22  strikes output coupler  30 , output coupler  30  may redirect image light  22  out of waveguide  26  towards eye box  24  (e.g., back in the −Y direction). In scenarios where cross-coupler  32  is formed at waveguide  26 , cross-coupler  32  may redirect image light  22  in one or more directions as it propagates down the length of waveguide  26 , for example. In this way, display module  14 A may provide image light  22  to eye box  24  over an optical path that extends from display module  14 A, through collimating lens  34 , input coupler  28 , cross coupler  32 , and output coupler  30 . 
     Input coupler  28 , cross-coupler  32 , and/or output coupler  30  may be based on reflective and refractive optics or may be based on holographic (e.g., diffractive) optics. In arrangements where couplers  28 ,  30 , and  32  are formed from reflective and refractive optics, couplers  28 ,  30 , and  32  may include one or more reflectors (e.g., an array of micromirrors, partial mirrors, louvered mirrors, or other reflectors). In arrangements where couplers  28 ,  30 , and  32  are based on holographic optics, couplers  28 ,  30 , and  32  may include diffractive gratings (e.g., volume holograms, surface relief gratings, etc.). 
       FIG.  3    is a top view of display module  14 A. As shown in  FIG.  3   , display module  14 A may include illumination optics  36  that provide illumination light  38  to fLCOS display panel  40 . fLCOS display panel  40  may modulate images onto illumination light  38  to produce image light  22 . 
     Illumination optics  36  may include one or more light sources  48  such as a first light source  48 A, a second light source  48 B, and a third light source  48 C. Light sources  48  may emit illumination light  52 . Prism  46  (e.g., an X-plate) in illumination optics  36  may combine the illumination light  52  emitted by each of the light sources  48  to produce the illumination light  38  that is provided to fLCOS display panel  40 . In one suitable arrangement that is sometimes described herein as an example, first light source  48 A emits red illumination light  52 A (e.g., light source  48 A may be a red (R) light source), second light source  48 B emits green illumination light  52 B (e.g., light source  48 B may be a green (G) light source), and third light source  48 C emits blue illumination light  52 C (e.g., light source  48 C may be a blue (B) light source). This is merely illustrative. In general, light sources  48 A,  48 B, and  48 C may respectively emit light in any desired wavelength bands (e.g., visible wavelengths, infrared wavelengths, near-infrared wavelengths, etc.). 
     An arrangement in which illumination optics  36  includes only one light source  48 A, one light source  48 B, and one light source  48 C is sometimes described herein as an example. This is merely illustrative. If desired, illumination optics  36  may include any desired number of light sources  48 A (e.g., an array of light sources  48 A), any desired number of light sources  48 B (e.g., an array of light sources  48 B), and any desired number of light sources  48 C (e.g., an array of light sources  48 C). Light sources  48 A,  48 B, and  48 C may include LEDs, OLEDs, uLEDs, lasers, or any other desired light sources. An arrangement in which light sources  48 A,  48 B, and  48 C are LED light sources is described herein as an example. Light sources  48 A,  48 B, and  48 C may be controlled (e.g., separately/independently controlled) by control signals received from control circuitry  16  ( FIG.  2   ) over control path(s)  42 . The control signals may, for example, control light sources  48 A,  48 B, and  48 C to emit illumination light  52  using a corresponding illumination sequence in which one or more of the light sources emits illumination light at any given time and the active light sources cycle over time. 
     Illumination light  38  may include the illumination light  52 A,  52 B, and  52 C emitted by light sources  48 A,  48 B, and  48 C, respectively. Prism  50  may provide illumination light  38  to fLCOS display panel  40 . If desired, additional optical components such as lens elements, microlenses, polarizers, prisms, beam splitters, and/or diffusers (not shown in  FIG.  3    for the sake of clarity) may be optically interposed between light sources  48 A-C and fLCOS display panel  40  to help direct illumination light  38  from illumination optics  36  to fLCOS display panel  40 . 
     Prism  50  may direct illumination light  38  onto fLCOS display panel  40  (e.g., onto different pixels P* on fLCOS display panel  40 ). Control circuitry  16  may provide control signals to fLCOS display panel  40  over control path(s)  44  that control fLCOS display panel  40  to selectively reflect illumination light  38  at each pixel location to produce image light  22  (e.g., image light having an image as modulated onto the illumination light by fLCOS display panel  40 ). As an example, the control signals may drive fLCOS drive voltage waveforms onto the pixels of fLCOS display panel  40 . Prism  50  may direct image light  22  towards collimating lens  34  of  FIG.  2   . 
     In general, fLCOS display panel  40  operates on illumination light of a single linear polarization. Polarizing structures interposed on the optical path between light sources  48 A-C and fLCOS display panel  40  may convert unpolarized illumination light into linearly polarized illumination light (e.g., s-polarized light or p-polarized illumination light). The polarizing structures may, for example, be optically interposed between prism  50  and fLCOS display panel  40 , between prism  46  and prism  50 , between light sources  48 A-C and prism  46 , within light sources  48 A-C, or elsewhere. 
     If a given pixel P* in fLCOS display panel  40  is turned on, the corresponding illumination light may be converted between linear polarizations by that pixel of the display panel. For example, if s-polarized illumination light  38  is incident upon a given pixel P*, fLCOS display panel  40  may reflect the s-polarized illumination light  38  to produce corresponding image light  22  that is p-polarized when pixel P* is turned on. Similarly, if p-polarized illumination light  38  is incident upon pixel P*, fLCOS display panel  40  may reflect the s-polarized illumination light  38  to produce corresponding image light  22  that is s-polarized when pixel P* is turned on. If pixel P* is turned off, the pixel does not convert the polarization of the illumination light, which prevents the illumination light from reflecting out of fLCOS display panel  40  as image light  22 . 
     Control circuitry  16  ( FIG.  2   ) may drive image data onto fLCOS display panel  40  using fLCOS drive voltage waveforms (e.g., based on control signals provided to fLCOS display panel  40  over control path(s)  44  of  FIG.  2   ).  FIG.  4    is a timing diagram of two illustrative fLCOS drive voltage waveforms that may be used to drive fLCOS display panel  40 . 
     As shown in  FIG.  4   , fLCOS drive voltage waveform (curve)  170  plots the fLCOS drive voltage as a function of time for producing image light  22  with a gray level of zero. fLCOS drive voltage waveform (curve)  172  plots the fLCOS drive voltage as a function of time for producing image light  22  with a gray level of 128 (e.g., in a 256-bit field). The fLCOS drive voltage may vary between a first drive voltage V OFF  (e.g., a negative voltage level) and a second drive voltage V ON  (e.g., a positive voltage level). 
     Waveforms  170  and  172  may be at first drive voltage V OFF  prior to time TA. At time TA, waveform  170  may begin to increase to a peak at second drive voltage V ON . Waveform  170  may return to first drive voltage V OFF  at time TB. The time period between times TA and TB may sometimes be referred to herein as dark gap  174 . Dark gap  174  may be used to reset fLCOS display panel  40 , for example. 
     The time period between times TB and TD may form a duty period  180  during which at least one light source  48  (e.g., red light source  48 A of  FIG.  3   ) may be turned on to provide illumination light  38  to fLCOS display panel  40 . Because waveform  170  is at first drive voltage V OFF  during duty period  180 , the fLCOS display panel may not produce image light during duty period  180  when driven using waveform  170 . The time period between times TA and TD may sometimes be referred to as field period  176 . Field period  176  may be associated with the illumination of fLCOS display panel  40  by a corresponding field of illumination light (e.g., illumination light of a particular color) and may include the reset time (e.g., a portion of dark gap  174 ) required to reset the fLCOS display panel to begin reflecting the field of illumination light as image light  22 . 
     At time TD, waveform  170  may to increase to a peak at second drive voltage V ON . Waveform  170  may return to first drive voltage V OFF  at time TE. The time period between times TD and TE may sometimes be referred to herein as the dark gap  182 . The time period between time TD and the time when waveform  170  reaches second drive voltage V ON  may sometimes be referred to herein as reset time T_RESET. Reset time T_RESET may allow time for fLCOS display panel  40  to reset for the next field of the image. The time period between the time when waveform  170  reaches second drive voltage V ON  and time TE may sometimes be referred to herein as off time T_OFF. The duration of dark gap  174  (e.g., off time T_OFF) may be adjusted to control the overall power consumption of display module  14 A. 
     The time period between times TE and TF may form a duty period  181  during which a light source other than the light source activated during duty period  180  may be turned on to provide illumination light  38  to fLCOS display panel  40 . A subsequent dark gap may begin at time TF, as waveform  170  increases back to second drive voltage V ON . This cycle may continue for each of the fields in the image frame to be displayed. The time period between times TE and TF may sometimes be referred to as field period  178 . 
     As shown in  FIG.  4   , waveform  172  may remain at second drive voltage V ON  after time TA and until time TC. By driving fLCOS display panel  40  at second drive voltage V ON  during a portion of duty period  180  (e.g., between times TB and TC), fLCOS display panel  40  may reflect some of the illumination light  38  incident during duty period  180  (as image light  22 ). This may allow fLCOS display panel  40  to produce image light  22  at a higher gray level when driven by waveform  172  than when driven by waveform  170 , for example. 
     The example of  FIG.  4    is merely illustrative. In general, any desired fLCOS drive voltage waveforms may be used to drive fLCOS display panel  40  to produce any desired pixel values of any desired colors in image light  22 . If desired, the optical performance of fLCOS display panel  40  may be optimized by overdriving or underdriving the fLCOS drive voltage provided to fLCOS display panel  40 . The example of  FIG.  4    in which the drive voltage waveform follows a reset-based driving scheme is merely illustrative. In another suitable arrangement, a reset-less driving scheme may be used (e.g., there may not be dark gaps between each of the color fields and, if desired, an inverse waveform pattern may be used after each waveform pattern for charge balancing). 
       FIG.  5    is a timing diagram showing one example of how fLCOS display panel  40  may be overdriven to optimize optical performance. As shown in  FIG.  5   , fLCOS display panel  40  may be driven using fLCOS drive voltage waveform (curve)  192 . Curve  190  of  FIG.  5    plots the corresponding reflectance of fLCOS display panel  40  when driven using fLCOS drive voltage waveform  192 . 
     In the example of  FIG.  5   , fLCOS drive voltage waveform  192  has four possible voltage levels (e.g., a first drive voltage level VB, a second drive voltage level VC, a third drive voltage level VD, and a fourth drive voltage level VE). First drive voltage level VB may be less than second drive voltage level VC, second drive voltage level VC may be less than a voltage level of zero, third drive voltage level VD may be greater than a voltage level of zero, and fourth drive voltage level VE may be greater than third drive voltage level VE. This example is merely illustrative. In general, fLCOS drive voltage waveform  192  may have any desired number of possible voltage levels of any desired magnitudes. In one suitable arrangement that is sometimes described herein as an example, first drive voltage level VB may be −1.8V, second drive voltage level VC may be −1.5V, third drive voltage level VD may be 1.5V, and fourth drive voltage level VE may be 1.8V. Other drive voltage levels may be used if desired. 
     As shown by fLCOS drive voltage waveform  192 , when fLCOS display panel  40  is not being overdriven, fLCOS drive voltage waveform  192  may include square wave pulses such as square wave pulse  196  (e.g., where the fLCOS drive voltage rises from second voltage level VC to third voltage level VD at time T 3  and falls back to second voltage level VC at time T 4 ). Square wave pulse  196  may produce a corresponding spike in the reflectance of fLCOS display panel  40  from a reflectance of zero to a reflectance of R (e.g., a value greater than 0 and less than 1.0), as shown by curve  190 . 
     In order to overdrive fLCOS display panel  40 , control circuitry  16  may drive fLCOS display panel  40  using a non-square wave fLCOS drive voltage waveform, such as an fLCOS drive voltage waveform that includes non-square wave pulses such as non-square wave pulse  194  of fLCOS drive voltage waveform  192 . For example, at time T 1 , fLCOS drive voltage waveform  192  may increase from second voltage level VC to fourth voltage level VE (sometimes referred to herein as overdrive voltage level VE). If desired, at time T 1 ′, fLCOS drive voltage waveform  192  may decrease to third voltage level VD. At time T 2 , fLCOS drive voltage waveform  192  may decrease to first voltage level VB. At time T 2 ′, fLCOS drive voltage waveform  192  may increase back to second voltage level VC. 
     Non-square wave pulse  194  of fLCOS drive voltage waveform  192  may produce a corresponding spike in the reflectance of fLCOS display panel  40  from a reflectance of zero at time T 1  to a reflectance greater than reflectance R at or near time T 1 ′ (e.g., a reflectance at or near 1.0). In other words, overdriving fLCOS display panel  40  in this way may serve to increase the reflectance of fLCOS display panel  40  relative to scenarios where fLCOS display panel  40  is not overdriven, thereby maximizing the overall optical efficiency of display module  14 A in producing image light  22 . 
     The example of  FIG.  5    is merely illustrative. In practice, curve  192  and non-square wave pulse  194  may have other shapes. In general, fLCOS display panel  40  may be overdriven using any desired non-square wave fLCOS drive voltage waveform (e.g., a waveform having non-square wave pulses that reach an overdrive voltage level such as fourth voltage level VE). Another example of a non-square wave pulse  194  that may be used to overdrive fLCOS display panel  40  is shown by dashed curve  193  of  FIG.  5   . In this example, the fLCOS drive voltage rises to voltage level VF at time T 1 , drops continuously to voltage level VD between times T 1  and T 2 , drops to voltage level VA at time T 2 , and rises continuously to voltage level VC between times T 2  and T 2 ′. Voltage level VF may be greater than 1.8V (e.g., 2.0V) and voltage level VA may be less than −1.8V (e.g., −2.0V), as one example. The precise shape of curve  193  between times T 1  and T 2  and between times T 2  and T 2 ′ may, for example, be altered to optimize the performance of fLCOS display panel  40 . The example of  FIG.  5    in which fLCOS display panel  40  is overdriven is merely illustrative and, if desired, fLCOS display panel  40  may be underdriven. Different non-square wave fLCOS drive voltage waveforms may be used to drive fLCOS display panel  40  at different times (e.g., depending on the operating conditions of display  14 ). 
     In practice, the optimal overdrive or underdrive waveform for fLCOS display panel  40  may vary as the operating temperature of fLCOS display panel  40  changes over time. If desired, control circuitry  16  may overdrive or underdrive fLCOS display panel  40  based on the temperature of display  14  (e.g., the temperature of fLCOS display panel  40 ).  FIG.  6    is a flow chart of illustrative steps that may be performed by control circuitry  16  ( FIG.  2   ) in overdriving or underdriving fLCOS display panel  40  based on the temperature of display  14 . 
     At step  200 , control circuitry  16  may gather temperature sensor data using one or more temperature sensors  19  in system  10  ( FIG.  1   ). If desired, control circuitry  16  may estimate the temperature of fLCOS display panel  40  based on the gathered temperature sensor data (e.g., using a temperature model for system  10 ). In scenarios where multiple temperature sensors  19  are used to gather temperature sensor data, the temperature sensors may be placed at different locations across system  10  if desired. Control circuitry  16  may also determine whether a trigger condition has been met before proceeding. 
     The trigger condition may be a predetermined change in the gathered temperature sensor data, may occur when the gathered temperature data reaches a threshold temperature level, may be based on the content of the image(s) to be displayed using fLCOS display panel  40 , may be based on a software call issued by one or more programs running on system  10 , may be based on a user input provided by a user of system  10 , etc. Once the trigger condition has been met, processing may proceed to step  204  as shown by arrow  202 . 
     At step  204 , control circuitry  16  may identify a non-square wave fLCOS drive voltage waveform with which to overdrive or underdrive fLCOS display panel  40  based on the gathered temperature sensor data. For example, control circuitry  16  may identify a non-square wave fLCOS drive voltage waveform that optimizes the optical performance (e.g., reflectance) of fLCOS display panel  40  for its current temperature (e.g., as determined while processing step  200 ). If desired, control circuitry  16  may store predetermined (optimal) non-square wave fLCOS drive voltage waveforms for different temperature values of fLCOS display panel  40  (e.g., in a look-up table or other data structure) and may identify the stored non-square wave fLCOS drive voltage waveform corresponding to the current (e.g., estimated) temperature of fLCOS display panel  40 . The stored non-square wave fLCOS drive voltage waveforms may be determined during the design, manufacture, assembly, testing, and/or calibration of system  10  if desired. 
     At step  206 , control circuitry  16  may drive fLCOS display panel  40  using the non-square wave drive voltage waveform identified while processing step  204 . Driving fLCOS display panel  40  in this way may maximize the reflectance of fLCOS display panel  40  for the current operating temperature of the display panel, for example. Control circuitry  16  may continue to overdrive fLCOS display panel  40  for a predetermined time period, until a new trigger condition is detected, for a predetermined number of frames, etc. 
     The example of  FIG.  6    in which control circuitry  16  overdrives fLCOS display panel  40  based on the temperature of display  14  is merely illustrative. In another suitable arrangement, control circuitry  16  may overdrive or underdrive fLCOS display panel  40  based on frame history information.  FIG.  7    is a flow chart of illustrative steps that may be performed by control circuitry  16  ( FIG.  2   ) in overdriving or underdriving fLCOS display panel  40  based on frame history information. 
     At step  210 , control circuitry  16  may identify frame history information for fLCOS display panel  40 . The frame history information may include, for example, information about the image frames that have been previously displayed using fLCOS display panel  40 . Control circuitry  16  may also determine whether a trigger condition has been met before proceeding. 
     The trigger condition may be a predetermined change in the gathered temperature sensor data, may occur when the gathered temperature data reaches a threshold temperature level, may be based on the content of the image(s) to be displayed using fLCOS display panel  40 , may be based on a software call issued by one or more programs running on system  10 , may be based on a user input provided by a user of system  10 , etc. In one suitable arrangement that is described herein as an example, the trigger condition may occur when the previous image frame displayed was fully on or fully off. Once the trigger condition has been met, processing may proceed to step  214  as shown by arrow  212 . 
     At step  214 , control circuitry  16  may identify a non-square wave fLCOS drive voltage waveform with which to overdrive or underdrive fLCOS display panel  40  based on the identified frame history information. For example, control circuitry  16  may identify a non-square wave fLCOS drive voltage waveform that optimizes the optical performance (e.g., reflectance) of fLCOS display panel  40  depending on the immediately previous image frame(s) displayed by fLCOS display panel  40  (e.g., a first fLCOS drive voltage waveform when the previous image frame was fully on, a second fLCOS drive voltage waveform when the previous image frame was fully off, etc.). 
     At step  216 , control circuitry  16  may drive fLCOS display panel  40  using the non-square wave drive voltage waveform identified while processing step  214 . Driving fLCOS display panel  40  in this way may maximize the reflectance of fLCOS display panel  40  for the current operating temperature of the display panel, for example. Control circuitry  16  may continue to overdrive fLCOS display panel  40  for a predetermined time period, until a new trigger condition is detected, for a predetermined number of frames, etc. 
     Overdriving fLCOS display panel  40  (e.g., using non-square wave fLCOS drive voltage waveforms as identified while processing step  204  of  FIG.  6    or step  214  of  FIG.  7   ) may, for example, serve to reduce the duration (width) of the dark gap of fLCOS display panel  40  relative to scenarios where fLCOS display panel  40  is driven using a square wave fLCOS drive voltage waveform. This may serve to further optimize power consumption in display module  14 A, for example. Control circuitry  16  may therefore sometimes be referred to herein as reducing the duration of the dark gap of fLCOS display panel  40  based on gathered temperature sensor data or identified frame history information. The arrangement of  FIG.  7    may be combined with the arrangement of  FIG.  6    if desired (e.g., control circuitry  16  may identify a non-square wave fLCOS drive voltage that optimizes the optical performance of fLCOS display panel  40  given both the current temperature of fLCOS display panel  40  and the frame history information of fLCOS display panel  40 ). If desired, the non-square wave drive voltage waveform to use may be selected based on the previous frame&#39;s target reflectance state and temperature information. For example, a look up table may modify the non-square wave drive voltage waveform for the current frame based on any previous state. As one example, if the previous frame was on for one-half the illumination field time, it would have a different non-square wave drive voltage for the current frame when the previous frame was on for 98% of the illumination field time. In driving fLCOS panel  40 , the percent on (duty cycle) during the illumination time may be selected to control the grey level for the field. 
     Overdriving fLCOS display panel  40  may also serve to optimize the optical performance of display module  14 A by reducing the response time of fLCOS display panel  40 .  FIG.  8    is a plot showing how overdriving fLCOS display panel  40  may reduce the response time of fLCOS display panel  40  across a wide range of operating temperatures. 
     In the example of  FIG.  8   , the horizontal axis plots the temperature of fLCOS display panel  40  (e.g., in degrees Celsius) and the vertical axis plots the response time of fLCOS display panel  40  (e.g., in microseconds). Curve  220  plots the response time of fLCOS display panel  40  when driven using square-wave fLCOS drive voltage pulses (e.g., pulses such as pulse  196  of  FIG.  5   ). As shown by curve  220 , the response time of fLCOS display panel  40  may decrease as temperature increases. 
     Curve  222  plots the response time of fLCOS display panel  40  when (over) driven using non-square-wave fLCOS drive voltage waveform pulses having a first peak voltage level (e.g., pulses such as pulse  194  of  FIG.  5    having a peak voltage given by fourth voltage level VE). Curve  224  plots the response time of fLCOS display panel  40  when (over) driven using a non-square-wave fLCOS drive voltage waveform pulses having a second peak voltage level that is higher than the first peak voltage level. The peak voltage level of the square-wave fLCOS drive voltage pulses associated with curve  220  may be 1.5V, the first peak voltage level associated with curve  222  may be 1.65V, and the second peak voltage level associated with curve  224  may be 1.8V, as one example. In general, the first peak voltage level may be any desired voltage greater than 1.5V (e.g., in scenarios where V ON  of  FIG.  4    is 1.5V), greater than 1.6V, greater than 1.7V, greater than 1.8V, etc. 
     As shown by curves  222  and  224 , overdriving fLCOS display panel  40  may serve to reduce the response time of fLCOS display panel  40  across all temperatures. As shown by curve  224 , overdriving fLCOS display panel  40  with a non-square wave fLCOS drive voltage waveform having a greater peak voltage level may serve to further decrease the response time of fLCOS display panel  40 . In this way, overdriving fLCOS display panel  40  may serve to further optimize the optical performance of display module  14 A by reducing the response time of fLCOS display panel  40  across a wide range of operating temperatures. The example of  FIG.  8    is merely illustrative. In practice, curves  220 ,  222 , and  224  may have other shapes. 
     The foregoing is merely illustrative and various modifications can be made to the described embodiments. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20210827
Publication Date: 20231031
Grant Date: 20231031
Priority Date: 20200828
Inventors: HOLSTEEN, AARON L.
LI, XIAOKAI
CHEN, YUAN
GE, ZHIBING
Assignee: APPLE INC
CPC Classifications: [{"code": "G09G3/3696", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/1352", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02F1/1358", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2230/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G3/3696", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/1358", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G2230/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "G02F1/1352", "inventive": true, "first": false, "tree": "[]"}, {"code": "G09G3/3629", "inventive": true, "first": true, "tree": "[]"}, {"code": "G09G2320/041", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2230/00", "inventive": false, "first": false, "tree": "[]"}, {"code": "G09G2320/0252", "inventive": false, "first": false, "tree": "[]"}]
Family ID: 88534540