Interlaced liquid crystal display panel and backlight used in a head mounted display

A liquid crystal display (LCD) device is driven in interlaced scan to accommodate for liquid crystal (LC) setting times without sacrificing brightness. The LCD device includes an LCD panel including a first group of (e.g., even) pixel lines and a second group (e.g., odd) pixel lines, a backlight disposed behind the LCD panel to emit light toward the even and odd pixel lines, a shift grating disposed between the LCD and the backlight, the shift grating configured to block the light from the backlight from reaching either the first group of pixel lines or the second group of pixel lines, and a controller. The controller drives the LCD panel using an interlaced scan, coordinates the activation of the backlight (e.g., a strobed backlight), and changes the state of the shift grating to block the light from the backlight from reaching either the first group of pixel lines or the second group of pixel lines.

BACKGROUND

Edge-lit backlights provide illumination for pixels of liquid crystal displays (LCD) panels of LCD devices. Each pixel of the LCD panel includes liquid crystals that are set to a particular state such that light from the backlight passes through or is blocked by the liquid crystals and produces a particular pixel color output accordingly. The liquid crystals have a set time between states that impacts how quickly the pixel can transition in response to programming from an input control signal. The setting times for liquid crystals may vary based on factors such as the material type, cell gap, initial state, and final state.

In progressive readout displays, a progressive scan is used where different pixels are programmed at different times based on their location on the LCD panel. The transition between two states of a liquid crystal depends on the timing of input control signals and the setting time of the liquid crystal. If a pixel (e.g., at the end of the progressive scan) is illuminated by the backlight when the liquid crystals of the pixel are not set to the desired state, the pixel may fail to output the desired pixel color. This can result in undesirable effects that reduce the quality of the LCD device output, such as ghosting (trailing images), motion blur, or smearing. While slowing the refresh rate or periodicity of a strobed backlight can help accommodate for liquid crystal (LC) setting time, this results in reduced brightness for the backlight. Thus, there is a need to coordinate backlight control with LC setting times without sacrificing brightness.

SUMMARY

Head-mounted displays (HMDs) and display devices optimized for HMDs are discussed herein. Some embodiments include a display device, comprising: a liquid crystal display (LCD) panel including first a group of (e.g., even) pixel lines and a second group of (e.g., odd) pixel lines; a backlight disposed behind the LCD panel to emit light toward the first group and second group of pixel lines; a shift disposed between the LCD and the backlight, configured to block the light from the backlight from reaching either the first group of pixel lines or the second group of pixel lines; and a controller. The controller is configured to: set the first group of pixel lines with first group line data for a video frame; control the shift grating and backlight such that the backlight illuminates the first group of pixel lines when the first group of pixel lines are set with the first group line data. While the backlight is illuminating the first group of pixel lines and the first group line data is set on the first group of pixel lines, the controller is configured to: set the second group of pixel lines with second group line data for the video frame; and control the shift grating and the backlight such that the backlight illuminates the second group of pixel lines when the second group of pixel lines are set with the second group line data.

For example, the backlight is a strobed backlight that is flashed on and off. The shift grating is transitioned between first and second states to block the light from the backlight such that the backlight alternatively illuminates the first group of pixel lines or the second group of pixel lines. The controller controls the strobed backlight and the shift grating according to a periodic signal or duty cycle.

In some embodiments, the first group of pixel lines and the second group of pixel lines include pixel line pairs, each pixel line pair including a first pixel line and an adjacent second pixel line. The LCD device includes micro-optics elements in front of the LCD panel configured to, for each pixel line pair, spread light from the first pixel line and the adjacent second pixel line across a pixel space of the pixel line pair.

Some embodiments may include a HMD including an LCD display device. The LCD device includes an LCD panel, a backlight disposed behind the LCD panel to emit light toward a first group of and a second group of pixel lines; a shift grating disposed between the LCD and the backlight, configured to block the light from the backlight from reaching either the first group of pixel lines or the second group of pixel lines; and a controller to drive the LCD panel in interlaced scan, and control the shift grating and backlight.

DETAILED DESCRIPTION

Configuration Overview

Techniques for providing an LCD device optimized for head-mounted displays (HMD) are discussed herein. The LCD device includes an LCD panel including different groups of pixel lines, such as even pixel lines and odd pixel lines. The LCD device also includes a backlight disposed behind the LCD panel to emit light toward the even and odd pixel lines, a shift grating disposed between the LCD and the backlight, the shift grating configured to block the light from the backlight from reaching either the even pixel lines or the odd pixel lines, and a controller that coordinates setting of the pixel lines, flashing of the backlight, and state change of the shift grating. For example, the controller drives the LCD panel using an interlaced scan for the even and odd pixel lines, and coordinates the activation of the backlight (e.g., a strobed backlight), and changes the state of the shift grating to block the light from the backlight from reaching either the even pixel lines or the odd pixel lines.

For each video frame, the controller generates even line data and odd line data for the even and odd pixel lines respectively. The controller sets the even pixel lines with the even line data, in a first step of the interlaced scan. The shift grating is set to an even state to prevent the strobed backlight from illuminating the odd line pixels. When the even pixel lines are set, the even pixel lines are illuminated with the strobed backlight, which is flashed on and off according to a periodic signal. While the even pixel lines are illuminated, the controller sets the odd pixel lines with the odd line data in a second step of the interlaced scan. The controller sets the shift grating to an odd state to prevent the strobed backlight from illuminating the even line pixels. When the odd pixel lines are set, the odd pixel lines are illuminated with the strobed backlight.

The interlaced scan may be repeated for additional video frames. The even line data for the next video frame, for example, is set on the even pixel lines while the odd pixel lines are illuminated with the odd pixel line data of the current video frame, and so forth. Advantageously, the allotted setting time for each pixel of the LCD panel is increased (e.g., doubled) to two on-off periods of the strobed backlight. Reducing the periodicity or duty cycle of the strobed backlight results in reduced brightness, which is not desirable for HMDs and many other types of displays. Thus, it is desirable that liquid crystals of the pixels are allotted sufficient time to completely transition to a desired state prior to illumination by a strobed backlight—without necessarily requiring a reduction in the periodicity or duty cycle for the strobed backlight.

Some embodiments discussed herein provide a single backlight solution for interlaced LCD panels by leveraging a shift grating that transitions between the even and odd states. In response to a shift grating control signal from the controller, the shift grating blocks backlight illumination to either the even or odd pixel lines of the LCD panel.

Some embodiments of the LCD device further include micro-optic elements disposed in front of the LCD panel. The even and odd pixel lines may define pixel line pairs, where each pixel line pair includes an even pixel line and an adjacent odd pixel line. For a frame of video, the controller sets even line data and odd line data for a pixel line pair with the same data. The micro-optic elements distribute light from the even or odd pixels of a pixel line pair across the pixel space of the pixel line pair. As such, a full image is provided across the pixel space of all pixels of the LCD panel throughout the interlaced scan, even though the strobed backlight alternatively illuminates even or odd pixel lines.

System Overview

FIG. 1shows a system100including a head-mounted display (HMD). The system100may be for use as a virtual reality (VR) system, an augmented reality (AR) system, a mixed reality (MR) system, or some combination thereof. In this example, the system100includes a HMD105, an imaging device110, and an input/output (I/O) interface115, which are each coupled to a console120. WhileFIG. 1shows a single HMD105, a single imaging device110, and a I/O interface115, in other embodiments, any number of these components may be included in the system. For example, there may be multiple HMDs105each having an associated input interface115and being monitored by one or more imaging devices110, with each HMD105, I/O interface115, and imaging devices110communicating with the console120. In alternative configurations, different and/or additional components may also be included in the system100. The HMD105may act as a VR, AR, and/or a MR HMD. An MR and/or AR HMD augments views of a physical, real-world environment with computer-generated elements (e.g., images, video, sound, etc.).

The HMD105presents content to a user. Example content includes images, video, audio, or some combination thereof. Audio content may be presented via a separate device (e.g., speakers and/or headphones) external to the HMD105that receives audio information from the HMD105, the console120, or both. The HMD105includes an electronic display155, an eye tracking module160, an optics block165, one or more locators170, an internal measurement unit (IMU)175, head tracking sensors180, and a scene rendering module185, and a vergence processing module190.

As discussed in greater detail below, the electronic display155is an LCD device including a LCD panel, a shift grating, a backlight, and a controller. The controller coordinates interlaced scanning and setting of pixels of the LCD panel, the selective blocking of illumination from the backlight on odd and even pixel lines by the shift grifting, and the flashing of the strobed backlight. Among other advantages, the electronic display155increases (e.g., doubles) the amount of time available for liquid crystal setting before illumination by the strobed backlight without requiring a change in periodicity or duty cycle for the strobed backlight that would decrease brightness.

The optics block165adjusts its focal length responsive to instructions from the console120. In some embodiments, the optics block165includes a multi multifocal block to adjust a focal length (adjusts optical power) of the optics block165

The eye tracking module160tracks an eye position and eye movement of a user of the HMD105. A camera or other optical sensor inside the HMD105captures image information of a user's eyes, and the eye tracking module160uses the captured information to determine interpupillary distance, interocular distance, a three-dimensional (3D) position of each eye relative to the HMD105(e.g., for distortion adjustment purposes), including a magnitude of torsion and rotation (i.e., roll, pitch, and yaw) and gaze directions for each eye. The information for the position and orientation of the user's eyes is used to determine the gaze point in a virtual scene presented by the HMD105where the user is looking.

The vergence processing module190determines a vergence depth of a user's gaze based on the gaze point or an estimated intersection of the gaze lines determined by the eye tracking module160. Vergence is the simultaneous movement or rotation of both eyes in opposite directions to maintain single binocular vision, which is naturally and automatically performed by the human eye. Thus, a location where a user's eyes are verged is where the user is looking and is also typically the location where the user's eyes are focused. For example, the vergence processing module190triangulates the gaze lines to estimate a distance or depth from the user associated with intersection of the gaze lines. The depth associated with intersection of the gaze lines can then be used as an approximation for the accommodation distance, which identifies a distance from the user where the user's eyes are directed. Thus, the vergence distance allows determination of a location where the user's eyes should be focused.

The locators170are objects located in specific positions on the HMD105relative to one another and relative to a specific reference point on the HMD105. A locator170may be a light emitting diode (LED), a corner cube reflector, a reflective marker, a type of light source that contrasts with an environment in which the HMD805operates, or some combination thereof. Active locators170(i.e., an LED or other type of light emitting device) may emit light in the visible band (˜380 nm to 850 nm), in the infrared (IR) band (˜850 nm to 1 mm), in the ultraviolet band (10 nm to 380 nm), some other portion of the electromagnetic spectrum, or some combination thereof.

The locators170can be located beneath an outer surface of the HMD105, which is transparent to the wavelengths of light emitted or reflected by the locators170or is thin enough not to substantially attenuate the wavelengths of light emitted or reflected by the locators170. Further, the outer surface or other portions of the HMD105can be opaque in the visible band of wavelengths of light. Thus, the locators170may emit light in the IR band while under an outer surface of the HMD105that is transparent in the IR band but opaque in the visible band.

The IMU175is an electronic device that generates fast calibration data based on measurement signals received from one or more of the head tracking sensors180, which generate one or more measurement signals in response to motion of HMD105. Examples of the head tracking sensors180include accelerometers, gyroscopes, magnetometers, other sensors suitable for detecting motion, correcting error associated with the IMU175, or some combination thereof. The head tracking sensors180may be located external to the IMU175, internal to the IMU175, or some combination thereof.

Based on the measurement signals from the head tracking sensors180, the IMU175generates fast calibration data indicating an estimated position of the HMD105relative to an initial position of the HMD105. For example, the head tracking sensors180include multiple accelerometers to measure translational motion (forward/back, up/down, left/right) and multiple gyroscopes to measure rotational motion (e.g., pitch, yaw, and roll). The IMU175can, for example, rapidly sample the measurement signals and calculate the estimated position of the HMD105from the sampled data. For example, the IMU175integrates measurement signals received from the accelerometers over time to estimate a velocity vector and integrates the velocity vector over time to determine an estimated position of a reference point on the HMD105. The reference point is a point that may be used to describe the position of the HMD105. While the reference point may generally be defined as a point in space, in various embodiments, a reference point is defined as a point within the HMD105(e.g., a center of the IMU175). Alternatively, the IMU175provides the sampled measurement signals to the console120, which determines the fast calibration data.

The IMU175can additionally receive one or more calibration parameters from the console120. As further discussed below, the one or more calibration parameters are used to maintain tracking of the HMD105. Based on a received calibration parameter, the IMU175may adjust one or more of the IMU parameters (e.g., sample rate). In some embodiments, certain calibration parameters cause the IMU175to update an initial position of the reference point to correspond to a next calibrated position of the reference point. Updating the initial position of the reference point as the next calibrated position of the reference point helps reduce accumulated error associated with determining the estimated position. The accumulated error, also referred to as drift error, causes the estimated position of the reference point to “drift” away from the actual position of the reference point over time.

The scene rendering module185receives content for the virtual scene from a VR engine145and provides the content for display on the electronic display155. Additionally, the scene rendering module185can adjust the content based on information from the IMU175, the vergence processing module190, and the head tracking sensors180. The scene rendering module185determines a portion of the content to be displayed on the electronic display155based on one or more of the tracking module140, the head tracking sensors180, or the IMU175.

The imaging device110generates slow calibration data in accordance with calibration parameters received from the console120. Slow calibration data includes one or more images showing observed positions of the locators170that are detectable by imaging device110. The imaging device110may include one or more cameras, one or more video cameras, other devices capable of capturing images including one or more locators170, or some combination thereof. Additionally, the imaging device110may include one or more filters (e.g., for increasing signal to noise ratio). The imaging device110is configured to detect light emitted or reflected from the locators170in a field of view of the imaging device110. In embodiments where the locators170include passive elements (e.g., a retroreflector), the imaging device110may include a light source that illuminates some or all of the locators170, which retro-reflect the light towards the light source in the imaging device110. Slow calibration data is communicated from the imaging device110to the console120, and the imaging device110receives one or more calibration parameters from the console120to adjust one or more imaging parameters (e.g., focal length, focus, frame rate, ISO, sensor temperature, shutter speed, aperture, etc.).

The I/O interface115is a device that allows a user to send action requests to the console120. An action request is a request to perform a particular action. For example, an action request may be to start or end an application or to perform a particular action within the application. The I/O interface115may include one or more input devices. Example input devices include a keyboard, a mouse, a hand-held controller, a glove controller, or any other suitable device for receiving action requests and communicating the received action requests to the console120. An action request received by the I/O interface115is communicated to the console120, which performs an action corresponding to the action request. In some embodiments, the I/O interface115may provide haptic feedback to the user in accordance with instructions received from the console120. For example, haptic feedback is provided by the I/O interface115when an action request is received, or the console120communicates instructions to the I/O interface115causing the I/O interface115to generate haptic feedback when the console120performs an action.

The console120provides content to the HMD105for presentation to the user in accordance with information received from the imaging device110, the HMD105, or the I/O interface115. The console120includes an application store150, a tracking module140, and the VR engine145. Some embodiments of the console120have different or additional modules than those described in conjunction withFIG. 1. Similarly, the functions further described below may be distributed among components of the console120in a different manner than is described here.

The application store150stores one or more applications for execution by the console120. An application is a group of instructions, that when executed by a processor, generates content for presentation to the user. Content generated by an application may be in response to inputs received from the user via movement of the HMD105or the I/O interface115. Examples of applications include gaming applications, conferencing applications, video playback application, or other suitable applications.

The tracking module140calibrates the system100using one or more calibration parameters and may adjust one or more calibration parameters to reduce error in determining position of the HMD105. For example, the tracking module140adjusts the focus of the imaging device110to obtain a more accurate position for observed locators170on the HMD105. Moreover, calibration performed by the tracking module140also accounts for information received from the IMU175. Additionally, if tracking of the HMD105is lost (e.g., imaging device110loses line of sight of at least a threshold number of locators170), the tracking module140re-calibrates some or all of the system100components.

Additionally, the tracking module140tracks the movement of the HMD105using slow calibration information from the imaging device110and determines positions of a reference point on the HMD105using observed locators from the slow calibration information and a model of the HMD105. The tracking module140also determines positions of the reference point on the HMD105using position information from the fast calibration information from the IMU175on the HMD105. Additionally, the tracking module160may use portions of the fast calibration information, the slow calibration information, or some combination thereof, to predict a future location of the HMD105, which is provided to the VR engine145.

The VR engine145executes applications within the system100and receives position information, acceleration information, velocity information, predicted future positions, or some combination thereof for the HMD105from the tracking module140. Based on the received information, the VR engine145determines content to provide to the HMD105for presentation to the user, such as a virtual scene, one or more virtual objects to overlay onto a real world scene, etc.

In some embodiments, the VR engine145maintains focal capability information of the optics block165. Focal capability information is information that describes what focal distances are available to the optics block165. Focal capability information may include, e.g., a range of focus the optics block165is able to accommodate (e.g., 0 to 4 diopters), a resolution of focus (e.g., 0.25 diopters), a number of focal planes, combinations of settings for switchable half wave plates (SHWPs) (e.g., active or non-active) that map to particular focal planes, combinations of settings for SHWPS and active liquid crystal lenses that map to particular focal planes, or some combination thereof.

The VR engine145generates instructions for the optics block165, the instructions causing the optics block165to adjust its focal distance to a particular location. The VR engine145generates the instructions based on focal capability information and, e.g. information from the vergence processing module190, the IMU175, and the head tracking sensors180. The VR engine145uses the information from the vergence processing module190, the IMU175, and the head tracking sensors180, or some combination thereof, to select an ideal focal plane to present content to the user. The VR engine145then uses the focal capability information to select a focal plane that is closest to the ideal focal plane. The VR engine145uses the focal information to determine settings for one or more SHWPs, one or more active liquid crystal lenses, or some combination thereof, within the optics block165that are associated with the selected focal plane. The VR engine145generates instructions based on the determined settings, and provides the instructions to the optics block165.

The VR engine145performs an action within an application executing on the console120in response to an action request received from the I/O interface115and provides feedback to the user that the action was performed. The provided feedback may be visual or audible feedback via the HMD105or haptic feedback via the I/O interface115.

FIG. 2shows a head-mounted display (HMD)105, in accordance with some embodiments. The HMD105includes a front rigid body205and a band210. The front rigid body205includes an electronic display (not shown), an inertial measurement unit (IMU)175, one or more position sensors180, and locators170. In some embodiments, a user movement is detected by use of the inertial measurement unit175, position sensors180, and/or the locators170, and an image is presented to a user through the electronic display according to the user movement detected. In some embodiments, the HMD105can be used for presenting a virtual reality, an augmented reality, or a mixed reality to a user.

A position sensor180generates one or more measurement signals in response to motion of the HMD105. Examples of position sensors180include: one or more accelerometers, one or more gyroscopes, one or more magnetometers, another suitable type of sensor that detects motion, a type of sensor used for error correction of the IMU175, or some combination thereof. The position sensors180may be located external to the IMU175, internal to the IMU175, or some combination thereof. InFIG. 2, the position sensors180are located within the IMU175, and neither the IMU175nor the position sensors180are visible to the user.

Based on the one or more measurement signals from one or more position sensors180, the IMU175generates calibration data indicating an estimated position of the HMD105relative to an initial position of the HMD105. In some embodiments, the IMU175rapidly samples the measurement signals and calculates the estimated position of the HMD100from the sampled data. For example, the IMU175integrates the measurement signals received from the accelerometers over time to estimate a velocity vector and integrates the velocity vector over time to determine an estimated position of a reference point on the HMD105. Alternatively, the IMU175provides the sampled measurement signals to a console (e.g., a computer), which determines the calibration data. The reference point is a point that may be used to describe the position of the HMD105. While the reference point may generally be defined as a point in space; however, in practice the reference point is defined as a point within the HMD105(e.g., a center of the IMU175).

The locators180are located in fixed positions on the front rigid body205relative to one another and relative to a reference point215. InFIG. 2, the reference point215is located at the center of the IMU175. Each of the locators170emits light that is detectable by an imaging device (e.g., camera or an image sensor). Locators170, or portions of locators170, are located on a front side240A, a top side240B, a bottom side240C, a right side240D, and a left side240E of the front rigid body205in the example ofFIG. 2.

FIG. 3shows a cross section of the front rigid body205of the HMD105shown inFIG. 2. The front rigid body205includes an optical block230that provides altered image light to an exit pupil250. The exit pupil250is the location in the front rigid body205where a user's eye245is positioned. For purposes of illustration,FIG. 3shows a cross section associated with a single eye245, but the HMD105may include another optical block that provides altered image light to another eye of the user.

The optical block230includes the electronic display155, the optics block165, and an eye cup255. The eye cup255is mechanically secured with the front rigid body205, and holds the optics block165. The electronic display155emits image light toward the optics block165. The optics block165magnifies the image light, and in some embodiments, also corrects for one or more additional optical errors (e.g., distortion, astigmatism, etc.). The optics block165directs the image light to the exit pupil250for presentation to the user. In some embodiments, the optics block165and the eye cone255may be omitted from the optical block230.

FIG. 4shows an exploded front view of an example of an electronic display155. Although the HMD105may include various types of displays, the electronic display155in this embodiment is a LCD device including a liquid crystal display (LCD) panel410, shift grating415, a strobed backlight420, and a controller440. The strobed backlight420emits light through the shift grating415, and towards the exit pupil250through the LCD panel410in a direction405. The LCD panel410is disposed between the strobed backlight420and the exit pupil250, and controls an amount of light from the backlight420to pass through in the direction405. In other embodiments, the electronic display155includes different, or fewer components than shown inFIG. 4.

The controller440coordinates the control of the LCD panel410, shift grating415, and strobed backlight420. The LCD panel410includes interlaced groups of pixel lines, which are referred to herein as even pixel lines and odd pixels lines. For a frame of video, the controller440generates first group data (or “even line data”) for the first group of pixel lines (or “even pixel lines”) and second group data (or “odd line data”) for the second group of pixel lines (or “odd pixel lines”) of the LCD panel410.

The strobed backlight420flashes on and off as set by the controller420. The controller440is configured to provide a light intensity control signal to the strobed backlight420that controls the timing of the flashing. The flashing uses a fast duty cycle such that the strobed backlight420appears to provide a constant and even source of illumination to a user viewing the LCD panel410. In some embodiments, the backlight is not strobed, but kept on throughout interlaced scans of the LCD panel410.

The shift grating415is disposed between the LCD panel410and the strobed backlight420. The shift grating415selectively blocks light from the strobed backlight420such that the strobed backlight420alternatively illuminates the even pixel lines or the odd pixel lines. The controller440is configured to provide a shift grating control signal465to the shift grating415to select the blocking of light from the strobed backlight420to either the even pixel lines or the odd pixel lines of the LCD panel410.

For a video frame, the controller440sets the even pixel lines with even line data, and controls the shift grating415and the strobed backlight420such that the strobed backlight420illuminates the even pixel lines when the even pixel lines are set with the even line data. While the strobed backlight420is illuminating the even pixel lines and the even line data is set on the even pixel lines, the controller440sets the odd pixel lines with odd line data for the video frame. The controller440controls the shift grating415and the strobed backlight420such that the strobed backlight420illuminates the odd pixel lines when the odd line pixel lines are set with the odd line data.

While the strobed backlight420is illuminating the odd pixel lines and the odd line data is set on the odd pixel lines, the controller440sets the even pixel lines with second even line data for a second (e.g., next) video frame, and controls the shift grating415and the strobed backlight420such that the strobed backlight420illuminates the even pixel lines when the even pixel lines are set with the second even line data for the second video frame. While the strobed backlight420is illuminating the even pixel lines and the second even line data is set on the even pixel lines, the controller440sets the odd pixel lines with second odd line data for the second video frame, and controls the shift grating415and the strobed backlight420such that the strobed backlight420illuminates the odd pixel lines when the odd pixel lines are set with the second odd line data for the second video frame.

The interlaced scan and control may be repeated for multiple video frames. Because even line pixels are transitioned between states while the odd line pixels are set at a state and illuminated, and vice versa, the amount of time available for LC setting before illumination of a pixel by the strobed backlight420is increased for a constant period or duty cycle of the strobed backlight420. For example, each pixel does not need to be completely set within an on-off period of the strobed backlight420because each pixel is illuminated every other on-off period.

The strobed backlight420includes light sources430that generate light. In some embodiments, the light sources430include edge-lit LEDs arranged along one or more edges of the display panel410. The edge-lit LEDs may include white LEDs, or color LEDS (e.g., red, green, and blue LEDs). The edge-lit LEDs emit light into a light guide, and the light guide directs and distributes the light to the pixels of the LCD panel410. When color LEDs are used for the light sources430, the light guide outputs a combined light having a color corresponding to a combination of colors of the received light from the color LEDs. In some embodiments, the light sources430are direct-lit LEDs arranged (e.g., in a 2 dimensional array) behind the display panel410to illuminate the pixels of the pixels of the display panel410.

In some embodiments, the intensity and timing of light from a light source430of the strobed backlight420is adjusted according to the light intensity control signal460from the controller440. The light sources430may be switched on and off over time according to a periodic signal or duty cycle. The light intensity control signal is a signal indicative of intensity of light to be output for each light source430. In some embodiments, different colored light sources430can output corresponding light with different intensity, according to the light intensity control signal. For example, a red light source outputs red light with an intensity corresponding to ‘10’ out of ‘255’, a green light source outputs green light with an intensity corresponding to ‘30’ out of ‘255’, and a blue light source outputs blue light with an intensity corresponding to ‘180’ out of ‘255,’ according to the light intensity control signal. A light source430may adjust its duty cycle of or an amount of current supplied to LEDs according to light intensity control signals. For example, the current supplied to the LEDs is coordinated in time with the switching of the shift grating415and the setting of LCs for pixels of the LCD panel410. In another example, reducing current supplied to the LED or reducing the ‘ON’ duration of the duty cycle renders intensity of light from a light source to be reduced (i.e., light to be dimmed).

FIG. 5shows a cross sectional side view of the electronic display155, in accordance with some embodiments. The cross sectional side view is taken along line A for the electronic display155as shown inFIG. 4. The strobed backlight420is disposed behind the LCD panel410along a depth dimension d. The strobed backlight420includes light sources430, a light guide510, a reflective surface520, and an optical film stack530. The light guide510may be composed of a glass material or a transparent plastic material, and refractive and/or reflective components for receiving light from the light sources430in a first direction550and projecting light towards the LCD panel410in a second direction560. For example, the light guide510may include a structure having a series of unevenly spaced bumps that diffuse propagating light. The density of the bumps increase with distance to the light sources430according to a diffusion equation. In some embodiments, the light guide510receives light with different colors from the light sources430, and directs combined light including a combination of the different colors in a different direction toward the LCD panel410to illuminate the LCD panel410. The combined light from separately controllable color LEDs may include improved spectrum intensity across different wavelengths compared with using white LEDs.

The optical film stack530may be disposed between the light guide510and the LCD panel410. The optical film stack530may include a diffuser that facilitates the uniform distribution of light from the light guide510across the pixels of the LCD panel410. The optical film stack530may additionally or alternatively include a reflective polarizer film that reflects unpolarized light back toward the LCD panel410that would otherwise be absorbed.

The light guide510directs light towards its top and bottom surfaces, where the top surface faces the LCD panel410and the bottom surface faces the reflective surface520. The reflective surface520includes an optical mirror that reflects light directed from the bottom surface of the light guide510towards the LCD panel410.

The electronic display155may further include micro-optic elements540(not shown inFIG. 4). As discussed in greater detail below, the micro-optic elements540distribute light from interlaced even or odd pixels of a pixel pair across the pixel space of the pixel pair. As such, a full image is provided across the pixel space of all pixels of the LCD panel even though the strobed backlight420alternatively illuminates even or odd pixel lines.

Returning toFIG. 4, the LCD panel410receives a liquid crystal (LC) control signal470from the controller440, and passes light from the strobed backlight420towards the exit pupil in the direction405, according to the LC control signal. The LC control signal is a signal indicative of an amount of light to be passed through a liquid crystal layer of the LCD panel410for different pixels. The LC control signal operates the LCD panel410as an interlaced display with even and odd pixel lines. The LCD panel410includes a plurality of liquid crystals, and an orientation of the liquid crystals can be changed according to the light crystal control signal applied across electrodes of the liquid crystal layer.

The controller440is a circuitry that receives an input image data, and generates control signals for driving the LCD panel410, the shift grating415, and the LED light sources430. The input image data may correspond to an image or a frame of a video in a virtual reality and/or augmented reality application. The controller440generates the light intensity control signal460for controlling intensity of light output by the light sources430. The controller440generates the LC control signal470for controlling an amount of light passing from the backlight420towards the exit pupil250through the LCD panel410according to the input image data. The controller440also generates the shift grating control signal465to control the selective blocking of light directed from the strobed backlight420by the shift grating415. As discussed in greater detail below, the controller440provides the light intensity control signal to the light sources430, the LC control signal to the liquid crystal layer410, and the shift grating control signal to the shift grating415at a proper timing to display images.

FIGS. 6A and 6Bshow an LCD panel410, in accordance with some embodiments. With reference toFIG. 6A, the LCD panel410includes a two-dimensional array of pixels, such as pixel605. The pixels of the LCD panel410form pixel lines, such pixel row line610or pixel column line615. Each pixel605includes LCs that can be controlled to transition between states based on the LC control signal470from the controller440.

With reference toFIG. 6B, the LCD panel410is driven using interlaced scan by LC control signals from the controller440. The LCD panel410includes even pixel lines (shown without hatching) and odd pixel lines (shown with hatching), such as even pixel line625and odd pixel line630. During interlaced scan, the LC control signals470set the LCs of even pixel lines in a first scan, and then set the LCs of odd pixel lines in a second scan. In some embodiments, each of the first scan and the second scan of the interlaced scan may use a progressive scan. For example, the even pixel lines for a video frame may be set from left to right and top to bottom; then the odd pixel lines for the video frame may be set from left to right and top to bottom. Although the interlaced even and odd pixel lines are vertical pixel column lines inFIG. 6B, depending on the design and/or orientation of the LCD panel410, the interlaced even and odd pixel lines may be horizontal pixel row lines, or diagonal pixel lines.

FIG. 7shows a shift grating415, in accordance with some embodiments. The shift grating415selectively blocks light from the strobed backlight from illuminating either the even pixel lines or the odd pixel lines of the LCD panel410. In an even state of the shift grating415, grating elements702of the shift grating415are aligned with the even pixel lines625to block light from the strobed backlight420from reaching the even pixel lines625. In an odd state of the shift grating415, the grating elements702of the shift grating415are aligned with the odd pixel lines630to block light from the strobed backlight420from reaching the odd pixel lines630. The shift grating415switches between the even and odd states based on the shift grating control signal from the controller440.

In some embodiments, the grating elements702may include piezoelectric transducers to provide small, accurate movements of the grating in response to the shift grating control signal. Various other components may be used to alternatively block light to the odd or even pixel lines of the LCD panel. In some embodiments, a spatial light modulator may be used as an alternative to a shift grating to spatially modulate the light input into the LCD panel. In some embodiments, liquid crystal (LC) lines may be used that switch between on and off at a fast rate (for fast switching LC the full on to full off is actually one of the quicker transitions). In some embodiments, an aligned polarizer alternates horizontal and vertical polarization for each even and odd pixel line. An output polarizer complements the input polarizer. The polarizers are switched from one polarization state to another.

FIG. 8shows a micro-optics element540, in accordance with some embodiments. The micro-optics element540includes a prism802and a negative cylindrical lens804. The micro-optics element540is disposed above at least two pixels806and808of the LCD panel410. The even pixel806and odd pixel808are adjacent pixels respectively from an even pixel line and an adjacent odd pixel line, where the even and odd pixel limes form a pixel line pair. As such, even pixel806and odd pixel808represent a pixel pair810.

When the even pixel806is illuminated by the strobed backlight420, the micro-optics element540spread light from the even pixel806across a pixel space812of the pixel pair810. When the odd pixel808is illuminated by the strobed backlight420, the micro-optics element540spread light from the odd pixel808across a pixel space812of the pixel pair810. The pixel space812of the pixel pair810is defined by the pixel space of the even pixel806and the pixel space of the odd pixel808.

As shown by light beams814emitted from the odd pixel808, the prism802includes two sloped surfaces defining a triangular shape. The sloped surfaces of the prism802couple with the light beams814from the odd pixel808, and refracts the light beams814through the prism802to distribute the light beams814across the pixel space812. The negative cylindrical lens804couples with the light beams814from the prism802, and diverges the light beams814outwards such that the light beams814are spread across a pixel space812of the pixel pair810.

Although not shown inFIG. 8to ovoid overcomplicating the drawing, the micro-optics element540operates in an analogous way for light beams emitted from the even pixel806. For example, the sloped surfaces of the prism802couple with the light beams from the even pixel806, and refracts the light beams through the prism802to distribute the light beams across the pixel space812. The negative cylindrical lens804couples with the light beams from the prism802, and diverges the light beams814outwards such that the light beams814are spread across a pixel space812of the pixel pair810.

In some embodiments, each pixel pair810is associated with a separate micro-optic element540. In another example, multiple pixel pairs may share a micro-optic element540. In another example, the prism802and negative cylindrical lines804extend across the length of the pixel lines such that each pixel line pair shares a micro-optic element540. The electronic display155may include multiple micro-optic elements540disposed in front of the LCD panel410. In some embodiments, the micro-optic elements540may form a layer of connected micro-optic elements. In some embodiments, individual micro-optic elements540are disposed on the surface of the LCD panel410.

Interlaced LCD Control

FIG. 9shows a process900for interlaced LCD device control, in accordance with some embodiments. Process900can be performed by, for example, the components of the electronic display155, as shown inFIG. 4. In other embodiments, some or all of the steps may be performed by other entities. In addition, some embodiments may perform the steps in parallel, perform the steps in different orders, or perform different steps. Process900is discussed with reference to timing diagrams1002and1004shown inFIG. 10, respectively showing control of the even and odd pixel lines, and other display components such as the strobed backlight420and shift grating415, over time for a video frame.

At905, a controller440of an LCD display155is configured to generate even line data and odd line data for a frame of video. The even line data refers to data for setting the even pixel lines of the LCD panel410, and the odd line data refers to data for setting the odd line pixels of the LCD panel420.

For example, the controller440receives input image data from the console110or other processor that defines an image of the video frame in a virtual reality and/or augmented reality application. Separating the input image data for the video frame into the even line data and odd line data prepares the input image data for an interlaced scan to the even and odd pixel lines of the LCD panel410respectively according to embodiments herein.

In some embodiments, the even line data and odd line data for a frame video frame are the same for each pixel line pair of the LCD panel410. As discussed above, each pixel line pair includes an even pixel line and an adjacent odd pixel line, and the LCD panel410includes multiple pixel line pairs. In one example, the even line data includes the input image data from the console110distributed across the even pixel lines, and the odd line data includes the input image data from the console110distributed across the odd pixel lines.

At910, the controller440is configured to set the even pixel lines of the LCD panel410with the even line data. The controller440generates LC control signals to set the pixel lines. Setting pixels or pixel lines may include transitioning the LCs of the pixel from a first state (e.g., of the previous video frame) to a second state (e.g., of the current video frame). The pixels of the LCD panel410may include LCs that change physical state, such as twist or untwist, based on parameters of the LC control signal such as voltage level. The state of the LCs determines the level of light transmission through the LCs, and thus the output illumination of the pixels when illuminated by the strobed backlight420. Thus setting the even line pixels with the even line data prepares the even line pixels for illumination by the strobed backlight420.

With reference to the even pixel line timing diagram1002shown inFIG. 10, the controller440sets the even line pixels by providing the LC control signal beginning at the start of the frame at time t0by performing a progressive scan of the even line pixels until time t1. At time t1, each of the even line pixels (from the first to the last row of pixels) has received the LC control signal.

At time t2, each of the even line pixels is set and transitioned to the desired state for the video frame. The delay between t1and t2represents the LC setting time for the even line pixels.

Although not limited to any particular type of scan, in the embodiment ofFIG. 10, the even pixel lines for a video frame may be set from left to right and top to bottom. Here, the top, first pixel row line is set from left to right for the even line pixels, then the next pixel row line is set from left to right for the even line pixels, and so forth until each even pixel line has been set.

With reference to the odd pixel line timing diagram1004shown inFIG. 10, the odd line pixels are not set simultaneously with the progressive scan of the even line pixels between t0and t2. Instead, the odd line pixels may be illuminated with odd line data of a previous video frame while the even line data is being set on the even line pixels of the current video frame as shown between t0and t5.

While the even line pixels are being set between t0and t2, the even line pixels are not illuminated by the strobed backlight420. For example, the controller440sets the shift grating415to the odd state to block light from the strobed backlight420from reaching the even pixel lines between t4and t5, where the strobed backlight420is flashed on to illuminate the odd pixel lines for the previous video frame. In the odd state, the shift grating415permits light from the strobed backlight420to reach the odd line pixels. Thus the odd line pixels may be illuminated when the strobed backlight420is flashed on between t4and t5, while the even pixel lines are not illuminated when the even pixel lines are being set with even line data and transitioning between LC states between t0and t2.

At915, the controller440is configured to control the shift grating415and strobed backlight420such that the strobed backlight420illuminates the even pixel lines when the even pixel lines are set with the even line data. With reference to even pixel line timing diagram1002, the controller440provides the light intensity control signal to the strobed backlight420to flash between t2and t3, after all pixels of the even pixel lines are set with the even line data at t2. The controller440also provides a shift grating control signal to the shift grating415that sets the shift grating415to the even state to permit light from the strobed backlight420to reach the even pixel lines when the even pixel lines are set with the even line data. In the even state, the shift grating blocks light from the strobed backlight420from reaching the odd pixel lines. Therefore, the odd pixel lines are not illuminated by the strobed backlight420between t2and t3.

At920, for each pixel line pair of the LCD display410, a micro-optics element540spread light from the even pixel line across a pixel space of the pixel line pair. The pixel space of a pixel line pair refers to a combined pixel width defined by two adjacent pixels of an even pixel line and an adjacent odd pixel line. Here, the even pixel lines are set with even line data and illuminated, while the odd pixel lines are not illuminated. The micro-optics effectively projects the even line data on the even pixel lines across pixel space defined by both the even and odd pixel lines of the LCD panel410. Therefore, even though only the even pixel lines are illuminated between t2and t3, the image output from the LCD panel410appears to project from all pixel lines of the LCD panel410rather than only the even pixel lines.

At925, while the strobed backlight420is illuminating the even pixel lines and the even line data is set on the even pixel lines, the controller440is configured to set the odd pixel lines with the odd line data for the video frame. For example, the controller sets the odd pixel lines with odd line data between t5and t7while the strobed backlight420is illuminating the even pixel lines between t2and t3. In some embodiments, the controller440sets the odd line pixels based on a progressive scan of the odd line pixels. For example, the odd pixel lines for the video frame may be set from left to right and top to bottom. The top pixel row line is set from left to right for the odd line pixels, then the next pixel row line is set from left to right for the odd line pixels, and so forth until each odd line pixel has been set.

At930, the controller440is configured to control the shift grating415and strobed backlight420such that the strobed backlight420illuminates the odd pixel lines when the odd line pixel lines are set with the odd line data.

The controller440provides the light intensity control signal to the strobed backlight420to flash between t7and t8, after all pixels of the odd pixel lines are set with the odd line data at t7. The controller440also provides a shift grating control signal to the shift grating415that sets the shift grating415to the odd state to permit light from the strobed backlight420to reach the odd pixel lines when the odd pixel lines are set with the odd line data. In the odd state, the shift grating blocks light from the strobed backlight420from reaching the even pixel lines between t7and t8.

At935, for each pixel line pair of the LCD display410, the micro-optics element540spread light from the odd pixel line across a pixel space of the pixel line pair. Here, the odd pixel lines are set with odd line data and illuminated, while the even pixel lines are not illuminated. The micro-optics effectively projects the odd line data on the odd pixel lines across pixel space defined by both the even and odd pixel lines of the LCD panel410. Therefore, even though only the odd pixel lines are illuminated between t7and t8, the image output from the LCD panel410appears to project from all pixel lines of the LCD panel410rather than only the odd pixel lines.

At940, while the strobed backlight420is illuminating the odd pixel lines and the odd line data is set on the odd pixel lines, process900may return to805for a second (e.g., next) video frame. Process900may be repeated for multiple video frames. For each video frame, even line data and odd line data may be handled using the process900. With reference toFIG. 10, the controller440sets the even pixel lines of the LCD panel410with the even line data of the second video frame between t3and t9. This occurs while the strobed backlight420is illuminating the odd pixel lines between t7and t8.

Advantageously, process900results in a doubling of the time allotted for pixel line scanning and LC setting before pixel illumination. For example, by running the LCD panel410at a 90 Hz interlaced refresh rate, the strobed backlight420is flashed on and off at the 90 Hz refresh rate, and the shift grating415is switched between even and odd states at the 90 Hz refresh rate such that the strobed backlight420alternatively illuminates the even or odd pixel lines per flash. However, each pixel does not need to transition at the 90 Hz refresh rate, and instead can be set at a 45 Hz refresh rate. For each video frame, this doubles the amount of time for LCs of the pixels to complete state transition before illumination by the strobed backlight420. In some embodiments, the periodicity and/or duty cycle of illuminations by the strobed backlight420and shift grating415can be set to compensate for slower or variable LC response times.

In some embodiments, the controller440sets each of the even and odd pixel lines at a first refresh rate, such as 45 Hz. The controller controls the backlight to flash on and off using a periodic signal defining a second refresh rate, such as 90 Hz. The controller controls the shift grating to block the light from the backlight from reaching either the even pixel lines or the odd pixel lines using a periodic signal defining the second refresh, where the first refresh rate is half the second refresh rate.

ADDITIONAL CONFIGURATION INFORMATION

The foregoing description of the embodiments has been presented for the purpose of illustration; it is not intended to be exhaustive or to limit the patent rights to the precise forms disclosed. For example, the even-odd interlaced scan as discussed herein is not limited to two groups of pixel lines, and may be extended (e.g., interlacing of three groups of pixel lines) to provide additional LC setting time for LCs between flashes of a strobed backlight. Persons skilled in the relevant art can appreciate that many modifications and variations are possible in light of the above disclosure.