HMD Pixel Rescan Overdrive for LCD Ghosting
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Solution Overview
Problem
Head-mounted display (HMD) devices face challenges in updating pixel elements quickly enough to prevent ghosting and visual artifacts due to the settling time of liquid crystal display (LCD) pixels, especially in virtual reality applications where precise voltage control is required to maintain immersion.
Innovation Solution
A method and apparatus for updating pixel elements in an HMD device that involves scanning and rescanning rows of a pixel array, with overdrive circuitry determining target and overdrive voltages to ensure pixel elements settle at their target values, and using light sources to illuminate the array during display periods while updating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If LCD pixels are updated by successively scanning rows with target voltages, then power consumption is reduced and manufacturing is simplified, but pixel settling time is insufficient causing ghosting and visual artifacts
Solution Approach 1:
The patent applies overdrive voltages to pixel elements in advance before the actual display frame is shown. During a rescan period before the frame is displayed, pixels that require transition are driven with overdrive voltages to accelerate their settling. This preliminary action ensures pixels reach their target states before being illuminated, preventing ghosting while maintaining power efficiency during normal display operation.
Solution Approach 2:
The patent implements periodic rescanning of pixel rows at specific intervals before frame display. Instead of continuous overdrive, the system periodically applies overdrive voltages to selected rows during designated rescan periods. This periodic approach maintains pixel transition reliability while controlling power consumption by activating overdrive only when and where needed, rather than continuously across all pixels.
2Loss of time
If overdrive voltages are applied to accelerate pixel transitions, then pixel settling time is reduced preventing ghosting, but device complexity and power consumption increase
Solution Approach 1:
The patent applies overdrive voltages selectively to specific rows of pixels that require transition, rather than uniformly to all pixels. The system identifies which rows contain pixels needing updates and applies overdrive only to those rows during rescan periods. This localized approach reduces the complexity of voltage control by limiting the scope of overdrive application to only where necessary.
Solution Approach 2:
The patent changes the voltage parameter by applying overdrive voltages that exceed the normal target voltages during rescan periods. These elevated voltages accelerate liquid crystal rotation and pixel settling. After the rescan period, the system returns to normal target voltages for frame display. This dynamic parameter change enables fast transitions when needed while maintaining standard operation otherwise, managing device complexity through controlled parameter variation.
3Reliability
If rescanning is performed to correct pixel transitions, then visual artifacts are reduced, but the time available for frame display is reduced
Solution Approach 1:
The patent performs pixel rescanning and overdrive application in advance before the frame display period begins. The rescan operation prepares pixels by accelerating their transitions during a preliminary period, ensuring they settle to correct values before the frame is illuminated. This preliminary action separates the pixel correction phase from the display phase, preventing interference with frame display time.
Solution Approach 2:
The patent maintains continuous pixel updating by overlapping the rescan operation with the frame preparation period. Instead of interrupting frame display to perform rescans, the system continuously updates pixels during intervals when frames are being prepared or transmitted. This continuous useful action ensures image quality improvement without sacrificing frame display time, as pixel updates and frame display proceed in coordinated parallel operations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach reduces motion blur and visual artifacts by allowing for precise control of pixel transitions, enhancing the immersion and clarity of virtual reality experiences in HMD devices.
Implementation Method 1
The voltage applied on the data line changes the color and/or brightness of the pixel element by changing the physical state of (e.g., rotating) the particular pixel element
Implementation Method 2
A pixel element is driven to a higher voltage than the target voltage associated with the desired color and/or brightness level. The higher voltage causes the liquid crystal to rotate faster, and thus reach the target brightness in less time
Data Source
AI summary
A method and apparatus for updating pixel elements of a display device. The display device comprises a pixel array including a plurality of pixel elements and one or more light sources to illuminate the pixel array at a first instance of time. A data driver is configured to receive a frame of display data corresponding to an image to be displayed on the pixel array at a first instance of time. The data driver scans each row of the pixel array, during a pixel adjustment period prior to the first instance of time, to drive a plurality of first voltages onto the plurality of pixel elements, respectively, based on the received frame. The data driver further rescans a subset of rows of the pixel array, during the pixel adjustment period, to drive second voltages onto respective pixel elements in the subset of rows based on the received frame.