Interlaced LCD Panel with Shift Grating for HMD Ghosting
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Solution Overview
Problem
In liquid crystal display (LCD) devices, particularly in progressive readout displays, the transition time of liquid crystals between states can lead to undesirable effects like ghosting, motion blur, or smearing due to misalignment with backlight illumination, and reducing backlight refresh rate to accommodate this results in reduced brightness.
Innovation Solution
A display system with an LCD panel having even and odd pixel lines, a shift grating between the LCD and backlight to block light alternately, and a controller that coordinates the backlight and shift grating to ensure liquid crystals are set before illumination, using an interlaced scan and strobed backlight to double the setting time without reducing brightness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the backlight refresh rate is slowed to accommodate liquid crystal setting time, then ghosting and motion blur are reduced, but brightness is reduced
Solution Approach 1:
The pixel lines are divided into two separate groups (even and odd lines) that are illuminated alternately at different times. This segmentation allows the system to provide sufficient setting time for liquid crystals in each group without requiring the entire backlight to operate at a lower refresh rate, thereby maintaining overall brightness while eliminating ghosting and motion blur.
2Reliability
If the liquid crystal setting time is increased to reduce ghosting and motion blur, then image quality improves, but the refresh rate must be reduced which lowers brightness
Solution Approach 1:
The system uses periodic strobing of the backlight in alternation with the interlaced scanning of even and odd pixel lines. This periodic action synchronized with the liquid crystal setting time ensures that each group of pixel lines is illuminated only after its liquid crystals have fully transitioned, eliminating ghosting while maintaining a high effective refresh rate and brightness.
3Ease of manufacture
If progressive scan is used to program different pixels at different times, then manufacturing is simplified, but ghosting and motion blur occur due to timing mismatch with backlight illumination
Solution Approach 1:
The system performs preliminary setting of liquid crystals in each pixel line group before illuminating that group with the backlight. By using interlaced scanning, the even pixel lines are set first and then illuminated, followed by setting and illumination of odd pixel lines. This preliminary action ensures that liquid crystals are fully transitioned before illumination occurs, eliminating ghosting and motion blur while maintaining the simplicity of progressive-like control.
Data Source
AI summary
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.