VR HMD Backlight Timing for Ghosting Reduction
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Solution Overview
Problem
Conventional head-mounted displays (HMDs) suffer from low refresh rates due to long liquid crystal settling times, which degrade the user experience in virtual reality applications, and attempts to improve refresh rate through early backlight illumination result in unwanted ghosting.
Innovation Solution
Implementing a short persistence global backlight illumination pulse that is activated during the liquid crystal settling time of non-dominant eye rows, while deactivating it during dominant eye row updates to minimize perceived ghosting without compromising refresh rate improvement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If backlight illumination is activated during liquid crystal settling time to improve refresh rate, then refresh rate is improved, but ghosting is introduced
Solution Approach 1:
The display is divided into first and second portions of rows, with the backlight illumination timing differentiated between these portions. The first portion of rows receives illumination during liquid crystal settling time, while the second portion receives illumination after settling is complete, allowing selective optimization to reduce perceived ghosting while maintaining refresh rate benefits
Solution Approach 2:
Different illumination timing strategies are applied to different portions of the display. The first portion (non-dominant eye rows) uses early illumination during settling for refresh rate improvement, while the second portion (dominant eye rows) uses delayed illumination after settling to prevent ghosting, creating locally optimized quality
2Productivity
If conventional LCD pixel update operations are used sequentially row by row, then device complexity is reduced, but refresh rate is limited by liquid crystal settling time
Solution Approach 1:
The backlight illumination is activated during the liquid crystal settling time period before the sequential row update is complete. This preliminary illumination action allows the display to present updated content to the user while the liquid crystals are still settling, effectively increasing refresh rate without requiring complex parallel update hardware
Solution Approach 2:
The illumination timing is dynamically adjusted based on the liquid crystal settling state. The system transitions from static sequential illumination to dynamic illumination timing that coordinates with the liquid crystal response characteristics, enabling higher refresh rates through temporal modulation rather than structural complexity
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 enhances the refresh rate of HMDs by allowing backlight illumination during liquid crystal settling without causing ghosting, thereby improving the user experience by reducing latency and image persistence.
Implementation Method 1
one of a first state configured to block light from LCD pixels of the first row and a second state configured to allow light into LCD pixels of the first row
Implementation Method 2
triggering a production of light for each of the plurality of rows of LCD pixels for an interval of time during which the first row is updated
Data Source
AI summary
Head-mounted displays (HMDs) for virtual reality (VR) provide backlit illumination when the LCD rows corresponding to a non-dominant eye of the viewer are being updated. For example, when a human viewer operates a VR computer in the form of a smartphone with an LCD screen embedded in specialized goggles (e.g., Google Cardboard), the human viewer may specify that his/her right eye is dominant. In this case, the VR computer times the backlit illumination to be activated when the rows of LCD pixels in the field of view of the non-dominant, i.e., left, eye are being updated. When the rows of LCD pixels in the field of view of the dominant, i.e., right eye are being updated, the VR computer deactivates the backlit illumination.