Pixel Circuits with Bridge Transistors for HMD Display Quality
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Solution Overview
Problem
Current display technologies for head-mounted displays (HMDs) face challenges in achieving high frame rate, low latency, high brightness, high contrast ratio, and high resolution, which are crucial for preventing cybersickness and motion blur, especially in varying ambient light conditions.
Innovation Solution
The development of pixel circuits for light emitting elements, including global emission and discharge control, and the use of bridge transistors for voltage boosting, which reduce display motion blur, increase brightness control granularity, and enhance the withstand voltage and contrast ratio of HMDs without significantly increasing the pixel circuit area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional pixel circuits are used in HMDs, then device complexity is reduced, but display quality (frame rate, latency, brightness, contrast ratio, resolution) is insufficient
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks including a driving transistor for current control, a switching transistor for signal input, a storage capacitor for voltage holding, and an emission control transistor for timing control. This segmentation allows each component to be optimized for its specific function, improving overall display quality while managing complexity through modular design.
Solution Approach 2:
The patent introduces a dual-gate transistor configuration where a second gate can independently control the transistor's operation. This adds a control dimension that enables precise timing of light emission and improved voltage management without requiring additional transistors, thereby enhancing display performance while limiting circuit area growth.
2Measurement precision
If pixel circuit area is increased to improve display specifications, then brightness control precision and contrast ratio improve, but pixel density and resolution are reduced
Solution Approach 1:
The storage capacitor serves multiple functions: it holds the voltage for the driving transistor during the display period, enables gray scale control through voltage level adjustments, and works with the emission control transistor to timing the light output. This multi-functionality allows precise brightness control without requiring separate dedicated circuits for each function, thereby improving precision while minimizing area increase.
Solution Approach 2:
The emission control transistor is integrated into the existing pixel circuit architecture, sharing the same physical space and electrical nodes as other components. By combining the emission control function with the existing transistor network rather than adding completely separate control circuits, the patent achieves precise timing control and brightness modulation without proportionally increasing the pixel area.
3Productivity
If frame rate is increased to reduce latency and motion blur, then display responsiveness improves, but power consumption increases
Solution Approach 1:
The pixel circuit is designed to operate in discrete periods corresponding to frame cycles, with the emission control transistor enabling light output only during specific time windows within each frame period. This periodic operation allows the display to maintain high frame rates for responsiveness while controlling power consumption by limiting the duration of high-current light emission events to necessary intervals only.
Solution Approach 2:
The storage capacitor pre-charges to the required voltage level during the programming phase before the emission period begins. This preliminary action allows the driving transistor to immediately source the required current when the emission control transistor activates, enabling fast response at high frame rates without requiring sustained high power consumption throughout the entire frame period.
Data Source
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AI summary
Embodiments of pixel circuits for light emitting elements are disclosed herein. In one example, a pixel circuit includes a pixel driver and a bridge transistor. The pixel driver is configured to receive a data signal and drive a light emitting element based on the data signal. The bridge transistor includes a gate terminal receiving a first bias signal, a source terminal coupled to the pixel driver, a drain terminal coupled to a terminal of the light emitting element, and a body terminal coupled to the source terminal or receiving the data signal. The first bias signal controls a voltage at the source terminal.