Semi-transmissive LCD Driving Method for Power and Contrast
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Solution Overview
Problem
Liquid crystal display devices face challenges in reducing power consumption while maintaining image contrast, particularly due to light scattering in reflective pixel portions and high backlight power consumption.
Innovation Solution
A method for driving a semi-transmissive liquid crystal display device that alternates between light-transmitting and reflective pixel portions, using oxide semiconductor transistors to minimize off-state current, allowing for reduced refresh rates and power consumption without increasing complexity, by controlling pixel transistors and supply of driver circuit signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If field sequential driving is used in a semi-transmissive liquid crystal display device, then power consumption is reduced, but contrast of the display image deteriorates due to light scattering in reflective pixel portions
Solution Approach 1:
The pixel portion is divided into a light-transmitting pixel portion and a reflective pixel portion, which are driven independently through separate transistor control paths. This segmentation allows the light-transmitting portion to be refreshed at higher rates while the reflective portion uses lower refresh rates, reducing overall power consumption without compromising the contrast of the reflective portion.
Solution Approach 2:
The driving method dynamically adjusts the refresh rate for different pixel portions based on their display requirements. The light-transmitting pixel portion receives continuous refresh signals while the reflective pixel portion receives refresh signals at a lower frequency, creating a dynamic, adaptive driving scheme that optimizes both contrast and power consumption.
2Use of energy by moving object
If refresh rate is lowered for still image display, then power consumption is reduced, but power consumption of backlight remains high
Solution Approach 1:
The display device implements periodic action by alternating between different driving modes: for moving images, the light-transmitting pixel portion is refreshed at high frequency with backlight on, while for still images, the reflective pixel portion is refreshed at low frequency with backlight off, utilizing reflected ambient light instead. This periodic switching reduces overall power consumption including backlight usage.
3Use of energy by moving object
If semi-transmissive liquid crystal display device structure is used, then power consumption can be reduced, but device structure becomes more complex
Solution Approach 1:
The liquid crystal display device achieves multi-functionality by incorporating both light-transmitting and reflective pixel portions within the same display panel, allowing it to operate in different modes (transmissive for moving images, reflective for still images) without requiring separate display devices. This universal design reduces power consumption while avoiding the complexity of multiple independent display systems.
Data Source
AI summary
In an image signal writing period, a first image signal is supplied to a first liquid crystal element and a first capacitor from a first signal line. In a backlight lighting period, display is performed in a light-transmitting pixel portion in response to the first image signal. In a black grayscale signal writing period, a signal for black display is supplied to a second liquid crystal element and a second capacitor from a second signal line. In a still image signal writing period, a second image signal is supplied to the first liquid crystal element, the first capacitor, the second liquid crystal element, and the second capacitor from the first signal line. In a still image signal holding period, display is performed in the reflective pixel portion in response to the second image signal.