LC Display Black Level Degradation via Wavelength Plate Segmentation
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Solution Overview
Problem
Liquid crystal display devices in the normally white mode face challenges with black level degradation due to difficulties in minimizing light transmittance during black display, affecting display quality across a wide frequency band and viewing angles.
Innovation Solution
A liquid crystal display device configuration that includes a liquid crystal layer with specific retardation values, a half-wavelength plate, and a quarter-wavelength plate, where the slow axes of these components are oriented to intersect at specific angles, ensuring proper black and white levels are maintained across a wide viewing angle, preventing black level degradation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional liquid crystal display configuration is used in normally white mode, then the display can operate in normally white mode, but black level degradation occurs due to inability to minimize light transmittance
Solution Approach 1:
The patent segments the optical path by introducing multiple wavelength plates (half-wavelength plate and quarter-wavelength plate) with specific slow axis orientations. This segmentation allows independent control of light polarization states at different stages, enabling minimal light transmittance in black display state by precisely configuring the optical path segments to cancel out light transmission.
Solution Approach 2:
The patent changes the retardation parameters of the liquid crystal layer and wavelength plates to achieve optimal black level. Specifically, the liquid crystal layer retardation is set to 1/4 to 1/2 of the half-wavelength plate retardation, and the slow axes are oriented at specific angles (45° for quarter-wavelength plate, 90° for half-wavelength plate relative to polarizer). These parameter changes enable the system to minimize light transmittance effectively.
2Illumination intensity
If optical compensation layers are added to improve black level, then black level degradation is reduced, but device complexity increases
Solution Approach 1:
The wavelength plates serve multiple functions: they compensate for liquid crystal layer retardation, control light polarization orientation, and enable minimal light transmittance in black state. By making these components multi-functional, the patent reduces the need for additional separate compensation layers, thereby controlling device complexity while achieving improved black level.
3Adaptability or versatility
If liquid crystal layer retardation is increased to improve viewing angle, then viewing angle performance improves, but black level degradation worsens
Solution Approach 1:
The patent establishes a specific parameter relationship where liquid crystal layer retardation is set to 1/4 to 1/2 of the half-wavelength plate retardation, and the slow axis of the liquid crystal layer is oriented at 45° to the polarizer's transmission axis. This parameter configuration achieves a balance between viewing angle performance and black level maintenance by controlling the optical path in a way that preserves black level while allowing adequate viewing angle.
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
The configuration achieves high-quality display with reduced black level degradation and improved visibility in both black and white states, even at oblique viewing angles, by ensuring the liquid crystal layer's retardation is between one-quarter and one-half of the half-wavelength plate's retardation.
Implementation Method 1
a half-wavelength plate 7 and a first quarter-wavelength plate 8 disposed between the liquid crystal display panel 5 and the first polarizing plate 6
Implementation Method 2
a liquid crystal layer 2, and a light reflective layer 4 which reflects incident light from a display surface 3 side having passed through the liquid crystal layer 2
Data Source
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AI summary
The present disclosure relates to a liquid crystal display device of an electrically controlled birefringence type which carries out display in a normally white mode, which can attain a proper black level to reduce the appearance of black level degradation and ensure high-quality display on a wide frequency band and attain a proper white level to ensure high-quality display. A liquid crystal display device of an electrically controlled birefringence type which carries out display in a normally white mode, includes a liquid crystal display panel (5) including a light reflective portion (47), a first polarizing plate (6) located on a display surface (3)-facing side, a half-wavelength plate (7) and a first quarter-wavelength plate (8) disposed between the liquid crystal display panel (5) and the first polarizing plate (6). A liquid crystal layer (2) corresponding to the light reflective portion (47) exhibits a retardation which is less than one-half of a retardation of the half-wavelength plate (7). The first quarter-wavelength plate (8) has a slow axis which intersects a liquid-crystal molecular orientation axis at a time of no electric field application. The expression nx1 > nz1 > ny1 is satisfied, where nx1, ny1 and nz1 are the refractive indices at each orientation of the half-wavelength plate (7), and the expression nx2 > nz2 = ny2 is satisfied, where nx2, ny2 and nz2 are the refractive indices at each orientation of the first quarter-wavelength plate (8).