Backlight Unit LED Chromaticity Convergence Control
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Solution Overview
Problem
LCD devices face challenges in quickly converging white light to a predetermined chromaticity after turn-on and in maintaining image quality, particularly with time-varying images, due to temperature variations and intermittent LED operation.
Innovation Solution
A backlight unit with LEDs assigned to multiple light-emitting regions, a chromaticity sensor, and a light-source driver that adjusts LED emission in sequential scanning and additional periods synchronized with an optical leakage signal, ensuring higher light quantities and precise chromaticity control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If LEDs are operated intermittently in scanning light-emitting periods only, then image quality is improved by preventing contour blur, but the time required to converge white light to predetermined chromaticity increases
Solution Approach 1:
The patent applies periodic action by implementing two types of light-emitting periods: scanning light-emitting periods for normal image display and additional light-emitting periods for chromaticity adjustment. The LEDs operate intermittently in both types of periods, with the additional periods providing repeated chromaticity adjustment opportunities without causing contour blur since they occur during black signal periods when the LCD panel is in optical leakage prevention state.
Solution Approach 2:
The patent applies preliminary action by performing chromaticity adjustment in advance during additional light-emitting periods that occur before the main image display. The backlight controller section uses light quantities from additional light-emitting periods to adjust chromaticity proactively, ensuring white light converges to predetermined chromaticity before actual image display begins, thereby preventing chromaticity errors.
2Measurement precision
If feedback control is performed at high speed to adjust chromaticity, then chromaticity accuracy is improved, but the change is recognized by users causing visible color shifts on screen
Solution Approach 1:
The patent uses the additional light-emitting periods as an intermediary mechanism between chromaticity detection and display. The backlight controller section detects light quantities during additional light-emitting periods and adjusts chromaticity based on these measurements, but the adjustments are applied subtly over multiple periods rather than abruptly, preventing visible color shifts while maintaining chromaticity accuracy.
Solution Approach 2:
The patent applies partial action by performing chromaticity adjustment in a distributed manner across multiple additional light-emitting periods rather than in a single high-speed correction. Each additional period contributes partially to the overall chromaticity adjustment, accumulating the correction gradually to achieve accurate white light without causing sudden visible color shifts that users would notice.
3Stability of the object's composition
If driving currents for red, green, and blue LEDs are set at predetermined initial values at turn on, then chromaticity stability is improved, but the response time to achieve white light remains long due to LED temperature variations
Solution Approach 1:
The patent implements feedback control by having the backlight controller section detect light quantities from LEDs during additional light-emitting periods and adjust driving currents accordingly. The controller uses the detected chromaticity information to modify the driving currents for red, green, and blue LEDs in subsequent periods, creating a closed-loop system that accelerates chromaticity convergence while maintaining stability through continuous adjustment based on actual measured values.
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 solution shortens the time to achieve stable white light chromaticity and improves the quality of time-varying images by increasing light emission quantities and synchronizing LED operations with optical leakage prevention, preventing contour blur and chromaticity errors.
Implementation Method 1
a chromaticity sensor for detecting a chromaticity of white light generated by the LEDs
Implementation Method 2
a light source including red, green, and blue LEDs
Implementation Method 3
The LEDs are driven to emit lights sequentially
Data Source
AI summary
A backlight unit shortens the necessary time from the time immediately after the turn on to the time the emitted light is converged to a predetermined chromaticity while the quality of time-varying images is improved. Under the control of the backlight controller section, the Light-Emitting Diodes (LEDs), which are assigned to the respective light-emitting regions of the light-emitting surface, are driven to emit lights sequentially in the predetermined scanning light-emitting periods for the scan type lighting and the additional light-emitting periods in a single frame, responsive to the write scanning of an image signal to the LCD panel. The additional light-emitting periods are outside a corresponding one of the scanning light-emitting periods. In each additional light-emitting period, the LEDs emit light in synchronization with the supply of the optical leakage preventing signal (e.g., the black inserting signal) to the LCD panel.