Backlight Unit Row Scanning Brightness Compensation
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Solution Overview
Problem
Liquid crystal displays experience brightness differences between rows due to capacitance changes in liquid crystal cells when scanned, leading to a 'waterfall' effect caused by varying light transmittance, which affects image quality.
Innovation Solution
A backlight control circuit supplies pulse width modulation signals to adjacent rows to adjust brightness, with pre-scanning and post-scanning techniques that reduce brightness differences by using pulse width modulation signals with lower brightness levels than those applied to scanned rows, thereby minimizing the 'waterfall' effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the backlight unit is scanned in the row direction to reduce motion blur, then motion blur is reduced, but brightness differences occur between rows causing waterfall effect
Solution Approach 1:
The patent applies different brightness levels to different row groups within the same scanning period. Specifically, odd-numbered row groups are displayed at full brightness while even-numbered row groups are displayed at reduced brightness (e.g., 50% or 75% of full brightness). This local differentiation in illumination quality compensates for the capacitance changes that occur during sequential row scanning, thereby preventing the waterfall effect while maintaining the benefits of row-by-row scanning for motion blur reduction.
Solution Approach 2:
The patent implements a periodic brightness modulation scheme where the backlight unit alternates between full brightness and reduced brightness in a regular pattern corresponding to the scanning sequence. By periodically adjusting the brightness of alternating row groups (e.g., bright-dim-bright-dim pattern), the system creates a temporal compensation mechanism that counteracts the cumulative capacitance changes during scanning, thus eliminating brightness non-uniformity across rows.
2Illumination intensity
If pulse width modulation signals are supplied to adjust brightness of adjacent rows, then brightness differences are reduced, but device complexity increases
Solution Approach 1:
The patent divides the backlight unit into multiple independent row groups (odd-numbered and even-numbered rows separated into distinct groups). Each row group is controlled by separate pulse width modulation signals with different brightness levels. This segmentation allows independent control of brightness for different row groups, enabling the compensation of capacitance-induced brightness variations while using relatively simple per-group control logic rather than complex pixel-level control.
Solution Approach 2:
The patent applies pulse width modulation signals selectively to specific row groups (odd or even rows) rather than uniformly to all rows. By applying brightness adjustment only to the rows that require compensation (e.g., reducing brightness of even rows that would otherwise appear darker), the control circuit achieves brightness uniformity with minimal additional complexity, avoiding the need for complex control of every single row.
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 solution effectively reduces brightness differences between rows, minimizing the 'waterfall' effect and enhancing image quality by compensating for capacitance changes in liquid crystal cells during scanning.
Implementation Method 1
The backlight control circuit supplies a pulse width modulation signal to rows adjacent to rows being scanned
Data Source
AI summary
A liquid crystal display includes a liquid crystal panel that displays an image signal, a backlight unit supplying light to the liquid crystal panel, and a backlight control circuit to scan the backlight unit. The backlight control circuit supplies a pulse width modulation signal to rows of the backlight unit, which are adjacent to rows being scanned, such that the rows adjacent to the rows being scanned have a brightness lower than a brightness of the rows being scanned.