LCD Scanning Backlight Timing to Prevent Pseudo Contour
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Solution Overview
Problem
Liquid crystal display devices with scanning-type backlights suffer from pseudo contour and flickering due to insufficient response control and time lag in backlight activation, leading to poor moving image quality and noticeable double edging, especially at 60 Hz driving clock frequency.
Innovation Solution
The implementation of a backlight turning-ON drive circuit with a controller that synchronizes direct-type backlights to turn ON discretely over continuous frames, alternating their activation timing between odd and even frames, and adjusting the frequency to 2/(2n+1) of the refresh period, along with identical ON and OFF periods, to prevent pseudo contour and flickering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If backlights are turned on in sync with scanning signal at 60 Hz, then moving image response performance is improved, but double edging and pseudo contour occur due to insufficient response control
Solution Approach 1:
The patent applies dynamics by making the backlight timing adjustable and adaptable rather than fixed. The system dynamically adjusts the backlight turning-on timing relative to the scanning signal based on the liquid crystal response characteristics, allowing optimization for different display conditions while maintaining luminance uniformity and preventing double edging.
Solution Approach 2:
The patent changes the timing parameter of backlight activation relative to the scanning signal. By adjusting the phase relationship between backlight turning-on and scanning signal, the system optimizes the liquid crystal response while preventing display artifacts such as double edging and pseudo contour, thus resolving the contradiction between response speed and luminance uniformity.
2Manufacturing precision
If backlights are turned on discretely over continuous frames, then pseudo contour and flickering are prevented, but device complexity increases due to additional control circuitry
Solution Approach 1:
The patent implements multi-functionality by integrating the backlight control function into the existing scanning signal processing circuitry. The same control system that generates scanning signals also controls backlight timing, eliminating the need for separate dedicated backlight control circuits and reducing overall device complexity while maintaining display quality.
Solution Approach 2:
The patent merges the backlight control function with the scanning signal control function. By combining these two control functions into a single integrated control mechanism, the system prevents pseudo contour and flickering while avoiding the complexity of separate control circuits, thus resolving the contradiction between display quality and device complexity.
3Object-affected harmful factors
If backlights are turned on at 120 Hz to prevent flickering, then flickering is reduced, but double edging problem persists and power consumption increases
Solution Approach 1:
The patent changes the frequency parameter of backlight activation from 120 Hz to 60 Hz, matching the scanning signal frequency. This parameter change eliminates the need for high-frequency backlight switching, reducing power consumption while preventing flickering through proper timing synchronization between backlight and scanning signal.
4Speed
If backlights are turned on in sync with scanning signal, then moving image display performance is improved, but flickering occurs due to frame rate synchronization
Solution Approach 1:
The patent applies periodic action by synchronizing backlight activation with the periodic scanning signal at 60 Hz. This periodic synchronization ensures that backlight turns on at consistent intervals matched to the display refresh rate, improving moving image performance while preventing flickering through proper phase alignment rather than continuous or high-frequency operation.
Data Source
AI summary
Provided are data lines, scanning lines crossing the data lines, and a switching element in vicinity of each intersection of the data lines and the scanning lines, the data lines being connected via the switching elements with pixel electrodes arranged in matrix. Direct-type backlights arranged in parallel with the scanning lines are provided, and a backlight turning-ON drive circuit for turning the direct-type backlights in order at a predetermined frequency in sync with a scanning signal is provided. In at least one embodiment, the backlight turning-ON drive circuit includes a controller for controlling the direct-type backlights to turn ON in order in sync with the scanning signal in such a manner that the direct-type backlights are turned ON discretely over frames being continuous based on a vertical sync signal. In at least one embodiment, this provides a liquid crystal display device, which adopts scanning-type backlights and in which the pseudo contour and the flickering can be prevented with a driving clock of 60 Hz, which is generally adopted in liquid crystal display devices.