Backlight Driver Vsync Filter PWM Duty Ratio Stability
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Solution Overview
Problem
Conventional backlight drivers for liquid crystal display devices experience flicker and wavy noise due to distortions in PWM drive frequency when the input vertical synchronization signal's frequency changes, leading to unsynchronized operation and image quality issues.
Innovation Solution
A backlight driver that includes a vertical synchronization signal filter to generate a second synchronization signal based on the input signal, selecting between the original and filtered signals based on period differences, and a duty ratio detector to maintain a constant PWM signal duty ratio, thereby preventing flicker and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the PWM drive frequency is slowly changed when the input Vsync frequency changes, then backlight flicker is prevented, but synchronization with the input Vsync is distorted causing wavy noise
Solution Approach 1:
The patent introduces a synchronization signal filter as an intermediary component that processes the input Vsync signal before it reaches the PWM generator. This filter generates a filtered Vsync signal that maintains stable frequency characteristics, acting as a mediator between the variable input Vsync and the PWM drive circuit. The filter smooths out frequency variations without causing the distortion that leads to wavy noise, thus resolving the contradiction between preventing flicker and avoiding noise.
Solution Approach 2:
The patent changes the parameter of the synchronization signal by filtering it to produce a version with stabilized frequency characteristics. The filter modifies the temporal parameters of the Vsync signal, creating a version that maintains the essential timing information while removing frequency instability. This parameter transformation allows the system to maintain stable PWM drive frequency without sacrificing synchronization accuracy.
2Stability of the object's composition
If the PWM drive frequency tracks the input Vsync frequency changes, then synchronization is maintained, but PWM duty ratio distortion occurs leading to backlight flicker
Solution Approach 1:
The synchronization signal filter serves as an intermediary that decouples the direct relationship between input Vsync frequency variations and PWM drive frequency. By filtering the Vsync signal, the system maintains synchronization through the filtered signal while preventing duty ratio distortion. The filter mediates between the need for synchronization and the need for stable duty ratio by providing a smoothed version of the synchronization signal.
Solution Approach 2:
The filter provides beforehand cushioning by pre-processing the Vsync signal to remove frequency variations before they can affect the PWM duty ratio. This prior filtering action cushions the system against the harmful effects of frequency jitter, preventing duty ratio distortion before it occurs while still maintaining the essential synchronization timing.
3Reliability
If a filter is applied to the input Vsync signal, then PWM duty ratio stability is improved, but system complexity increases
Solution Approach 1:
The synchronization signal filter is implemented as a dedicated intermediary component with a specific function - filtering the Vsync signal. By giving this filtering function a separate, specialized module, the complexity is localized and manageable rather than distributed throughout the entire system. This modular approach to complexity makes the system easier to design, implement, and maintain while achieving the desired flicker prevention.
Data Source
AI summary
A backlight driver and a method of driving the same are disclosed. The backlight driver includes a vertical synchronization signal filter for generating a second vertical synchronization signal based on an input first vertical synchronization signal, and selecting one of the first vertical synchronization signal and the second vertical synchronization signal as a third vertical synchronization signal according to whether a period difference between adjacent first vertical synchronization signals satisfies a preset threshold range, a duty ratio detector for detecting a duty ratio of an input pulse width modulation (PWM) signal, a PWM generator for generating an output PWM signal synchronized with the third vertical synchronization signal output from the vertical synchronization signal filter and having the duty ratio and outputting the output PWM signal to a backlight unit.