Variable Refresh Rate Backlight Control Circuit
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Solution Overview
Problem
Existing backlight control methods for display panels with variable refresh rates face challenges in maintaining a stable and consistent duty cycle, leading to issues like image blinking and blurring due to asynchronous control schemes, and the inability to synchronize with variable frame periods in synchronous schemes.
Innovation Solution
A method and circuit for generating a first backlight control signal in fixed periods and a second signal in variable periods, with compensation pulses in subsequent frames to maintain a consistent duty cycle, ensuring the backlight control signal does not overlap with liquid crystal transition times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If synchronous backlight control scheme is applied, then backlight control signal is synchronous to vertical synchronization signal, but duty cycles of backlight control signals will not be consistent in different frame periods since frame period length is variable, causing blinking image
Solution Approach 1:
The patent divides the backlight control into two independent parts: a first backlight control signal generated in the fixed active period and a second backlight control signal generated in the variable blank period. This segmentation allows each signal to be optimized independently - the first signal maintains synchronization with the fixed active period while the second signal adapts to the variable blank period length, resolving the duty cycle consistency problem.
Solution Approach 2:
The patent introduces a dynamic adjustment mechanism where the second backlight control signal's duty cycle is calculated based on the actual length of the variable blank period. The formula `Duty Cycle2 = (Blank Period Length - Liquid Crystal Transition Time) / Blank Period Length` dynamically adapts to different frame rates, ensuring consistent overall duty cycle across variable frame periods.
2Productivity
If asynchronous backlight control scheme is applied, then pulses of backlight control signal are output in predetermined frequency, but output pulses may easily overlap liquid crystal transition time, causing blurring display image
Solution Approach 1:
The patent performs preliminary action by calculating and accounting for the liquid crystal transition time when generating the second backlight control signal in the blank period. The signal generation is delayed by the liquid crystal transition time, ensuring the backlight pulse does not overlap with the liquid crystal transition period, thus preventing image blurring.
Solution Approach 2:
The patent introduces the liquid crystal transition time as an intermediary parameter that mediates between the backlight control signal and the display output. By incorporating this intermediary timing information, the system ensures proper spacing between the backlight pulse and the liquid crystal transition, preventing overlap and blurring.
3Adaptability or versatility
If variable refresh rate is applied, then display panel can adapt to GPU processing speed, but existing backlight control methods cannot maintain stable duty cycle, causing image blinking and blurring
Solution Approach 1:
The patent segments the backlight control into two independent signals: the first signal handles the fixed active period and the second signal handles the variable blank period. This segmentation enables the system to adapt to variable refresh rates while maintaining stable duty cycle - the first signal maintains consistency with fixed active period regardless of frame rate, while the second signal dynamically adapts to variable blank period length.
Solution Approach 2:
The patent changes the parameter approach by introducing a dynamic duty cycle calculation for the second backlight control signal based on the actual blank period length. The formula `Duty Cycle2 = (Blank Period Length - Liquid Crystal Transition Time) / Blank Period Length` allows the system to adapt to different refresh rates by adjusting the duty cycle parameter dynamically, maintaining overall control stability across variable frame periods.
Data Source
AI summary
A method of backlight control for a display panel is provided. The display panel is configured to display with a variable refresh rate in a plurality of frame periods each having a fixed period and a variable period. The method includes steps of: generating a first backlight control signal in the fixed period of a frame period; determining whether a liquid crystal (LC) transition time corresponding to the frame period ends before an end time of the variable period of the frame period; generating a second backlight control signal in the variable period of the frame period when the LC transition time ends before the end time of the variable period of the frame period; and generating a compensation backlight control signal in a next frame period according to a backlight duty cycle of the frame period.