Gate Driving Circuit With Mesh VDD Supply for OLED Luminance Uniformity
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Solution Overview
Problem
Existing OLED display devices face issues with luminance non-uniformity due to variations in threshold voltage and mobility of driving TFTs, leading to mura defects and IR drop phenomena, which are not effectively addressed by current pixel circuits like 6T1C and 7T1C, and the 8T1C circuit faces challenges in supplying high-level supply voltage VDD using a mesh structure.
Innovation Solution
A gate driving circuit with a mesh structured supply line for high-level supply voltage VDD, incorporating a reference voltage/high-level supply voltage output unit to compensate for TFT variations, ensuring stable luminance by compensating for threshold voltage and mobility deviations, and allowing repair of supply lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel circuit (6T1C or 7T1C) is used to drive OLED elements, then the circuit can control driving current, but luminance non-uniformity occurs due to TFT threshold voltage and mobility variations
Solution Approach 1:
The patent introduces a compensation circuit that generates a compensation voltage to counterbalance the threshold voltage variations of the driving TFT. By applying this compensation voltage to the gate of the driving TFT, the circuit effectively cancels out the unwanted voltage shifts caused by TFT parameter variations, thereby maintaining uniform luminance across the display.
Solution Approach 2:
The patent implements a feedback mechanism where the actual driving current or voltage is sensed and used to adjust the gate voltage of the driving TFT. This closed-loop control ensures that variations in TFT characteristics are continuously compensated, maintaining stable luminance output despite manufacturing tolerances and aging effects.
2Reliability
If the 8T1C pixel circuit is used to compensate for TFT variations, then threshold voltage compensation is achieved, but IR drop phenomenon still occurs and high-level supply voltage cannot be effectively supplied
Solution Approach 1:
The patent divides the power supply function into multiple independent paths: one path supplies reference voltage for compensation purposes, while another path supplies high-level supply voltage for driving current. This segmentation allows each path to be optimized independently, ensuring that compensation functions work correctly without being affected by voltage drops in the power supply path.
Solution Approach 2:
The patent introduces an intermediary compensation circuit that acts as a mediator between the power supply and the OLED element. This intermediate stage adjusts and stabilizes the voltage before it reaches the driving TFT, preventing IR drop from affecting the final driving voltage and ensuring consistent luminance output.
3Ease of repair
If a mesh structured supply line is implemented, then supply line repair capability is enabled, but device complexity increases
Solution Approach 1:
The patent implements a dynamic mesh structure where the connectivity and activation of different paths can be changed based on operational needs. When a supply line fault is detected, the system dynamically reconfigures the mesh to activate alternative paths, enabling repair without physical intervention. This dynamic adaptability provides repair capability while maintaining relatively simple structural design.
Data Source
AI summary
A gate driving circuit includes a plurality of stages that are dependently connected, wherein an n-th one of the stages (n being a natural number) comprises a node controller for controlling voltages of set and reset nodes, a scan signal generator controlled in accordance with the voltages of the set and reset nodes, thereby outputting a scan signal to a scan line of a display panel, and a reference voltage/high-level supply power output unit controlled in accordance with the voltages of the set and reset nodes, thereby outputting a reference voltage or a high-level supply voltage to a reference voltage line of the display panel.