LCD Shift Register Circuit for Gate Bias Stress Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing drive circuits for liquid crystal display devices using amorphous silicon thin film transistors face issues with gate bias stress, which can lead to threshold voltage changes and malfunction in pull-down TFTs, affecting the lifespan and performance of the panel.
Innovation Solution
A shift register design that includes multiple stages with alternating AC voltage supply lines and DC voltage supply lines, along with dual clock signal supply lines, uses pull-up and pull-down TFTs controlled by node controllers to alternately charge and discharge nodes, minimizing direct current bias stress and preventing gate bias stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a pull-down TFT is continuously controlled by a single clock signal to output low-level voltage, then the circuit operation is simple, but the TFT experiences excessive gate bias stress leading to threshold voltage change and malfunction
Solution Approach 1:
The single pull-down TFT control function is segmented into two separate pull-down TFTs (first and second pull-down TFTs), each controlled by different clock signals (first and second clock signals with opposite phases). This segmentation distributes the operational stress across multiple devices, preventing any single TFT from experiencing continuous excessive gate bias stress while maintaining the overall circuit functionality.
Solution Approach 2:
The circuit implements periodic action by alternately activating the first and second pull-down TFTs using clock signals with opposite phases. During one half-cycle, the first pull-down TFT is active while the second is inactive, and vice versa during the other half-cycle. This periodic switching ensures that no single TFT remains continuously stressed, allowing each device to recover and preventing threshold voltage drift.
2Reliability
If AC voltage supply lines are added to alternately drive pull-down TFTs, then gate bias stress is reduced and reliability improves, but device complexity increases
Solution Approach 1:
The AC voltage supply lines serve multiple functions: they provide the alternating drive signals for the pull-down TFTs, establish the clock phases, and enable the periodic switching mechanism. By making the voltage supply system multi-functional, the patent reduces the need for separate dedicated components while achieving the reliability improvement through alternating TFT activation.
Data Source
AI summary
A shift register for use with a liquid crystal display device includes a plurality of stages. A stage of the shift register includes a first controller, a second controller and an output buffer. The first controller charges and discharges a first node. The second controller charges and discharges a second node and a third node. The output buffer outputs a first output signal in response to the state of the first node and a second output signal in response to the state of the second and third nodes. The shift register may be adaptive to avoid a malfunction caused by a gate bias stress.