Shift Register TFT Duty Cycle Reduction for Noise Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In shift register units for LCDs, the node connected to the gate of the lowering signal TFT is typically at a high level for most of the time, causing the lowering signal TFT to remain conductive and leading to a large threshold voltage offset, which can result in the TFT failing to suppress noise effectively, thereby affecting the overall performance of the shift register.
Innovation Solution
The shift register unit incorporates boosting and lowering signal TFTs, with specific drive TFTs and clock signals to manage the voltage levels, reducing the duty cycle of the lowering drive TFTs and preventing biasing effects, ensuring the lowering signal TFTs can effectively suppress noise and maintain the reliability of the shift register.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the lowering signal TFT is kept conductive to suppress noise during low-level driving signal period, then noise suppression is improved, but the threshold voltage offset increases and the TFT may fail to turn on
Solution Approach 1:
The lowering drive TFT is controlled to operate periodically rather than continuously. It is turned on only during specific periods when the driving signal is at low level and noise suppression is needed, and turned off during other periods. This periodic operation maintains noise suppression effectiveness while preventing continuous conduction that causes threshold voltage offset and reliability degradation.
Solution Approach 2:
The conduction state of the lowering signal TFT is dynamically changed by controlling the lowering drive TFT. The gate voltage of the lowering drive TFT is adjusted based on the driving signal level, causing the lowering signal TFT to switch between conductive and non-conductive states. This parameter change allows the TFT to suppress noise when needed while avoiding continuous conduction issues.
2Object-affected harmful factors
If the lowering drive TFT operates continuously to maintain low-level signal, then noise suppression is improved, but the duty cycle increases causing biasing effects
Solution Approach 1:
The lowering drive TFT operates periodically rather than continuously. It is activated only during periods when the driving signal is at low level and noise suppression is required, and deactivated during other periods. This reduces the duty cycle from near-continuous operation to intermittent operation, preventing biasing effects while maintaining noise suppression during critical periods.
Solution Approach 2:
The lowering drive TFT automatically activates and deactivates based on the state of the driving signal without requiring external control. When the driving signal transitions to low level, the lowering drive TFT self-activates to suppress noise, and when the signal returns to high level, it self-deactivates. This self-service operation naturally limits the duty cycle and prevents continuous conduction.
Data Source
Figure 1a
Figure 1b
Figure 2a
AI summary
A shift register comprising at least two shift register units is disclosed, wherein one shift register unit comprises a boost signal thin film transistor, boost driving thin film transistors, depression signal thin film transistors, depression driving thin film transistors and close-up driving thin film transistors. The kind of the shift register increases the number of depression driving thin film transistors and adds the mode that a clock signal is in turn applied every other frame, decreases the duty cycle of depression driving thin film transistors, thus efficiently preventing the biasing effect of depression driving thin film transistors, thereby ensuring the reliability of the shift register unit. A gate driving device and data line driving device for liquid crystal display are still disclosed.