Shift Register Circuit Bootstrap High-Impedance State
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing liquid crystal display devices face issues with reducing the manufacturing cost and improving image quality due to the use of scanning line driving circuits with high on-resistance amorphous silicon TFTs, which lead to delayed pulse rise and fall times, reduced contrast, and image quality degradation.
Innovation Solution
A shift register circuit using transistors of a single conductivity type, specifically N-channel TFTs, is designed to bring the scanning line into a high-impedance state through a bootstrap effect, reducing the load on the scanning line driving circuit and eliminating the need for additional switch TFTs, thereby improving pulse rise and fall characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon TFTs are used for pixel switches only with external semiconductor chips for scanning line driving, then manufacturing flexibility is maintained, but manufacturing cost increases and device complexity increases
Solution Approach 1:
The patent merges the scanning line driving circuit with the pixel switch TFTs by forming both on the same glass substrate using the same amorphous silicon TFT fabrication process. This integration eliminates separate semiconductor chips and mounting steps, directly reducing manufacturing cost and device complexity while maintaining ease of manufacture
Solution Approach 2:
The patent creates a universal TFT structure that can function both as pixel switches and as scanning line driving circuit transistors. By using the same amorphous silicon TFT technology for both functions, the system achieves multi-functionality without requiring different device types or additional manufacturing processes
2Ease of manufacture
If single conductivity type TFTs are used for scanning line driving circuit, then manufacturing cost is reduced, but pulse rise and fall times are delayed due to high on-resistance
Solution Approach 1:
The patent introduces a high-impedance state capability that dynamically changes the output impedance of the scanning line driving circuit based on operational requirements. By switching between low-impedance (active driving) and high-impedance (floating) states, the circuit achieves fast pulse transitions while maintaining the simplicity of single conductivity type TFTs
Solution Approach 2:
The patent changes the impedance parameter of the scanning line driving circuit output by controlling the state of specific TFTs. The output can be switched between low-impedance mode (for fast pulse output) and high-impedance mode (for floating state), optimizing performance without requiring dual conductivity types
3Reliability
If scanning line is kept in active state continuously, then driving capability is maintained, but voltage stress on TFTs increases causing image quality degradation
Solution Approach 1:
The patent implements periodic switching between active driving state and high-impedance floating state for the scanning lines. This periodic action allows the TFTs to rest during high-impedance periods, reducing cumulative voltage stress and preventing image quality degradation while maintaining driving capability during active periods
Solution Approach 2:
The patent applies preliminary anti-action by introducing the high-impedance floating state as a protective measure against voltage stress accumulation. This preventive mechanism reduces the harmful effects of continuous voltage application on TFTs before degradation occurs, extending device reliability
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enhances image quality by reducing voltage stress on TFTs, preventing contrast reduction, and lowering manufacturing costs by eliminating the need for semiconductor chips and flexible cables, while maintaining high reliability and reducing manufacturing complexity.
Implementation Method 1
A shift register circuit using transistors of a single conductivity type, specifically N-channel TFTs, is designed to bring the scanning line into a high-impedance state through a bootstrap effect
Data Source
AI summary
A one-stage shift register includes: a first transistor with a drain electrode connected to a corresponding scanning line and with a source electrode connected to a power supply; a second transistor of a same conductivity type, with a drain electrode connected to a gate electrode of the first transistor, with a source electrode connected to the power supply, and with a gate electrode connected to a first external control signal line; a third transistor of the same conductivity type as the fist transistor, with a drain electrode connected to the drain electrode of the second transistor, with a source electrode connected to the power supply, and with a gate electrode connected to a node that uses a bootstrap effect; and a load circuit with one end thereof connected to a second external control signal line and the other end thereof connected to the drain electrode of the second transistor.