Pull-Down Control Circuit for Shift Register Voltage Stress Relief
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Solution Overview
Problem
Conventional shift registers using amorphous silicon thin film transistors suffer from reliability issues due to prolonged high voltage stress, leading to transistor deterioration and reduced performance.
Innovation Solution
A pull-down control circuit with a release circuit and transistors T4, T5, T6, and T7, where the transistors are designed to alternate between on and off states, reducing stress on T5 and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If transistor T5 is continuously turned on for a long period to maintain voltage levels, then the voltage control function is achieved, but the transistor characteristics deteriorate due to prolonged high voltage stress
Solution Approach 1:
The patent applies periodic action by alternating transistor T5 between on and off states in a periodic manner. The control circuit switches T5 on during periods when voltage difference K(n)−P(n) is high, and turns it off during periods when the voltage difference is low, preventing continuous operation and reducing cumulative stress on the transistor.
Solution Approach 2:
The patent implements dynamics by making the transistor T5 state variable rather than static. The transistor dynamically transitions between on and off states based on real-time voltage conditions at nodes K and P, allowing the system to adapt its operation to minimize stress while maintaining necessary voltage control.
2Reliability
If high voltage is continuously applied to transistor T5, then the voltage difference K(n)−P(n) is maintained at high level, but the transistor may not function properly due to stress deterioration
Solution Approach 1:
The control circuit implements periodic action by applying high voltage to transistor T5 only during specific periods when needed (when voltage difference K(n)−P(n) is high), and reducing voltage application during other periods. This periodic voltage application maintains necessary voltage differences while preventing continuous high voltage stress that would lead to transistor deterioration.
3Reliability
If the pull-down control circuit uses a simple configuration with fewer transistors, then the circuit complexity is reduced, but the ability to manage voltage stress and improve reliability is limited
Solution Approach 1:
The patent introduces an intermediary control circuit comprising transistors T4, T6, and T7 that mediates between the voltage sources and transistor T5. These intermediary transistors sense voltage differences and control the timing of T5's operation, enabling stress reduction functionality while maintaining a manageable circuit complexity through a systematic four-transistor architecture.
Data Source
AI summary
The present invention relates to a pull-down control circuit and a shift register of using same. In one embodiment, the pull-down control circuit includes a release circuit and four transistors T4, T5, T6 and T7 electrically coupled to each other. The release circuit is adapted for causing the transistor T5 to be turned on and off alternately, thereby substantially reducing the stress thereon, improving the reliability and prolonging the lifetime of the shift register.