IGZO-TFT Shift Register Off Control Transistor Charge Discharge
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Solution Overview
Problem
IGZO-TFT liquid crystal panels face challenges with residual charges remaining after power supply is stopped, leading to display defects like flicker due to their excellent off characteristics, which require additional circuit elements and increase costs in dual power supply systems.
Innovation Solution
A display device with a scanning line drive circuit that includes a shift register with an off control transistor, using a single power supply system to generate scanning line selecting and unselecting voltages, ensuring charges are discharged by maintaining the off control transistor in an on state longer, reducing residual charges and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dual power supply system is used to discharge residual charges in IGZO-TFT liquid crystal panels, then display defects are prevented, but the number of circuit elements increases and cost increases
Solution Approach 1:
The patent combines the charge discharge function with the existing single power supply system by adding an off control transistor to the shift register circuit. This merges the power management and charge discharge functions into a unified circuit architecture, eliminating the need for separate dual power supply circuits while maintaining the ability to discharge residual charges effectively.
Solution Approach 2:
The off control transistor is configured to automatically activate when the power supply voltage drops during power off, creating a self-service mechanism that discharges residual charges without requiring external control signals or additional power management circuits. The circuit uses its own power supply voltage drop as the trigger for charge discharge.
2Reliability
If a dual power supply system is used to discharge residual charges, then residual charge accumulation is prevented, but manufacturing cost increases
Solution Approach 1:
The patent merges the charge discharge function with the existing shift register circuit by adding one off control transistor, rather than implementing a separate dual power supply system. This integration reduces the total component count and simplifies the manufacturing process, thereby reducing manufacturing costs while maintaining charge discharge performance.
Solution Approach 2:
The off control transistor is designed to be a simple, inexpensive component that activates temporarily during power off to discharge residual charges, then returns to its default state. This disposable-like approach uses a low-cost component to solve the residual charge problem without requiring expensive dual power supply infrastructure.
3Reliability
If the off control transistor remains in on state longer, then residual charges are discharged more effectively, but the transistor operates longer increasing energy consumption
Solution Approach 1:
The off control transistor operates periodically - remaining in the on state only during the power off transition period when charge discharge is needed, then returning to the off state during normal operation. This periodic activation ensures complete charge discharge while minimizing energy consumption by limiting the transistor's active duration to only when necessary.
Solution Approach 2:
The off control transistor is configured to activate automatically when the power supply voltage drops, creating a preliminary anti-action that counteracts residual charge accumulation before it can cause display defects. This automatic response occurs precisely when needed (during power off) without requiring continuous energy consumption to maintain the discharge state.
Data Source
AI summary
A configuration in which a voltage (a gate on voltage) of only one system is used as a voltage for turning scanning lines to a selected state is employed (single power supply system configuration). A unit circuit that constitutes a shift register within a gate driver includes a thin film transistor whose source terminal is connected to an output control node. In such a configuration, when the external power supply is stopped, a voltage supplied to a gate terminal of the thin film transistor and a voltage supplied to a drain terminal of the thin film transistor are set to the gate on voltage.