Active Matrix LCD Charge Discharge via Escaping Transistor
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Solution Overview
Problem
Active matrix liquid crystal display devices face challenges in quickly discharging pixel electrodes when powered off, leading to image retention due to differing polarities of pixel and sampling transistors, which complicates the process and requires special control signals.
Innovation Solution
Incorporating an electric charge escaping transistor on each source bus line with the same polarity as the pixel transistor, and using a voltage control mechanism to generate a gate control voltage that turns on the electric charge escaping transistor before the pixel transistor reaches GND level, allowing for efficient discharge without a special control signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the pixel transistor and sampling transistor have different polarities, then the device can achieve more flexible transistor configuration, but the electric charges cannot be let out at power-off causing image retention
Solution Approach 1:
The patent introduces an electric charge escaping transistor as an intermediary component between the source bus line and the common electrode. This mediator enables charge discharge regardless of the polarity relationship between pixel and sampling transistors, resolving the contradiction by adding a dedicated discharge path that works independently of the sampling transistor's polarity configuration.
Solution Approach 2:
The patent segments the discharge function from the sampling transistor function by adding a separate electric charge escaping transistor. This segmentation allows the discharge mechanism to operate independently of the sampling transistor's polarity, enabling reliable charge discharge even when pixel and sampling transistors have different polarities.
2Reliability
If a special control signal is used to discharge pixel charges, then the charge discharge can be controlled precisely, but the device complexity increases
Solution Approach 1:
The electric charge escaping transistor automatically responds to the power-off state by detecting the voltage level of the source bus line. When power is turned off and the source bus line voltage drops below a threshold, the transistor automatically turns on to discharge charges, eliminating the need for external control signals and reducing device complexity while maintaining reliable discharge control.
Solution Approach 2:
The electric charge escaping transistor uses feedback from the source bus line voltage to automatically control its own state. The transistor turns on when the source bus line voltage drops below a threshold during power-off, providing automatic discharge control without requiring external control signals, thus reducing device complexity.
3Speed
If the VSS voltage reaches GND before VDD voltage reaches GND, then the pixel transistor becomes half-open enabling charge escape, but the sampling transistor may not be electrically continuous when polarities differ
Solution Approach 1:
The electric charge escaping transistor serves as an intermediary that ensures reliable charge discharge even when the sampling transistor is not electrically continuous. It provides an alternative discharge path that activates when the pixel transistor becomes half-open during power-off, maintaining fast charge discharge speed regardless of the sampling transistor's continuity state.
Solution Approach 2:
The electric charge escaping transistor is prepared in advance during the power-off sequence to activate when needed. As the source bus line voltage drops below the threshold, the transistor automatically turns on before the discharge process completes, ensuring continuous and reliable charge discharge throughout the power-off period.
Data Source
AI summary
In one embodiment of the present invention, on each source bus line, an electric charge escaping transistor is provided having the same polarity as a pixel transistor and having a gate to which a turn-off voltage signal of the pixel transistor is supplied. When an active matrix liquid crystal display device is powered off, the turn-off voltage signal is made to reach the GND level before a turn-on voltage signal of the pixel transistor reaches the GND level, so that the pixel transistor and the electric charge escaping transistor are made half-open. This lets electric charges accumulated in the pixel escape to a common electrode TCOM.