Scan Driving Stage for AMOLED DC Bias Stability
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Solution Overview
Problem
The existing scan driving devices for AMOLED displays face instability in DC bias stress, leading to unstable operation of thin film transistors and subsequent issues with scan signal output, affecting the quality of the displayed image.
Innovation Solution
The proposed scan driving device incorporates a series of shift registers with specific terminal configurations and power voltage control mechanisms, including sustain signals and alternating clock signals, to improve DC bias stress stability and stabilize the output of scan signals, potentially converting DC driving to AC driving to alleviate transistor stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If DC bias is applied to thin film transistors in scan driving device, then the transistors can be operated in saturation mode, but DC bias stress causes instability in threshold voltage and output terminal node
Solution Approach 1:
The patent applies periodic AC driving signals instead of continuous DC bias to the thin film transistors. The scan driving device uses alternating high and low potential power source voltages in a periodic manner, which reduces DC bias stress accumulation while maintaining transistor switching functionality. This periodic action prevents threshold voltage drift and output node instability caused by sustained DC stress.
Solution Approach 2:
The patent changes the electrical parameters applied to the transistors by introducing multiple low potential power source voltages (e.g., VGL1, VGL2, VGL3 at different voltage levels) instead of a single DC voltage. By dynamically adjusting voltage levels and applying them periodically through sustain signals, the device maintains transistor operation while reducing bias stress and stabilizing threshold voltage.
2Reliability
If multiple low potential power source voltages are applied to shift registers, then DC bias stress stability is improved, but device complexity increases
Solution Approach 1:
The patent segments the power source voltage system into multiple distinct low potential voltages (VGL1, VGL2, VGL3) with different voltage levels. Each voltage serves specific functions in different stages or contexts of the scan driving device operation. This segmentation allows independent optimization of voltage levels for different operational requirements, improving DC bias stress stability while managing complexity through functional division.
Solution Approach 2:
The multiple low potential power source voltages are designed to serve multiple functions within the scan driving device. The same set of voltages is used across different shift register stages, for both forward and backward scanning directions, and for maintaining stability during different operational phases. This multi-functionality reduces the need for additional dedicated voltage sources, managing overall device complexity.
Data Source
AI summary
A scan driving device includes shift registers, each including a first signal terminal to which a forward direction driving start signal is transferred, a second signal terminal to which a backward direction driving start signal is transferred, a clock signal terminal and a clock bar signal terminal to which a clock signal and a clock bar signal are applied, a sustain signal terminal to which a sustain signal is transferred, a control signal terminal to which a control signal is transferred, a gate clock signal terminal to which a gate clock signal is transferred, and an output signal terminal, where driving power source voltages including a high potential power source voltage and low potential power source voltages is applied to each shift register, and an application of the low potential power source voltages to each shift register is controlled based on the sustain signal.