OLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
In organic light-emitting display devices, the crystallizing process for polysilicon thin film transistors can result in non-uniform threshold voltages due to unstable laser power, leading to complex pixel regions and reduced aperture ratios, which complicates threshold voltage compensation and increases power consumption.
Innovation Solution
The organic light-emitting display device incorporates a specific configuration of transistors and voltage control systems, including a drive transistor, storage capacitor, and additional transistors for threshold voltage sensing and power management, which allows for efficient threshold voltage compensation without adding complexity to the pixel region, thereby enhancing the aperture ratio and reducing power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If threshold voltage compensation is implemented by adding detection transistors and signal lines, then threshold voltage uniformity is improved, but device complexity increases and aperture ratio decreases
Solution Approach 1:
The patent combines the threshold voltage sensing function with the existing drive transistor by using the same transistor for both driving the OLED and sensing the threshold voltage. This is achieved by controlling the gate voltage of the drive transistor to be equal to the source voltage during a sensing period, allowing the threshold voltage to be detected without requiring separate detection transistors or additional signal lines, thus resolving the contradiction between improving threshold voltage uniformity and reducing device complexity
Solution Approach 2:
The drive transistor is given dual functionality: it serves both as the driving element for the OLED and as the sensing element for threshold voltage detection. By implementing threshold voltage sensing within the existing drive transistor structure, the patent eliminates the need for dedicated detection transistors and additional control lines, thereby maintaining threshold voltage compensation capability while reducing pixel region complexity and preserving aperture ratio
2Manufacturing precision
If threshold voltage compensation is implemented by adding detection transistors and signal lines, then threshold voltage uniformity is improved, but aperture ratio decreases
Solution Approach 1:
The patent merges the threshold voltage sensing function into the existing drive transistor structure, eliminating the need for separate detection transistors and their associated signal lines. This integration approach maintains the threshold voltage compensation capability while freeing up pixel area, thus improving aperture ratio without sacrificing threshold voltage uniformity
Solution Approach 2:
The patent extracts the threshold voltage sensing function from the traditional separate detection transistor architecture and integrates it into the drive transistor. By removing the unnecessary detection transistors and signal lines from the pixel structure, the patent reduces the occupied area and increases the aperture ratio while still achieving accurate threshold voltage compensation
3Productivity
If laser scanning mode is used for polysilicon crystallizing, then manufacturing efficiency is improved, but threshold voltage uniformity deteriorates due to unstable laser power
Solution Approach 1:
The patent implements a feedback mechanism where the threshold voltage of each pixel's drive transistor is sensed and used to adjust the data voltage applied to the OLED. By measuring the actual threshold voltage (which reflects the quality of polysilicon crystallization) and compensating for variations through feedback control, the system achieves uniform threshold voltages across pixels even when laser power during crystallization varies, thus resolving the contradiction between manufacturing efficiency and threshold voltage uniformity
Data Source
AI summary
Disclosed is an organic light-emitting display device defined into a non-display area and a display area which is provided with pixels. Each of the pixels includes: first through fourth nodes; an organic light emission element connected to the fourth node; a drive transistor disposed between the second, third, and fourth nodes and configured to generate a drive current which drives the organic light emission element to emit light; a storage capacitor disposed between the first and third nodes; first through fifth transistors; wherein the fifth transistor is disposed between the second node with the non-display area and a reference voltage line and configured to control an initialization of the second node.