5T1C AMOLED Pixel Driver Circuit Threshold Compensation
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Solution Overview
Problem
The existing AMOLED pixel driver circuits, particularly the 2T1C structure, are sensitive to threshold voltage drift in driving TFTs, leading to uneven light emission and brightness across pixels, resulting in 50% or more brightness unevenness in AMOLED displays due to the lack of compensation for threshold voltage and channel migration parameters.
Innovation Solution
The proposed solution involves an AMOLED pixel driver circuit with a 5T1C structure, comprising specific TFT configurations and a capacitor, which includes an initialization phase, threshold voltage compensation phase, and light-emitting phase to ensure that the current flowing through the OLED is independent of the threshold voltage of the driving TFT, using a source-following approach to stabilize light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a 2T1C pixel driver circuit is used, then the device complexity is reduced, but the brightness uniformity deteriorates due to threshold voltage drift
Solution Approach 1:
The pixel driver circuit is divided into multiple functional modules: initialization module (TFT1, TFT2), compensation module (TFT3, TFT4, TFT5), and light emission module (TFT6). Each module performs a specific function in the threshold voltage compensation process, allowing the system to achieve better brightness uniformity through specialized functional segmentation while managing overall complexity.
Solution Approach 2:
The circuit performs initialization and threshold voltage compensation operations before the light emission phase. During the initialization phase, TFT1 and TFT2 are activated to set initial conditions. During the compensation phase, TFT3, TFT4, and TFT5 are activated to compensate for threshold voltage drift before the actual display operation, ensuring stable brightness throughout the display's lifetime.
2Manufacturing precision
If compensation circuit is added to each pixel, then the brightness uniformity is improved, but the device complexity increases
Solution Approach 1:
The compensation circuit uses multiple TFTs that serve dual purposes: they are involved in both the initialization process and the threshold voltage compensation process. For example, TFT3 is used in both phases, reducing the need for entirely separate compensation circuits and thereby limiting the increase in device complexity while still achieving improved brightness uniformity.
3Reliability
If threshold voltage compensation is implemented, then the light emission stability is improved, but the circuit structure becomes more complex
Solution Approach 1:
The pixel driver circuit performs self-compensation for threshold voltage drift using its own internal TFTs and capacitors. The compensation process uses the circuit's existing components (TFT3, TFT4, TFT5, and associated capacitors) to automatically adjust for threshold voltage changes without requiring external intervention or additional complex control circuits, thereby improving light emission stability while limiting complexity increase.
Data Source
AI summary
The invention provides an AMOLED pixel driver circuit and pixel driving method, by using a pixel driver circuit of 5T1C structure to effectively compensate threshold voltage of driving TFT in each pixel through a source-following approach to compensate the threshold voltage of the driving TFT so that the current flowing through the OLED is independent of the threshold voltage of the first TFT, the threshold voltage of the OLED and the negative voltage of the power source to ensure even light-emission result of OLED and improve display result.