Dual-Gate Pixel Circuit for Low-Gray Luminance Uniformity
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Solution Overview
Problem
Existing display devices face challenges in precisely controlling the lighting current for light-emitting elements, particularly in the low-gray scale range, leading to luminance unevenness (MURA) due to small subthreshold factors in oxide semiconductor TFTs.
Innovation Solution
A dual-gate structure driving transistor is employed, where the first and second gate electrodes are controlled by first and second data signals with opposite polarity variations, allowing precise control of the lighting current through a predetermined relationship between the signals, especially in the low-gray scale range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional single-gate driving transistor is used, then the device complexity is low, but the subthreshold factor is small leading to luminance unevenness
Solution Approach 1:
The driving transistor is divided into two separate gate electrodes (first gate electrode and second gate electrode) instead of using a single gate. This segmentation allows independent control of the threshold voltage and the lighting current, enabling precise control in the low-gray scale range while reducing luminance unevenness. The first gate electrode controls the threshold voltage and the second gate electrode controls the lighting current, resolving the technical contradiction by improving display quality without excessive complexity increase.
2Measurement precision
If the first and second data signals are supplied independently without predetermined relationship, then the control flexibility is high, but the lighting current control precision is poor
Solution Approach 1:
A predetermined relationship is established between the first data signal and the second data signal, where the second data signal is generated based on the first data signal through a specific function (e.g., Vdata2 = f(Vdata1)). This feedback mechanism ensures that as the first data signal changes, the second data signal adjusts accordingly to maintain precise lighting current control. The relationship can be linear or non-linear depending on the desired gray scale characteristics, resolving the contradiction by providing precise control while maintaining adaptability through the functional relationship.
3Ease of manufacture
If oxide semiconductor TFTs are used for backplanes, then the manufacturing temperature can be kept low for large mother glass, but the subthreshold factor remains small causing luminance unevenness
Solution Approach 1:
The invention changes the electrical parameters of the driving transistor by introducing a dual-gate structure where the first gate electrode controls the threshold voltage and the second gate electrode controls the channel conductivity. This parameter control mechanism compensates for the inherently small subthreshold factor of oxide semiconductor TFTs, enabling precise lighting current control in the low-gray scale range without requiring higher manufacturing temperatures. The dual-gate structure allows independent optimization of threshold voltage and current control, resolving the contradiction between ease of manufacture and luminance uniformity.
Data Source
AI summary
Each pixel circuit includes a driving transistor, a first switching transistor and a second switching transistor. The driving transistor includes first and second gate electrodes. The first switching transistor is connected to a first data line and the first gate electrode, and controlled to be ON or OFF in accordance with a scanning signal supplied to a scanning line. The second switching transistor is connected to a second data line and the second gate electrode, and controlled to be ON or OFF in accordance with the scanning signal supplied to the scanning line. The voltage of the second data signal varies in the opposite direction to variation of voltage of the first data signal for at least a part of a gray scale range of the light-emitting element including the lowest gray scale level from the lowest gray scale level to the highest gray scale level.