Pixel Circuit Capacitive Threshold Sampling for High-Speed OLED Compensation
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Solution Overview
Problem
Conventional compensation methods in organic light-emitting display devices fail to adequately compensate for differences in driving characteristics of pixels, especially at high resolutions and speeds, leading to inaccurate threshold voltage sampling and potential short-circuits between pixel driving and initialization voltages.
Innovation Solution
A pixel circuit design that includes specific switch elements and capacitors, allowing for extended sampling time and preventing short-circuits by using a reference voltage greater than the initialization voltage, ensuring accurate threshold voltage sampling and uniform pixel driving characteristics, even during high-speed operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the one horizontal period is reduced to increase driving speed and resolution, then productivity is improved, but measurement precision of threshold voltage deteriorates due to insufficient sampling time
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a first switch element for sampling the threshold voltage, a second switch element for holding the sampled voltage, and a capacitor for storing the sampled threshold voltage. This segmentation allows the sampling operation to be separated from the data writing operation, enabling accurate threshold voltage measurement even when the horizontal period is reduced for high-speed driving.
Solution Approach 2:
The threshold voltage sampling operation is performed in advance before the data writing operation. By using the first switch element to sample the threshold voltage and store it in the capacitor during the initialization period, the system prepares the compensation value beforehand, allowing the data to be written quickly without compromising sampling accuracy.
2Loss of time
If the sampling time is reduced to match shorter horizontal period, then productivity is improved, but measurement precision of threshold voltage deteriorates
Solution Approach 1:
The threshold voltage is sampled and stored in the capacitor during the initialization period before the data writing begins. This preliminary sampling action ensures that the compensation value is ready when needed, allowing the system to maintain accurate threshold voltage measurement even when the overall timing period is reduced for high-speed operation.
Solution Approach 2:
The second switch element maintains the sampled threshold voltage continuously during the data writing period. By holding the sampled voltage in the capacitor and keeping it stable through the second switch element, the system ensures continuous availability of accurate compensation data without requiring extended sampling time.
3Device complexity
If conventional compensation method is used, then device complexity is reduced, but manufacturing precision of pixel driving characteristics deteriorates
Solution Approach 1:
Each pixel circuit performs self-compensation by sampling its own threshold voltage through the first switch element and storing it in the capacitor. This self-service approach allows each pixel to compensate for its individual manufacturing variations without requiring complex external compensation circuits, achieving uniform driving characteristics while keeping the device complexity manageable.
Solution Approach 2:
The system changes the operating parameters by introducing a reference voltage that is higher than the data voltage. This parameter change ensures that the first switch element can properly sample the threshold voltage without interference from the data writing operation, improving the precision of pixel driving characteristics through accurate threshold voltage compensation.
Data Source
AI summary
Embodiments disclose a pixel circuit including a driving element including a gate electrode connected to a first node, a first electrode connected to a second node, and a second electrode connected to a third node, a light-emitting element connected to the second electrode of the driving element, a first capacitor connected to the first node and a fourth node, a second capacitor connected to the fourth node and the second node, a first switch element connected to the first node and the third node, a second switch element connected to the fourth node and a reference voltage supply line, and a third switch element connected to the first node and an initialization voltage supply line, and a display device including the same.