Double-Gate Pixel Circuit for OLED Luminance Compensation
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Solution Overview
Problem
Luminance deviations occur in electroluminescent display pixels due to variations in the threshold voltage of the driving element, degrading display quality.
Innovation Solution
An electroluminescent display apparatus with internal compensation circuits that sample and compensate for the threshold voltage of the driving element by using a double-gate driving element and a sampling reinforcement voltage, ensuring the threshold voltage is accurately reflected in the gate-source voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional single-gate driving element is used, then the device complexity is low, but luminance deviation occurs due to threshold voltage variation
Solution Approach 1:
The driving element 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 and sampling of threshold voltage through the second gate electrode during the sampling period, while the first gate electrode controls the driving current during the emission period. The segmentation enables accurate threshold voltage compensation without requiring complex external circuits.
Solution Approach 2:
The second gate electrode serves multiple functions: it enables threshold voltage sampling during the sampling period by controlling the driving element's conductivity, and it can be repurposed during the emission period to maintain stable driving conditions. This multi-functionality allows a single additional electrode to perform both sampling and driving control, reducing the need for separate dedicated sampling circuits and maintaining manufacturing simplicity.
2Manufacturing precision
If threshold voltage sampling is not performed, then the device complexity is low, but luminance deviation degrades display quality
Solution Approach 1:
The pixel circuit performs threshold voltage sampling and compensation autonomously using its own internal components (second gate electrode, capacitors, and signal lines) without requiring external compensation circuits or additional processing steps. The sampling operation is integrated into the normal pixel operation timeline, where the second gate electrode naturally enables threshold voltage measurement during the sampling period before the emission period begins. This self-service approach eliminates the need for complex external compensation hardware.
3Manufacturing precision
If a sampling period is added before emission, then threshold voltage compensation is achieved, but the duration of action is reduced
Solution Approach 1:
The pixel operation is divided into periodic phases: a sampling period followed by an emission period. During the sampling period, the second gate electrode is activated to perform threshold voltage sampling. This periodic sampling action occurs at the beginning of each frame or refresh cycle, establishing accurate threshold voltage compensation before the emission period begins. The periodic structure ensures that threshold voltage variations are compensated regularly without continuously interfering with the emission process.
Solution Approach 2:
Threshold voltage sampling is performed in advance during the sampling period, which occurs before the emission period. This preliminary action ensures that the threshold voltage is accurately determined and compensated for before the actual light emission begins. By performing the sampling action beforehand, the emission period can proceed with optimal conditions already established, maximizing the effective display time without sacrificing accuracy.
Data Source
AI summary
An electroluminescent display apparatus includes a plurality of pixels that each include a driving element including a first gate electrode connected to a first gate node, a second gate electrode facing the first gate electrode, a source electrode connected to a source node, and a drain electrode, a light emitting device connected between the source node and an input terminal for a low level driving voltage to emit light during an emission period, and an internal compensation circuit including a first capacitor connected to the first gate node and the source node. The internal compensation circuit samples a threshold voltage of the driving element during a sampling period that precedes the emission period. A sampling reinforcement voltage for increasing a sampling current flowing in the driving element is applied to the second gate electrode of the driving element during the sampling period.