Test Pixel Mobility Sensing for OLED Luminance Compensation
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Solution Overview
Problem
Display devices, such as OLEDs, face challenges in compensating for changes in the mobility characteristic of driving transistors, which affect the luminance of pixels despite internal compensation operations for threshold voltage variations.
Innovation Solution
Incorporating a test pixel with a sensing line and a sensing circuit that measures the mobility characteristic of driving transistors by measuring current at the source node, allowing for accurate compensation of image data for normal pixels based on sensed mobility changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If internal compensation operation is performed to store threshold voltage in storage capacitor, then threshold voltage variation is compensated, but mobility characteristic change cannot be compensated
Solution Approach 1:
The patent divides the pixel into two functional parts: a normal pixel for display and a test pixel for mobility sensing. The test pixel includes a test transistor whose mobility characteristic is sensed by a sensing circuit, while the normal pixel uses this sensed information to compensate for its driving transistor's mobility changes. This segmentation allows independent optimization of threshold voltage compensation (in normal pixels) and mobility sensing (in test pixels).
Solution Approach 2:
The test pixel acts as an intermediary element between the sensing circuit and the normal pixels. It provides a controlled environment to measure mobility characteristics without directly affecting the display function, while the sensed data is then used to compensate normal pixels. The test pixel serves as a mediator that translates physical mobility changes into measurable electrical signals.
2Measurement precision
If source node of test pixel is electrically coupled to sensing line continuously, then mobility sensing is enabled, but data writing is distorted by parasitic capacitor
Solution Approach 1:
The patent makes the electrical connection between the test pixel's source node and the sensing line dynamic rather than static. A switching transistor controls the connection state based on the operational phase: disconnected during data writing to prevent parasitic capacitor distortion, and connected during emission period to enable mobility sensing. This dynamic switching resolves the contradiction between continuous sensing and accurate data writing.
Solution Approach 2:
The patent implements periodic switching of the connection between the test pixel source node and sensing line, synchronizing with the display timing: disconnected during data writing period, connected during emission period. This periodic action ensures that sensing occurs only when needed and does not interfere with data writing operations.
Data Source
AI summary
A display device includes: a display panel including a normal pixel in a display region and a test pixel in a peripheral region, a sensing line coupled to the test pixel, and a sensing circuit configured to sense a mobility characteristic of the test pixel by measuring a current at a source node of the test pixel through the sensing line. The source node of the test pixel is electrically separated from the sensing line in a data writing period of a frame period, and is electrically coupled to the sensing line in an emission period of the frame period.