OLED Subpixel Compensation Circuit for High-Speed Threshold Sampling
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Solution Overview
Problem
Conventional compensation methods for organic light emitting display devices fail to adequately compensate for differences in drive characteristics between pixels, particularly in high-resolution and high-speed driving scenarios, leading to luminance deviations and visible spots on the screen due to insufficient threshold voltage sampling.
Innovation Solution
The display device incorporates an internal compensation circuit with a compensation transistor and a wider gate ON pulse to extend the threshold voltage sampling period, and includes a compensation capacitor to maintain data voltage during an additional sampling period, utilizing oxide semiconductor transistors for improved pixel control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the horizontal period is reduced to increase resolution and driving speed, then productivity is improved, but measurement precision of threshold voltage deteriorates due to insufficient sampling time
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage sampling before the light emission period begins. The sampling transistor is activated during a dedicated sampling period that occurs prior to data writing and light emission, ensuring that threshold voltage measurement is completed in advance. This allows the main display operation to proceed at high speed without being constrained by sampling time requirements.
Solution Approach 2:
The patent segments the driving cycle into distinct periods: a sampling period for threshold voltage measurement, a data writing period, and a light emission period. By separating the sampling operation from the main display operation, the patent enables high-speed driving while maintaining accurate threshold voltage measurement. The sampling transistor is activated only during the sampling period, preventing interference with subsequent operations.
2Measurement precision
If the gate ON pulse width is increased to extend sampling period, then measurement precision is improved, but duration of action of stationary object increases
Solution Approach 1:
The patent segments the gate ON pulse into two distinct parts: a wide sampling period for accurate threshold voltage measurement, and a shorter data writing period. The sampling transistor remains ON during the entire sampling period to ensure accurate measurement, while the scan transistor is activated only briefly for data writing. This segmentation allows extended sampling without unnecessarily prolonging the overall gate ON duration.
Solution Approach 2:
The patent performs threshold voltage sampling in advance during a dedicated sampling period before data writing begins. By completing the sampling operation preliminarily, the patent can use a wider gate ON pulse for sampling without affecting the timing of subsequent display operations. This preliminary action resolves the conflict between sampling accuracy and operation duration.
Data Source
AI summary
A display device includes a display panel on which gate lines, data lines and subpixels are disposed; a gate driving circuit which drives the gate lines; and a data driving circuit which drives the data lines. Each of the subpixels includes: a light emitting device; a second transistor which has a first node, a second node that is a gate node, and a third node electrically connected to the light emitting device, and drives the light emitting device; a first transistor electrically connected between the third node and the data line; a third transistor electrically connected between the first node and the second node; and a fourth transistor electrically connected between the third node and the light emitting device. The third transistor performs a turn-off operation later than the first transistor, so that a voltage applied to the third node is transmitted to the second node via the first node.