AMOLED Pixel Circuit Resetting Cycle for Aging Compensation
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Solution Overview
Problem
Current active matrix organic light emitting device (AMOLED) displays face challenges in accurately measuring pixel characteristics and compensating for aging effects, as optical inspection fails to detect electrical faults and existing compensation systems cause visual artifacts and worsen pixel aging.
Innovation Solution
A voltage-programmed display system with reference pixels that remain unchanged by aging conditions, coupled with a readout circuit to adjust active pixel measurements, allowing for accurate determination and compensation of aging effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If optical inspection is used to test pixels prior to shipping, then manufacturing simplicity is maintained, but electrical faults that do not manifest in pixel output cannot be detected
Solution Approach 1:
The patent introduces a test transistor as an intermediary component that couples the pixel circuit to a readable node. This mediator allows electrical characteristics to be measured without requiring the pixel to display visible output, enabling detection of electrical faults that optical inspection would miss while maintaining manufacturing simplicity.
2Measurement precision
If pixel calibration occurs during each video frame by changing grayscale values, then accurate measurement of pixel characteristics is achieved, but visual artifacts appear and pixel aging is worsened
Solution Approach 1:
The patent performs pixel calibration and measurement during a relaxation sub-frame period, which occurs before the actual video display begins. By completing the measurement action in advance during a non-display period, the system achieves accurate pixel characteristic data without causing visual artifacts or accelerating pixel aging during normal operation.
Solution Approach 2:
The patent implements a periodic measurement cycle where pixel characteristics are measured during designated relaxation sub-frames that occur at regular intervals (e.g., every 16 frames). This periodic action separates measurement from display, allowing accurate calibration without continuous visual artifacts or excessive pixel stress.
3Measurement precision
If reference pixels are used to compensate for readout circuit changes, then measurement accuracy is improved, but device complexity increases
Solution Approach 1:
The patent creates simplified copies of pixel circuits called reference pixels that lack the OLED component but retain the drive transistor and readout circuitry. These reference copies are used to measure and compensate for readout circuit drift, providing accurate compensation without the full complexity of complete pixel structures.
Data Source
AI summary
A method of voltage-programming a pixel circuit in a display panel to remove, before programming the pixel circuit, effects due to short-term effects such as caused by fast light transitions or effects due to previous pixel circuit measurements such as charge trapping. During a resetting cycle, the pixel circuit is programmed with a reset voltage value corresponding to a maximum or a minimum voltage value. Then, during a calibration cycle, the pixel circuit is programmed with a calibration voltage based on previously extracted data for the pixel circuit, a pixel current of the pixel circuit is measured, and the extracted data for the pixel circuit is updated based on the measured pixel current. Then, the pixel circuit is programmed with a video data that is calibrated with the updated extracted data. The pixel circuit is finally driven according to the programmed video data and emits a commensurate amount of light.