OLED Pixel Circuit Threshold Voltage Compensation via Node Discharge
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Solution Overview
Problem
In organic electroluminescent displays, the variability in threshold voltages of driving transistors due to manufacturing processes and aging leads to uneven current distribution across pixels, resulting in inconsistent image brightness, which existing compensation methods fail to accurately address without affecting the OLED element's characteristics and lifespan.
Innovation Solution
A pixel circuit comprising a light emitting element, a driving control module, a resetting control module, a charging control module, a writing control module, and a light emitting control module, where the charging control module discharges the second node through the driving and resetting control modules, isolating the OLED element from the discharge path, ensuring accurate threshold voltage writing and optimizing compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the threshold voltage is written by discharging the driving transistor through the OLED element, then the threshold voltage compensation is achieved, but the characteristics and display lifespan of OLED element are affected and the accuracy of the written threshold voltage is reduced
Solution Approach 1:
The patent extracts the OLED element from the discharge path of the driving transistor. A dedicated discharge transistor is introduced to provide an alternative discharge path that bypasses the OLED element, allowing threshold voltage writing without subjecting the OLED to discharge current stress.
Solution Approach 2:
The patent introduces a discharge transistor as an intermediary component between the driving transistor and the OLED element. This intermediary enables the discharge function while protecting the OLED element from direct exposure to discharge current, thus resolving the conflict between compensation accuracy and OLED reliability.
2Adaptability or versatility
If the threshold voltage is written by discharging the driving transistor, then the current flowing through OLED element becomes independent of threshold voltage Vth, but the accuracy of the written threshold voltage Vth is affected and the compensation effect is worsened
Solution Approach 1:
The OLED element is extracted from the discharge path, allowing the discharge operation to proceed independently without involving the OLED. This separation enables accurate threshold voltage writing through the discharge transistor while maintaining the desired current independence characteristic.
Solution Approach 2:
The discharge function is segmented from the OLED element and assigned to a dedicated discharge transistor. This segmentation allows the discharge operation to be performed with high precision for threshold voltage writing while the OLED element remains unaffected, thereby improving both accuracy and adaptability.
3Ease of operation
If a stable voltage is used to control brightness in LCD, then the display is simple to control, but OLED requires stable current which is affected by threshold voltage variations
Solution Approach 1:
The patent implements a feedback mechanism through threshold voltage compensation. By measuring the threshold voltage of the driving transistor and adjusting the gate voltage accordingly, the system compensates for threshold voltage variations, ensuring stable OLED current despite manufacturing process variations and aging effects.
Solution Approach 2:
The patent changes the operating parameter from direct voltage control to compensated voltage control. By dynamically adjusting the gate voltage based on the measured threshold voltage, the system maintains stable OLED current while preserving the simplicity of voltage-based control interfaces.
Data Source
AI summary
A pixel circuit, a driving method, an organic electroluminescent display panel, and a display device, the pixel circuit includes a light emitting element, a driving control module, a resetting control module, a charging control module, a writing control module, and a light emitting control module; the resetting control module resets the first node and the light emitting element; the charging control module charges the second node through the light emitting control module and discharges the second node through the driving control module and the resetting control module; the writing control module writes a data signal to the second node; and the light emitting control module controls the driving control module to drive the light emitting element to emit light.