AMOLED Pixel Circuit Compensation for Brightness Uniformity
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Solution Overview
Problem
The existing pixel circuits in AMOLED displays face issues with poor brightness uniformity due to non-uniform threshold voltages of driving transistors and increased turn-on voltage of OLEDs over time, leading to reduced brightness and display quality.
Innovation Solution
A pixel circuit design incorporating a driving transistor, light emitting device, reset sub-circuit, light emitting control sub-circuit, compensation sub-circuit, and data writing sub-circuit, where the compensation sub-circuit acquires and writes a control voltage equal to the sum of the threshold voltage, data voltage, and turn-on voltage to the gate of the driving transistor, independent of the threshold voltage and operation voltage, thereby generating a driving current that is independent of the threshold voltage and positively correlated with the turn-on voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional pixel circuit is used in AMOLED display, then the circuit structure is simple, but the brightness uniformity is poor due to threshold voltage variations of driving transistors
Solution Approach 1:
The patent applies preliminary action by performing compensation operations before the light emitting stage. The compensation sub-circuit pre-acquires the threshold voltage of the driving transistor and the turn-on voltage of the OLED, and pre-calculates the control voltage that compensates for these variations. This preliminary compensation ensures that subsequent light emitting operations achieve uniform brightness across all pixels, resolving the contradiction between simple circuit structure and brightness uniformity.
Solution Approach 2:
The patent implements feedback mechanisms where the compensation sub-circuit continuously monitors and acquires the actual threshold voltage of the driving transistor and turn-on voltage of the OLED. Based on this feedback information, the circuit dynamically adjusts the control voltage applied to the driving transistor, ensuring that brightness uniformity is maintained despite variations in component characteristics. This feedback approach resolves the technical contradiction by enabling precision control without significantly increasing circuit complexity.
2Illumination intensity
If the driving current is increased to compensate for OLED aging, then the brightness is maintained, but the threshold voltage variations cause non-uniform brightness across pixels
Solution Approach 1:
The patent applies local quality by providing customized control voltages to each pixel's driving transistor based on its specific threshold voltage and the OLED's turn-on voltage. Rather than using a uniform driving current for all pixels, the compensation sub-circuit calculates and applies locally-optimized control voltages that account for individual pixel variations. This enables each pixel to achieve the required brightness while maintaining uniformity across the entire display panel.
Solution Approach 2:
The patent utilizes parameter changes by dynamically adjusting the control voltage parameter based on measured threshold voltage and turn-on voltage values. The compensation sub-circuit modifies the control voltage parameter in real-time to compensate for OLED aging and transistor variations, ensuring that brightness is maintained uniformly across all pixels despite changes in electrical characteristics over time and due to manufacturing tolerances.
3Manufacturing precision
If a compensation circuit is added to improve brightness uniformity, then the brightness uniformity improves, but the device complexity increases
Solution Approach 1:
The patent applies merging by integrating the compensation sub-circuit functions with the existing pixel circuit structure. The compensation sub-circuit shares nodes and components with the driving transistor and OLED, and the control voltage generation is merged with the existing data writing and reset circuits. This merging approach enables brightness uniformity compensation while minimizing the increase in device complexity by reusing existing circuit elements rather than adding completely separate compensation circuits.
Data Source
AI summary
The present disclosure discloses a pixel circuit, an array substrate, a display device and a pixel driving method, the pixel circuit including: a driving transistor, a light emitting device, a reset sub-circuit, a light emitting control sub-circuit, a compensation sub-circuit and a data writing sub-circuit, the compensation sub-circuit acquires a threshold voltage of the driving transistor and a turn-on voltage of the light emitting device in response to control of the second control signal and the third control signal, and writes a control voltage to a gate of the driving transistor in response to the first control signal, the control voltage is equal to a sum of the threshold voltage, the data voltage and the turn-on voltage, so that the driving current outputted by the driving transistor is independent of the threshold voltage of the driving transistor, and is positively correlated with the turn-on voltage of the light emitting device.