Pixel Drive Circuit Compensation for AMOLED Brightness Uniformity
Solution Overview
Problem
The existing pixel drive circuits for AMOLED displays suffer from poor panel uniformity due to resistance drop, causing the upper end of the panel to be dark and the lower end to be bright, leading to uneven brightness and image quality issues.
Innovation Solution
A pixel drive circuit with a shift register circuit and a pixel compensation circuit that performs pulse width modulation on the light-emitting time adjustment signal, compensating for threshold voltage drift and adjusting the light-emitting time to improve uniformity by varying the turn-on time of the light-emitting module based on the pulse width variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel drive circuit (2T1C or 7T1C) is used, then the circuit can drive the OLED, but the threshold voltage drift of the driver TFT causes driving current fluctuation and uneven brightness
Solution Approach 1:
The patent applies preliminary action by pre-compensating for the threshold voltage of the driver TFT during the data writing phase. The compensation circuit calculates and stores the threshold voltage value before the light-emitting phase, so that when the OLED is driven, the driving current is already adjusted to account for threshold voltage drift. This prevents brightness uniformity issues without requiring complex real-time adjustment mechanisms during operation.
Solution Approach 2:
The patent changes the parameter of driving current by dynamically adjusting it based on the compensated threshold voltage. Instead of using a fixed driving current, the circuit modifies the current parameter according to the measured threshold voltage drift, ensuring consistent brightness despite TFT aging or manufacturing variations. This is achieved through the compensation circuit that adjusts the gate-source voltage of the driver TFT.
2Reliability
If the light-emitting time is extended to compensate for resistance drop, then brightness uniformity improves, but the response time and frame rate are affected
Solution Approach 1:
The patent applies local quality by providing different light-emitting time adjustments to different regions of the display panel. Specifically, pixels in different rows or columns receive customized pulse width modulation based on their local resistance characteristics. This allows compensation for resistance drop in specific areas without globally extending the light-emitting time, thus maintaining high frame rates while achieving brightness uniformity locally across the panel.
Solution Approach 2:
The patent introduces dynamics by making the light-emitting time adjustable and region-specific rather than fixed and uniform. The pulse width modulation dynamically adjusts the light-emitting duration for different pixel groups based on their resistance characteristics, allowing the system to optimize both brightness uniformity and frame rate. This dynamic adjustment is controlled by the compensation circuit that calculates appropriate time parameters for different display regions.
3Reliability
If the driving current is increased to compensate for resistance drop, then brightness uniformity improves, but power consumption increases
Solution Approach 1:
The patent changes the parameter of driving current by dynamically adjusting it based on the compensated threshold voltage and local resistance characteristics. Instead of uniformly increasing the driving current across the entire panel, the circuit modifies the current parameter only where and when needed, based on measured threshold voltage drift and resistance drop. This selective parameter adjustment achieves brightness uniformity while minimizing overall power consumption increases.
Data Source
AI summary
A pixel drive circuit, a display device and a driving method. The pixel drive circuit, the display device and the driving method can effectively compensate for the problem of poor panel uniformity caused by the resistance drop and improve the uniformity of the panel.