Pixel Driving Circuit Threshold Compensation for AMOLED Uniformity
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Solution Overview
Problem
Conventional AMOLED panels face issues with poor luminance uniformity due to non-uniformity and drift of threshold voltages in drive transistors, leading to varying driving currents and brightness attenuation over time.
Innovation Solution
A pixel driving circuit with a reset unit, threshold compensation unit, data writing unit, drive transistor, and storage capacitors is implemented, where the threshold compensation unit writes a difference between a reference voltage and the threshold voltage into the drive transistor, making the driving current independent of the threshold voltage, ensuring uniformity and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a conventional 2T1C pixel driving circuit is used, then the circuit structure is simple, but the luminance uniformity is poor due to threshold voltage non-uniformity and drift
Solution Approach 1:
The pixel driving circuit is segmented into multiple functional units: reset unit, threshold compensation unit, data writing unit, and multiple storage capacitors (first storage capacitor and second storage capacitor). Each unit performs a specific function to address different aspects of the driving problem, allowing independent optimization of threshold voltage compensation and driving current control.
Solution Approach 2:
The threshold compensation unit performs preliminary compensation by writing the difference between reference voltage and threshold voltage into the first storage capacitor before the light emitting period. This preliminary action ensures that the driving current is pre-adjusted to account for threshold voltage variations, eliminating their influence on luminance uniformity.
2Manufacturing precision
If threshold voltage compensation is implemented, then luminance uniformity is improved, but the circuit complexity increases
Solution Approach 1:
The threshold compensation function is merged with the existing pixel driving circuit by integrating the threshold compensation unit and first storage capacitor into the conventional 2T1C structure. This combination allows threshold voltage compensation to be achieved without requiring a completely separate compensation circuit, thereby limiting the increase in overall circuit complexity.
3Duration of action of stationary object
If the drive transistor operates over time, then the display continues to function, but brightness attenuation occurs due to OLED aging and threshold voltage drift
Solution Approach 1:
The threshold compensation unit implements a feedback mechanism by continuously monitoring and compensating for threshold voltage drift through the first storage capacitor. During each frame cycle, the compensation unit adjusts the driving current based on the stored threshold voltage difference, providing real-time correction that maintains brightness stability over extended operation periods and counteracts OLED aging effects.
Data Source
AI summary
A pixel driving circuit, a pixel driving method and a display apparatus are provided. The pixel driving circuit includes a reset unit, a threshold compensation unit, a data writing unit, a drive transistor, a first storage capacitor and a light emitting device. According to the present disclosure, it is able to make the drive current generated by the drive transistor only related to the data voltage and the reference voltage but uncorrelated to the threshold voltage of the drive transistor when the drive transistor drives the light emitting device to display.