Pixel Drive Circuit Threshold Compensation AMOLED
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Solution Overview
Problem
In AMOLED displays, uneven threshold voltages across driving transistors lead to inconsistent driving currents, resulting in uneven brightness and image quality due to variations in threshold voltages, despite using the same driving voltage.
Innovation Solution
A pixel driving circuit that includes a compensating unit to adjust the threshold voltage, ensuring the driving current is independent of the threshold voltage, achieved through specific signal control phases and transistor configurations.
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 threshold voltage variations cause inconsistent driving currents and uneven brightness
Solution Approach 1:
The pixel driving circuit is divided into multiple functional modules: a driving unit (first transistor) for current generation, a compensating unit (second transistor) for threshold voltage compensation, a storage unit (capacitor) for voltage storage, and a light emission unit (OLED). This segmentation allows each module to perform its specific function independently, enabling threshold voltage compensation without significantly increasing overall circuit complexity.
Solution Approach 2:
A storage capacitor is introduced as an intermediary element between the driving transistor and the OLED. The capacitor stores the gate voltage of the driving transistor, allowing the driving current to be determined by the stored voltage rather than directly by the transistor's threshold voltage, thus compensating for threshold voltage variations and improving brightness uniformity.
2Manufacturing precision
If threshold voltage compensation is implemented, then the driving current consistency is improved, but the circuit complexity increases
Solution Approach 1:
The compensating transistor is merged with the driving transistor to form an integrated compensation structure. Both transistors share common terminals and are positioned within the same pixel structure, allowing threshold voltage compensation to be achieved without adding separate independent compensation circuits, thus limiting the increase in circuit complexity.
Solution Approach 2:
The storage capacitor serves multiple functions: it stores the gate voltage for the driving transistor, enables threshold voltage compensation, and maintains the driving voltage during the light emission period. This multi-functionality reduces the need for additional components, thereby limiting circuit complexity increase while achieving driving current consistency.
3Ease of operation
If the driving current depends on threshold voltage, then the circuit operation is simple, but the brightness uniformity deteriorates due to threshold voltage variations
Solution Approach 1:
The storage capacitor pre-stores the gate voltage of the driving transistor before the light emission phase. This preliminary action ensures that the driving current is determined by the stored voltage rather than by real-time threshold voltage variations, thereby improving brightness uniformity while maintaining simple circuit operation during the emission phase.
Solution Approach 2:
The compensating transistor provides feedback by adjusting its conduction state based on its own threshold voltage characteristics. This feedback mechanism compensates for threshold voltage variations in the driving transistor, ensuring consistent driving currents and uniform brightness without complicating the overall circuit operation.
Data Source
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AI summary
The present disclosure provides a pixel driving circuit, a pixel driving method for the same, and a display apparatus. A voltage related to a threshold voltage of a driving unit is stored in a storage unit by a charge controlling unit at a compensating phase for the pixel driving circuit, such that the driving unit can be compensated by the storage unit at a driving phase for the pixel driving circuit. Thus, an influence of the threshold voltage of the driving unit on an operating current of the driving unit can be eliminated, and the problem of uneven brightness of light emitting elements resulted from the threshold voltages being different can be solved, thereby improving a display quality of the display apparatus.