OLED Pixel Drive Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The existing driving circuits for Active Matrix Organic Light Emitting Diode (AMOLED) pixel units suffer from brightness uniformity issues due to variations in threshold voltages of driving transistors, particularly during the Low Temperature Polycrystalline Silicon (LTPS) manufacturing process, leading to inconsistent brightness.
Innovation Solution
A driving circuit comprising a driving thin-film transistor, a first switching element, a storage capacitor, and a driving control unit, where the storage capacitor is controlled to compensate the threshold voltage of the driving thin-film transistor using the gate-source voltage, ensuring operation in the saturation region and maintaining a stable voltage difference to achieve consistent driving current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a traditional 2T1C driving circuit is used, then the circuit structure is simple, but the brightness uniformity is poor due to threshold voltage variations
Solution Approach 1:
The circuit is segmented into multiple functional blocks: a driving transistor for current control, a compensation transistor for threshold voltage compensation, and a storage capacitor for voltage maintenance. This segmentation allows independent optimization of each function to achieve both simplicity and precision.
Solution Approach 2:
A compensation transistor is introduced as an intermediary element between the data line and the storage capacitor. This compensation transistor measures and compensates for the threshold voltage of the driving transistor, acting as a mediator that eliminates the harmful effect of threshold voltage variations on brightness uniformity.
2Manufacturing precision
If threshold voltage compensation is implemented, then brightness uniformity is improved, but the circuit complexity increases
Solution Approach 1:
The compensation function is merged with the existing driving circuit by using the same storage capacitor and integrating the compensation transistor into the pixel unit. This merging approach achieves threshold voltage compensation without requiring entirely separate compensation circuitry, thus limiting the increase in complexity.
Solution Approach 2:
The compensation transistor uses itself to measure its own threshold voltage, and this measured value is then used to compensate for the driving transistor's threshold voltage. The circuit performs self-diagnosis and self-correction, eliminating the need for external calibration equipment or complex control systems.
3Ease of operation
If the driving transistor operates without threshold voltage compensation, then the circuit operation is simple, but the driving current consistency is poor
Solution Approach 1:
The compensation transistor creates a feedback mechanism where the gate voltage of the driving transistor is adjusted based on the threshold voltage measurement. During the compensation phase, the compensation transistor measures the threshold voltage, and this information feeds back to adjust the stored voltage, ensuring consistent driving current despite threshold variations.
Solution Approach 2:
Threshold voltage compensation is performed preliminarily during the compensation phase before the actual light emission phase. By measuring and compensating for the threshold voltage in advance, the circuit ensures that the driving transistor will operate with consistent current during the subsequent light emission phase, improving reliability without complicating the main operation.
Data Source
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Figure 3a~3b
Figure 3c~3d
AI summary
The present invention provides a driving circuit and a method for a pixel unit, a pixel unit and a display apparatus. The driving circuit for a pixel unit comprises: a driving thin-film transistor, a first switching element, a storage capacitor and a driving control unit; a source of the driving thin-film transistor is connected to a data line via the first switching element; a drain of the driving thin-film transistor is connected to an anode of the OLED and a low level output of the driving power supply respectively via said driving control unit, a source of said driving thin-film transistor is connected to the high level output of the driving power supply, and a gate of the driving thin-film transistor is connected to the drain of the driving thin-film transistor; said driving control unit is used to control said storage capacitor to be charged/discharged so as to control said driving thin-film transistor to operate in a saturation region, so that the threshold voltage Vth of said driving thin-film transistor is compensated by utilizing the gate-source voltage of said driving thin-film transistor. The present invention can address the problems of ununiformity and attenuation of the brightness of OLED panel.