Pixel Driving Circuit Threshold Voltage Compensation
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Solution Overview
Problem
The non-uniformity of threshold voltage in Low Temperature Poly-Silicon (LTPS) transistors in AMOLED display panels leads to inconsistent driving current and brightness, causing afterimages and reduced display quality due to the drift of threshold voltage over time.
Innovation Solution
A pixel driving circuit comprising an electroluminescent element, a driving transistor, a switch unit, a charging unit, a compensation unit, a cutoff unit, and a storage unit, where the compensation unit pre-stores the threshold voltage into the storage unit, allowing the driving current to be independent of the threshold voltage, ensuring consistent brightness and improved user experience.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional 2T1C circuits are used with LTPS transistors, then the display panel can be manufactured with lower cost and simpler structure, but the threshold voltage uniformity is poor and brightness uniformity deteriorates
Solution Approach 1:
The compensation unit performs preliminary action by measuring and storing the threshold voltage of the driving transistor before the driving phase. The storage capacitor holds this threshold voltage information, which is then used during the driving phase to compensate for threshold voltage variations, ensuring uniform brightness across different pixel units.
2Device complexity
If conventional 2T1C circuits are used, then the device structure is simpler, but threshold voltage drift over time causes afterimages and reduces display quality
Solution Approach 1:
The compensation unit establishes a feedback mechanism that continuously monitors and compensates for threshold voltage drift. By measuring the actual threshold voltage and storing it in the storage capacitor, the circuit automatically adjusts for drift over time, preventing afterimages and maintaining display quality without requiring complex external calibration systems.
3Manufacturing precision
If threshold voltage compensation is implemented, then brightness uniformity is improved, but the circuit structure becomes more complex with additional transistors and capacitors
Solution Approach 1:
The compensation function is merged into the existing pixel circuit structure by integrating the compensation unit and storage capacitor within the pixel. This approach achieves brightness uniformity compensation while minimizing the increase in circuit complexity by sharing common elements and optimizing the layout of additional components.
4Manufacturing precision
If threshold voltage compensation is implemented, then driving current consistency is improved, but the manufacturing process becomes more complex
Solution Approach 1:
The invention changes the operating parameters of the pixel circuit by introducing threshold voltage measurement and storage capabilities. By modifying the circuit to measure and store threshold voltage parameters, the system achieves consistent driving current despite variations in transistor characteristics, balancing manufacturing precision requirements with ease of manufacture.
Data Source
AI summary
Provided are a pixel driving circuit, a driving method thereof and a display apparatus. The pixel driving circuit includes an electroluminescent element, a driving transistor, a switch unit, a charging unit, a compensation unit, a cutoff unit and a storage unit. The pixel driving circuit charges the storage capacitor by the charging unit first, and then uses the method of charging first and discharging later to make the voltage in the storage capacitor match the driving current quickly to perform fast compensation of the threshold voltage Vth, and thus make the driving current provided by the driving transistor not influenced by the threshold voltage Vth, thereby raising the consistency of the driving currents and improving the uniformity of brightness.