Pixel Driving Circuit Compensation for AMOLED Brightness Uniformity
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Solution Overview
Problem
Active Matrix Organic Light Emitting Diode (AMOLED) displays face issues of brightness nonuniformity due to threshold voltage differences in driving transistors, leading to mura and afterimage phenomena, which are exacerbated by the nonuniformity of low temperature polycrystal silicon TFTs and Oxide TFTs, and result in reduced fabrication yield and increased power consumption.
Innovation Solution
A pixel driving circuit design that includes a data line, gate line, power lines, reference signal line, storage capacitor, reset unit, data writing unit, compensation unit, and light emitting control unit, where the compensation unit counteracts the threshold voltage of the driving transistor by loading the first power voltage and threshold voltage onto a storage capacitor, thereby stabilizing the gate-source voltage and eliminating brightness nonuniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low temperature polycrystal silicon TFTs or Oxide TFTs are used to construct pixel driving circuit, then mobility and stability are improved, but nonuniformity in electrical parameters (threshold voltage, mobility) occurs due to crystallization process limitations
Solution Approach 1:
The patent applies preliminary action by introducing a compensation transistor and compensation capacitor that pre-compensate for threshold voltage nonuniformity before the display operation begins. The compensation circuit is configured to automatically adjust for parameter variations, eliminating the need for post-manufacturing calibration and ensuring uniform display performance across all pixels.
Solution Approach 2:
The patent implements feedback through a compensation circuit that continuously monitors and adjusts for threshold voltage variations in driving transistors. The compensation transistor and capacitor form a feedback mechanism that detects parameter nonuniformity and automatically corrects it, maintaining consistent display quality despite manufacturing variations.
2Manufacturing precision
If pixel circuit structure is designed with higher complexity to eliminate threshold voltage difference influence, then display uniformity is improved, but fabrication yield is reduced
Solution Approach 1:
The patent applies segmentation by dividing the pixel circuit into distinct functional modules: a driving transistor for normal operation, a separate compensation transistor for threshold voltage correction, and a compensation capacitor for storing correction values. This modular segmentation allows each component to perform its specific function efficiently, achieving display uniformity without excessive overall complexity.
Solution Approach 2:
The patent introduces a compensation transistor as an intermediary element that mediates between the driving transistor's threshold voltage variations and the display output. This intermediary component isolates the display function from manufacturing nonuniformities, achieving uniformity without requiring complex redesign of the entire pixel circuit.
3Speed
If large current is used to increase transient current for larger display size, then driving time is reduced, but power consumption increases and voltage drop in ITO line becomes too large
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the threshold voltage of the driving transistor through the compensation circuit, rather than increasing current amplitude. By modifying the voltage parameter through compensation, the circuit achieves faster response times and improved driving performance without the energy penalties associated with high-current operation.
Data Source
AI summary
Provided are a pixel driving circuit, a driving method, an array substrate and a display apparatus. The pixel circuit comprises: a data line, a gate line, a first power line, a second power line, a reference signal line, a light emitting device, a driving transistor, a storage capacitor, a reset unit, a data writing unit, a compensation unit and a light emitting control unit. The pixel driving circuit can compensate and eliminate the display nonuniformity caused by the threshold voltage difference of the driving transistors.