EL Display Precharge Voltage Compensation for Transistor Variation
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Solution Overview
Problem
Organic EL display panels face display irregularities due to variations in transistor characteristics, leading to insufficient writing in all tone regions, particularly in low tone regions, where current programming mode struggles to compensate effectively.
Innovation Solution
The EL display apparatus measures the gate terminal potential of driving transistors with a constant current and stores this data. This measured potential is converted into a reference voltage, which is used to precharge the source signal line, allowing for precise compensation of transistor characteristics by applying a target tone voltage, thereby eliminating insufficient writing across all tone regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current programming mode is used to compensate for transistor variations, then display irregularities are reduced, but insufficient writing occurs in low tone regions
Solution Approach 1:
The patent applies preliminary action by pre-charging the source signal line to a voltage level corresponding to the measured gate terminal potential before applying the video signal. This preliminary charging compensates for transistor variations in advance, enabling accurate current control even in low tone regions where conventional current programming fails.
Solution Approach 2:
The patent replaces the conventional current programming mechanism with a voltage-based compensation mechanism. Instead of relying solely on current control through the driving transistor, the system uses voltage pre-charging of the source signal line to compensate for transistor variations, substituting the control mechanism to achieve better performance.
2Manufacturing precision
If voltage programming mode is used, then insufficient writing in low tone regions is avoided, but display irregularities occur due to transistor variations
Solution Approach 1:
The patent merges the advantages of both voltage programming and current programming modes. It combines voltage-based pre-charging (to avoid insufficient writing) with current-based control (to compensate for transistor variations), creating a hybrid approach that achieves both writing accuracy and display uniformity simultaneously.
Solution Approach 2:
The patent implements feedback by measuring the gate terminal potential of each driving transistor and using this measured value to pre-charge the source signal line. This feedback loop allows the system to automatically compensate for transistor variations, maintaining display uniformity while ensuring accurate writing in all tone regions.
3Ease of manufacture
If transistor arrays with polysilicon are used, then manufacturing is simplified, but variations in transistor characteristics cause display irregularities
Solution Approach 1:
The patent applies self-service by having each pixel's driving transistor compensate for its own characteristic variations through the measurement and pre-charging mechanism. Each transistor measures its own gate terminal potential and uses this information to adjust its operation, enabling polysilicon transistor arrays to achieve uniform display without requiring higher-precision monocrystalline transistors.
Data Source
AI summary
A precharge voltage Vp is applied in period A. The precharge voltage Vp is generated by applying a constant current Iw to a pixel driving transistor of a display panel and using gate terminal voltage of the driving transistor which passes the constant current Iw. The gate terminal potential is held in memory. When displaying images on a display panel, the gate terminal potential is read out of memory, and used as the precharge voltage Vp after arithmetic processing. By the application of the precharge voltage Vp, a source signal line is charged and discharged quickly so that an almost target tone current will flow through the driving transistor. Furthermore, a more accurate program current is written into the pixel during period B.