OLED Pixel Circuit with Compensation Transistor for Leakage Current
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Solution Overview
Problem
Active matrix OLED displays face reduced display quality due to coupling or leakage currents caused by external voltages, affecting the current supplied to the organic light emitting diode and resulting in inconsistent light emission.
Innovation Solution
The proposed solution involves a pixel structure with specific transistors and capacitors that include a switching transistor, a driving transistor, a compensation transistor, and capacitors connected in a manner that allows for voltage resetting, threshold voltage compensation, and data voltage application to maintain stable operation, minimizing the impact of external voltage coupling and leakage currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pixel structure is used, then the device complexity is low, but coupling or leakage currents from external voltages reduce display quality
Solution Approach 1:
The pixel circuit is divided into multiple functional blocks: a switching transistor for data input, a driving transistor for OLED current control, a compensation transistor for threshold voltage correction, and multiple capacitors (first capacitor for data voltage storage, second capacitor for gate voltage storage). This segmentation isolates different functions to reduce coupling currents and improve display quality.
Solution Approach 2:
The compensation transistor and associated capacitors perform preliminary compensation of the driving transistor's threshold voltage before the main display operation. This preliminary action prevents threshold voltage variations from affecting the OLED current, thereby maintaining display quality without requiring a completely redesigned pixel structure.
2Reliability
If additional transistors and capacitors are added to compensate for threshold voltage and reduce leakage current, then the robustness to external voltage improves, but the device complexity increases
Solution Approach 1:
The first capacitor serves multiple functions: storing data voltage during the write period and maintaining it during the display period. The second capacitor similarly stores and maintains the gate voltage of the driving transistor. This multi-functionality reduces the need for additional components while improving robustness against external voltage variations.
Solution Approach 2:
The compensation transistor automatically compensates for threshold voltage changes in the driving transistor through self-regulation. When the threshold voltage shifts, the compensation transistor adjusts the gate voltage accordingly, making the pixel circuit self-correcting without requiring external intervention or additional complex control mechanisms.
3Ease of manufacture
If the pixel structure is simplified, then the ease of manufacture is high, but leakage currents affect the current supplied to OLED
Solution Approach 1:
The switching transistor acts as an intermediary between the data line and the driving transistor, controlling the flow of data voltage to the gate. The compensation transistor serves as an intermediary between the first capacitor and the driving transistor gate, adjusting the gate voltage to compensate for threshold variations. These intermediary elements ensure current stability without significantly complicating the manufacturing process.
Solution Approach 2:
The patent utilizes parameter changes in the capacitor voltages to maintain stable OLED current. The first capacitor maintains a stable data voltage parameter, while the second capacitor adjusts the gate voltage parameter of the driving transistor based on threshold voltage changes, ensuring current stability through dynamic parameter adjustment rather than structural complexity.
Data Source
AI summary
An organic light emitting diode (OLED) display device is disclosed. In one aspect, the display device includes a plurality of pixels. The plurality of pixels respectively include: 1) a first capacitor connected between a data line and a first node and 2) a switching transistor including a gate electrode connected to a scan line and first and second electrodes respectively connected to the first node and a second node. The display device also includes a driving transistor including a first electrode connected to a first power source voltage and a second electrode connected to an anode of an organic light emitting diode (OLED). The device further includes a compensation transistor including a first electrode connected to the first node and a second electrode connected to the second electrode of the driving transistor.