OLED Pixel Compensation Circuit Stabilizes Current Against Threshold Voltage Drift
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Solution Overview
Problem
Current Organic Light Emitting Diode (OLED) displays experience unstable current and uneven brightness due to the drift of the threshold voltage of the driving transistor, affecting display performance.
Innovation Solution
A pixel compensation circuit utilizing multiple thin-film transistors, including NMOS and PMOS transistors, with a specific configuration of switches and a storage capacitor to stabilize the current flowing through the OLED, independent of the threshold voltage drift, by managing voltage increments and differences across the transistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single driving transistor is used to control current through OLED, then the structure is simple, but the threshold voltage drift causes unstable current and uneven brightness
Solution Approach 1:
The patent divides the single driving transistor into multiple transistors (first driving transistor T1, second driving transistor T2, third driving transistor T3) with distinct functions. T1 controls the main current flow, T2 compensates for threshold voltage drift, and T3 provides additional stabilization. This segmentation allows each transistor to handle specific aspects of current control, thereby improving overall current stability while maintaining reasonable structural complexity.
Solution Approach 2:
The patent introduces a storage capacitor C1 as an intermediary element between the transistors and OLED. This capacitor stores charge and provides a stable voltage reference, mediating the effects of threshold voltage drift on the OLED current. By placing this intermediary storage element in the circuit, the system can maintain stable current flow even when transistor threshold voltages drift over time.
2Reliability
If multiple transistors are added to compensate for threshold voltage drift, then current stability improves, but device complexity increases
Solution Approach 1:
The patent combines multiple transistors and the storage capacitor into an integrated pixel circuit structure where all components work together within a single pixel unit. The first, second, and third driving transistors along with the storage capacitor are merged into a cohesive circuit block that collectively provides current stabilization, making the increased complexity manageable within the pixel architecture.
Solution Approach 2:
The multiple transistors in the patent serve multiple functions simultaneously. The first driving transistor T1 handles primary current control, the second driving transistor T2 provides threshold voltage compensation, and the third driving transistor T3 offers additional stabilization. This multi-functionality allows the circuit to address various aspects of current instability with a unified transistor array, improving reliability without requiring separate compensation circuits.
Data Source
AI summary
Pixel compensation circuit, method and flat display device. The circuit includes control terminals of first to fourth controllable and driving switches respectively connected with first to fourth scanning lines and second terminal of the second controllable switch, first terminal of the first controllable switch connected with data line; first terminal of the second controllable switch connected with second terminal of the first controllable switch; first terminal of the third controllable switch connected with the second terminal of the first controllable switch; the second terminal of the first controllable switch is connected with the second terminal of the driving switch through a storage capacitor; anode of an OLED connected with the second terminal of the driving switch, cathode is grounded; first terminal of the fourth controllable switch connected with second voltage terminal, which can avoid unstable current of the organic light emitting diode by drift of threshold voltage of driving transistor.