Pixel Mixed Compensation Circuit for AMOLED Drift
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Solution Overview
Problem
In active matrix organic light-emitting diode (AMOLED) displays, electrical drift in thin film transistors (TFTs) and organic light-emitting diodes (OLEDs) leads to display abnormalities over time, necessitating a compensation mechanism to maintain voltage stability.
Innovation Solution
A pixel mixed compensation circuit is introduced, featuring a fourth TFT and a second capacitor between the source and drain of a third TFT, with the fourth TFT only active during detection and the second capacitor feeding back changes in electric potential to a sensing line. An external compensation circuit detects these changes and adjusts the voltage at a first node to maintain a constant gate-source voltage (Vgs) of the first TFT.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fourth TFT is added to the pixel circuit to enable compensation detection, then compensation capability is improved, but device complexity increases
Solution Approach 1:
The pixel circuit is divided into distinct functional stages: a detection stage where the fourth TFT is activated to measure threshold voltage drift, and a lighting stage where the fourth TFT remains off to prevent interference. This temporal segmentation allows the compensation function to be added without creating continuous interference between adjacent rows.
Solution Approach 2:
The fourth TFT operates periodically rather than continuously - it is turned on only during specific detection periods and kept off during lighting periods. This periodic operation enables the compensation detection function while minimizing interference with normal display operations and adjacent row operations.
2Ease of operation
If the fourth TFT remains on during lighting process to simplify control, then ease of operation is improved, but harmful interference between different rows occurs
Solution Approach 1:
The fourth TFT is kept in an off state during the lighting process as a preliminary measure to prevent potential interference with adjacent row operations. By proactively disabling the TFT during periods when it is not needed for detection, the circuit design preemptively eliminates the harmful interference that would otherwise occur.
3Device complexity
If electrical drift is not compensated, then device complexity is reduced, but display stability deteriorates over time
Solution Approach 1:
The pixel circuit incorporates a feedback mechanism where the fourth TFT detects threshold voltage drift in the first TFT, and the detected information is used to adjust and compensate for the drift. This feedback loop maintains voltage stability over time by continuously counteracting the electrical drift that occurs in OLED and TFT components.
Data Source
AI summary
The disclosure provides a pixel mixed compensation circuit and a pixel mixed compensation method. The pixel mixed compensation circuit includes a plurality of pixel internal driving circuits arranged in an array and an external compensation circuit connecting with each of the internal driving circuits. A fourth TFT and a second capacitor are disposed between a source of a third TFT and a drain of a third TFT. The fourth TFT is turned on only during a detecting stage. The second capacitor is configured to feed back changes in electric potential of a second node to a sensing line. The external compensation circuits can detect changes in electric potential of the second node by the sensing line. The external compensation circuit can directly react to changes in current and can transmit a voltage value to a first node via data signals to adjust a voltage of the first node.