AMOLED Pixel Circuit Threshold Voltage Compensation
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Solution Overview
Problem
Active Matrix Organic Light Emitting Diode (AMOLED) display devices face issues with threshold voltage variations in thin film transistors, leading to display mura and reduced performance over time, which existing compensation methods fail to adequately address.
Innovation Solution
A pixel circuit comprising a driving circuit, data writing circuit, first and second compensation circuits, and a light emitting element, where the compensation circuits adjust voltages to compensate for threshold voltage variations, ensuring stable driving current and improved display quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a simple pixel circuit structure is used, then manufacturing cost and process complexity are reduced, but threshold voltage variations cause display mura and performance degradation
Solution Approach 1:
The pixel circuit performs preliminary compensation actions by measuring the actual threshold voltage of the driving transistor and storing this information in the compensation capacitor before the actual display operation. This advance preparation allows the circuit to compensate for threshold voltage variations during normal operation, preventing display mura while maintaining a relatively simple circuit structure.
Solution Approach 2:
The pixel circuit implements feedback by measuring the actual threshold voltage of the driving transistor and using this information to adjust the gate voltage accordingly. The compensation capacitor stores the measured threshold voltage, which is then fed back to the driving transistor's gate to compensate for variations, ensuring uniform display performance.
2Reliability
If compensation circuits are added to address threshold voltage variations, then display uniformity is improved, but circuit complexity increases
Solution Approach 1:
The pixel circuit merges the compensation function with the existing driving circuit structure. The compensation capacitor is integrated into the same circuit block as the driving transistor, and the measurement and compensation operations are combined into a single operational sequence. This merging approach provides effective compensation while minimizing the increase in circuit complexity.
Solution Approach 2:
The pixel circuit achieves multi-functionality by using the same circuit components for both the driving function and the compensation function. The compensation capacitor serves dual purposes: storing threshold voltage information for compensation and participating in the driving operation. This universal approach reduces the need for separate dedicated compensation components.
3Reliability
If existing compensation methods are used, then some threshold voltage drift is addressed, but display mura and performance degradation over time remain
Solution Approach 1:
The pixel circuit performs preliminary measurement and storage of the driving transistor's threshold voltage characteristics before the display operation begins. By capturing the initial threshold voltage and storing it in the compensation capacitor, the circuit prepares compensation data in advance, enabling continuous compensation throughout the display's operational lifetime and preventing performance degradation over time.
Solution Approach 2:
The pixel circuit implements continuous feedback by repeatedly measuring the actual threshold voltage and updating the compensation capacitor's stored value. This ongoing feedback mechanism ensures that threshold voltage drifts are continuously compensated, maintaining display uniformity throughout the device's operational lifetime and preventing the development of display mura.
Data Source
AI summary
A pixel circuit and a driving method thereof, and a display device are provided. The pixel circuit includes a data writing circuit, a driving circuit, a first compensation circuit, a second compensation circuit and a light emitting element. The driving circuit includes a control terminal, a first terminal and a second terminal, and is configured to control a driving current which runs through the first terminal and the second terminal and is used to drive the light emitting element to emit light; the data writing circuit is connected with the control terminal of the driving circuit, and is configured to write a data signal or a reference voltage signal to the control terminal of the driving circuit in response to a scan signal.