Pixel Circuit Replication Transistor Threshold Compensation
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Solution Overview
Problem
Conventional pixel circuits face issues with brightness uniformity due to the inconsistency in driving currents caused by different threshold voltages, which cannot be precisely compensated due to the influence of parasitic capacitors, leading to variations in driving currents across different pixel regions.
Innovation Solution
A pixel circuit design that includes a data compensation circuit, a storage circuit, and replication and driving transistors with the same structure, where the compensation voltage is calculated as the sum of the data voltage and the threshold voltage of the replication transistor, allowing for accurate threshold voltage compensation by isolating the parasitic capacitances' effect.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional pixel circuits are used, then the circuit structure is simple, but the brightness uniformity deteriorates due to driving current inconsistency caused by different threshold voltages
Solution Approach 1:
The patent introduces a replication transistor with the same structure as the driving transistor to copy its electrical characteristics. By measuring the threshold voltage of the replication transistor and using it to compensate the driving transistor, the system achieves brightness uniformity without significantly increasing circuit complexity. The replication transistor serves as a reference model that captures the threshold voltage variations across different pixel regions.
Solution Approach 2:
The patent employs an intermediate transistor and storage capacitor as mediators between the replication transistor and the driving transistor. The intermediate transistor transfers the compensation voltage, while the storage capacitor holds the threshold voltage information for subsequent compensation operations. These intermediary components enable precise threshold voltage compensation without requiring direct modification of the driving transistor structure.
2Reliability
If threshold voltage compensation is implemented, then the driving current consistency improves, but the circuit complexity increases due to additional compensation components
Solution Approach 1:
The replication transistor serves multiple functions: it acts as a reference device for threshold voltage measurement, a sensor for detecting threshold voltage variations, and a template for structuring the compensation circuit. By making the replication transistor structurally identical to the driving transistor, the same transistor design can be used for both light emission and threshold voltage sensing, reducing the need for entirely separate compensation circuitry.
Solution Approach 2:
The pixel circuit uses itself to perform compensation. The driving transistor's own threshold voltage characteristics are measured through the replication transistor and then used to compensate the driving transistor. This self-service approach eliminates the need for external compensation devices or complex control circuits, as the system compensates itself using internally generated threshold voltage information.
3Ease of manufacture
If parasitic capacitors are present in the circuit, then the circuit can be manufactured with standard processes, but the threshold voltage compensation precision deteriorates due to the influence of parasitic capacitances
Solution Approach 1:
The patent performs preliminary measurement of the threshold voltage using the replication transistor before the actual light emission phase. By measuring the threshold voltage in advance through the intermediate transistor and storing it in the storage capacitor, the system compensates for threshold voltage variations before they affect the driving current. This preliminary action ensures that the compensation is applied before parasitic capacitances can interfere with the measurement.
Solution Approach 2:
The patent divides the pixel circuit into functionally separate components: the replication transistor for threshold voltage measurement, the intermediate transistor for signal transfer, the storage capacitor for holding threshold voltage information, and the driving transistor for light emission. This segmentation allows each component to perform its specific function with minimal interference from parasitic capacitances, as the measurement and compensation paths are physically separated from the light emission path.
Data Source
AI summary
Provided are a pixel circuit, a display panel, a display device and a pixel driving method, the pixel circuit including: a data compensation circuit, a storage circuit, a driving transistor and a replication transistor, the replication transistor and the driving transistor have the same structure; the data compensation circuit writes, in an initialization stage, a first voltage into a first node under a control of a second control signal and a third control signal; and to write, in a data writing and compensation stage, under a control of the third control signal and a first control signal, a data voltage to a first electrode of the replication transistor to detect a threshold voltage thereof, write a compensation voltage to the first node for storage by the storage circuit, the compensation voltage being equal to a sum of the data voltage and the threshold voltage of the replication transistor.