Active Matrix LED Pixel Driver Circuit with Segmented Transistor Control
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Solution Overview
Problem
Active matrix LED displays suffer from non-uniform illumination due to sensitivity of LED driving current to circuit parameter variations, such as transistor threshold voltage and geometry variations, leading to inconsistent pixel performance.
Innovation Solution
A unit pixel driver circuit is designed with a current control block comprising transistors connected in both parallel and series, maintaining a common gate geometry size across all transistors to mitigate the effects of manufacturing process variations and ensure consistent current control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a simple transistor-based LED driving circuit is used, then the device complexity is reduced, but the manufacturing precision deteriorates due to sensitivity of LED driving current to circuit parameter variations
Solution Approach 1:
The patent divides the LED driving current control into multiple segments by using multiple transistors (M1, M2, M3, M4) arranged in specific configurations. Each transistor handles a portion of the current control function, which reduces the sensitivity of the overall system to individual transistor parameter variations. This segmentation allows the system to maintain current uniformity across different pixels even when individual transistor parameters vary during manufacturing.
Solution Approach 2:
The patent employs different gate geometry sizes for different transistors in the control block. Specifically, transistors M1 and M2 have different gate geometry sizes compared to M3 and M4, allowing each transistor to be optimized for its specific current control role. This parameter differentiation compensates for manufacturing variations by tailoring the electrical characteristics of each transistor to its functional requirements.
2Manufacturing precision
If transistor gate geometry sizes are made uniform, then the manufacturing precision is improved, but the adaptability deteriorates in terms of current control flexibility
Solution Approach 1:
The patent applies different gate geometry sizes to different transistors based on their specific functions within the control block. Transistors M1 and M2 have one gate geometry size optimized for their current control role, while transistors M3 and M4 have a different gate geometry size suited for their specific function. This local differentiation allows each transistor to be optimally tuned for its role while maintaining overall current uniformity across the LED array.
Data Source
AI summary
A unit pixel driver circuit includes a capacitor configured to store a voltage corresponding to a desired pixel brightness and a control block. The control block may include a first, second third and fourth transistors, all of which are connected together, both in parallel and in series. The control block controls, based on the voltage stored in the capacitor, the amount of current flowing through a pixel LED. The first transistor, second transistor, third transistor and fourth transistor all share a common gate geometry size.