TFT Driver Circuit for Micro-LED Matrix PWM and Current Sharing
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Solution Overview
Problem
Current methods for driving micro-LED displays face challenges due to the micrometer-scale size of μLEDs, which require precise contacting methods not feasible with traditional soldering or gluing, and the limitations of passive matrix drivers and active matrix architectures in maintaining performance and space efficiency.
Innovation Solution
A driver circuit is implemented on a TFT layer with embedded switches, sharing current sources and PWM transistors across multiple pixels, using external multiplexers and current mirrors to address each pixel individually, reducing power losses and visual artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional contacting methods (soldering, gluing) are used for μLEDs, then manufacturing process is simple, but positioning accuracy and contact precision are insufficient due to micrometer-scale size requirements
Solution Approach 1:
The patent replaces traditional mechanical contacting methods (soldering, gluing) with direct integration of TFT-based driver circuits on the same substrate as μLEDs. This eliminates the need for separate contacting processes and achieves micrometer-scale positioning accuracy through lithographic definition of contact pads and driver circuit integration, resolving the contradiction between manufacturing simplicity and positioning precision.
2Length of moving object
If PCB is used for μLED architecture, then wiring is simple, but wire dimensions become larger than LED sizes and manufacturing limitations occur
Solution Approach 1:
The patent merges the driver circuit and display substrate into a single integrated structure using TFT technology. The driver circuits are fabricated directly on the substrate alongside μLEDs through the same lithographic process, eliminating separate PCB wiring layers. This integration reduces wire dimensions to micrometer scale, matching LED sizes, and maintains manufacturing feasibility through standardized TFT fabrication processes.
3Length of stationary object
If passive matrix drivers are used, then chip-to-LED distance is minimized, but PWM generation and current sharing cause performance reduction due to parasitic effects
Solution Approach 1:
The patent segments the driver functionality into distributed TFT-based driver circuits integrated at each pixel location on the substrate. Each pixel has its own switching TFT that generates local PWM signals and controls current independently, eliminating the need for long current sharing paths from a centralized PM driver chip. This segmentation minimizes parasitic effects while maintaining short chip-to-LED distances through monolithic integration.
4Ease of operation
If active matrix architecture is used, then individual pixel control is achieved, but extra TFTs per pixel exceed available area in active matrix
Solution Approach 1:
The patent implements multi-functional TFTs at each pixel that simultaneously serve as switching elements for PWM generation, current control, and data latching. Each pixel's TFT performs multiple functions that would traditionally require separate components, including pixel selection, current modulation, and gray-scale control. This universal TFT design enables individual pixel control while minimizing the area occupied by driver circuitry within the active matrix.
Data Source
AI summary
A driver circuit for driving a matrix of N×M pixels of a light emitting module. Each pixel is composed of at least three types of light emitting elements. The light emitting elements are driven by a modulation control signal. The driver circuit is embedded in a TFT layer. It is configured to cooperate with N multiplexers provided in an external driver circuit, each multiplexer being configured to drive one line of M pixels. It is also configured to cooperate with one external current source per type of light emitting element, each external current source being mirrored M times on the matrix of the driver circuit and being arranged in series with a signal switch for generating the control signal provided for each of the M columns.