Micro-LED Pixel Circuit Current Control
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Solution Overview
Problem
Micro-LEDs with inorganic emission materials face challenges in expressing gradation due to varying emission wavelengths with driving current, making it difficult to achieve consistent brightness and color accuracy, especially when using a current-driven method.
Innovation Solution
A pixel circuit with a time-sharing driving method, including a constant current control circuit and a pulse width control circuit, compensates for transistor threshold voltage deviations within each pixel, ensuring accurate driving current and pulse width to maintain consistent emission across sub-pixels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a current-driven method is used to express gradation in micro-LED displays, then the emission wavelength varies with driving current, but this makes it difficult to achieve consistent brightness and color accuracy across sub-pixels
Solution Approach 1:
The patent changes the control parameter from current magnitude to pulse width duration. Instead of varying current amplitude to express gradation, the invention uses pulse width modulation where the emission duration is controlled by the data voltage, thereby maintaining constant current amplitude while achieving gradation expression without wavelength variation.
Solution Approach 2:
The patent segments the pixel circuit into distinct functional blocks: a constant current control circuit that generates stable driving current, a pulse width control circuit that determines emission duration, and compensation circuits for threshold voltage. This segmentation allows each block to optimize its function independently, ensuring current stability and precise pulse width control.
2Device complexity
If transistor threshold voltage variations are not compensated, then device complexity is reduced, but brightness consistency and color accuracy deteriorate across sub-pixels
Solution Approach 1:
The patent implements self-service compensation where each pixel circuit contains its own compensation mechanisms. The first capacitor stores compensation voltage for the first transistor's threshold voltage, and the second capacitor stores compensation voltage for the second transistor's threshold voltage. This allows each pixel to compensate for its own variations without requiring external calibration circuits.
Solution Approach 2:
The patent performs threshold voltage compensation in advance during the initialization phase. Before the emission phase, the compensation circuits calculate and store the threshold voltage values in capacitors, so that when the pixel operates, the compensation is already in place, ensuring immediate brightness consistency without real-time adjustment complexity.
3Manufacturing precision
If external compensation circuits are used to correct transistor variations, then color accuracy improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent merges the compensation function into the existing pixel circuit structure rather than adding separate external compensation circuits. The constant current control circuit and pulse width control circuit are integrated with the transistor switching structure, sharing common nodes and capacitors. This integration achieves compensation functionality while minimizing additional circuit elements.
Data Source
AI summary
A display panel, a pixel circuit, and a display device are disclosed. The display panel includes sub-pixels and a driver driving the sub-pixels. Each sub-pixel includes: an emission element; a first transistor configured to generate a driving current; a constant current control circuit configured to receive a reference voltage and a bias voltage for setting a value of the driving current and including a first capacitor configured to store a first compensation voltage generated by adding a threshold voltage of the first transistor to a difference between the bias voltage and the reference voltage; and a pulse width control circuit configured to receive a data voltage used to determine an emission duration of the emission element and including a second transistor configured to control a pulse width of the driving current according to the data voltage and a second capacitor configured to store a second compensation voltage corresponding to a threshold voltage of the second transistor.