Micro-LED Pixel Circuit With Threshold Compensation for Uniform Luminance
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Solution Overview
Problem
The uneven luminance across micro-LED pixel arrays due to process variation in silicon-based MOSFETs, limited operation range of gate voltage, and leakage paths affecting gate voltage, complicating data generation and requiring precise control, especially in high pixel density displays.
Innovation Solution
A pixel circuit design incorporating specific transistors and capacitors to initiate and compensate for threshold voltage, employing a voltage divider to enhance gray level step size and operation range, and isolating leakage paths to reduce DC power loss, ensuring luminance uniformity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If silicon-based MOSFETs are used to control micro-LEDs in pixel arrays, then the response speed and resolution are improved, but process variation causes threshold voltage differences resulting in uneven luminance across the pixel array
Solution Approach 1:
The patent applies preliminary action by performing threshold voltage compensation before the display data is written to the pixel circuit. The compensation circuit pre-calculates and stores the threshold voltage offset in a capacitor during a compensation phase, so that when the actual display data is applied, the threshold voltage variation has already been accounted for, ensuring uniform luminance output across all pixels despite process variations.
Solution Approach 2:
The patent implements feedback by using the pixel circuit's own threshold voltage characteristics to generate a compensation signal. The compensation circuit monitors the threshold voltage offset and feeds back a corrected gate voltage to the driving transistor, creating a closed-loop system that automatically compensates for manufacturing variations and maintains luminance uniformity.
2Measurement precision
If the mobility of silicon-based MOSFET is significantly higher than alternative substrate-based MOSFET, then the driving current control is improved, but the operation range of gate voltage becomes very limited requiring precise gate voltage control and complicating data generation
Solution Approach 1:
The patent applies parameter changes by transforming the driving mechanism from direct voltage control to current control. By using a current source or current mirror circuit instead of directly controlling gate voltage, the system changes the control parameter from voltage (with limited range) to current (with wider dynamic range), thereby expanding the operation range and simplifying data generation while maintaining precise driving current control.
3Manufacturing precision
If micro-OLED-based pixel array with high pixel density is used, then the resolution is improved, but no DC current is allowed except in emission stage and hold capacitor forms leakage path affecting gate voltage
Solution Approach 1:
The patent applies the taking out principle by extracting and isolating the leakage path formed by the hold capacitor. The compensation circuit separates the leakage current from the main data writing path, allowing the hold capacitor to maintain gate voltage while its leakage effect is compensated for independently. This enables high pixel density operation without excessive DC power loss from capacitor leakage.
4Area of stationary object
If hold capacitor is used to store gate voltage without occupying too much circuit area, then the circuit area is reduced, but the hold capacitor forms a leakage path between supply terminal and ground terminal affecting gate voltage
Solution Approach 1:
The patent introduces an intermediary compensation circuit that mediates between the hold capacitor's leakage path and the gate voltage requirement. This intermediate circuit monitors the voltage drop caused by leakage and actively compensates by adding corrective current or voltage, thus maintaining gate voltage stability despite the presence of the small hold capacitor with leakage path.
Data Source
AI summary
A pixel circuit includes a sample circuit, a first transistor, a second transistor, a third transistor, a light-emitting diode, and a fourth transistor. The first transistor includes a control terminal coupled to the sample circuit, a first terminal coupled to a supply terminal, and a second terminal. The second transistor coupled to the control terminal and the second terminal of the first transistor. The third transistor includes a first terminal coupled to the second terminal of the first transistor, and a second terminal. The light-emitting diode includes a first terminal coupled to the second terminal of the third transistor, and a second terminal coupled to a ground terminal. The fourth transistor includes a first terminal coupled to the first terminal of the light-emitting diode and a second terminal, and a second terminal coupled to a reset terminal.