Micro LED Pixel PWM Circuit for Color-Stable Grayscale Display
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Solution Overview
Problem
Micro LED displays experience a color shift due to wavelength shift when driven in pulse amplitude modulation (PAM) manner, which affects grayscale display performance.
Innovation Solution
A pixel design incorporating a pulse width modulation (PWM) adjustment circuit with low-temperature polycrystalline silicon and oxide thin-film transistors (LTPO TFTs) to control light emission periods, along with a constant current (CC) generating circuit, to stabilize micro LED operation for grayscale display.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If micro LED is driven in pulse amplitude modulation (PAM) manner, then brightness control is achieved, but color shift occurs due to wavelength shift
Solution Approach 1:
The patent changes the modulation parameter from pulse amplitude modulation (PAM) to pulse width modulation (PWM). In PWM, the brightness is controlled by varying the duty cycle (width of the pulse) rather than the amplitude, which prevents wavelength shift and color accuracy degradation while still achieving brightness control.
2Stability of the object's composition
If PWM adjustment circuit is added to control light emission period, then grayscale display stability is improved, but device complexity increases
Solution Approach 1:
The pixel circuit is segmented into distinct functional modules: a PWM adjustment circuit that controls the light emission period based on grayscale data, and a constant current generation circuit that provides stable current during emission. This segmentation allows independent optimization of each function while managing overall complexity through modular design.
Solution Approach 2:
The patent implements periodic light emission control using PWM signals. The micro LED emits light in periodic pulses with variable width according to the grayscale level, rather than continuous emission. This periodic action enables precise grayscale control while reducing power consumption and heat generation.
3Reliability
If constant current generation circuit is implemented, then micro LED operation stability is improved, but device complexity increases
Solution Approach 1:
The circuit is divided into functional segments including a constant current generation circuit that operates specifically during the light emission period. This circuit segment ensures stable current supply to the micro LED, improving reliability while the segmentation allows the rest of the circuit to be optimized for other functions.
Solution Approach 2:
The constant current generation circuit ensures continuous and stable current supply to the micro LED during the entire light emission period, regardless of variations in voltage or other environmental factors. This continuity of useful action maintains reliable operation and consistent brightness output throughout the emission phase.
Data Source
AI summary
A pixel may include a micro LED, a pulse width modulation (PWM) adjustment circuit that includes an inverter, and controls a light emission period of the micro LED on the basis of an output of the inverter according to a data voltage which is provided to an input terminal of the inverter and a duty driving signal, and a constant current (CC) generating circuit that provides a constant current to the micro LED for the light emission period. The inverter may be implemented with low-temperature polycrystalline silicon and oxide thin-film transistors (LTPO TFTs).