Pixel Circuit With Constant-Current PWM for Wavelength Stability
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Solution Overview
Problem
Existing display technologies using micro light-emitting diodes face issues with wavelength shifts due to variations in driving current amplitude, leading to inefficiencies and increased power consumption.
Innovation Solution
A pixel design utilizing pulse width modulation to control emission time while maintaining a constant driving current, combined with a sweep signal that boosts and decreases voltage levels to optimize power usage, incorporating transistors and capacitors to manage signal transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse amplitude modulation is used to control brightness by adjusting driving current amplitude, then brightness control is achieved, but wavelength shifts occur in micro light-emitting diodes
Solution Approach 1:
The patent changes the control parameter from current amplitude (PWM) to emission time duration while maintaining constant current amplitude. This parameter change resolves the wavelength shift issue by eliminating amplitude variations while still achieving brightness control through temporal modulation of the light emission.
2Illumination intensity
If driving current amplitude is increased to improve brightness, then illumination intensity increases, but power consumption increases
Solution Approach 1:
The patent employs periodic pulsed current delivery where the micro light-emitting diode receives current in discrete emission periods rather than continuous operation. By controlling the emission time duration within each period while maintaining constant current amplitude, the system achieves brightness control without the proportional increase in power consumption that would result from continuous high-amplitude current delivery.
3Duration of action of moving object
If data voltage and gate voltage are increased to extend emission time, then brightness control is improved, but power consumption increases
Solution Approach 1:
The patent changes the control approach from increasing voltage levels to extending the emission time duration. By maintaining constant current amplitude and controlling only the temporal duration of emission, the system achieves brightness modulation without the quadratic power increase that would result from higher gate voltages extending the emission period.
Data Source
AI summary
A pixel includes a light-emitting element including a first electrode and a second electrode connected to a low power line which transmits a low power voltage, a pulse width modulator which controls an emission time duration of the light-emitting element based on a data voltage and a sweep signal, and a constant current generator which supplies a driving current having a constant level to the light-emitting element based on a constant current generation voltage. The sweep signal has a first high voltage level in a non-emission period, and is boosted to a second high voltage level, which is higher than the first high voltage level, before decreasing to a low voltage level lower than the first high voltage level in an emission period.