Pixel Circuit PWM-PAM Control for Micro LED Color Stability
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Solution Overview
Problem
Existing pixel circuits for micro LED displays face challenges in achieving high grayscale expressiveness and contrast ratio while minimizing color deviation, particularly due to issues with current-induced color shifts and global shutter methods that impair image quality.
Innovation Solution
A pixel circuit design incorporating a first circuit with a first capacitor and a second circuit with a second capacitor, along with charging and discharging mechanisms, to control current and emission time independently for each sub-pixel, using pulse width modulation (PWM) and pulse amplitude modulation (PAM) data voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the current flowing through the LED is increased to improve brightness, then luminous efficiency is improved, but color shift occurs which degrades color reproduction
Solution Approach 1:
The pixel circuit is divided into two independent control paths: one for brightness (amplitude modulation) and one for emission duration (pulse width modulation). This segmentation allows independent optimization of brightness and color control, preventing color shift while maintaining high luminous efficiency.
Solution Approach 2:
The patent changes the control parameters from single-current-density control to dual-parameter control (amplitude and duration). By controlling brightness through amplitude modulation and emission time through pulse width modulation, the system can maintain optimal current density for color stability while achieving desired brightness levels.
2Manufacturing precision
If PWM method is used to maintain constant current density and regulate emission time, then color reproduction is improved, but grayscale expressiveness is limited
Solution Approach 1:
The patent merges pulse width modulation (PWM) for emission time control with pulse amplitude modulation (PAM) for brightness control. This combination allows independent adjustment of both emission duration and brightness amplitude, significantly enhancing grayscale expressiveness while maintaining color accuracy through constant current density.
3Device complexity
If global shutter method is used to emit light from all pixel lines simultaneously, then circuit simplicity is maintained, but contrast ratio is degraded
Solution Approach 1:
The patent introduces dynamic control of emission timing for different pixel lines through the pulse width modulation circuit. Each pixel line can have independently adjustable emission duration, enabling local optimization of contrast ratio while maintaining relatively simple circuit architecture through shared control components.
4Device complexity
If different colored sub-pixels are controlled with same current and emission time, then circuit complexity is reduced, but individual sub-pixel performance is compromised
Solution Approach 1:
The patent applies local quality control by allowing each sub-pixel to have independent amplitude and duration control through the dual-circuit architecture. Different colored sub-pixels can be optimized with specific current amplitudes and emission durations tailored to their characteristics, improving overall display reliability and performance.
Data Source
AI summary
A pixel circuit can include a light-emitting element configured to emit light, a driving transistor configured to supply a current to the light-emitting element, a first circuit including a first capacitor charged with a first data voltage, and a second circuit including a second capacitor charged with a second data voltage and configured to adjust the current supplied by the driving transistor to the light-emitting element, Also, the first circuit is configured to output a discharge control signal that instructs the second capacitor to discharge in response to a voltage change in the first capacitor for turning the light-emitting element off.