Display Panel PWM Grayscale Control for Luminous Efficiency
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Solution Overview
Problem
In display devices with high and low grayscale areas, the decrease in driving current leads to increased power dissipation and reduced efficiency, particularly affecting red, green, and blue pixels, with red pixels showing the largest drop in efficiency.
Innovation Solution
A display device with a control system that uses pulse width modulation (PWM) circuits to control sub-pixel circuits based on lookup tables, adjusting luminous time and intensity through PWM data and amplitude modulation, and a ramp signal to optimize grayscale values for improved efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the driving current of the light emitting element is decreased to achieve lower grayscale values, then the luminous intensity is reduced, but the luminous efficiency drops significantly and power dissipation increases
Solution Approach 1:
The patent applies pulse width modulation (PWM) to control the light emitting element by periodically switching the driving current on and off. Instead of using a continuously decreased current for low grayscale values, the system maintains high current amplitude during the on-period, ensuring the light emitting element operates at high efficiency points. The duty cycle of the PWM signal is adjusted to achieve different grayscale levels while maintaining high luminous efficiency throughout the modulation process.
2Use of energy by moving object
If the driving current is reduced to display low grayscale values, then the power consumption decreases, but the overall display efficiency drops significantly
Solution Approach 1:
The system uses PWM to achieve low grayscale values through periodic switching rather than continuous low current. The high current amplitude during the on-period maintains high display efficiency and luminous output, while the reduced duty cycle achieves the desired low grayscale level. This approach maintains high power utilization efficiency while achieving low average power consumption for dark display regions.
3Measurement precision
If different grayscale values are used for red, green, and blue pixels, then the color accuracy is maintained, but the efficiency drop varies across different color channels with red showing the largest drop
Solution Approach 1:
The patent applies PWM uniformly across red, green, and blue pixel channels, allowing each to maintain high current amplitudes during their respective on-periods. This ensures that all color channels operate at high efficiency points regardless of their target grayscale levels. The different duty cycles for each channel achieve the required color accuracy while preventing the efficiency drops that would occur with continuous low current driving.
Solution Approach 2:
The system allows each color channel (red, green, blue) to have independent PWM control with channel-specific duty cycles tailored to their grayscale requirements. This local optimization enables each pixel type to maintain its efficiency characteristics while achieving the overall grayscale and color accuracy needed for the display image.
Data Source
AI summary
A display device includes a display panel and a control system. The display panel includes multiple pixel groups. Each pixel group includes several sub-pixel circuits and a pulse width modulation (PWM) circuit. The sub-pixel circuit receives pulse amplitude modulation (PAM) data and controls the luminous intensity. The PWM circuit receives PWM data and controls the luminous time. The control system is used to receive image information that includes current grayscale values of the sub-pixel circuits; to establish the PWM data based on the current grayscale values through a first look-up table; to convert the current grayscale values to target grayscale values through a second look-up table, in which the target grayscale values corresponds to the PAM data; and to output image information including the PWM data and the target grayscale value.