LED Package Current-Source PWM for High Dynamic Range
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Solution Overview
Problem
Existing LED display technologies face challenges in achieving high dynamic range and resolution with small pixel pitches due to limitations in current driving techniques, which require high frequencies and result in brightness discontinuities and increased complexity.
Innovation Solution
Implementing multiple current sources at different current levels for each LED chip within a package, allowing for varying current pulse width modulation (PWM) to increase the dynamic range without increasing frequency, by selectively turning on and off different combinations of current sources during a PWM period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional current driving techniques are used to achieve high resolution with small pixel pitches, then the display resolution is improved, but the dynamic range is limited and brightness discontinuities occur
Solution Approach 1:
The current driving signal is segmented into multiple discrete current levels (e.g., 0, 1, 2, 3, 4, 5, 6, 7 levels) within each PWM period. This segmentation allows the LED to be driven at different current levels to produce monotonic brightness transitions, eliminating brightness discontinuities while maintaining high display resolution.
Solution Approach 2:
The patent implements dynamic current level adjustment within each PWM period by selectively activating different numbers of current sources (e.g., 1st current source, 1st and 2nd current sources, etc.). This dynamic adjustment enables the system to achieve high dynamic range (greater than 1000:1 up to 16,000,000:1) without increasing PWM frequency, thereby maintaining brightness continuity across all gray levels.
2Reliability
If high PWM frequency is used to increase dynamic range, then the brightness range is improved, but power consumption increases and parasitic effects are exacerbated
Solution Approach 1:
Instead of changing PWM frequency to increase dynamic range, the patent changes the current level parameter within each PWM period. By varying the current level (e.g., from 1st current level to 7th current level) while maintaining a constant PWM frequency, the system achieves high dynamic range (greater than 1000:1 up to 16,000,000:1) without the power consumption penalties and parasitic effects associated with high-frequency PWM operation.
3Reliability
If multiple current sources are added to each LED chip, then the dynamic range is increased, but the device complexity increases
Solution Approach 1:
Multiple current sources (e.g., 1st current source, 2nd current source, 3rd current source, etc.) are merged into a single LED package with each LED chip. These current sources are controlled by a unified PWM signal that selectively activates different combinations of current sources within each PWM period. This merging approach increases dynamic range while avoiding the need for separate driver circuits for each current level, thereby limiting the increase in overall device complexity.
4Illumination intensity
If high current levels are used to increase brightness, then the luminous output is improved, but power consumption and heat generation increase
Solution Approach 1:
The patent employs periodic PWM action with varying current levels within each period. Instead of continuously applying high current, the system uses periodic pulses at different current levels (e.g., 1st current level, 2nd current level, up to 7th current level) to achieve the desired brightness. This periodic action with variable current levels allows the LED to reach high luminous output when needed while reducing average power consumption and heat generation compared to continuous high-current operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances the dynamic range of LED displays to greater than 1000:1 up to 16,000,000:1, ensuring monotonic brightness transitions and reducing power consumption, while eliminating brightness discontinuities and parasitic effects.
Implementation Method 1
Light-emitting diodes (LEDs) are solid-state devices that convert electrical energy to light and generally include one or more active layers of semiconductor material (or an active region) arranged between oppositely doped n-type and p-type layers. When a bias is applied across the doped layers, holes and electrons are injected into the one or more active layers where they recombine to generate emissions such as visible light or ultraviolet emissions.
Data Source
AI summary
Light-emitting diode (LED) packages and, more particularly, LED packages with varying current pulse width modulation (PWM) signals and related methods are disclosed. Varying current PWM is provided by having multiple current sources at different current levels for each LED chip in an LED package. An output PWM signal for each LED chip is routed to selectively turn on and off different combinations of current sources to provide varying current levels associated with varying brightness levels for each LED chip. By providing multiple current sources for each LED chip, the dynamic range of current levels and corresponding brightness levels may be increased for a same PWM clock frequency.