Scrambled PWM Display Driver Circuit for LED Panel EMI Reduction
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Solution Overview
Problem
High-frequency switching in LED display technology leads to increased loading on power converters and electromagnetic interference (EMI), as the number of LEDs and PWM signals rise, necessitating a more efficient control method to manage power distribution and reduce EMI.
Innovation Solution
A display driver circuit with scrambled PWM signals and current regulators, where each LED string receives PWM signals with different duty cycles and random pulse adjustments to distribute power more evenly and stagger current draws, reducing the load on power converters and mitigating EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the number of LEDs and PWM signals is increased to achieve high resolution and high refresh rate, then the display quality is improved, but the loading on the power converter and EMI are increased
Solution Approach 1:
The patent applies periodic action by using pulse width modulation (PWM) signals with different duty cycles to control LED brightness. By varying the pulse frequency and duty cycle periodically, the system achieves high refresh rates while distributing power consumption over time, thereby reducing peak EMI levels.
Solution Approach 2:
The patent changes parameters by adjusting PWM duty cycles and pulse frequencies dynamically. Different LED strings receive PWM signals with varying duty cycles to achieve desired brightness levels while staggering their operation to reduce simultaneous switching, thus lowering EMI and power converter loading.
2Manufacturing precision
If the number of LEDs is increased to achieve high resolution, then the display quality is improved, but the loading on the power converter is increased
Solution Approach 1:
The patent segments the LED display into multiple independent LED strings, each controlled by separate current regulators. This segmentation allows the power converter to supply power to different strings at different times through staggered PWM signaling, reducing the peak power loading while maintaining high resolution across the entire display.
Solution Approach 2:
By using periodic PWM signals with varying duty cycles for different LED strings, the system distributes power consumption over time. This periodic action allows the power converter to handle increased total LED count for high resolution without experiencing excessive peak loading.
3Productivity
If high-frequency switching is used to achieve high refresh rate, then the productivity is improved, but the EMI is increased
Solution Approach 1:
The patent introduces asymmetry by assigning different duty cycles and pulse patterns to different LED strings. This asymmetric PWM control staggers the switching events across multiple strings, breaking up the synchronous high-frequency switching that causes EMI, while maintaining the overall high refresh rate through the combined effect of all strings.
4Productivity
If multiple PWM signals are output simultaneously to drive increasing number of LEDs, then the productivity is improved, but the loading on the power converter is increased
Solution Approach 1:
The patent uses periodic PWM signals with staggered timing for multiple LED strings. By coordinating the periodic switching of multiple strings with different duty cycles, the system achieves high refresh rates while distributing the power draw over time, reducing peak loading on the power converter.
Data Source
AI summary
A display driver circuit for controlling a display panel having a plurality of light-emission diode (LED) strings includes a plurality of current regulators and a control circuit. Each of the plurality of current regulators is configured to control one of the plurality of LED strings. The control circuit, coupled to the plurality of current regulators, is configured to generate a plurality of pulses in a plurality of pulse width modulation (PWM) signals and output each of the plurality of PWM signals to a respective current regulator among the plurality of current regulators. Wherein, the plurality of pulses are scrambled.