Sigma-Delta LED Driver Circuit for High-Resolution Color Mixing
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Solution Overview
Problem
Modern illumination systems and displays require high brightness resolution for multi-color LEDs, which is challenging with pulse width modulation due to electromagnetic compatibility issues and color hue variations with current adjustments.
Innovation Solution
A circuit arrangement using sigma-delta modulators to control the current sources for LEDs, providing pulse-density modulated bit-streams that adjust the mean current values, thereby improving electromagnetic compatibility and maintaining consistent hue while achieving high brightness resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulse width modulation is used to control LED brightness with high resolution, then brightness resolution is improved, but electromagnetic compatibility deteriorates due to fast switching currents
Solution Approach 1:
The patent applies periodic action by using pulse-density modulation instead of conventional PWM. The sigma-delta modulator generates a periodic bit-stream signal that controls the LED current in a periodic manner, achieving high brightness resolution through density variation of pulses rather than extremely fast switching edges, thereby reducing electromagnetic interference while maintaining precision.
Solution Approach 2:
The patent changes the control parameter from duty cycle (in PWM) to pulse density. The sigma-delta modulator transforms the control approach by varying the density of pulses within a fixed period rather than changing the width of individual pulses, which reduces the need for extremely fast switching and improves electromagnetic compatibility while maintaining high brightness resolution.
2Object-affected harmful factors
If continuous current control is used to adjust LED brightness, then electromagnetic compatibility is improved, but color hue stability deteriorates due to wavelength variation with current
Solution Approach 1:
The patent uses periodic pulse-density modulated signals to control LED current rather than continuous analog current control. This periodic control method maintains better color hue stability because the LED operates in a more consistent switching regime, and the sigma-delta modulator ensures precise average current control that minimizes wavelength variation while maintaining good electromagnetic compatibility.
3Measurement precision
If high frequency PWM is used for multi-color LED control, then brightness resolution is improved, but device complexity increases due to fast switching requirements
Solution Approach 1:
The patent introduces a sigma-delta modulator as an intermediary device between the digital control signal and the LED current control. This intermediary component converts standard digital signals into high-resolution pulse-density modulated bit-streams, eliminating the need for complex fast-switching circuitry while achieving high brightness resolution through the modulator's digital processing capabilities.
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
The solution enables efficient and high-resolution brightness control for multi-color LEDs with improved electromagnetic compatibility, reducing electromagnetic interference and maintaining consistent color hue across brightness adjustments.
Implementation Method 1
A first light emitting diode and a second light emitting diode emitting light of different colors arranged adjacent to each other for additive color mixing
Data Source
AI summary
A circuit arrangement includes a first light emitting diode and a second light emitting diode emitting light of different colors arranged adjacent to each other for additive color mixing. A first and second controllable current sources are connected to the first and second light emitting diode, respectively, such that the load currents of the light emitting diodes depend on respective control signals received by the current sources. First and second sigma-delta modulators are connected to the first and second light emitting diodes, respectively, and provide bit-streams as control signals to the current sources. The mean value of each bit-stream corresponds to the value of an input signal of the respective sigma-delta modulator.