LED Intensity Control Using Delta-Sigma Modulation to Reduce EMI
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Solution Overview
Problem
Conventional pulse width modulation (PWM) for controlling light-emitting diodes (LEDs) in ambient lighting systems generates electromagnetic interference (EMI) due to a fixed uniform frequency, which worsens when multiple LEDs are used for color mixing, as all light sources are modulated at the same frequency, independent of duty cycle.
Innovation Solution
Implementing delta-sigma signal density modulation (DSSD) to control the intensity of LEDs, where a delta-sigma modulator generates a waveform with variable frequency based on signal density, allowing for independent modulation of each LED source, reducing EMI by varying the frequency according to the desired intensity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional PWM with uniform frequency is used to control LED intensity, then the LED can be switched on and off instantaneously for intensity control, but electromagnetic interference (EMI) is generated due to fixed frequency modulation
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed uniform frequency PWM to a variable frequency delta-sigma modulation scheme. The modulation frequency dynamically changes based on the desired intensity level, with higher frequencies at lower intensity levels and lower frequencies at higher intensity levels. This dynamic frequency adjustment reduces EMI by avoiding a single dominant frequency and its harmonics, while maintaining the instantaneous switching capability of PWM for effective LED intensity control.
2Adaptability or versatility
If multiple light sources are used for color mixing with conventional PWM, then color mixing capability is achieved, but EMI is multiplied because all sources are modulated at the same frequency
Solution Approach 1:
The patent applies local quality by assigning different modulation characteristics to different LED channels. Each LED channel (red, green, blue) uses delta-sigma modulation with frequency determined by its specific intensity level rather than a uniform frequency. This allows each light source to operate at its own optimized frequency, enabling color mixing functionality while preventing EMI multiplication that occurs when all sources modulate at the same frequency.
3Device complexity
If fixed frequency PWM is used for LED control, then the control circuit is simple with uniform frequency square waves, but the spectral content includes fixed fundamental frequency and harmonics that cause EMI
Solution Approach 1:
The patent applies parameter changes by modifying the frequency parameter of the modulation signal based on the intensity level. Instead of using a fixed frequency, the system dynamically adjusts the modulation frequency as a function of the desired LED intensity. This parameter change transforms the spectral content from a fixed fundamental and harmonics to a distributed spectrum that reduces EMI, while the control circuit remains relatively simple by using standard delta-sigma modulation techniques.
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 delta-sigma signal density modulation effectively reduces EMI by increasing the frequency range and minimizing harmonic levels, providing a more efficient method for controlling LED intensity without the interference issues associated with conventional PWM.
Implementation Method 1
Light-emitting diode (LED) technology has advanced to the point where LEDs can be used as energy efficient replacements for conventional incandescent and/or fluorescent light sources
Data Source
AI summary
A controller for optical transducers uses delta-sigma signal density modulation to reduce electromagnetic interference.