Pulse Density Modulation for Vehicle LED EMC Reduction
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Solution Overview
Problem
Existing pulse width modulation (PWM) methods for controlling lighting devices, such as LEDs, in vehicles lead to significant electromagnetic compatibility (EMC) issues due to strong interference spectra, particularly at higher frequencies, which are difficult to manage and mitigate.
Innovation Solution
A method for generating a sequence of binary code words using pulse density modulation (PDM) or spread spectrum pulse density modulation, where code words are divided into classes based on the number of one-bits, and their stochastic or deterministic variation is used to control LEDs, reducing interference spectra and improving EMC by selecting specific energy levels and correlating control signals only after a predetermined number of cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulse width modulation (PWM) is used to control lighting devices, then precise control of lighting intensity is achieved, but strong interference spectra are generated causing EMC problems
Solution Approach 1:
The patent changes the fundamental parameters of the modulation signal from PWM (pulse width modulation) to PDM (pulse density modulation). This involves changing how the control signal is structured: instead of varying pulse width at a fixed frequency, the invention uses stochastic or pseudorandom binary sequences with varying pulse densities to represent control values. This parameter change transforms the deterministic interference spectrum of PWM into a stochastic one, significantly reducing electromagnetic compatibility issues while preserving precise lighting control capability
Solution Approach 2:
The patent converts the harmful deterministic interference pattern of PWM into a beneficial stochastic pattern through the use of pseudorandom sequences. By introducing controlled randomness into the modulation process, the previously harmful concentrated interference spectra are transformed into a dispersed, predictable stochastic spectrum that is easier to manage and filter, thereby converting an EMC problem into a solution
2Adaptability or versatility
If PWM signals are used for controlling multiple LEDs, then individual control of each LED is possible, but EMC compliance becomes difficult to achieve
Solution Approach 1:
The patent applies parameter changes to the control signal generation method by replacing PWM with PDM using pseudorandom sequences. Each LED receives a control signal based on a pseudorandom binary sequence where the density of pulses corresponds to the desired intensity level. This fundamental parameter change maintains individual LED control capability while transforming the electromagnetic interference characteristics to achieve better EMC compliance
Solution Approach 2:
The patent employs periodic refresh of the pseudorandom sequences at controlled intervals while maintaining the stochastic nature of the individual pulse patterns. This periodic structure allows for synchronized control of multiple LEDs while the underlying pseudorandom patterns ensure that interference from different channels does not constructively add up, thereby maintaining both individual control and EMC compliance
Data Source
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AI summary
The invention relates to a method for generating a sequence of binary code words of a multi-bit code for a control signal, wherein in the method, a multi-bit code having a plurality of binary code words each having the same number of n bits, is provided with n > 1, which can be sub-divided into at least two code classes of code words, wherein at least one code class has a plurality of code words having the same number of one bits, and the number of one bits of the code words of the code classes varies from code class to code class. The control signal is generated as a sequence of the code words of a code class, wherein the code words of said code class are randomly, or quasi randomly controlled in the control signal, or sequentially in randomly varying or deterministically varying order, wherein from the number of code words of a code class, a subset of code words comprising at least two code words is selected, and wherein the code words of said subset are utilized for generating the control signal.