Stochastic Signal Density Modulation for LED EMI Reduction

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Solution Overview

Problem

Conventional LED intensity control methods using pulse width modulation (PWM) generate high spectral content and electromagnetic interference (EMI), which can affect nearby sensitive devices and systems.

Innovation Solution

Implementing stochastic signal density modulation (SSDM) to control light-emitting diodes (LEDs) by using a pseudorandom modulation waveform that eliminates discrete spectral lines and reduces EMI, achieved through a stochastic signal density modulator coupled with a controllable current supply and an n-bit stochastic state machine.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Illumination intensity

If pulse width modulation (PWM) is used to control LED intensity, then intensity control is achieved, but electromagnetic interference (EMI) increases due to high spectral content

Engineering Contradiction:

ImproveLED intensity controlVSAvoidelectromagnetic interference (EMI)

Core Design Contradiction:

Illumination intensityVSObject-generated harmful factors

Solution Approach 1:

The patent changes the fundamental parameter of the modulation waveform from periodic square waves to stochastic waveforms with random transitions. This parameter change transforms the spectral characteristics from discrete lines at fundamental and harmonic frequencies to a continuous, distributed spectrum, thereby reducing EMI while maintaining intensity control capability

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

Instead of using deterministic periodic switching patterns (PWM), the patent inverts the approach by using stochastic random switching patterns. This inversion changes the spectral distribution from concentrated discrete lines to distributed continuous spectrum, eliminating the harmful EMI effect while preserving the intensity modulation function

Inventive Principle:

Principle #13The other way round (Inversion)

2Ease of manufacture

If square wave modulation is used for LED control, then simple implementation is achieved, but spectral energy concentrates at discrete frequencies causing EMI

Engineering Contradiction:

Improvecontrol circuit implementationVSAvoidspectral energy concentration

Core Design Contradiction:

Ease of manufactureVSObject-generated harmful factors

Solution Approach 1:

The patent changes the waveform parameter from deterministic square waves to stochastic waveforms with random transitions. This parameter change distributes spectral energy across a continuous frequency spectrum rather than concentrating it at discrete fundamental and harmonic frequencies, thereby reducing EMI while maintaining implementation feasibility through digital logic circuits

Inventive Principle:

Principle #35Parameter changes

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 SSDM approach effectively reduces EMI by distributing spectral energy, minimizing interference and allowing for more effective filtering, while enabling precise intensity control of LEDs without sharp spectral peaks, thus enhancing the reliability of LED-based lighting systems.

Implementation Method 1

providing a stochastic control signal to the controllable current supply, wherein the stochastic control signal has a selected stochastic signal density to control an output intensity of the light-emitting diode

Methodology Applied

Scientific EffectLight-emitting diode (LED) electroluminescence: Electroluminescence

Data Source

PatentUS10334672B2Stochastic signal density modulation for optical transducer control

Publication Date: 2019.06.25 CYPRESS SEMICONDUCTOR CORP

AI summary

A controller for optical transducers uses stochastic signal density modulation to reduce electromagnetic interference.