Digital Active EMI Filter Noise Cancellation
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Solution Overview
Problem
Existing EMI filtering technologies, both passive and active analog, face limitations in effectively reducing electromagnetic interference (EMI) noise in power circuits, particularly due to size, weight, reliability issues, and performance constraints at high frequencies, with passive filters being inadequate for stringent noise reduction and analog filters requiring additional passive elements that can impact power converter stability.
Innovation Solution
A digital active EMI filter that combines an EMI compensation signal with noise generated by the power circuit, samples and processes this signal using high pass and low pass filters, and digital converters to produce an adjusted compensation signal, which is then injected back into the circuit to minimize or remove EMI noise, utilizing digital signal processing and high impedance elements to prevent high frequency components from being conducted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If passive EMI filters are used, then the filtering is simple and cost effective, but the size, weight, and reliability become significant design challenges when stringent noise reduction is required
Solution Approach 1:
The patent replaces passive mechanical filtering components (inductors, capacitors) with an active digital filtering system that uses a microcontroller, ADC, DAC, and software-based signal processing to generate compensation signals, thereby achieving superior noise reduction without the size and weight penalties of passive filters
Solution Approach 2:
The patent dynamically adjusts filtering parameters through digital signal processing, allowing the filter characteristics to be programmatically optimized for different noise conditions and frequency ranges, unlike fixed passive filters
2Reliability
If active analog EMI filters are used, then better noise suppression is achieved, but additional passive elements are required that impact power converter stability and increase device complexity
Solution Approach 1:
The patent substitutes analog active components (op-amps, analog multipliers) with a digital microcontroller-based system that performs noise cancellation through software algorithms, eliminating the need for additional passive stability-compromising elements
Solution Approach 2:
The microcontroller serves multiple functions: it samples the noise signal via ADC, processes the signal through digital algorithms, generates compensation signals via DAC, and controls the overall filtering operation, replacing multiple dedicated analog components with a single multi-functional device
3Reliability
If analog active EMI filters are used, then noise cancellation is achieved, but performance is limited at high frequencies by the frequency characteristics of the active device
Solution Approach 1:
The patent replaces frequency-limited analog active devices with a digital microcontroller system that can process signals across a broader frequency range, using software-based filtering algorithms that are not constrained by analog component bandwidth limitations
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 digital active EMI filter effectively reduces EMI noise by over 20 dBuV, outperforming passive filters and maintaining stability, with the ability to be implemented in both differential-mode and common-mode configurations, overcoming the limitations of existing technologies.
Implementation Method 1
Sampling may include using a high pass filter and an analog to digital converter to produce the digital noise signal. Constructing may include using a digital to analog converter and a low pass filter to produce the EMI compensation signal
Implementation Method 2
Sampling may include using a high pass filter and an analog to digital converter to produce the digital noise signal
Implementation Method 3
Constructing may include using a digital to analog converter and a low pass filter to produce the EMI compensation signal
Implementation Method 4
The method may include using an element having high impedance at high frequency at an input of the power circuit. The element having high impedance at high frequency may be inserted between a sampling node and a node where the EMI compensation signal is combined with EMI noise
Data Source
AI summary
The invention provides a digital active EMI filter that removes, minimizes, or reduces unwanted interference (i.e., EMI noise) generated by a power circuit such as, for example, a power converter. Digital active filtering includes digital sampling of the incident noise signal amplitude and frequency, discrete time conversion of the EMI noise source, processing (e.g., inverting) the digital signal, and then constructing an analog output signal (i.e., an EMI compensation signal) which is injected to the input of the power circuit. A digital EMI filter as described herein may be used in both differential-mode and common-mode configurations, and overcomes limitations of passive and active analog EMI filters.