Active Noise Filter Circuit for EMI Reduction
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Solution Overview
Problem
Current EMI noise reduction techniques, particularly passive filters, face challenges such as space inefficiency, high energy consumption, limited bandwidth, and the need for variable capacitors which are not available as standard components, leading to suboptimal filtering effects and stability issues with active filters.
Innovation Solution
A noise filter circuit with a sensor coupled to a power converter's switching node, processing the sensor signal to generate a correction signal for open-loop noise cancellation, using an active circuit with an amplifier to provide a 180-degree phase shift for effective EMI noise reduction without bulky passive components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If passive filters are used to reduce EMI noise, then filtering effectiveness is improved, but PCB space consumption increases and energy consumption rises
Solution Approach 1:
The patent replaces passive mechanical filter components (inductors and capacitors) with an active electronic system consisting of a sensor, processing stage, and correction signal generator. This substitution eliminates the need for bulky passive filter components while maintaining EMI noise reduction effectiveness through electronic signal processing and injection of correction signals.
Solution Approach 2:
The patent changes the approach from passive parameter-based filtering to active parameter modulation. By sensing the EMI noise characteristics and dynamically generating correction signals with adjusted amplitude and phase, the system adapts to different noise conditions without requiring physical filter component changes, thereby reducing PCB space requirements.
2Object-affected harmful factors
If passive filters are used to reduce EMI noise, then filtering effectiveness is improved, but energy consumption increases
Solution Approach 1:
The patent replaces energy-consuming passive filter components with an active electronic system that processes signals electronically. The sensor detects EMI noise, the processing stage analyzes the signal characteristics, and the correction signal is generated and injected, all without the continuous energy dissipation inherent in passive filter components.
Solution Approach 2:
The system uses the EMI noise signal itself as the input for generating the correction signal. By processing the sensed noise signal through the processing stage and inverting it, the system creates a self-correcting mechanism that eliminates the need for external energy input required by passive filters to maintain their filtering function.
3Object-affected harmful factors
If passive cancellation techniques are used, then EMI noise reduction is achieved, but the bandwidth is limited to around 1 MHz
Solution Approach 1:
The patent replaces passive filter components with an active electronic signal processing system that can operate at higher frequencies. The sensor, processing stage, and correction signal injection mechanism are designed to function effectively across a broader frequency range, enabling EMI noise reduction beyond the 1 MHz limitation of passive cancellation techniques.
4Ease of manufacture
If fixed valued capacitors are used in passive cancellation, then standard components are used, but amplitude mismatch occurs causing rapid degradation of filtering effect
Solution Approach 1:
The system uses the actual EMI noise signal sensed by the sensor as the basis for generating the correction signal. By processing this sensed signal through the processing stage, the system automatically adapts to the actual noise amplitude and characteristics, eliminating the need for precise manual capacitor value matching and preventing amplitude mismatch degradation.
Solution Approach 2:
The patent transitions from static fixed-value capacitor components to a dynamic system that continuously senses and processes the EMI noise signal. The processing stage dynamically adjusts the correction signal amplitude and phase based on real-time noise characteristics, providing adaptive filtering that maintains effectiveness without requiring precise component matching.
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
This solution enables compact, efficient, and effective EMI noise reduction across a broader bandwidth without stability issues, using standard components and eliminating the need for variable capacitors, thus enhancing electromagnetic compatibility.
Implementation Method 1
the voltage on the switching node comprises a switch waveform which gives rise to current noise as a result of parasitic capacitance
Implementation Method 2
A phase shift of 180 degrees can be used to provide a cancellation function so that part of the original noise and the injected noise cancel
Data Source
AI summary
A noise filter circuit uses open loop signal processing to process the signal that causes the noise and generate a signal to be fed back into the system to cancel noise currents.