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EMI Mitigation & Filtering

EMI is prevented, not patched. From layout to filtering to compliance testing, our systems are engineered for electromagnetic compatibility from the ground up.


At MarSum Solutions, electromagnetic interference (EMI) is treated as a first-order constraint, not a post-hoc problem. Whether your system is targeting CISPR 25, struggling with common-mode noise, or pushing immunity limits in demanding environments, we solve it at the source.


We model and manage EMI across converters, inverters, harnesses, and PCBs — addressing both differential- and common-mode paths, conducted and radiated emissions, and full-system EMC compliance.


We support the full EMI lifecycle: simulation, mitigation, filtering, shielding, and pre-compliance testing — integrated into the hardware development flow.

EMI Root Cause Analysis & Simulation

We begin by analyzing EMI at the source, combining topology review, field theory, and simulation to identify root causes before layout is locked in.

We evaluate:

  • Converter topology and modulation scheme
  • Parasitic inductance/capacitance from layout, magnetics, cabling
  • Switching transitions, dead-time overlap, PWM spectral spread
  • Loop area, return paths, high-dv/dt node placement
  • Grounding, shielding, and signal reference integrity
     

Simulation toolchain:

  • LTspice / PSpice – Time-domain noise modeling
  • Ansys® EMA3D / SiWave or CST® Studio Suite – 3D field simulation
  • Sigrity PowerSI / PowerDC – Plane impedance and PDN resonance analysis
  • Filter design tools – e.g., FilterDesigner-X or equivalent synthesis tools
     

We validate these models through:

  • E- and H-field near-field probe scanning (30 kHz–3 GHz), with 3-axis mapping at sub-10 mm resolution
  • Spectrum capture and time-domain analysis for high-speed transients

Filter Design & Component Selection

Every successful EMI mitigation plan includes correctly designed filtering tailored to the system’s EMI signature and regulatory class.

We design:

  • Input filters – For conducted emissions compliance and grid noise rejection
  • Output filters – To suppress switching edges and cable-borne noise
  • DC link filters – For ripple control and internal EMI containment
  • Auxiliary/signal line filters – For comms and low-level analog integrity
     

Techniques and components:

  • Common-mode chokes (saturation-rated and frequency-optimized)
  • Differential-mode inductors with low DCR and high impedance profile
  • Safety-rated X and Y capacitors selected for proximity and creepage
  • Snubbers, ferrites, Pi/T filters, and feedthrough caps
  • LCL filters for harmonic distortion and THD compliance in grid-tied systems
     

Design drivers:

  • Required insertion loss profile and corner frequency placement
  • Damping vs. resonance tradeoff and parasitic interactions
  • Attenuation targets vs. physical size and thermal constraints

PCB Layout for Low-Noise Performance

Filtering performance is only as good as the layout that supports it. We implement layout practices that control impedance, isolate domains, and block coupling paths.

Key techniques:

  • Minimized switching loop areas (e.g., FET + diode + cap)
  • Star-point or hybrid grounding with return path control
  • Stackup design for impedance control and layer symmetry
  • Kelvin sensing for gate drive and current shunts
  • Controlled impedance for high-speed comms lines
  • Guard traces, zone boundary shielding, and dv/dt node isolation
  • Split- or stitched-ground strategies only where isolation demands it
     

Simulation with tools like PowerSI confirms layout parasitics; oscilloscope and probe-based measurements verify real-world noise propagation.

System-Level EMC Strategy

Effective EMI control extends beyond the PCB. We address the full signal and power path, including cable harnesses, chassis integration, and enclosure interfaces.

We design for:

  • Cable shield termination: 360° contacts (>30 MHz) or short pigtails for legacy/LF use
  • Chassis bonding and multi-point ground hierarchy
  • Connector isolation, surge protection (MOV, TVS), and transient immunity
  • Enclosure shielding: EMI gasketing, filter compartmentalization
  • Common-mode path minimization through physical separation and routing control
  • Isolation reinforcement for ESD, EFT, and magnetic field immunity
     

Our systems are built to comply with:

  • CISPR 25 (automotive)
  • CISPR 32, FCC Part 15 Class A/B (ITE)
  • CISPR 11 Group 1, EN 61800-3 (industrial)
  • ISO 7637-2, SAE J1113-11/42 (transient immunity)

Pre-Compliance Testing & Validation

We reduce EMI risk by verifying early — before formal lab time. Our staged validation ensures each revision is quieter than the last.

Test methods include:

  • Conducted emissions: LISN-based with 5 µH/50 Ω (CISPR 25), 50 µH/50 Ω (CISPR 32)
  • Radiated emissions: Near-field scanning, semi-anechoic pre-scans
  • Conducted immunity: BCI, capacitive clamp, voltage dips
  • ESD/EFT: Contact and air discharge, plus surge robustness
     

Post-scan support:

  • Filter retuning, shield enhancement, layout rework recommendations
  • Diagnostic capture and signal-path tracing
  • Firmware adjustments (e.g., spread spectrum, dither) if applicable
     

Typical result:

  • CISPR 25 Class 5 margin ≥ –6 dBµV up to 400 MHz for traction inverters

Talk To Us About Your Project

Meet the Expert

Joe Marcinkiewicz

Joe Marcinkiewicz leads EMI Mitigation & Filtering strategy at MarSum Solutions. With over 30 years in power electronics design and electromagnetic compliance, Joe specializes in:

  • Converter and inverter topology-based EMI behavior
  • Preemptive EMI design during schematic and layout
  • Filter synthesis with SmartCtrl and empirical tuning
  • Shielding, grounding, and compliance test planning
  • Solving tough EMI problems across multiple industries
     

Joe's experience spans both ultra-low-noise consumer products and EMI-critical aerospace systems. He’s brought dozens of designs across the finish line — compliant, reliable, and production-ready.

Contact Joe About EMI & Filtering Strategy

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