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SAMD Solutions

Common EMC problems

Most EMC problems follow known patterns. Here you will find common causes and proven starting points from practice – as orientation, not as a recipe: what works in a specific case is shown by the measurement.

Typical patterns from practice

Recurring starting points that have proven themselves in many projects. Whether they work in a specific case is shown by the measurement.

  • The antenna rule of thumb

    Any unshielded cable longer than λ/10 becomes an antenna. At 100 MHz that is just 30 cm.

  • Ground is not simply ground

    A good RF ground needs low impedance, not just low resistance. Short and wide beats long and thin.

  • Filters in the right place

    Mains filters belong as close as possible to where the cable enters the enclosure. Every centimetre of distance reduces the effect.

  • Bond shields properly

    A shield is only as good as its bond. A 360° contact beats a pigtail by orders of magnitude.

From symptom to the next measurement step

Anomalies can be narrowed down in three steps instead of swapping components on suspicion.

  1. Step 1

    Describe the symptom

    Which anomaly occurs, in which operating state, in which frequency range? First the symptom, then the theory.

  2. Step 2

    Narrow down the possible cause

    The candidates are source, coupling path and victim. After narrowing down, two or three plausible causes usually remain.

  3. Step 3

    Define the next measurement step

    One measurement that distinguishes between the candidates – for example near-field work on the assembly, or measuring with and without a cable.

Recognising and solving problems

Radiated emissions too high

Symptoms

  • Limit exceeded in the 30–300 MHz range
  • Peaks at clock frequencies and their harmonics
  • Broad disturbance spectra with switched-mode power supplies

Causes

  • Long unshielded cables acting as antennas
  • Missing or poorly bonded shielding
  • Insufficient filtering where cables leave the enclosure
  • Large current loops on the board

Solutions

  • Use shielded cables with 360° shield bonding
  • Ferrite cores on critical lines
  • EMC gaskets at openings in the enclosure
  • Layout optimisation: short traces, small loops

Conducted emissions (CE)

Symptoms

  • Limits exceeded in the 150 kHz – 30 MHz range
  • Peaks at the switching frequency of the power supply
  • Common-mode disturbances dominate

Causes

  • Insufficient mains filtering
  • Missing Y capacitors (common mode)
  • Poor ground bonding of the filter
  • Disturbances injected through parasitic capacitances

Solutions

  • Choose a mains filter with sufficient attenuation
  • Y capacitors (class Y2) for common-mode suppression
  • Place the filter directly at the mains input
  • Keep the connection between filter and chassis ground short

ESD sensitivity

Symptoms

  • The device drops out when touched
  • Spontaneous resets or crashes
  • Data loss or communication errors
  • Permanent damage to ICs

Causes

  • Unprotected interfaces (USB, HDMI and similar)
  • Missing TVS diodes at inputs and outputs
  • Poor enclosure design with gaps
  • Direct access to sensitive components

Solutions

  • TVS diodes on all external interfaces
  • Discharge paths through the enclosure rather than the PCB
  • Observe clearance and creepage distances
  • Protection circuitry ahead of sensitive ICs

Burst and surge problems

Symptoms

  • Failures when switching occurs nearby
  • Malfunctions during thunderstorms
  • Problems when other equipment is switched on or off

Causes

  • Insufficient surge arresters
  • Missing series impedance in signal lines
  • No galvanic isolation
  • Discharge current capability too small

Solutions

  • Varistors or gas discharge tubes at the input
  • TVS diodes as fine protection
  • Series resistors or inductors
  • A multi-stage protection concept (coarse and fine)

RF immunity

Symptoms

  • Disturbances near radio transmitters
  • Problems with mobile phones nearby
  • Noise or dropouts in analogue circuits

Causes

  • Long cables acting as receiving antennas
  • Missing RF filtering at inputs
  • Unshielded enclosures
  • Sensitive analogue circuits without protection

Solutions

  • Ferrite cores and filter capacitors
  • Shielded enclosures with good shielding effectiveness
  • RF bypass capacitors at sensitive ICs
  • Layout optimisation for short signal paths

Clock harmonics

Symptoms

  • Narrow peaks at exact frequencies
  • Peaks at multiples of the clock frequency
  • The problem grows at higher frequencies

Causes

  • Steep clock edges generate high harmonics
  • Long clock lines radiate
  • Missing series termination
  • Insufficient supply decoupling

Solutions

  • Spread-spectrum clocking (SSC) where possible
  • Series termination of clock signals
  • The shortest possible clock lines
  • Enough decoupling capacitors (100 nF + 10 µF)

When to bring in support

  • Several attempts have failed: when you have already tried a number of suppression measures and the problem persists.

  • The cause is unclear: when you are not sure where the disturbance comes from – we have the equipment to diagnose it.

  • Time pressure: when the market launch is approaching and you need results quickly.

  • Preventively: ideally already during development, to avoid problems in the first place.

These services apply here

An anomaly in your setup?

We narrow down the cause, derive concrete measures and verify their effect in a re-measurement.

Request a measurement slot+49 1511 0988717