Electromagnetic compatibility (EMC) should be considered at the design stage for electrical and electronic products, long before the EMC compliance testing stage. However, sometimes EMC and EMI evaluation and simple checks are overlooked. This checklist provides a quick glance at what should be considered.
Identify potential EMI sources
- Varying voltage and/or circuit conditions can generate EMI.
- Identify potential EMI sources. Brush Motors, IC/clocks, relays, Triac circuits, Thermostats, switchers, etc.
- Will each source be either a broadband or Narrow-band emission?
Filtering
- Apply EMI filtering to relevant lines using standard good practices and principles.
- Off the shelf, filters are general filters designed for many applications but you may require customer filters for certain applications to ensure the correct performance of your product.
- Always ensure that the filter is suitably rated your product
- Integrated filter circuits are better than clamp for or retrospective filtering.
Grounding
- Ensure a good solid ground point.
- A single point low impedance ground will help avoid ground loops.
- Use ground planes whenever possible.
- Keep ground runs as short as possible, including the return path.
- DC ground paths are often high impedance RF grounds.
- Use thicker wires for ground whenever possible.
Printed Circuit Board
- Avoid single layer boards if possible and use multi-layer PC boards (PCBs).
- Place supply rails on opposite sides of a multi-layer board.
- Limit track lengths to be as short as possible.
- Avoid clock signal trace loops.
- Avoid sharp corners on traces, i.e. replace 90º with 2 x 45º angles.
- Decoupling capacitors should be used throughout.
- Decouple RF currents and RF ground circuits
- Terminated all inputs and outputs.
- Apply filtering to all inputs and outputs.
Component Layout
- Group similar circuitry components together help with isolating them.
- Section high emission circuit and components to allow for isolation from the rest of the board.
- Isolate the RF ground separate from power, logic or digital ground.
- Use thick but short ground traces whenever possible.
- Grouping circuitry can greatly reduce the chance of inter-board interference.
Power Supply
- Avoid single layer boards if possible and use multi-layer PC boards (PCBs).
- Decoupling capacitors should be as close to the component pins as possible.
- Twisted pair wires can reduce the common mode interference.
- Ensure a good single point or star grounding.
- Decouple from supply rails to ground at both inputs and outputs.
- Keep ground runs as short as possible, including the return path.
- Incorporate separate analog, digital, power supply rails and grounds.
- Avoid sharp corners on traces, i.e. replace 90º with 2 x 45º angles.
- Do not run filtered and unfiltered wires parallel to each other.
