Designing PCBs for Low Electromagnetic Interference by Ken Wyatt
In a recent webinar, Ken Wyatt, Principal Consultant at Wyatt Technical Services LLC (Colorado), shared effective design techniques to reduce Electromagnetic Interference (EMI) risk in Printed Circuit Board (PCB) design. The webinar, titled "PCB Design for Low EMI," aims to provide a competitive advantage by understanding how digital signals propagate in PCBs.
The webinar is based on over a decade of experience as an EMC consultant, during which Wyatt has reviewed or helped troubleshoot hundreds of electronic products. The event explains why reducing circuit loop areas is only part of the solution for low EMI, and proper board design requires understanding how signals propagate in boards.
The guide covers explanations of signal integrity issues, understanding transmission lines and controlled impedance, the selection process of high-speed PCB materials, and high-speed layout guidelines. It is important to note that for high-frequency signals (greater than 50 to 100 kilohertz), the return conduction current path is relatively confined along the return plane and directly underneath the signal trace, due to mutual inductance between the trace and plane. On the other hand, for low-frequency signals (less than 50 to 100 kilohertz), the return conduction current path is relatively spread out along the return plane and mostly takes the path of least resistance.
Good board design practices include minimizing loop areas by keeping return paths short and well-defined, using ground planes effectively, and carefully routing high-speed signals to reduce radiated emissions and susceptibility. Utilizing PCB-mounted shielding cans and enclosures helps contain electromagnetic emissions. Integration of filters at input/output points works synergistically with shielding to prevent conducted and radiated EMI. He highlights the importance of choosing appropriate filters and placing them correctly to maximize effectiveness.
Paying attention to cable routing, segregation of noisy and sensitive signals, and proper grounding practices also contribute significantly to reducing EMI risks. The webinar will explain that signals move via electromagnetic fields, which should make board stack-up and trace routing clear for designing a low-EMI board.
The webinar is downloadable and is part of a holistic EMI risk mitigation approach. While the search results reference his work in the context of power electronics and general EMI issues, they emphasize that EMI reduction is seldom a single-step solution but rather a comprehensive design methodology involving PCB layout, filtering, shielding, and cabling together.
A High-Speed PCB Design Guide, consisting of 8 chapters, 115 pages, and a 150-minute read, is also mentioned. The guide delves deeper into the topics covered in the webinar, providing a comprehensive resource for engineers designing high-speed PCBs for compliance with EMC/EMI standards.
For AC circuits, the standard circuit theory model cannot be modeled as simple wires but as transmission lines. The actual signal in the form of an electromagnetic wave travels through the dielectric space between the trace and return plane. The cross-section of a standard microstrip consists of a trace, dielectric, and return plane. The H field flux wraps around the trace while the E field is mainly concentrated between the trace and return plane in a standard PC board.
Understanding these concepts and applying them in practical, commonly encountered issues related to PCB layout, shielding, filtering, and cabling can significantly reduce EMI risks, making your designs more efficient and reliable.
The webinar "PCB Design for Low EMI" discusses the significance of understanding transmission lines and controlled impedance, key technology aspects, in the design of Printed Circuit Boards (PCBs). Proper board design requires not only minimizing loop areas but also understanding the propagation of signals in boards, including the role of controlled impedance in high-speed PCB design.
