Designing PCBs for Minimized Electromagnetic Interference by Ken Wyatt
In the realm of high-speed PCB design, minimizing Electromagnetic Interference (EMI) is crucial for ensuring optimal performance and compliance with industry standards. A new webinar titled "PCB Design for Low EMI" offers valuable insights into this topic, presented by Ken Wyatt, Principal Consultant at Wyatt Technical Services LLC (Colorado).
The webinar explains the importance of understanding proper board design to minimize EMI. It delves into the fact that signals in the form of electromagnetic waves travel through the dielectric space between the trace and return plane, and for AC circuits, they should be modeled as transmission lines rather than simple wires.
The guide, spanning 8 chapters, 115 pages, and a 150-minute read, promises to provide guidance on designing a low-EMI board the first time. It offers key techniques to tackle high-frequency signals, focusing on controlling current loops, managing return paths, and using proper grounding and layout strategies.
Minimizing Loop Areas
One of the primary strategies for low EMI design is to keep power and signal traces as short as possible to reduce loop area. Large loops act as antennas, radiating EMI. For signals above 100 MHz, trace lengths ideally should be under 10 mm.
Component Placement for Return Paths
Component placement plays a significant role in EMI reduction. Placing components belonging to related signal paths close together minimizes return path length and loop area, while critical components should be arranged to maintain continuous and short return paths on ground or power planes, reducing EMI and signal delay.
Solid Ground Planes
Maintaining solid ground planes rather than hatched ground planes provides better signal integrity and controlled impedance, as solid planes offer a direct return path and better capacitive coupling that reduces EMI.
Avoiding Splitting Ground or Power Planes
Splitting these planes breaks return paths and increases EMI, so high-speed signals should be routed over continuous reference planes.
Routing Guidelines
Proper routing guidelines are essential for low EMI design. Use controlled impedance microstrip or stripline routing, keep traces away from board edges, and separate high-speed traces from noisy power or analog sections to preserve signal integrity and reduce EMI.
Material and Safety Considerations
For high voltage or high-frequency circuits, using materials with high dielectric strength and low loss is crucial to minimize noise coupling and signal degradation.
By implementing these strategies, high-frequency PCB designs can be optimized to reduce EMI by controlling current flow paths, minimizing loop areas, and ensuring solid and continuous reference planes.
References: - Minimizing loop areas and short trace lengths to reduce EMI radiation - Component placement to shorten return paths and maintain signal integrity - Preference for solid ground planes over hatched ground planes for EMI control - Avoiding plane splits that disrupt return current paths - Material considerations relevant to signal integrity at high frequency and voltage - 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. - The movement of electrons does not occur at near light speed in AC circuits; they move at about one centimeter per second. - The path of least resistance is important for low-frequency signals, while the path of least impedance is important for high-frequency signals. - The webinar promises to show design techniques for reducing the EMI risk of a board. - The H field flux wraps around the trace in a microstrip, while the E field is mainly concentrated between the trace and return plane.
In the realm of low EMI PCB design, practitioners can benefit from implementing strategic tactics such as maintaining solid ground planes for enhanced signal integrity and controlled impedance (science and technology). Proper component placement also plays a significant role in EMI reduction, as arranging components close together shortens return paths and reduces loop areas (engineering). This results in lower EMI radiation, contributing to overall board optimization in high-speed design (technology).
