Designing PCBs for Low Electromagnetic Interference by Ken Wyatt
In the fast-paced world of technology, understanding how digital signals propagate in PC boards can provide a significant competitive advantage. This knowledge is crucial in designing low-EMI boards, ensuring signal integrity, and managing thermal performance in high-frequency circuits.
Low EMI PCB Design Techniques
The webinar, titled "PCB Design for Low EMI," led by Ken Wyatt, Principal Consultant at Wyatt Technical Services LLC (Colorado), offers guidance on minimizing electromagnetic interference (EMI) through a series of effective strategies.
One such strategy is the use of a solid ground plane, which provides a close return path underneath high-speed traces, reducing loop area and EMI coupling. Proper grounding and power planes, maintaining continuous and unbroken planes, are also essential to avoid noise coupling.
Reducing loop areas by organizing components and routing signals is another key technique. Sharp 90° trace angles should be avoided, with smooth or 45° angles used instead to reduce impedance discontinuities and EMI. Filtering components and shielding grounded sections can suppress EMI at the source and prevent its spread.
Minimizing via effects, ensuring controlled impedance, and understanding the concepts of the path of least resistance and impedance are also important considerations in low EMI design.
High-Speed PCB Layout Guidelines
The High-Speed PCB Design Guide, a comprehensive resource, 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.
Material selection, trace design, differential pair routing, component placement, thermal management, return path continuity, and the use of stitching capacitors and vias are all crucial aspects of high-speed PCB layout.
By integrating these low EMI and high-speed design strategies, you can enhance PCB performance, reduce interference, and improve reliability in high-frequency, high-speed applications such as telecom and data centers.
Understanding Signal Propagation
For AC circuits, the standard circuit theory model cannot be modeled as simple wires but as transmission lines. For PC boards, signals move in a way that is related to both the circuit theory point of view and the field's point of view.
The signal, in the form of an electromagnetic wave, travels through the dielectric space between the trace and return plane. The H field flux wraps around the trace in a standard microstrip, while the E field is mainly concentrated between the trace and return plane.
For low-frequency signals (less than 50 to 100 kilohertz), the return conduction current path is relatively spread out along the return plane and takes a direct path from load back to the source. However, 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.
In a simulation of this concept, for low-frequency signals, the return current is spread out and travels directly back to the source, while for high-frequency signals, the return current is located directly underneath the circuit trace.
The webinar, based on the author's 10+ years of experience as an EMC consultant, underscores the importance of understanding signal propagation in low EMI design. It explains that reducing circuit loop areas is only part of the solution, and proper understanding of signal propagation is essential.
For those seeking to improve their PCB design skills, these techniques and guidelines offer a solid foundation for creating high-performing, low-EMI boards. The High-Speed PCB Design Guide and the "PCB Design for Low EMI" webinar provide valuable resources for designers looking to stay ahead in the competitive world of electronics.
Technology plays a crucial role in controlling impedance in high-speed PCB design. Maintaining controlled impedance is an essential aspect of high-speed PCB layout, as addressed in the High-Speed PCB Design Guide.
Understanding signal propagation in PCBs using technology such as transmission lines aids in designing low EMI boards that ensure signal integrity, particularly in high-frequency circuits, as highlighted in both the High-Speed PCB Design Guide and the "PCB Design for Low EMI" webinar.
