Streamlining Printed Circuit Boards and Electromagnetic Compatibility

Semiconductor Review | Friday, July 21, 2023

Understanding PCB design factors enables the development of well-designed PCBs that optimize signal integrity and enhance electromagnetic compatibility.

FREMONT, CA: Printed circuit boards (PCBs) are the foundation for electronic systems, with components interconnected through copper traces. EMC (Electromagnetic Compatibility) engineers pay close attention to PCB layouts as they are crucial in determining the potential for electromagnetic interference. Well-designed PCBs minimize radiation, reduce noise coupling to cables or external objects, and optimize electromagnetic compatibility. This article explores the significance of PCB layouts and discusses circuits of interest in noise generation and susceptibility.

The placement of components and routing of traces greatly influence electromagnetic compatibility. A well-laid-out PCB minimizes radiation and reduces the chances of external currents or fields interfering with the circuit. It aims to prevent noise coupling to cables or other objects off the board, ensuring the system's integrity.

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Synchronous digital circuits utilize system clocks, constantly switching and generating narrowband harmonics. These clock signals are often energetic and can result in narrowband radiated emission peaks at harmonics of the clock frequency. EMC engineers must consider the potential noise sources and take necessary measures to mitigate their impact.

Analog signals can be broadband or narrowband, high frequency or low frequency. Understanding the characteristics of analog signals in both time and frequency domains is essential. Narrowband, high-frequency analog signals have the potential to be strong emission sources. Managing the path of these signal currents becomes crucial, as they will follow the path of least inductance and minimize loop areas. Low-frequency analog signals can be more susceptible to interference from other low-frequency sources sharing the same current path. Evaluating current flow and coupling is important to address noise concerns.

Switch-mode power supplies, DC-DC converters, and power inverters generate different voltages by rapidly switching the current on and off. This switching action creates current spikes that can introduce noise to power distribution nets and couple with other devices and circuits. Depending on the switching frequency, the noise can appear as narrowband harmonics or even broadband noise. Effective mitigation strategies involve carefully controlling switch nodes and current loops and employing suitable filtering components to minimize field-coupled and conducted noise.

Understanding the implications of PCB layout on electromagnetic compatibility is crucial for EMC engineers and board designers. By recognizing circuits that are potential noise sources and those that are most susceptible, appropriate measures can be taken to mitigate electromagnetic interference. Considering clock signals, analog signals, and switch-mode power supplies allows for developing well-designed PCBs that minimize noise radiation, optimize signal integrity, and enhance electromagnetic compatibility in electronic systems.

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