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Design007-Jan2022

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JANUARY 2022 I DESIGN007 MAGAZINE 93 ferent operational environments bring with them unique tolerances for EMI. An electronic device that is part of a billionaire's space- ship near other devices on board would have a much lower EMI tolerance than a moisture evaporator operating in the middle of a desert. Everyone from the FCC to the DoD to a slew of international regulatory bodies are at hand to dictate the amount of interference that a device can give off, depending on its intended use. ese regulations have been put in place for per- sonal safety and to ensure an electronic device will be able to carry out its function long term. It's also important to determine your device's inherent ability to operate in the presence of EMI, regardless of whether it is EMI-created within the device or bombarding it from exter- nal sources. Too much exposure to interfer- ence can negatively impact the functionality of some systems and you will need to design shielding, grounding, or other protection. Poor PCB design is many times the culprit when it comes to intolerable levels of EMI. e issues that oen cause problems can be traced to design flaws that cause interference among the traces, circuits, vias, PCB coils, and other elements. Limiting the EMI in a PCB layout can be an effective method for reducing emissions, meet- ing FCC regulations, and keeping your design signals clean so the system works as expected. Designing With EMI in Mind Here are a few items to consider during the planning and schematic stages of your design that will set you on the right path. • Choose SMD components over through- hole parts. Generally, the leads on the through-hole parts create higher levels of inductance and thus opportunity for EMI. • Maximize ground area, so signals can disperse more easily with more area. If you need to keep the area of your ground plane as small as possible, create a multi-layer PCB. • Design with multilayers—add a ground plane on the layer directly below the exter- nal signals (2 and n-1). e presence of these planes near the signal will effectively reduce the return path, keep signals clean, and limit EMI emission. • Connecting decoupling or bypass capaci- tors to these planes offers another effective technique for reducing EMI because of the short and logical return paths created. • If you are using split planes to avoid having too many ground planes in your design, be sure they are only connected at a single point to avoid creating loops that effec- tively become antennas that radiate EMI. • In multi-layer PCBS, use solid ground planes rather than hashed planes to reduce impedance levels. • Limit the operating current and/or the rise times of the signals to help reduce larger fluctuations in current offering lower EMI emission rates. • Match the impedance on signals. is is a critical practice of design especially at higher signal speeds that will reduce the opportunity for signal reflection, harmon- ics, ringing, and overshooting digital signals—all of which increase the EMI radiation. Don't let yourself be surprised by EMI. It can create issues with your projects that could result in delays, budget overrun, and missed deadlines. Considering EMI during the pre-planning stage of your PCB design can help save you time and effort in the prototyp- ing and testing phases. DESIGN007 Matt Stevenson is the VP of sales and marketing at Sunstone Circuits. To read past columns or contact Stevenson, click here.

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