The most common electromagnetic compatibility (EMC) issues in general electronic products are: RE (Radiated Emission), CE (Conducted Emission), and ESD (Electrostatic Discharge).
Communication electronics not only include the above three, but also Surge (surge protection due to lightning or electrical faults).
Medical devices are particularly prone to ESD (Electrostatic Discharge), EFT (Electrical Fast Transient), CS (Conducted Susceptibility), and RS (Radiated Susceptibility) issues.
In dry regions of the north, such as parts of China, the requirement for ESD protection is especially high due to low humidity and increased static buildup.
In areas like Sichuan and other southwestern provinces, where lightning strikes are frequent, EFT (Electrical Fast Transient) protection is crucial for ensuring system reliability.
To improve the anti-interference capability and electromagnetic compatibility (EMC) of electronic products, the following systems should be given special attention:
- A system with a very high clock frequency and fast bus cycle.
- A system that includes high-power, high-current drive circuits, such as relays that generate sparks or high-current switches.
- A system containing weak analog signal circuits or high-precision A/D converters, which are more sensitive to noise.
To enhance the system’s immunity against electromagnetic interference, consider the following measures:
- Select a microcontroller with a lower clock frequency: Using a microcontroller with a lower external clock frequency can significantly reduce noise and improve system stability. Square waves contain much more high-frequency content than sine waves. Although the amplitude of these high-frequency components is smaller than the fundamental wave, they are more likely to radiate as noise. The main source of high-frequency noise from a microcontroller is typically around three times the clock frequency.
- Minimize signal distortion during transmission: High-speed CMOS microcontrollers have high input impedance and low input current. However, long signal lines can cause reflections and distortions, increasing noise. When the signal delay time (Td) exceeds the rise time (Tr), it becomes a transmission line problem requiring careful impedance matching. On printed circuit boards, signal speed is about 1/3 to 1/2 the speed of light, and typical delay times for logic gates range from 3 to 18 ns. Keeping signal traces short and limiting via count helps reduce interference.
Signal reflections on long traces can create cross-talk, especially when multiple signals are close together. To minimize this, use ground planes beneath signal lines, increase spacing between signal traces, and consider local shielding if necessary. - Reduce power supply noise: Power supplies can introduce noise into the system, especially affecting reset and interrupt lines. Even in battery-powered systems, internal noise can still be problematic. Analog circuits are generally more immune to power supply noise than digital ones.
- Consider high-frequency characteristics of PCBs and components: At higher frequencies, parasitic inductance and capacitance in leads, vias, resistors, and capacitors become significant. For example, a via adds about 0.6 pF, and an IC package introduces 2–6 pF. These small values can affect high-speed designs, so careful layout and component selection are essential.
- Proper component placement and partitioning: Grouping similar functions together and separating noisy components from sensitive ones can greatly improve EMC performance. Keep high-noise areas away from analog or precision sections of the board.
By implementing these strategies, engineers can significantly improve the electromagnetic compatibility and overall reliability of their electronic designs, especially in environments with high levels of interference or extreme conditions.
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