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 from lightning or thunder).
Medical devices typically face challenges such as ESD (Electrostatic Discharge), EFT (Electrical Fast Transient), CS (Conducted Susceptibility), and RS (Radiated Susceptibility).
In dry regions of the North, the ESD requirements for products are particularly strict due to the high risk of static buildup.
In areas like Sichuan and parts of the Southwest, where lightning is more frequent, EFT (Electrical Fast Transient) protection becomes a critical design consideration.
To enhance the anti-interference capability and electromagnetic compatibility 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 conversion circuits.
1. Use a low-frequency microcontroller:
Choosing a microcontroller with a lower external clock frequency can significantly reduce noise and improve the system's resistance to interference. Square waves contain much more high-frequency components compared to sine waves of the same frequency. Although the amplitude of these high-frequency components is smaller than the fundamental wave, their higher frequencies make them more likely to radiate noise. The most significant high-frequency noise generated by a microcontroller is around three times the clock frequency.
2. Minimize signal distortion during transmission:
Microcontrollers are typically built using high-speed CMOS technology. They have a high input impedance, low static current (around 1 mA), and small input capacitance (about 10 pF). However, when signals travel through long lines, reflections become a major issue, leading to signal distortion and increased noise. If the signal delay time (Td) exceeds the rise time (Tr), it becomes a transmission line problem requiring careful impedance matching.
3. Reduce cross-interference between signal lines:
Cross-talk occurs when signals on one line interfere with another. For example, if a signal with a rise time Tr travels along a line AB, reflections at the end of the line can cause pulses at other points, such as point D or C. These pulses can interfere with other signals, especially in analog circuits. To minimize this, use a large ground plane, keep signal lines away from each other, and consider shielding where necessary.
4. Minimize power supply noise:
The power supply can introduce noise into the system, which affects reset and interrupt lines of the microcontroller. Even battery-powered systems can suffer from high-frequency noise. Analog circuits are generally more resistant to power supply noise than digital ones.
5. Consider high-frequency characteristics of PCBs and components:
At high frequencies, parasitic inductance and capacitance in leads, vias, resistors, capacitors, and PCBs become significant. For instance, a via may add about 0.6 pF of capacitance, while a connector might introduce 520 nH of inductance. These small values can affect performance in high-speed systems, so they must be carefully considered during design.
6. Proper component placement and layout:
Partitioning the board into functional sections and placing sensitive components away from high-noise areas can greatly improve EMC. Avoid routing high-speed signals over long distances and ensure proper grounding to reduce interference.
By implementing these strategies, you can significantly improve the electromagnetic compatibility and overall reliability of your electronic designs.Switch Cabinet,Innovative Low Voltage Switchgear Cabinet,Switch Rack Cabinet,Switch Cabinet Wall Mount
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