Electromagnetic compatibility (EMC) has become a key factor in ensuring that electronic devices and systems can coexist without interfering with each other in today's highly electronic age. EMC involves the ability of an electronic device or system to function properly in its electromagnetic environment without adversely affecting other devices in the same environment. With the rapid development of technologies such as the Internet of Things, 5G communication, and smart grid, electromagnetic compatibility has become increasingly important and has become an important indicator to measure product quality, safety, and reliability.

Basic principles and test standards of EMC

EMC covers two main areas: electromagnetic interference (EMI) and electromagnetic sensitivity (EMS). EMI refers to the impact of electromagnetic energy generated during the operation of the equipment on the surrounding environment, while EMS is the ability of the equipment to resist external electromagnetic interference.

Internationally, the IEC (International Electrotechnical Commission) and CISPR (International Special Committee on Radio Interference) have developed a series of EMC standards, such as the IEC 61000 series and CISPR 22/EN 55022, which set specific test requirements and limits for different types of electronic products.

Why do electromagnetic compatibility design?

Electromagnetic compatibility (EMC) design is a key step in ensuring that an electronic device or system can function properly in its electromagnetic environment without creating unacceptable electromagnetic interference from other devices in the same environment, while also maintaining its own anti-interference capability, that is, not being affected by external electromagnetic interference. Here are some of the main reasons for an EMC design:

1. Meet product functional requirements: The Electromagnetic compatibility design prevents Electromagnetic Interference (EMI) from affecting the normal operation of the internal circuits of the product and ensures that the product can operate stably according to the intended function.

2. Reduce commissioning time: Good EMC design can avoid many electromagnetic interference problems early in product development, reducing later commissioning and correction efforts, reducing time to market, and reducing development costs.

3. Compliance with regulations and standards: there are strict electromagnetic compatibility standards and regulations around the world, such as the European Union's CE mark requirements, the United States FCC standards. Products must pass the appropriate EMC tests to demonstrate compliance with these standards before they can be legally sold in the appropriate market.

4. Protect other equipment: A proper EMC design prevents the product from becoming a source of electromagnetic interference and from causing interference or damage to other sensitive equipment in the same electrical environment (such as medical equipment, communication systems, etc.), thereby maintaining the stability and security of the entire system.

5. Improve user experience: Electromagnetic compatibility problems may lead to reduced product performance, such as water ripples in the TV picture, noise generated by audio equipment, etc., affecting the user experience. Good EMC design improves overall product quality and user satisfaction.

6. Avoid legal liability: Products that do not comply with EMC standards may result in user losses or public safety issues, and manufacturers may face serious consequences such as legal action, fines, or product recalls.

What can be involved in EMC design?

1. Circuit design and device selection

Circuit design is the cornerstone of EMC design. In the early stages of design, the proper selection of components is crucial to controlling Electromagnetic Interference (EMI). Engineers should consider the radiation characteristics of components, frequency response, switching speed and other factors. For example, low-noise, low-power integrated circuits (ics) and passive components such as inductors and transformers with good shielding function can effectively reduce EMI. In addition, the use of highly integrated chips not only reduces wiring, but also reduces radiation and improves the overall EMC performance of the system.

2. Software design

Emc considerations at the software design level focus on control strategies, such as optimizing code to reduce unnecessary high-frequency switching operations, using soft start techniques to reduce inrush current at startup, and implementing appropriate signal filtering algorithms to smooth pulse signals. The software can also realize dynamic adjustment of operating frequency, power level and other strategies to adapt to different electromagnetic environment requirements, thereby reducing interference to external equipment.

3. Circuit board layout

Circuit board (PCB) layout is one of the key factors affecting EMC performance. A good layout should consider the principle of minimization of signal path, separation of high-speed signal and low-speed signal, and minimization of loop area of key signal. In addition, the use of multi-layer board design, reasonable layout of the ground plane and power plane, can effectively suppress electromagnetic interference and provide a good signal return path. In high-density designs, the application of blind and buried hole technologies can also significantly improve EMC performance.

4. Shielding structure

Physical shielding is an effective means to reduce electromagnetic radiation. By installing a metal shield around the sensitive circuit or outside the entire device, external interference can be blocked from entering or internal interference leakage. In the design, attention should be paid to the continuity and grounding treatment of the shield to ensure that it can form an effective Faraday cage. In addition, the choice of shielding materials, such as copper, aluminum or electrically coated plastics, is also considered based on the specific application and cost effectiveness.

5. Filter signal cables and power cables

In order to prevent conductive interference, it is necessary to implement appropriate filtering measures for signal lines and power lines. This usually includes the addition of filters in the input/output ports, such as low-pass filters to suppress high-frequency noise, as well as the use of common mode and differential mode chokes, capacitor arrays, etc. Reasonable filter design can not only suppress the conducted interference, but also help to improve the stability and reliability of the system.

6. Circuit grounding policy

Grounding design is another important step in EMC design. The correct grounding strategy can provide a stable reference potential for the circuit, effectively suppress the ground loop current and reduce the common mode interference. Common grounding modes include single-point grounding, multipoint grounding, and hybrid grounding. Select a proper grounding policy based on the circuit frequency characteristics, interference source type, and system layout.

7. Cable management and bundling

Cable is not only the main way of EMI transmission, but also the sensitive object of receiving interference. Therefore, cable management and bundling are critical to controlling EMC. It is recommended to use twisted cables to reduce electromagnetic radiation, arrange the cable direction to avoid large loops, use shielded cables and ensure that the shielding layer is well grounded, and use straps or clips to secure cables to reduce interference caused by mechanical vibration.

8. Testing and verification

Finally, any EMC design must undergo rigorous testing and verification to ensure its effectiveness. This includes pre-compatibility testing (such as simulations using simulation software), conducted and radiative emission testing, immunity testing, etc. Test results should be used as feedback for design iterations to help engineers identify and resolve potential EMC issues until the product meets the appropriate international or regional standards (e.g. IEC 61000 series, FCC Part 15, etc.).

What are the common problems of EMC rectification?

Electromagnetic Compatibility (EMC) rectification is a corrective action taken when a product is found not to meet the requirements of EMC standards during the design phase or after certification testing. The process is often complex and challenging, involving multiple steps such as identifying interference sources, analyzing interference paths, and designing and implementing solutions. The following are common problems encountered in EMC's rectification process, rectification process and specific suggestions:

Q&A

Confusion after a failed test: When the first test fails, inexperienced design teams may feel at a loss and unsure of where to start.

Interference source location is difficult: Electromagnetic interference can come from a variety of factors such as circuit design, layout, power supply, and connection lines, and accurately identifying the main interference source is a challenge.

The effect of rectification is not obvious: even if the rectification measures are implemented, the repeated tests are still unqualified because the measures are not targeted enough or the problems are not completely solved.

Transient interference is difficult to capture: Some transient interference or narrowband interference is difficult to be directly observed by the spectrum analyzer under conventional test conditions, increasing the difficulty of rectification.

Cost and time pressure: The rectification process can lead to project delays and cost increases, and how to complete the rectification efficiently and cost-effectively is a major challenge.

Rectification process

1. Detailed analysis of the test report: First, carefully study the test report, identify which test items are not up to standard, and understand the specific degree and frequency range of exceedances.

2. Interference source identification: The use of spectrum analysis, near-field probes, current probes and other tools, combined with different working conditions such as switching, load changes, to locate the main interference sources and propagation paths.

3. Design a rectification plan based on the interference source analysis results. The rectification plan may include hardware modification (for example, adding filters or changing the layout), software optimization (for example, adjusting control policies), and shielding improvement.

4. Implement corrective actions: Implement corrective actions step by step and keep records to track the impact of each change.

5. Re-test and verification: After rectification, re-test the EMC to verify the rectification effect. If there is still a problem, it is necessary to analyze the cause again and carry out iterative rectification.

Specific rectification suggestions

• Dealing with transient interference: For the transient interference that is difficult to be directly observed by the spectrum analyzer, an oscilloscope can be used with a high-voltage differential probe to capture, analyze its characteristics and timing, and then add decoupling capacitors, transient voltage suppressors (TVS) or use RC filtering networks to absorb these transient energies.

• Where to start: Priority is usually given to the easiest and most effective rectification items, such as optimizing the filter design of the power supply part, strengthening the shielding and filtering of important signal lines, and checking and improving the grounding system. These tend to be common areas of interference or interference.

• Comprehensive consideration of cost and benefit: the rectification needs to balance cost and effect, giving priority to low-cost and cost-effective measures, such as optimizing the layout rather than directly replacing expensive components. At the same time, consider the long term and avoid sacrificing product quality or future upgrade space for short-term compromises.

EMC rectification is a systematic project that requires patient and detailed analysis, scientific and reasonable planning and implementation, as well as continuous testing and verification. Through continuous learning and practice and accumulated experience, we can more effectively deal with various rectification challenges, ensure that products successfully pass EMC tests and meet market access requirements.