Preface

The majority of domestic electromagnetic capacity books have a common defect, which is the lack of connections between design and testing. The discussion of the approach and techniques of EMC design should be based on EMC testing, not only because the first challenge of EMC design is the EMC test but also because those key factors like interference source, receiving antenna, and equivalent radiated antenna, which are critical to EMC analysis, will only exist during the EMC test. Taking the conducted emission test as an example, its essence is the voltage across a resistor in the line impedance stabilization network (LISN), when the resistance is fixed, the level of conducted disturbance depends on the current passing through the LISN resistor. EMC design is to reduce the current flow through the resistor. Possible tests include the typical immunity test, electrical fast transient/burst (EFT/B) test, big current injection (BCI) test, and electrostatic discharge (ESD) test, which is a typical common mode immunity test. The source of disturbance is a common-mode disturbance, referred to the reference ground plane, i.e. the reference point of these disturbance sources is the reference ground plane used in the test, which means that the current generated by the disturbance will eventually return to the reference ground plate. This is the basic starting point to analyze such disturbance problems.

Imagine, for the above-mentioned conducted disturbance test, that during the product testing, that the disturbance current does not flow through the LISN resistor, and at the same time, for the immunity test, that this disturbance current never passes through the product circuit, it is certainly very favorable for this product to pass the EMC tests, and this is what product design needs to consider. Therefore, the EMC design must be started from the EMC test. Electromagnetic Compatibility (EMC) Design and Test Case Analysis, as a project reference book, makes a close connection with the EMC test substance, EMC design principles, and specific product design to narrate EMC design methodology. Highly integrating the practical and theoretical contents is the biggest characteristic of this book.

The book is divided into seven chapters, in which the basic EMC knowledge is described in Chapter 1, mainly served for the 2-7 chapters. When readers read those later sections, if some basic concept is vague and not clearly explained, it can be easily consulted and checked from Chapter 1. Chapters 2-7 includes cases, which are typical and representative. Case descriptions use the same format: [Symptoms], [Analyses], [Solutions], and [Inspirations]. By analyzing each case, we introduce the practical information about EMC design and diagnostic technology to the designers to reduce the mistakes made by the designer in the product design and the diagnostic of EMC problems, and achieve good product EMC performance. At the same time, illustrating the design principles through EMC cases enables readers to achieve better understanding on the origin of the design. [Inspirations] section actually sums up the problem and highlights related issues. It can be used as a checklist of product EMC design. The cases are divided into the following six categories:

1. Products' structural framing, shielding, and grounding versus EMC. For most devices, shielding is necessary. Especially with the increasing frequency in the circuit, relying solely on the circuit board design often fails to meet EMC standards. Proper shielding can greatly strengthen EMC performance, but an unreasonable shielding design can not only fail to play its desired effect but also oppositely cause additional EMC problems. In addition, grounding will not only help solve the safety problem but is also very important for EMC. Many EMC problems are caused by an unreasonable grounding design, as the ground potential is a reference potential of the entire circuit. If the ground is not properly designed, the ground potential may be unstable, which leads to failed circuits. It may also generate additional EMI problems. The purpose of the grounding design is to ensure that the ground potential is as stable as possible, to reduce the voltage drop on the ground, thereby eliminating the interference.
2. Cables of products, connectors, and interface circuit versus EMC. Cable is always the path, which gives rise to radiation or bringing in the major disturbance. Because of their length, the cable is not only the transmitting antenna but also a good receiving antenna. And the cable has the most direct relationship, with the connector and interface circuit. Good interface circuit design not only can make the internal circuit noise well suppressed, so that there is no driving source for the transmitting antenna, but can also filter out the cable disturbance signal received from outside. Proper connector design of cable and interface circuit provides a good matching path.
3. Filtering and suppressing. For any devices, filtering and suppressing are key techniques to resolve electromagnetic interference (EMI). This is because the conductor of the device is acting as a highly efficient receiving and radiating antenna, and therefore, most of the radiation generated by the device is achieved through a variety of wires, while the external disturbance is often received by the conductor first, then brought into the device. The goal of filtering and suppressing is to eliminate these interfering signals on the wire, to prevent circuit interference signals being transferred onto the wire and then radiated through the wire, and also to prevent the conductors receiving the disturbance and taking them into the circuit.
4. Bypass, decoupling, and energy storage. When the device is operating, the signal level of the clock and data signals pins changes periodically. In this case, decoupling will provide enough dynamic voltage and current for the components when the clock and data are changing in normal operation. Decoupling is accomplished by providing a low-impedance power supply between the signal and power planes. As the frequency increases, before reaching the resonant point, the impedance of the decoupling capacitors will decrease, so that the high-frequency noise is effectively discharged from the signal line. Then the remained low-frequency RF energy will not be affected. Best results can be achieved through storage capacitors, bypass capacitors, and decoupling capacitors. These capacitance values can be calculated and obtained by specific formula. In addition, the capacitor insulation material must be correctly selected, rather than randomly selected based on the past usage and experience.
5. PCB design versus EMC. Whether the device emits electromagnetic interference or is affected by outside disturbance, or generates mutual interference between the elects, PCB is the core of the problem (the component layout or the circuit routing of the PCB), and will have an impact on the nature of the product overall EMC performance. For example, a simulated interface connector position will affect the direction of common mode current flows in, and the path of the routing will affect the size of the circuit loop, these are the key factors of EMC. Therefore, a properly designed PCB is important to ensure good EMC performance for the product. The purpose of PCB design is to reduce the electromagnetic radiation generated by the circuit on the PCB and susceptibility to outside interference, and to reduce the interaction between the PCB circuits.
6. Components, software, and frequency jittering technique. Circuits are composed of components, but the EMC performance of the components is often overlooked. In fact, the packaging, the rising edge, the pinout of the component, and the ESD immunity of the device itself have a huge impact on the performance of a product's EMC performance. Although the software does not belong to EMC academic areas, in some cases software fault-tolerant technique can be used to avoid the impact on the products from the outside interference. Frequency Jittering is a popular technique to reduce the conducted and radiated emission from circuits in recent years, but the technology is not foolproof. This chapter will give details to the substance of the case and precautions for frequency jitter technique.

In fact, EMC design rules are just like traffic regulations. Noncompliance will certainly not result in a traffic accident, but the risk is bound to increase. EMC design is in accordance, noncompliance of some rules may also be able to pass the test, but the risk is bound to be increased. So there is an urgent need to introduce the product design risk awareness to the industry. The purpose of EMC design is to minimize the risk of EMC test, as only for those products complying with all the EMC, and traffic rules have the lowest EMC risk. Most of the listed problems in this book are originated from EMC problems encountered in practical work, each case is originated from the experience of these cases, which come from the accumulation of a large number of typical EMC cases the author encountered. For those classic cases, there are more detailed theoretical analysis. Each of the results of those cases is formed with one or more of EMC design rules, and it is worth learning and referring. As the engagement of the author is limited, this book may not contain all kinds of EMC issues in electronics and electrical products.

If readers discover any mistakes due to the author's incomprehensive knowledge, leading to unreasonable or inaccurate descriptions or even critical mistakes, please feel free to contact...