Chapter 1 described the mechanism of causing interference by electromagnetic noise and the overview of noise suppression. Noise suppression is mainly implemented in the noise transmission path with use of shields and filters as the typical means. In order to use these means efficiently, it is important to have a deep understanding of the mechanism of the occurrence and propagation of electromagnetic noise.
With close reference to the principle of noise occurrence described in Chapter 1 in terms of noise source, there are three factors: noise source origin, transmission path and antenna (assuming that the noise interference is eventually propagated in the form of electromagnetic waves, antenna is included here) [Reference 1] as shown in Fig. 2-1-1(a). In case of becoming a noise victim, exactly the same schematic diagram can be used as shown in Fig. 2-1-1(b) by flipping the drawing horizontally and replacing the noise source origin with a noise receiver. That means the mechanism can be considered as the same in both cases of generating and receiving noise.Therefore, in order to have a deep understanding of the mechanism of noise interference, Chapters 2 to 5 focus on the issues regarding the noise source side and describe the basic theory of the mechanisms of causing, transmitting and emitting noise. In these chapters, shields for shutting out noise and ground connections are also briefly described. Another important factor “filter” will be described in detail in a later chapter.
First of all, Chapter 2 will describe the mechanism of causing noise.
2-2. Noise source origin
There are various situations to cause an electric current that can be a noise source. For example, a certain signal component is needed for the operation of one circuit while causing
Fig. 2-2-1 Analog signal and digital signal
(1) Analog circuit
From the viewpoint of noise source origin, analog circuits tend to generate relatively less
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