Harmonizing Circuit Design and EMC DesignPart 16 EMC Calculation Methods and EMC Simulations (1): Overview of Calculation Methods

Hello! I’m Inagaki, at ROHM.

Starting with this 16th article, I would like to discuss EMC (electromagnetic compatibility) calculation methods and simulations.

Where EMC is concerned, the degree of accomplishment of a semiconductor integrated circuit (LSI) is judged in part by its conformance to international EMC standards, and it is no exaggeration to say that this is an absolute condition for product adoption. For this reason, engineers addressing EMC issues are mainly engaged in work at EMC sites and in radio-frequency anechoic chambers to perform measurements on prototypes and mass-produced items. At ROHM also, we are constantly specifying that tasks be performed with emphasis on “measurement accuracy and measurement reproducibility”. Emphasis on measurement accuracy means striving to perform measurements that, as the words indicate, are of high precision and yield values close to the true value; for this purpose, a proper environment must be constructed, and measurement technology is needed. Measurement reproducibility, on the other hand, means obtaining the same measured value for the same sample no matter how many times the measurement is performed. In EMC measurements, the disparity between maximum and minimum measured values is quite large (for example, from 60 to 100 dB), and a further characteristic of such measurements is that precision comparable to that required when designing semiconductor integrated circuits (LSIs), such as 0.1 dB, is not necessary. However, both of these, accuracy and reproducibility, are important parameters that are closely related to the EMC calculation methods I will be describing shortly.

In relation to EMC calculation methods, many EDA vendors sell electromagnetic field analysis tools, which are used by EMC engineers in various applications. The greatest number of such tools are used for printed circuit board (PCB) simulations. Recent PCBs tend to have multiple layers, and such tools contribute to reduction of the number of prototypes and the amount of prototyping time needed to eliminate EMC problems. If it were possible to perform simulations to judge conformance to international EMC standards, this would be enormously useful for LSI suppliers, but at present there are hardly any such tools available.

I looked into the extent of general knowledge relating to EMC calculations and simulations. The International Electrotechnical Commission (IEC) has defined EMC models for semiconductor integrated circuits (LSIs), and has published the following. It should be noted that a Part 5 has not yet been proposed.

IEC 62433 Standard

Among these standards, the following are two important definitions. They are extremely important and fundamental concepts, which can be applied to both conduction and to radiation.

There are a number of effective calculation methods. Data assimilation is a method in which actual measured values are input into a model to obtain highly precise results; it is applied in weather forecasting and in seismic observations. Recently news media reported that the Institute of Physical and Chemical Research used this data assimilation technique to begin calculations of the spread and status of infection of the novel coronavirus. This is a step forward from the conventional approaches that rely only on measurements or only on simulations, and can be said constitute merging of measurements with calculations.

In addition, the method of noise reduction is also highly effective. The volumes of both measured data and calculated values describing EMC phenomena are enormous, and if the data at the respective frequencies is left unmodified, the expected results cannot generally be obtained. It is for such cases that the method of noise reduction was developed. The method itself, however, is simple enough: the envelope of measured values and calculated values is detected. This technique can cause a complete change in circumstances.

These are concepts needed to perform EMC calculations and simulations. If we then utilize circuit analysis, electromagnetic field analysis, and numerical analysis to construct a (shell) script, we should be able to run trials to judge conformance to international EMC standards using a tool not commercially marketed. In calculation trials, the different analyses methods are used selectively as follows.

For reference, current examples of electromagnetic compatibility (EMC) calculation trials are as follows. The main area of application is semiconductor integrated circuits (LSIs), and so product sets and systems cannot yet be addressed. However, research, development, and prototyping are in progress so as to gradually increase the scope of international EMC standards for which such evaluations can be made. From the next article, I would like to introduce a number of representative applications chosen from among these.

This concludes the main discussion, but from here on, some readers may find that things get a bit complicated. To be honest, in the space allotted to me for this column, I may not always be able to provide a detailed explanation of the matters to be addressed.

Thank you for your kind attention.