Harmonizing Circuit Design and EMC DesignPart 15 EMC Overview (3) What is Electromagnetic Compatibility?

Hello! I’m Inagaki, at ROHM.

In this 15th installment, I will explain electromagnetic compatibility (EMC) phenomena in detail. Once again, semiconductor integrated circuits (ICs) take center stage.

We’ll begin with cases of electromagnetic interference (EMI, emission). We consider cases in which a semiconductor integrated circuit (IC) is operated using switching technology, and EMC measures on the printed circuit board (PCB) are inadequate. This happens when, for example, an EMI filter is poorly designed, so that for example the cutoff frequency of a low-pass filter (LPF) is higher than 1/10 of the switching frequency. In such cases, when the semiconductor integrated circuit (IC) is operated, there is the possibility of occurrence of such phenomena as:

• ・Worsening of the reception sensitivity of an AM/FM radio placed in the vicinity, resulting in beeping or squawking noises and the like
• ・Cutoff of equipment connected via Bluetooth etc.
• ・Pauses in videos being played on a smartphone

Next are cases of electromagnetic susceptibility (EMS, immunity). These are instances of ill effects resulting from electromagnetic noise near a semiconductor integrated circuit (IC). Here too, cases are imagined in which EMC countermeasures on the printed circuit board (PCB) are insufficient. These may be cases in which there is no noise filter, or the frequency characteristic of the noise filter may be such that the electromagnetic noise is not adequately attenuated. Such cases may result in the occurrence of:

• ・At its normal operating point, an operational amplifier (op-amp) bas a bias voltage of VCC (power supply voltage)/2, but the bias voltage may fluctuate to near VCC or to near GND voltage
• ・In data transmission/reception by semiconductor integrated circuits (ICs) for data communication, the received data may be inverted when electromagnetic noise is occurring
• ・In low-voltage digital circuits (CPUs, memory devices), control logic errors may occur while electromagnetic noise is occurring

It may be difficult to grasp this simply in terms of conforming or not conforming to the international standards for electromagnetic compatibility (EMC) that were explained in the previous column, but from actual cases, it should be easy to understand that such events may lead directly to serious damage and malfunctions. In this way, phenomena relating to electromagnetic compatibility (EMC) are very important. Particularly where products and components relating to space and aviation, medicine, vehicles, or other areas relating to human lives are concerned, there are circumstances that must not be allowed to occur even very rarely. For this reason, engineers in various industries, from component manufacturers to set manufacturers, are working hard on electromagnetic compatibility (EMC) to ensure that products and components are safe and secure after sufficient verification.

Well then, why is electromagnetic compatibility (EMC) the focus of so much attention just now?

Where electromagnetic interference (EMI) is concerned, higher operating frequencies are highly relevant. In contrast with times past when 100 MHz was regarded as super-fast, many of today’s products run at from 1 to 10 GHz. Naturally such harmonic components are a cause of electromagnetic interference (EMI), and consequently the frequency range of electromagnetic interference (EMI) is dramatically expanded. And, the higher the frequencies involved, the more readily radiation occurs, requiring greater attention.

Where electromagnetic susceptibility (EMS) is concerned, lower power supply voltages can be cited as one cause. The H or high and L or low voltages (V_IH/V_IL) are completely different for 5 V logic and for 0.9 V logic. The lower the power supply voltage, the poorer the resistance to electromagnetic noise tends to be.

Furthermore, the scale of semiconductor integrated circuits (ICs) and the number of elements they comprise are increasing every year. We are now in an era in which from 500 million to one billion transistors are fabricated on a silicon chip. As a result, the number of locations where electromagnetic compatibility (EMC) problems occur has increased and the probability is higher. Hereafter as well, if device integration and scale proceed apace according to Moore’s law and the integration level of semiconductor integrated circuits (ICs) continues to rise, electromagnetic compatibility (EMC) characteristics will steadily worsen.

All of you engineers working onsite are already aware: whereas previously it was not necessary to pay too much attention in particular to electromagnetic compatibility (EMC), when it comes to recent products and components, one has the feeling that if proper attention is not paid to electromagnetic compatibility (EMC) characteristics, something horrendous may happen. Thus it may be more accurate and closer to reality to say, not that we are “paying attention”, so much as that we “have no choice but to pay attention” to these issues.

From the next column, I will be explaining pragmatic aspects of electromagnetic compatibility (EMC) relating to design and fabrication, in the form of EMC calculation methods and EMC simulations. I trust you will find it useful.

Thank you very much for your attention.