Two major keywords in EMC
Following the scale down of the integrated circuit technology and the continuous shift toward very high frequencies, the electromagnetic compatibility problems at IC level have recently risen in importance.
| Susceptibility | Emission | |||
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| To an electromagnetic wave | of electromagnetic energy |
Susceptibility to radio frequency interference is becoming a major concern for integrated circuits, with the multiplication of powerful parasitic sources such as mobile phones, high speed networks and wireless systems.
On the other hand, the parasitic emission due to the integrated circuit is continuously increased, and may jeopardize the electromagnetic compatibility (EMC) of the whole electronic system.
Susceptibility to radio frequency interference is illustrate in the case of a very high radar wave illuminating an airplane. This situation is very common at the proximity of airports. A Giga-watt pulse is received by the the plane, which captures some energy which may flow to the equipment, the board and finally to the component.
On the other hand, the parasitic emission due to the integrated circuit inside a car may jeopardize the correct behavior of personal devices such as mobile phones, and RF links. In some case, the parasitic energy may be high enough to parasite the safety systems of the car.
An example of measured emission is given here, corresponding to an electronic board. A maximum level is specified by the equipment designer to ensure electromagnetic compatibility between boards within a given equipment. The X axis is given in log scale to cover from 1 to 1000 MHz. The Y axis is in dBµV. Most peaks are below 60 dBµV, equivalent to 1mV.
The measurement of susceptibility is slightly different from emission. A susceptibility level is specified by the equipment designer, at 0 dBmA from 1 to 100MHz in this particular case. When the measured susceptibility is lower than this limit, the board do not ??? With the ???. A current injection limit is fixed at 40 dBmA. It means that no RF power should be injected to this equipment above that limit.
Two boards within an electronic equipment may be incompatible if one board generates a very high level of parasitic emission while an other board can fail at a very low level of injected parasitic disturbance. The risk zone is between the emission and susceptibility overlap. A safe margin is around 20 dB. An unsafe margin is below 10 dB.
An electromagnetic wave can couple to a wire
Two main concepts are described in this slide: the magnetic & electrical coupling. An electromagnetic (EM) wave is a combination of electrical & magnetic wave. The electromagnetic wave creates a voltage in a conductor, which acts as an antenna. This magnetic wave creates currents in conductor loops. In real case example such as a car, an EM wave illuminates internal wires which act as loops and antenna. The result is a voltage and current noise added to normal signals.
| MAGNETIC Coupling | ELECTRICAL Coupling |
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| A current is generated | A voltage is generated |