[电磁兼容]集成电路(IC)电磁兼容(EMC)设计与分析/Integrated Circuit EMC [复制链接]

Integrated circuITs (ICs) are generally the ultimate source of unintentional electromagnetic emissions from electronic devices and systems. However, ICs are too small to radiate significantly themselves. In order to radiate fields strong enough to cause an interference problem, energy must be coupLED from the IC package to larger structures that act as antennas such as circuit board planes, heatsinks or cables.

There are only three ways that energy can be coupled from an IC to surrounding structures:

• Conducted on two or more pins;
• Electric field coupled;
• Magnetic field coupled.

Several test procedures have been proposed to measure the conducted noise coupling from integrated circuits [1, 4 – 6]. Unfortunately, each of these measurements loads the outputs of the device-under-test with an impedance that may or may not represent the load impedance that the device will see in a real application. It isn’t possible to fully characterize an unknown source with a single voltage or current measurement. More information is required if we want to know how much conducted noise will be generated in different situations.

In theory, a circuit source can be fully characterized by two measurements; an open-circuit voltage measurement and a short-circuit current measurement. In reality, at high frequencies open-circuit loads can have significant capacitance and short-circuit loads can have significant inductance. However, when these parasitic capacitances and inductances are known and controlled, it is still possible to characterize the source (at least the source parameters that will matter in real-world applications) using one high-impedance and one low-impedance measurement. These measurements results can then be used to build a Thevenin equivalent source model as shown in the figure below. Since the source voltage will depend on a variety of factors including software, the device should be measured in various situations and the worse-case parameters entered into the model. Also, since this is a one-port measurement, all possible ports (pin pairs) should be evaluated.

Voltages and currents can be difficult to measure directly when the load impedances are very high or very low. For this reason, it may be desirable to set the high impedance at a few hundred ohms and the low impedance at a few ohms. This will be sufficient to characterize most IC sources in the frequency ranges of interest.

The Thevenin equivalent model in the figure is much simpler than ICEM and LECCS models, which serve a similar function. However, this model is sufficient for many types of worst-case emissions modeling and the complexity of the model is consistent with the number of measurements used to derive it.

ELECTRIC FIELD COUPLINGThe figure below illustrates an example of electric field coupling from an IC. In this case, the “antenna” is a large heatsink being driven against the circuit board ground plane. This is an important coupling mechanism and the noise coupled from an IC/package structure through electric-field coupling is very dependent on the design of the IC and package. Unfortunately, existing field-coupling measurements for ICs [2, 5] are incapable of distinguishing between electric and magnetic field coupling. Because of this, measurement results cannot be used to represent the IC in EM coupling models.