Coupling approach:
Integrated circuits (ICs) are often the ultimate source of unintentional electromagnetic radiation from electronic devices and systems. However, ICs are too small to radiate on their own. In order to radiate a field strong enough to cause interference problems, the IC IC's EMC interference coupling method must transfer energy from the IC package to other ancillary equipment, such as circuit board planes, heat sinks, or cables, via conduction coupling, electric field coupling, magnetic field coupling, and so on. So the radiated energy can only be coupled from the IC to the surrounding structure in the following three ways:
- between two or more pins of the chip under test.
- Electric field coupling.
- Magnetic field coupling.
1. Conduction coupling
The figure below shows magnetic field near-field scanning-conduction coupling directly above the IC package surface. The magnetic field is strongest above the lead frame and the current is strongest. As shown, the strongest currents flow into and out of the IC through the VCC and GND pins. this is an example of simultaneous switching noise. The high-frequency currents conducted from the chip through these pins can cause significant radiated emissions by exciting the power supply layer or other larger structures on the printed circuit board where the IC is used. Note that while the results in the figure below involve near-magnetic field measurements, the near-field scan of the chip shows the way in which interference reaches the chip pins from inside the chip by conduction coupling
Near-field scanning-conduction coupling of RDR memory modules
Several test procedures have been proposed to measure the conducted noise coupling of integrated circuits [1,4-6]. Unfortunately, each of these measurements loads the output of the device under test with an impedance that may or may not be representative of the load impedance that the device will see in a real-world application. Unknown sources cannot be fully characterized using individual voltage or current measurements. More information is needed if we want to know how much conducted noise will be generated under different circumstances.
Theoretically, a circuit source can be fully characterized by two measurements; an open circuit voltage measurement and a short circuit current measurement. In practice, at high frequencies, open circuit loads may have significant capacitance and short circuit loads may 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 are important in practical applications) using one high impedance and one low impedance measurement. These measurements can then be used to construct a Davening equivalent source model as shown below. Since the source voltage depends on a variety of factors, including software, the device should be measured in a variety of cases and the worse case parameters should be entered into the model. In addition, since this is a single port measurement, all possible ports (pin pairs) should be evaluated.
Davinin equivalent source
When the load impedance is very high or very low, it may be difficult to measure voltage and current directly. Therefore, it may be necessary to set the high impedance to a few hundred ohms and the low impedance to a few ohms. This is sufficient to characterize most IC sources in the frequency range of interest.
Davening equivalence model
The Davening equivalent model in the figure is much simpler than the ICEM and LECCS models, which have similar capabilities. However, the model is adequate for modeling many types of worst-case emissions, and the complexity of the model is consistent with the number of measurements used to derive it.
2、Electric field coupling
The figure below illustrates an example of electric field coupling of an IC. In this case, the heat sink on top of the chip becomes the coupling "antenna", the heat sink is not grounded and there is a certain gap between the heat sink and the ground plane, so the heat sink and the ground plane through the form of electric field coupling to the circuitry around the chip, which is an important coupling mechanism, the IC and its package structure through the electric field coupling noise. greatly depends on the design of the IC and the package. Unfortunately, existing field coupling measurements of ICs cannot distinguish between coupling modes belonging to electric and magnetic field coupling, and we can only assume that this mode belongs to electric field coupling based on theory.
Example of electric field coupling of ICs - electric field around a heat sink
Recent studies have helped to quantify how ICs couple to structures on printed circuit boards that act as antennas, leading to radiated emission problems [7]. Most of the electric flux lines emanating from the IC are captured by the circuit board or nearby metallic objects and do not contribute significantly to radiated emissions below 1 GHz. On the other hand, electric field lines escaping the immediate environment of the IC / package structure induce common mode currents in cables and chassis components. These common mode currents are usually the cause of unwanted radiated emissions.
Recently, studies have shown that mixingTEM cell Measurements are able to quantify the electric field coupling potentials of IC / package configurations [8].TEM cell measurements can be used to create models that represent the ability of an IC to couple to external objects. These models can replace the complex IC/package structure in full-wave system models. Thus, with a single, repeatable measurement, all relevant information about the IC / package's ability to couple noise to external objects via the electric field can be captured.
3、Magnetic field coupling
Example of magnetic field coupling of an IC - PCB and cable driven by magnetic field
The figure above illustrates an example of magnetic coupling of an IC. In this case, the "antenna" is a cable in close proximity to the chip.The magnetic flux generated by the IC surrounds the board and generates a voltage on the board that can drive a high-frequency current into the cable, thereby generating magnetic field radiation.
The same hybrid TEM cell setup used to measure electric field coupling can be used to measure magnetic field coupling. Typically, magnetic fields from the IC / package structure cause radiated emission problems when wrapped around other conductors (e.g., the ground plane of a circuit board) and generate voltages on the conductors that drive common mode currents into cables or other conductive objects. Antennas.
Hybrid TEM cell measurements quantify the ability of an IC/package to couple to nearby objects in this manner. Just as electric field hybrid TEM cell measurements can be used to determine the "electric moment"; magnetic field hybrid TEM cell tests can be used to determine the "magnetic moment", which can be representative of the IC/package in full-wave simulations [9,10].
Ltd. provides test instruments in accordance with IEC 61967, and test equipment and test systems in accordance with IEC 62132, which can be used by chip developers and research institutes for IC EMC testing and R&D. The test methods of the two standards are similar to the EMC standards for products, and so they also stipulate a wide range of radiated and conducted EMC test methods for IC integrated circuits. The two standards are similar to the EMC standard for products, so they also specify a variety of radiated and conducted IC IC EMC test methods, please contact us for more information.
References:
- [1] IEC 61967-1 Integrated circuits - Measurements of electromagnetic radiation from 150 kHz to 1 GHz - Part 1: General conditions and definitions, International Electrotechnical Commission, Geneva, Switzerland, March 2002.
- [2] IEC 61967-2 Integrated circuits - Measurement of electromagnetic radiation from 150 kHz to 1 GHz - Part 2: Measurement of radiated emissions, TEM-cell and broadband TEM-cell methods, International Electrotechnical Commission, Geneva, Switzerland, Draft 47A / 619 / NP, October 2001.
- [3] IEC 61967-3 Integrated circuits - Measurement of electromagnetic radiation from 150 kHz to 1 GHz - Part 2: Measurement of radiated emissions, Surface scanning method, International Electrotechnical Commission, Geneva, Switzerland, Draft 47A / 620 / NP, October 2001.
- [4] IEC 61967-4 Integrated circuits - Measurement of electromagnetic radiation, 150 kHz to 1 GHz - Part 4: 1Ω/150Ω direct coupling method, International Electrotechnical Commission, Geneva, Switzerland, April 2002.
- [5] IEC 61967-5 Integrated circuits - Measurement of electromagnetic radiation from 150 kHz to 1 GHz - Part 5: Bench Faraday cage method, International Electrotechnical Commission, Geneva, Switzerland, February 2003.
- [6] IEC 61967-6 Integrated circuits - Measurement of electromagnetic radiation from 150 kHz to 1 GHz - Part 5: Magnetic Probe Method, International Electrotechnical Commission, Geneva, Switzerland, June 2002.
- [7] H. Shim and T. Hubing, " A model for estimating radiated emissions from printed circuit boards with connecting cables using a voltage-driven source," IEEE Transactions on Electromagnetic Compatibility, vol. I. 47, no. 4, Nov. 2005, pp. 899-907.
- [8] S. Deng, T. Hubing, and D. Beetner, " Characterization of electric field coupling from IC heatsink structures to external cables using TEM cell measurements," IEEE Transactions on Electromagnetic Compatibility, vol. I. 49, no. 4, November 2007, pp. 785-791.
- [9] T. Hubing, S. Deng, and D. Beetner, " Characterizing IC coupling to cables and enclosures using electric and magnetic 'moments ", Proceedings of the EMC Compo 2007 conference, Turin, Italy, November 2007 .
- [10] S. Deng, T. Hubing, and D. Beetner, " Using TEM cell measurements to estimate the maximum radiation from a PCB with cables attached due to magnetic field coupling," IEEE Transactions on Electromagnetic Compatibility, vol. 50, no. 2, May 2008, pp. 419-423.