The electromagnetic compatibility (EMC) test is a critical evaluation for electronic products that are about to be released to the market. However, traditional testing methods only indicate whether the product passes or fails, without providing detailed insights for improvement. This article discusses the use of high-speed automated scanning technology to measure electromagnetic radiation and detect changes in the electromagnetic field on the PCB. This approach allows PCB engineers to identify and address potential issues before performing standard EMC tests.
Currently, most hardware engineers rely on their experience to design the PCB. During the debugging phase, many signal traces or chip pins that need to be monitored are often hidden within the inner layers of the PCB, making them difficult to detect with conventional tools like oscilloscopes. If the product fails functional testing, there are no effective methods to pinpoint the root cause of the issue. To assess the product’s EMC performance, the only option is to take the product to a certified EMC measurement lab. However, this testing only measures the product’s external radiation and, even in the case of failure, fails to provide actionable data for troubleshooting. As a result, engineers must rely on their experience to make modifications to the PCB and retest, a costly and time-consuming process that can delay the product’s time to market.
1. Of course, many high-speed PCB analysis and simulation design tools are available to assist engineers in solving various problems, but there are still numerous limitations concerning device models. For instance, the IBIS model, which is commonly used for signal integrity (SI) simulation, lacks models for many devices, or the available models may not be sufficiently accurate. To precisely simulate EMC issues, SPICE models are essential; however, almost all ASICs currently fail to provide SPICE models. Without these models, EMC simulations cannot account for the device’s radiation, which is significantly higher than the radiation from transmission lines.
2. It is well understood that the return path for high-frequency signals in a multi-layer PCB should ideally lie on the reference ground plane (either the power layer or ground layer) adjacent to the signal line layer. This arrangement minimizes return current flow and impedance. However, actual ground or power layers often have partitions or voids, which alter the return path, resulting in a larger return area that can lead to electromagnetic radiation and ground bounce noise. If engineers can fully comprehend the return current path, they can avoid large return paths and effectively manage electromagnetic radiation. However, the signal return path is influenced by numerous factors, including signal routing, PCB power and ground distribution, power supply points, decoupling capacitors, as well as device placement and quantity. Consequently, it is extremely difficult to theoretically predict the return path in a complex system.
3. **High-speed Electromagnetic Field Scanning Measurement Technology**
Among various electromagnetic radiation measurement techniques, near-field scanning stands out as a method capable of addressing this issue. This method is based on the principle that electromagnetic radiation is generated by high-frequency current loops within the device under test (DUT). For example, the electromagnetic radiation scanning system from Canadian company EMSCAN is designed based on this principle. It utilizes H-field array probes (32×40 = 1280 probes) to detect current on the DUT. During measurements, the DUT is placed directly on the scanner, and these probes can sense changes in electromagnetic fields resulting from variations in high-frequency currents. The system offers a visual representation of the spatial distribution of RF currents across the PCB.
4. The Emscan electromagnetic compatibility (EMC) scanning system has been widely adopted in industries such as communications, automotive, office equipment, and consumer electronics. By analyzing the current density maps generated by the system, engineers can identify areas with potential EMI problems before performing EMC standards testing, allowing them to take appropriate corrective actions.
5. **Near-field Scanning Principle**
Emscan’s measurements are primarily conducted within the active near-field region (r < λ/2π). A high-current, low-voltage source is mainly related to the magnetic field, while a high-voltage, low-current source is primarily linked to the electric field. On a PCB, pure electric or pure magnetic fields are rare. In RF and microwave circuits, components such as microstrip or stripline connections are designed to have a characteristic impedance of 50 ohms. This low-impedance design results in large currents and small voltage variations. Furthermore, digital circuits are increasingly using logic devices with smaller voltage differences, and in the active near-field region, the wave impedance of the magnetic field is much smaller than that of the electric field. Consequently, most of the energy in the active near-field region of the PCB is contained within the magnetic field. Thus, the magnetic field loop employed in the Emscan scanning system is well-suited for near-field diagnosis of these PCBs.
6. The loops in the system are identical in design but vary in their positions within the feedback network. This enables the feedback network to detect the response from each loop. The system then measures and interprets the response of each loop relative to the reference source as a filter transfer function. To ensure measurement accuracy, Emscan evaluates the reciprocal of this transfer function.
7. By leveraging array antennas and electronic automatic switching technology, Emscan greatly accelerates measurement speed—thousands of times faster than manual single-probe measurements and hundreds of times faster than automatic single-probe systems. This allows engineers to quickly assess the impact of circuit changes. The fast scanning technology, combined with advanced amplitude-maintaining and synchronous scanning techniques, ensures that transient events are captured effectively. Additionally, Emscan incorporates technology that enhances the measurement accuracy of spectrum analyzers, improving both measurement precision and repeatability.
8. **Measurement Methods for Evaluating PCB Near-field Radiation Interference**
The evaluation of PCB radiation interference is typically performed in several steps. First, the area to be scanned is identified, and then a probe (with a grid of 7.5mm) is chosen to fully sample the designated area. A spectrum scan is performed across the frequency range of 0–3 GHz, and the maximum level at each frequency point is recorded. Note that significantly large frequency points should be further investigated within the scanning area using spatial scanning, which helps pinpoint interference sources and critical circuit paths.
9. The board under test should be positioned as close to the scanner board as possible. Increasing the distance between them will degrade the signal-to-noise ratio, causing a “separation” effect. Typically, the distance should be less than 1.5 cm. Measurement issues may arise if components are too tall, as this could affect the accuracy of the measured voltage level. Thus, component height must be considered and corrected during voltage level measurement. In basic inspections, adjustments for separation distance are essential.
10. While measurement results can be obtained quickly, they do not directly indicate whether the product meets EMC requirements. The measured values represent the electromagnetic near field generated by high-frequency currents on the PCB. Standard EMC tests must be performed in an open-area test site (OATS) or a shielded room, at a distance of 3 meters (far field).
11. Although Emscan measurements cannot replace standard EMC tests, practical experience has shown that they provide significant value. Analyzing the measurement results offers useful insights that help guide the further development of the product. In addition to providing voltage levels, the following information is crucial: interference generation points, interference distribution, large-area interference conduction paths, localized interference areas on the PCB, internal coupling between adjacent I/O modules, and the effects of separating digital and analog circuits.
12. The measurements can serve as a standard for evaluating PCB design quality. Furthermore, if the EMC characteristics of a similar PCB are already known, reliable early-stage evaluations can be made regarding the product’s EMC performance, such as whether shielding is required.
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Currently, most hardware engineers rely on their experience to design the PCB. During the debugging phase, many signal traces or chip pins that need to be monitored are often hidden within the inner layers of the PCB, making them difficult to detect with conventional tools like oscilloscopes. If the product fails functional testing, there are no effective methods to pinpoint the root cause of the issue. To assess the product’s EMC performance, the only option is to take the product to a certified EMC measurement lab. However, this testing only measures the product’s external radiation and, even in the case of failure, fails to provide actionable data for troubleshooting. As a result, engineers must rely on their experience to make modifications to the PCB and retest, a costly and time-consuming process that can delay the product’s time to market.
1. Of course, many high-speed PCB analysis and simulation design tools are available to assist engineers in solving various problems, but there are still numerous limitations concerning device models. For instance, the IBIS model, which is commonly used for signal integrity (SI) simulation, lacks models for many devices, or the available models may not be sufficiently accurate. To precisely simulate EMC issues, SPICE models are essential; however, almost all ASICs currently fail to provide SPICE models. Without these models, EMC simulations cannot account for the device’s radiation, which is significantly higher than the radiation from transmission lines.
2. It is well understood that the return path for high-frequency signals in a multi-layer PCB should ideally lie on the reference ground plane (either the power layer or ground layer) adjacent to the signal line layer. This arrangement minimizes return current flow and impedance. However, actual ground or power layers often have partitions or voids, which alter the return path, resulting in a larger return area that can lead to electromagnetic radiation and ground bounce noise. If engineers can fully comprehend the return current path, they can avoid large return paths and effectively manage electromagnetic radiation. However, the signal return path is influenced by numerous factors, including signal routing, PCB power and ground distribution, power supply points, decoupling capacitors, as well as device placement and quantity. Consequently, it is extremely difficult to theoretically predict the return path in a complex system.
3. **High-speed Electromagnetic Field Scanning Measurement Technology**
Among various electromagnetic radiation measurement techniques, near-field scanning stands out as a method capable of addressing this issue. This method is based on the principle that electromagnetic radiation is generated by high-frequency current loops within the device under test (DUT). For example, the electromagnetic radiation scanning system from Canadian company EMSCAN is designed based on this principle. It utilizes H-field array probes (32×40 = 1280 probes) to detect current on the DUT. During measurements, the DUT is placed directly on the scanner, and these probes can sense changes in electromagnetic fields resulting from variations in high-frequency currents. The system offers a visual representation of the spatial distribution of RF currents across the PCB.
4. The Emscan electromagnetic compatibility (EMC) scanning system has been widely adopted in industries such as communications, automotive, office equipment, and consumer electronics. By analyzing the current density maps generated by the system, engineers can identify areas with potential EMI problems before performing EMC standards testing, allowing them to take appropriate corrective actions.
5. **Near-field Scanning Principle**
Emscan’s measurements are primarily conducted within the active near-field region (r < λ/2π). A high-current, low-voltage source is mainly related to the magnetic field, while a high-voltage, low-current source is primarily linked to the electric field. On a PCB, pure electric or pure magnetic fields are rare. In RF and microwave circuits, components such as microstrip or stripline connections are designed to have a characteristic impedance of 50 ohms. This low-impedance design results in large currents and small voltage variations. Furthermore, digital circuits are increasingly using logic devices with smaller voltage differences, and in the active near-field region, the wave impedance of the magnetic field is much smaller than that of the electric field. Consequently, most of the energy in the active near-field region of the PCB is contained within the magnetic field. Thus, the magnetic field loop employed in the Emscan scanning system is well-suited for near-field diagnosis of these PCBs.
6. The loops in the system are identical in design but vary in their positions within the feedback network. This enables the feedback network to detect the response from each loop. The system then measures and interprets the response of each loop relative to the reference source as a filter transfer function. To ensure measurement accuracy, Emscan evaluates the reciprocal of this transfer function.
7. By leveraging array antennas and electronic automatic switching technology, Emscan greatly accelerates measurement speed—thousands of times faster than manual single-probe measurements and hundreds of times faster than automatic single-probe systems. This allows engineers to quickly assess the impact of circuit changes. The fast scanning technology, combined with advanced amplitude-maintaining and synchronous scanning techniques, ensures that transient events are captured effectively. Additionally, Emscan incorporates technology that enhances the measurement accuracy of spectrum analyzers, improving both measurement precision and repeatability.
8. **Measurement Methods for Evaluating PCB Near-field Radiation Interference**
The evaluation of PCB radiation interference is typically performed in several steps. First, the area to be scanned is identified, and then a probe (with a grid of 7.5mm) is chosen to fully sample the designated area. A spectrum scan is performed across the frequency range of 0–3 GHz, and the maximum level at each frequency point is recorded. Note that significantly large frequency points should be further investigated within the scanning area using spatial scanning, which helps pinpoint interference sources and critical circuit paths.
9. The board under test should be positioned as close to the scanner board as possible. Increasing the distance between them will degrade the signal-to-noise ratio, causing a “separation” effect. Typically, the distance should be less than 1.5 cm. Measurement issues may arise if components are too tall, as this could affect the accuracy of the measured voltage level. Thus, component height must be considered and corrected during voltage level measurement. In basic inspections, adjustments for separation distance are essential.
10. While measurement results can be obtained quickly, they do not directly indicate whether the product meets EMC requirements. The measured values represent the electromagnetic near field generated by high-frequency currents on the PCB. Standard EMC tests must be performed in an open-area test site (OATS) or a shielded room, at a distance of 3 meters (far field).
11. Although Emscan measurements cannot replace standard EMC tests, practical experience has shown that they provide significant value. Analyzing the measurement results offers useful insights that help guide the further development of the product. In addition to providing voltage levels, the following information is crucial: interference generation points, interference distribution, large-area interference conduction paths, localized interference areas on the PCB, internal coupling between adjacent I/O modules, and the effects of separating digital and analog circuits.
12. The measurements can serve as a standard for evaluating PCB design quality. Furthermore, if the EMC characteristics of a similar PCB are already known, reliable early-stage evaluations can be made regarding the product’s EMC performance, such as whether shielding is required.
If you have any PCB manufacturing needs, please do not hesitate to contact me.Contact me
