EMI pre-compliance test solution based on Agilent CXA signal analyzer

　　Main advantages of EMI pre-compliance solution

　　Unlike ordinary spectrum measurements, the response standards for EMI measurements have a series of mandatory requirements for software and hardware functions, including EMC dedicated detectors (quasi-peak detectors, EMC average detectors, and RMS detectors), CISPR 6 dB bandwidth filters, logarithmic frequency axis display, standard-related limit lines, and variable sweep points to obtain sufficient frequency resolution. Using an ordinary spectrum analyzer without professional functions for EMI-related tests may result in very different results.

　　Agilent's latest W6141AEMC measurement application software based on the N9000A CXA signal analyzer provides professional functions that fully comply with CISRP-16-1 requirements, good RF performance, and fast test speed. It can capture small-amplitude, transient interference signals, making low-cost professional EMI pre-compliance testing no longer just a dream.

　　The W6141A EMC measurement application software provides all the functions required by CISPR-16-1, and also has a series of additional functions to make pre-compliance testing easier.

　　1) Scan list based on standard presets

　　Users who are not familiar with EMC standards only need to select the frequency band in the list to automatically set all parameters, as shown in Figure 3.

Figure 3 Scan List

　　2) Signal list

　　Dedicated EMC detectors, such as quasi-peak detectors, need to stay at each scanning point for a certain time for time domain weighting. This results in a full-band scan taking several hours. The W6141A measurement application software adopts the method of pre-scanning with a common positive peak detector first, and then automatically performing a dedicated detector measurement on the peak signal exceeding the limit line. This usually only takes a few minutes, greatly improving the test efficiency. According to theory, the amplitude reading value of the positive peak detector after the maximum hold must be equal to or greater than the reading value of the EMC professional detector. Therefore, this method can ensure that there will be no false detection or missed detection.

Figure 4 W6141A EMC measurement application software

　　The signal list function of W6141A is also important for radiation leakage testing. We can perform two measurements with the DUT turned off and on. In this way, most environmental interference signals will appear twice in the signal list. W6141A provides the functions of marking duplicate signals and deleting marked signals to remove these environmental interference signals at one time.
 

　　EMI pre-compliance testing and troubleshooting using near-field probes

　　diagnosis

　　In the absence of an anechoic chamber, it is difficult to completely eliminate environmental interference such as broadband signals or frequency hopping signals. A more cost-effective solution is to use a signal analyzer and near-field probe instead of a broadband antenna to perform radiation leakage pre-compliance testing, fault diagnosis, and improvement effect verification.

　　Formal radiation leakage testing, whether it is the three-meter method or the ten-meter method, all performs far-field measurements. The near-field probe measures near-field electromagnetic waves. The test results of the two cannot be mathematically derived and converted. In this way, we cannot directly convert the near-field test results with the far-field test results. But a basic principle is that the greater the radiation in the near field, the greater the radiation in the far field. This provides a theoretical basis for near-field probe testing. When using near-field probe testing, we need to compare the test results of the new DUT with the near-field probe test results of a known qualified DUT. For this step of testing, it is recommended to use an electric field probe or a larger magnetic field probe. These two types of probes are generally more sensitive and less sensitive to distance.

Figure 5: EMI troubleshooting using a near-field probe

　　If a new product fails in EMI pre-compliance testing or standard compliance testing, fault diagnosis and improvement are urgent. Without the right tools, it is difficult for engineers to find the crux and prescribe the right remedy. The N9000A has excellent test sensitivity and can work perfectly with near-field probes. In the process of fault location, smaller magnetic field probes can do a better job. Small magnetic field probes have lower sensitivity but higher spatial resolution. By slowly moving the probe over the DUT or circuit and observing the changes in the spectrum amplitude on the N9000A, engineers can accurately locate the area of ​​the suspected radiation source to a very small circuit.

　　By using a near-field probe, we can easily find the suspected area where the radiation source exists. If we need to further find out which circuit, pin or even chip is the culprit, we can use an oscilloscope probe or a high-frequency probe to make contact measurements. Agilent 85024A and U1818A high-frequency probes can test signals up to 3 GHz and 6 GHz respectively, which are very suitable for circuit contact measurements, especially for circuits with high-frequency clock signals. However, when using a high-frequency probe for testing, you need to pay attention to protecting the probe and spectrum analyzer from being damaged by high voltage.

　　in conclusion

　　Agilent N9000A CXA signal analyzer and W6141A EMC measurement application software provide all electronic engineers with an efficient and economical professional EMI pre-compliance test solution. It is also a professional, powerful and flexible fault diagnosis tool that can be applied to the entire product life cycle from R&D to formal production.