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Oscilloscope for EMI debugging? Still not convinced? (Part 2)

16 Aug 2013  | Alvin Ding

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With oscilloscopes, you can trigger on the particular bus signals and observe for repeatable emission in device state changes. Similarly unintended emissions radiated from changes of states in power supplies can be measured.

For example in figure 4, there are instances where EMI events occur only at specific times when communication on a CAN bus happens. You can correlate time and spectrum data using gated FFT along the trace to deduce that the emissions were caused by transmission of CAN signals.


Top: CAN bus signal in time; centre: decoded CAN protocol; bottom left: spectrum on the whole time signal; bottom right: spectrum on the gated white box.

Figure 4: Top: CAN bus signal in time; centre: decoded CAN protocol; bottom left: spectrum on the whole time signal; bottom right: spectrum on the gated white box only. The spectrum on the right shows FFT of the gated white box in time traces on top, when there is no CAN data transmission. Noisy emissions are observed in the range of 50MHz on the bottom left spectrum.


The scenarios we discussed here are just a few examples how modern oscilloscopes may contribute to EMI debugging. In the next article, we will explore in-depth EMI debugging setups—from handling near field probes, capturing relevant signals to the analysis of radiated emissions.

About the author

Alvin Ding
Business Development
Rohde & Schwarz
Alvin Ding has years of experience in the test & measurement industry, with extensive knowledge and focus on the latest and emerging technologies, such as high-speed serial data and RF. Alvin received his bachelor's degree with honours in electrical and electronics engineering (EEE) from Nanyang Technological University, Singapore. Alvin received the EEE Excellence award for his outstanding contributions and excellence in academic performance throughout his study.


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