Test and debug your circuit design for EMI compliance

This article is part of the TechXchange: Dive into EMI, EMC and Noise

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What you will learn:

  • What is Conducted EMI Measurement?
  • Using FFT-based measurement receivers for CISPR 32.
  • Combine debug and pre-compliance modes in test equipment.

EMC compliance testing of a manufacturer’s product can be quite expensive and time-consuming, particularly if the product’s initial submission fails the test house, requiring the manufacturer to resolve the issue and submit it to new to EMC testing. An obvious solution to reducing compliance costs is to perform basic pre-compliance measurements and debugging at manufacturer facilities before submitting them to an EMC test house.

Conducted EMI measurement

Conducted EMI measurement,1 a critical EMC compliance measurement, can be done quite easily at the manufacturer’s site. Amazingly, all you need is a basic oscilloscope and cloud computing.

Compared to a test house, the manufacturer’s facility will likely be a noisy environment in which to perform the EMI measurement performed. However, the conducted EMI measurement is performed at frequencies between 150 kHz and 30 MHz, where the conducted emission is dominant.

The main pathway for electromagnetic interference will be the connection between the equipment under test (EUT) and the power supply. It will be possible to perform this conducted EMI measurement at the manufacturing site as long as there is a good separation between the power supply and the EUT. An EMI separation device must be used to separate the power supply from the EUT (see picture).

The EMI separation device contains an improved EMI filter capable of providing 62 to 82 dB attenuation for common mode EMI and 78 to 90 dB attenuation for differential mode EMI at frequencies ranging from 150 kHz to 30 MHz . After the EMI separation device, the environmental noise will be 15 dB below the limiting line given by the EMC regulations, which satisfies the environmental noise requirement for a standard conducted EMI measurement.

An even less expensive way to perform this EMI measurement, without an EMI receiver, is an app developed in Reference 1. Running in a smartphone, it controls a general scope oscilloscope that measures EMI from the EUT through the EMI splitter device. EMI data can then be automatically uploaded to the cloud for further processing (Reference 1 has all the details).

FFT-based measurement receivers for EMI compliance measurements against CISPR 32

Users of CISPR 322 can immediately use a Fast Fourier Transformer (FFT)-based measurement receiver for EMI compliance measurements if the instrument meets the requirements of CISPR 16-1-1. Two different types of FFT receivers are available:

  • Instruments that digitize the input signal with an analog-to-digital converter (ADC) into baseband.
  • Instruments that digitize the signal with an ADC at the output of the broadband IF filter.

Comparison of measurements from conventional (single-frequency) EMI receivers and FFT-based time-domain scanning proved that these results are identical.

The use of pre-selection filters is necessary for maximum dynamic range and to avoid overloading. This is especially true for quasi-peak measurements of weak pulsed signals in the presence of high amplitude carriers.

Trends in EMI pre-compliance debugging

The latest test instruments frequently combine debug and pre-compliance modes to help engineers save valuable time and resources in their design process.4

Engineers need to visualize and solve more problems earlier in the design. This requires flexible solutions that can capture and visualize all issues in digital, analog and RF domains. In addition to traditional EMI pre-compliance analysis, there are new solutions that enable real-time emission capture, time-domain EMI debugging, and combining all of these capabilities into multi-domain analysis.

EMI pre-compliance measurements give valuable information to engineers throughout the design process. Flexible real-time spectrum and time domain analysis for multi-domain debugging will allow designers to discover problems faster and solve complex problems on the bench. This effort will lead to faster time to market, enable real-time debugging, and build confidence in a design as a project progresses to final EMI compliance testing faster.


Businesses need to enable speed and efficiency throughout the electronics design process. A big part of accelerating time to market is performing pre-compliance testing on the same test bench where RF and embedded signal debugging takes place. Using the latest instruments that can combine pre-compliance modes and debugging will allow designers to accelerate product turnaround.

Read more articles in the TechXchange: Diving into EMI, EMC and Noise

The references

1. “Low-Cost Onsite EMI Measurement for Product EMC Pre-Compliance,” IEEE 2019.

2. “Use of FFT-based measurement receivers for EMI compliance measurements against CISPR 32”, 2017 Asia-Pacific International Symposium on Electromagnetic Compatibility (APEMC), June 20-23, 2017, Seoul, Korea.

3. “LCL Filter Design and Analysis of Grid-Connected Converter for Power Quality and EMI Compliance”, 7th Asia-Pacific International Symposium on Electromagnetic Compatibility, IEEE 2016

4. Power Electronics Guide 2021 by interference technology

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