Electromagnetic emissions are an important topic for any electronic device. They affect their functionality and their regulatory compliance. Any kind of electronic device needs to pass strict test to ensure they are safe to use (they will not harm anybody) and they will not interfere with other equipment. There are different types of tests and checks and they all fell into two categories: conducted emissions and radiated emissions.
We will learn about both types of tests, their differences and their details.
Conducted Emissions (CE)
What are Conducted Emissions (CE)?
They refer to unwanted electrical signals transmitted through power lines or signal cables. Cables carry wanted energy (TV signal, voltage charging your mobile phone). Unwanted emissions are superposed to the wanted energy, affecting other devices sharing the same distribution network.
For example, a poorly designed motor might create unwanted high-frequency signals. These signals travel through the motor’s cord to the power grid, becoming a source of electromagnetic interference (EMI).
If you want to go for a deeper dive into conducted emissions, you can explore these resources:
Sources of Conducted Emissions
Now that we know what Conducted Emissions are, the next question is: where do they come from?
There is not a single source of conducted emissions and that is one of the reasons why it is so difficult to get rid of them. Here there are some causes:
- Switching Power Supplies: The fast edges and fast switching of high amounts of energy generate a lot of noise.
- Motors and Generators: They often generate broadband noise that easily couples over other parts of the electronic device.
- Digital Circuits: High-frequency clocks, rapid signal transitions, reduced space are transitions are common sources of emissions.
Measurement Techniques for Conducted Emissions
Testing conducted emissions involves specific tools and setups. There are two methods:
- Using a Line Impedance Stabilization Network (LISN). A LISN is connected between the power source and the device under test (DUT), ensuring consistent impedance for accurate measurements. We use an Spectrum Analyzer (SA) or an EMI receiver to capture the emitted signals.
- Using a Current Probe. Current probes are high-frequency transformers and they have the advantage of not being intrusive, i.e. there is no need to open the cables. The current probe is installed around the wiring harnessess and the voltage is measured with a Spectrum Analyzer (SA) or an EMI receiver.
Radiated Emissions (RE)
What are Radiated Emissions (RE)?
Radiated emissions are interferences that propagate through space, usually free air. Think of it as noise coming from a radio tower—except in this case, the “tower” is an electronic device unintentionally emitting signals. A concise explanation of the concept can be found at Conducted Vs. Radiated Emissions.
There are many radiated emissions around us and around any electronic device. The key aspect is the difference between wanted (a phone call) and unwanted signals (another phone call nearby). We want to maximize the wanted emissions while keeping unwanted signals minimum.
Sources of Radiated Emissions
As it happens with Conducted Emissions, it is impossible to define just one source of Radiated Emissions. Here are some common sources of radiated emissions:
- Antennas: Designed for intentional radiation, but they can also emit unintended signals.
- High-Frequency Circuits: Circuits operating at high speeds can inadvertently act as radiating structures.
- Cables: Long cable runs can act as antennas, emitting electromagnetic noise.
Measurement Techniques for Radiated Emissions
Testing radiated emissions accurately requires specialized facilities. An anechoic chamber, which absorbs reflections, prevents external noise from interfering with the test. Equipment such as spectrum analyzers captures emitted signals, while calibrated antennas measure field strength. The setup ensures the device complies with regulatory limits.
Key Differences Between Conducted and Radiated Emissions
Transmission Medium
The biggest difference lies in the travel path. Conducted emissions use cables and wiring, while radiated emissions propagate through space like air. This distinction affects how they’re controlled and mitigated.
Testing Environments
Conducted testing can often occur in labs with minimal spatial requirements; all you need is a LISN or a current probe and the appropriate setup. However, radiated emissions testing calls for controlled environments like anechoic chambers to minimize external noise and reflections.
Both methods must limit ambient interference, but the setup complexity varies greatly.
Conclusion
Both conducted and radiated emissions tests play vital roles in ensuring that devices meet regulatory standards and don’t interfere with other equipment. For Hardware designers, Startup founders and CTOs, understanding these differences is essential. It’s not just about compliance; it’s about creating reliable, high-quality products.
Addressing these tests from the design phase will save you time and resources in the long run. Whether testing conducted emissions through power lines or analyzing radiated noise in anechoic chambers, preparation and knowledge are your best tools for success.
What is next?
Grab your guide about Current Probes to start measuring the conducted emissions of your electronic device