Conducted Susceptibility Testing: Electronic Reliability in DFM Procedures

April 29, 2020 Cadence PCB Solutions

Key Takeaways

  • Define conducted susceptibility testing within your electronics realms
  • Determine how conducted susceptibility testing can add relevance and security to your designs
  • Understand the importance in reliability testing for your electronic hardware designs

Controlled electronics testing in a laboratory


I’ve always thought that acupuncture is all about piercing dozens of needles into your flesh. My assumption goes well as I sought treatment over a sprained neck, but I started panicking when I saw wire clips attached to the needles. Without warning, a switch was turned on somewhere and jolts of electricity pulsed through my body. 

Strangely, the combination of electrical pulses and acupuncture needles seem to have a healing effect on my neck. The same cannot be said about sending random electrical pulses onto a PCB. Some electronics stop functioning even at the slightest electrical interference, which calls for conducted susceptibility testing. 

What Is Conducted Susceptibility Testing

In a perfect lab condition, a correctly designed PCB will function just fine. However, most PCBs are meant to be deployed in environments where they are subjected to external electrical noise. Some PCBs may stop functioning or produce erroneous results when electrical noise is introduced into the circuit. 

Conducted susceptibility testing is a test procedure that determines how well a device or circuit performs when a certain amount of electrical noise is injected into the circuit. As the term implies, conducted susceptibility testing only evaluates noise that is directly coupled into the conductors.

The test is performed by introducing low to medium frequency noise over a few points of a circuit. Usually, the noises are applied to power and signal lines. If the circuit continues to function after a specified range of frequency, it passes the conducted susceptibility test. 

Conducted susceptibility testing that involves RF noise coupled into conductors is based on the IEC-61000-4-6 standard. The standard defines the frequency range and test level for equipment under test (EUT). Specifically, the test frequency ranges from 150 kHz to 80 Mhz. 

In cases where conducted common-mode disturbances need to be evaluated, IEC 61000-4-16 is the reference standard. This test involves simulating common-mode noise ranging from 15 Hz to 150 kHz into the power, signal and communication lines. 

Conducted Emission Sources

Getting conducted susceptibility tests done allows you to anticipate potential issues when the PCB is deployed. Plus, you’ll need to budget in the testing fees. For all these troubles, you’ll want to know what are the possible sources of conducted emission that may trouble the design.

One of the most notorious conducted emission sources is a switching power supply. The high-frequency switching introduces noise onto the voltage line. It’s an unavoidable tradeoff for the efficiency provided by switching power supply. Different models of the power supply may have different levels of noise. Your PCB may work fine on one and shows peculiar behavior when connected to another.

Another source of rather sporadic conducted emission is from the electrical motor. The sudden changes in current, particularly on PWM-controlled motors, causes EMI to be introduced to the cable. Often, the conducted emission by an electric motor is compounded by the length of the cable, which results in a larger loop. 


switching power supply with an enclosure

Switching power supplies can introduce conducted emission.


In general, if you have fast switching signals on your PCB, be it from a microcontroller or communication signal, there’s a chance for conducted emission on the circuit. Sometimes, noise is introduced into the ground plane, which results in ground bounce and causes logic ICs to function erroneously. 

Optimizing For Conducted Susceptibility Test

It’s good to pass the conducted susceptibility test but it’s even more important to ensure a robust design that operates flawlessly in a robust environment. This means preventing conducted emission from affecting the circuit.

For a start, you can protect the power input of the PCB by adding an LC filter on the voltage line. Instead of the usual iron core inductors, use a ferrite bead to block high-frequency noise from passing through. Placing a decoupling capacitor in parallel helps to channel the conducted noise to the ground. 


LC Filter diagram in a schematic

An LC filter helps to reduce noise from conductive EMI. 


Layout for sensitive components like audio amplifiers and microcontrollers must also be done with care. Placing bypass capacitors near the power pins helps to stabilize the supply. Return paths for sensitive signals must be kept as short as possible and minimize loop areas.

EMC testing is costly but with the suite of advanced layout and analysis tools from Cadence, you can start preparing for conducted susceptibility testing during the design cycle. Furthermore, start your board design and verification right with Allegro PCB Designer and its strong capabilities for creating high-quality circuits. 

If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts

About the Author

Cadence PCB solutions is a complete front to back design tool to enable fast and efficient product creation. Cadence enables users accurately shorten design cycles to hand off to manufacturing through modern, IPC-2581 industry standard.

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