Tips on Filtering Out Noise

By Michael Jermann, Assistant Editor

As processing speeds in electronics continue to rise, and packaging continues to shrink, sensitive internal components are located closer and closer together. Higher clock speeds coupled with increased density of components leads to increasing amounts of electromagnetic interference (EMI) and Radio Frequency Interference (RFI) noise.

Failure to address EMI/RFI/EMP protection along with that of transient voltages during the design and test phases of a project usually results in devices failing compliance testing and incurring high costs in redesigning and retesting the electronic systems or components.

Filtered connectors, where the filter is contained in the device connector, are a higher-performance approach to eliminating EMI/RFI noise.

EMI suppression is often handled by filters designed to meet the increased performance demands levied during testing from MIL-STD-461, RTCA-DO-160, CISPRE, and CE Mark, and so on.

Essentially, there are four ways to address EMI/EMC filtering requirements. Filtering can be designed onto the PCB or in a device during the initial engineering phase. Otherwise, the filtering requirement can be handled by one of three devices after the device has already been designed: (1) filter inserts, which are installed in front of device connectors, (2) filtered connectors, where the filter is contained in the device connector, and (3) filter / Transient Voltage Suppression (TVS) interface modules that are add-ons to an existing device.

“The filter insert is a quick and simple solution. It allows to you to simply pop a filter into your existing system and see if simple chip cap level of filtering will solve your EMI issues. If they solve the problem, it won’t cost you a lot,” said Bob Ydens, President of EMI Solutions Inc.

The next tier in EMI Filtering is the filter connector, which is a higher-performance approach to eliminating EMI/RFI noise. This solution is more expensive than the basic filter insert, but has the ability to include chip capacitors, such as what is in filter inserts, discoids, ferrites, TVS components, and Pi tubes, including a broad range of configurations and mounting arrangements.

Filter modules are add-on components that are attached to an existing device or “box.” These modules can include any filter type, with or without transient voltage protection. Some of the advantages include more sophisticated filtration, avoidance of the need to insert additional PCB design integration into your already functioning fielded unit, and avoidance of the costly time it takes to re-layout and re-test the circuitry.

Custom solutions

Custom solutions—including design consulting, troubleshooting, device modification, and pre-certification testing —may be appropriate when it comes to choosing the appropriate filtering or product modifications.

Some EMI filtration companies provide design and re-engineering services to expedite any necessary product modifications and keep costs to a minimum. Pre-certification testing is performed in a chamber at their facilities so that the customer can evaluate the impacts of changes and modification and achieve a greater confidence that the unit will pass when it goes to the certification test lab.

The pre-certification testing process at EMI Solutions is an iterative process whereby changes and modifications are made incrementally and then tested to determine the results. Additional filtering modifications are then applied until testing in their onsite chamber establishes a solution that meets the customer’s requirements. One of the principal benefits of this approach is that the test lab has the staff and filter technology available on site to implement these modifications quickly, which is valuable in terms of the time and costs involved.

Although filter inserts are generally considered the lower end of the spectrum in terms of cost and filtering limitations, they are a practical solution for many applications.

In some cases the device being tested requires upgrading or modifications simply because the original design has been outmoded, or the end-user has specified a special application or environment.

“We were having multiple EMI issues with units being tested in connection with two government projects,” said John Eckland, Test & Integration Engineer at Curtiss Wright Controls.

“One of the units is a complex, multi-purpose computer unit. The other one is a high-capacity, high-throughput Ethernet switch unit. Both have military applications. We had to switch power supplies on both systems, which caused us to have significant EMI problems,” Eckland said. “We were unable to do a redesign on the fly due to time constrains. So, the only solutions available to us were either to do extensive internal changes within both units, or to contact EMI Solutions and see if they could develop a solution that required only limited changes within the units.”

In both cases, the solution required only a modification at the connector to the power supply, where filter inserts were placed on the power connectors.

EMI Solutions, Inc.
www.4emi.com