This was also confirmed by our later EMI scan in a 10-meter anechoic chamber. Without the help of the scanner, we probably would never know it.
Yuting Feng, Hardware Engineer | Aksys Networks Inc., Calgary, AB, Canada – March 18, 2009
Aksys Networks Inc. rented EMxpert EHX for testing.
Aksys Networks Inc. designs a revolutionary VoIP phone system. The complexity in hardware and software results in difficulty in controlling the RF emission. Among all the troublesome frequencies we are facing, the clock signal for the SDRAM chips has always been the most critical one.
With EMSCAN’s innovative magnetic near-field scanner along with its accompanying software EMxpert, we not only confirmed that the clock signal is the biggest contributor of that particular frequency, but also we found that the processor couples the same frequency onto the power plane. This was also confirmed by our later EMI scan in a 10-meter anechoic chamber. Without the help of the scanner, we probably would never know it.
From the plots that the near-field scanner generated, we clearly saw the areas around the microprocessor, along the SDRAM clock track and near the terminating SDRAM chips are much hotter than other places at that frequency as well as its second harmonics. The first thing we did was to bury this clock signal deep down inside the inner layers and covered with GND planes on the two sides of it. Then according to the hot areas, we carefully designed a RF shield that covers most of them.
For the power planes that are affected by the high frequency noise, we carefully chose groups of capacitors with proper values to decouple the noise from them and at the same time, we redesigned the shape and size of the power and ground planes so they are less prone to such high frequency noise. We then brought the new product to the EMI lab and the result was very encouraging.
In general, the scanner and the EMxpert software provide direct and intuitive way for an engineer to find the source of the emission as well as the strength of each troubled zone. They can bring huge convenience for an engineer to troubleshoot and thus save a lot time and money. We feel lucky that we had the chance to use this equipment and software to help us debug the emission problem. Therefore, we highly recommend the use of the near-field scanner to expedite the overall R&D process.
EMSCAN is the world leading developer of FAST magnetic very-near-field measurement technologies and applications since 1989, providing real-time test solutions to antenna and PCB designers and verification engineers, without the need for a chamber.
The EMxpert, a family of compact EMC and EMI diagnostic tools, and the RFxpert, a family of antenna measurement tools, enable engineers to quickly optimize their designs. EMSCAN solutions dramatically increase designer productivity and substantially reduce time-to-market and project development costs. www.emscan.com