Demos kick off EMC Symposium

IEEE International Symposium on Electromagnetic Compatibility, www.emc2010.org, Ft. Lauderdale, FL, July 25-30.

Martin Rowe, Senior Technical Editor -- Test & Measurement World, 7/28/2010 1:45:35 PM

Professor Frank Leferink explained how PCB vias and traces can affect radiated emissions.

After committee meetings over the weekend and workshops Monday, the 2010 IEEE EMC Symposium continued with technical demonstrations on Tuesday.

As part of his "EMI at the PCB Level" demonstration, Professor Frank Leferink of University of Twente in the Netherlands used several PCBs to demonstrate EMI at the board level. Leferink showed how vias in boards may form current loops that can radiate energy. He explained how placing bypass capacitors on the underside of a board can defeat the purpose of the bypass capacitor. The loop inductance from an IC to its bypass capacitor can radiate emissions that the capacitor should squelch.

Leferink also showed how the layout of PCB traces can result in crosstalk. A coupling path can cause signals in a trace to appear on an adjacent trace. Differences in line terminations can create coupling paths.

EMC consultant Ken Wyatt showed emissions in the frequency and time domains with a spectrum analyzer and oscilloscope.

In his EMC troubleshooting demonstration, EMC consultant Ken Wyatt explained how capacitance coupling can send emissions from an oscillator to a cable. Wyatt used a circuit that contains a 19-MHz oscillator connected to a 50-Ω load in parallel with a variable capacitor. That capacitance, combined with inductance in the PCB traces, can produce electric fields that can interfere with other circuits. Wyatt used a portable spectrum analyzer and oscilloscope to show the how current can create unwanted fields.