IEEE-EMC continues with more technical information
IEEE International Symposium on Electromagnetic Compatibility, Detroit, MI, August 18-22
Martin Rowe, Senior Technical Editor -- Test & Measurement World, 8/22/2008 9:23:00 AM
DETROIT, MI—Wednesday’s EMC Symposium technical sessions featured a new session on Jitter and BER measurements. This session is in addition to two sessions on signal integrity, which were added a few years ago. Engineers are beginning to see that signal integrity and EMI are linked. Now, we’re beginning to see how jitter affects EMI. For example, data-dependent jitter in a high-speed serial link can affect a system’s radiated emissions. This session was sparsely attended and attendees asked few questions. Perhaps that’s because the concept of jitter-induced EMI is a new field of study.
Another session focused on EMC education. Professor Nathan Ida from the University of Akron presented a paper called "GET NAME" where he covered his required course for second-semester juniors majoring in computer engineering. “CE majors need an understanding of EMC as it relates to high-speed digital communications,” he said. The course covers basic concepts of EMC through theory and research projects. “The course is optional for EE majors and they make up about half the class of 24 to 28 students,” he said. The course runs three hours a week for 15 weeks. Professor Ida devotes three hours to measurements, six hours to regulator compliance, one hour to ESD, and five hours to designing for EMC, which includes PCB layout bypass capacitors, and other topics.
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EMC exhibits and demonstrations kick off Symposium in the Motor City |
Professor Arnold de Beer from the University of Johannesburg followed by discussing his paper “Problematic Concepts in the Introduction of EMC." deBeer teaches a 2-3 day course on EMC, which is not covered in the university’s EE curriculum. de Beer told the audience of about 50 engineers that “common-mode is a difficult concept to grasp, and it’s crucial to EMC.” He also covers orders of magnitude, decibels, parasitic capacitance and inductance, and grounding. "Parasitic capacitance and inductance are the undocumented circuit components,” he said. “They’re not on a schematic and digital engineers just want to see clean gates.” He noted that some students have a hard time believing that a wire is an inductor at high frequencies and a capacitor’s parasitic inductance dominates its capacitance at frequencies above the resonant frequency.
The exhibit hall again held several hardware and software demonstrations, with hardware demonstrations attracting far more engineers. Orin Laney from Atwood Research demonstrated how skin effects, impedance, and resonance in ground planes affect EMI performance. Using an Agilent oscilloscope, Laney demonstrated how ground planes act like low-pass filters, removing high-frequency content from signal edges and slowing them.
When Laney completed one of his presentations, the crowd of about 15 engineers moved over to the next hardware demonstration, which covered shielding in cables. Randall Vaughn of Silent Solutions used a Rohde & Schwarz spectrum analyzer to show how poor shield due to “pigtails” decreases a cable’s shielding effectiveness. Vaughn passed around cables with DB-9 connectors that had openings in the cases so engineers could see three methods of connecting a cable’s shield braid to ground pins and how to minimize loops caused by pigtails. "If you can, add a second connection from the shield to ground and make sure to place the extra line on the opposite side of the signal-carrying wire. You’ll minimize loops that can radiate emissions,” he said.
Vaughn then demonstrated how a product’s enclosure becomes a tuned cavity. “Microwave engineers understand the concept,” he said, “but others may not.” In his demonstration, Vaughn mounted BNC connectors on a cookie tin, then connected one BNC to the spectrum analyzer’s tracking generator and the other to the input. When he put the cover on the tin, you could clearly see how the enclosure produced a peak, thus amplifying the signal at a frequency he calculated based on the side of the tin. The peak vanished when he removed the cover. “If an enclosure has openings,” he said, “those openings can let emissions escape, depending on the size of the openings and the frequencies inside the enclosure.”
New products on the EMC show floor
Agilent Technologies unveiled an EMC option for its MXA and EXA series of spectrum analyzers. The option adds CISPR emissions limits, an rms detector, a quasi-peak detector, EMI averaging, noise figure measurements, phase noise measurements, and analog demodulation. You can compensate for losses caused by antennas, cables, and connectors. Antenna factors are available for most EMC antennas that the instrument uses to compensate for losses over frequency.
AR Worldwide introduced the CER 2018A EMI receiver. This instrument requires a PC with software and it operates at frequencies from 9 kHz to 18 GHz. AR also introduced the PL7004 laser-powered probe for characterizing chambers. The probe measures pulsed outputs that simulate radar pulses. A fiber-optic cable sends power to the probes and it carries received signals (in optical form) to a laser-interface unit. From there, the interface unit connects to a PC through GPIB, RS-232, USB, or Ethernet ports. The company also demonstrated high-gain horn antennas and a transient-generator test system for automotive EMC testing.
The company’s power amplifiers, used for radiated immunity testing, now amplify signals up to 20 GHz. These amplifiers produce 35 W and you can use up to four amplifiers to get 140 W. Other amplifiers that cover the 4-GHz to 11-Ghz range produce up to 20 W and you can connect four units to get 80 W.
LeCroy demonstrated an EMC option for its WaveRunner Xi 2 GHz oscilloscopes. The software, which runs on all LeCroy oscilloscopes of 500 MHz or higher bandwidth, performs analysis on electrostatic discharge, electrical fast-transient, and surge waveforms. It measures rise and fall times as well as pulse-width level.
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