The influence of test parameters on TEM cell measurements of ICs

The IEC 61967-2 TEM cell standard allows for variations in test parameters which may cause variations in the measured emissions from integrated circuits (ICs). To test the impact of these parameters, two printed circuit boards were designed within the IEC standard using ldquopoorrdquo PCB design strategies and using ldquogoodrdquo design strategies. Emissions from three pin-for-pin compatible 8051 microcontrollers were tested. Emissions were measured using both PCBs, changing the PCB configuration, and changing test parameters like the program running on the IC, the rise time of the input clock, and I/O switching. Emissions from the ldquopoorrdquo PCB were about 3-8 dB higher than emissions from the ldquogoodrdquo PCB. A change in the program run by the IC, the clock rise-time, and I/O caused a 4-15 dB change in emissions. Emissions differed considerably among the ICs. Possible causes for variations in emissions with the test parameters are discussed.