Investigation of the theoretical basis for using a 1 GHz TEM cell to evaluate the radiated emissions from integrated circuits

This study was initiated in order to gain a better understanding of the basis for using a 1 GHz TEM cell to evaluate the radiated emissions from integrated circuits (ICs). The authors have been involved for several years with the effort to develop procedures and standards for evaluating the EMC of ICs. One of these standards, SAE J1752/3, is being used by the IC industry to characterize high speed VLSI ICs and survey the variation of RF emissions due to changes in IC process and package parameters. This standard specifies a radiated emissions measurement system using a 1 GHz TEM cell with the IC under test on a test board that is a part of the wall above the septum of the TEM cell. In order to investigate the theoretical basis for this procedure, a model of the IC lead frame as a current loop was developed and analyzed for coupling to the septum of the TEM cell at different orientations. Test boards with current loops orientated both parallel and orthogonal to the TEM cell wall were evaluated for correlation with the model. Using a microprocessor on a test board, a comparison was made of the measured data from the 1 GHz TEM cell, the EMSCANTM circuit board analysis system and radiated field measurements using an antenna. Methods for calibration of the TEM cell were also investigated.