Measurement of IC-Conducted Emissions by Employing a Backward-Wave Directional Coupler

Semiconductor technology has progressed over the last few years to the point where modern integrated circuits (ICs) have become the main sources of electromagnetic emissions (EMEs) at the electronic system level. As new generations of technology have become accessible, die dimensions and clock frequencies have increased causing ever-larger switching currents to be drawn from the power supply. Interconnections routed at the chip level, bonding wires and package frames act as antennas that cause parasitic radiation (IC radiated emissions) while radio frequency (RF) currents that superimpose the nominal currents (power and signal currents) at the IC ports drive the unintentional emissions of printed circuit board (PCB) traces (IC-conducted emissions). Recognizing the importance of IC EMEs, equipment manufacturers are beginning to require semiconductor companies to specify the IC emission levels. For these reasons, research activities in the field of characterization techniques of ICs in terms of EMEs are receiving increasing attention, and several methods have been proposed to measure the EMC performances of ICs. A new method to measure IC-conducted EMEs using a backward-wave (BW) directional coupler is presented in this paper. The coupler consists of two-coupled microstrip lines employed to measure the spectrum of the current delivered through IC pins with low invasiveness and high repeatability. The operation principle of the method is described and the design criteria for the coupler are given. The results of experimental tests performed using the coupler are compared with those obtained with a standard technique to prove the effectiveness of the method.