In this paper, we describe how we modeled EMI noise from the power-pin current of an LSI that has two ports: a power-ground port and a driver output port. We called this the “Linear Equivalent Circuit and Current Source for I/O (LECCS-I/O)” model, and have evaluated it using the measured power current and power-ground impedance of a small-scale IC (74LVC04) under various combinations of loading capacitances and decoupling inductances. Results showed that up to 500 MHz, the LECCS-I/O model was able to predict peak and valley frequencies of the power current spectra within an error of 2. 5 MHz, and where the peak current error was less than 5dB. The application range of the LECCS-I/O model was valid where the shortest data duration was longer than twice the decay time constant of the power current under-damping waveform. © 2004, The Japan Institute of Electronics Packaging. All rights reserved.