Estimation of Current from Near-Field Measurement

Knowledge of high-frequency currents in the chip and chip-package are necessary for EMI analysis and prediction, though measurement of these currents may be difficult to obtain in many cases. One possibility is to estimate currents from near-field scan data. In this paper, measurements were made of the magnetic field over a simple circuit and a chip package. The current flowing in the circuit and the chip lead frame was estimated from the compensated near-field data and compared with measurements made directly on the pins. Estimation was performed both with and without structural information of the lead frame. The susceptibility of estimated currents to measurement errors was analyzed. Results show this technique can be a powerful tool for analyzing high frequency chip currents.