Measurements of magnetic field emission of various digital circuit layouts

Abstract

Signal or power to ground traces on a printed circuit board of digital products may act as an efficient loop antenna radiating magnetic field when the length is greater than the wavelength of the highest frequency current. Employment of proper routing of the return current path, filtering and damping resistor are best practices in the design criteria to minimize sources of electromagnetic emission at printed circuit board level. It is important to indicate that the use of guard traces, filtering at supply network of critical component and damping resistor on signal traces can be the options of emission reduction techniques on double sided assemblies as it will reduce the emission level. In this study, three double sided test boards are developed to evaluate the impact of the aforementioned mitigation methods on near magnetic field emission. The magnetic field distributions over each layout are measured in order to reveal the profile of radiation to gain further understanding on the net current distribution on the traces of the digital circuit. It is seen that by proper design of return current path, the magnetic field is reduced by average of 16.5 dB. It can be concluded that proper design of return current path is an important design criteria in the reduction of magnetic emission level. © 2011 Asian Network for Scientific Information.