Technique for Controlling Radiated Emissions Due to Common-mode Noise in Electronic Data Processing Systems

Abstract

Most electronic data processing systems are composed of a central control unit and several peripheral units. The units cctnmunicate among each other by inter­ connecting cables. Because of ccirmon-mode noise prop­ agation, the interconnecting cables also become a major source of radiated noise in the higher frequen­ cies, 30 MHz. to 200 MHz. A camton-mode transformer is one technique to help solve the radiated problem, but most of the available theoretical information is based on lower frequency usage below 10 MHz. and for application to conducted emissions problems. There­ fore, a new set of equations must be generated for use in the higher frequency range and how to apply this information toward radiated emissions problems. These ccramon-mode transformers are usually wound on a toroidal core. However, alternate transformer techniques and alternate common-mode filtering methods are tested to compromise physical space limitation, ease of implementation and cost to performance.