Interference in digital circuits and some techniques for EMI suppression

Abstract

Noise generated by a logic gate in a simple digital circuit is considered in this paper. Appropriate circuit design and usage of electromagnetic interference (EMI) components are methods intended to suppress noise radiation by reducing/eliminating the noise flowing through conductive lines. Because of that, commercially available ferrite component is tested in a simple digital circuits realized on a PCB. Different configurations of digital circuit are analyzed: circuit printed on single-sided and double-sided board, with and without EMI suppressors placed on the conductive line at the input of circuit. With attention to the current distribution, the mounting position is observed for ferrite where it has significant noise effect. The measurements are obtained by digital oscilloscope TDS 2024B in the frequency range up to 200 MHz, and CTM030 Scan EM-EC magnetic probe with frequency response 2 MHz - 2 GHz which observe the waveform of the current. The measured data showed variations in noise suppressing effect depending on the design of circuit and by adding EMI suppressors.