Method and apparatus for alleviating esd induced emi radiating from i/o

Abstract

A solution to the problem of I/O card faults caused by spurious RF energy induced by ESD related currents in the vicinity of an aperture in a chassis is to reduce the efficiency of the radiating antenna created by the aperture and decouple any remaining spurious RF energy from any would-be receiving antenna in the I/O card. A conductive boot covers the I/O cable as it emerges from the chassis. The boot is physically attached and AC coupled (as well as probably ohmically connected) to the chassis at one end and tapers down to a small aperture at a distal end to permit egress of the I/O cable. The aperture at the distal end is considerable smaller than the aperture at the chassis, which is no longer visible to ESD induced currents anyway, since its edge has been replaced by the surface of the boot. The smaller aperture is a less efficient antenna at the frequencies of interest and it is now further removed from components that might act as receiving antennae. The intervening length of the conductive boot also acts as a filter to obstruct passage of the reduced amount of spurious RF energy that still does radiate from the small aperture toward the I/O card. The boot may be of metal, or of plastic that has been coated with a suitable conductive paint on its inner surface.