Flexible PCB grounding connections for hybrid systems

The connection of the logic ground to the chassis can influence a number of EMC factors such as emissions, RF immunity, and ESD immunity. Improper connections can turn the chassis into an unintended radiator. Historically, two different grounding strategies have been used. Printed circuit boards are either connected in many locations through low impedance paths, or a single point connection is used with any other connections using high-impedances. Both have been applied successfully in the past, but mixing the two could have unintended consequences. In order to adapt to such environments a designer may desire some flexibility, such as the ability to open or short a particular ground connection without major PCB changes. This paper discusses utilizing components such as 0-ohm resistors in place of direct short connections between logic ground and the chassis. The additional parasitic inductance incurred is quantified relative to direct connections for a number of configurations.