ANALYSIS OF ESD IMMUNITY OF ELECTRONIC EQUIPMENT BASED ON GROUND POTENTIAL VARIATIONS

This paper proposes a method to predict and control noise voltage caus ed by electrostatic discharge (ESD) to electronic equipment. The relat ionship of grounding system configurations for a typical set of equipm ent to ESD immunity has been derived using a mechanism of ground poten tial variations. The equivalent circuit representing ground elements a s lumped constants enables us to predict the transient ground potentia l differences between PCB (Printed Circuit Board) ground planes connec ted via signal cables and induced noise voltage at the receiving end. The calculation shows that the contribution of ground potential differ ences to noise voltage is comparable to that of the electromagnetic co upling between the discharge current on the enclosure and the circuit loops. The calculation also shows some characteristic results, such as ; the induced noise voltage is remarkably dependent on the unbalance i n ground cable lengths and on the impedance of ground conductors conne cting PCBs, especially when the equipment uses a single-point groundin g system. These characteristics were confirmed by measurements of indu ced ground potential differences, noise voltage and immunity levels. T hus the proposed method is shown to be very effective to analyze the d ependency of grounding conditions on ESD immunity and to improve ESD i mmunity in equipment design.