 The drain of the ggNMOS is connected to the I/O pad under protection.A parasitic NPN bipolar junction transistor (BJT) is thus formed with the drain (n-type) acting as the collector, the base/source combination (n-type) as the emitter, and the substrate (p-type) as the base.As is explained below, a key element to the operation of the ggNMOS is the parasitic resistance present between the emitter and base terminals of the parasitic npn BJT.