In a multiple input ESD protection structure, the inputs are isolated from
the substrate by highly doped regions of opposite polarity to the input
regions. Dual polarity is achieved by providing a symmetrical structure
with n+ and p+ regions forming each dual polarity input. The inputs are
formed in a p-well which, in turn, is formed in a n-well. Each dual
polarity input is isolated by a PBL under the p-well, and a NISO
underneath the n-well. An isolation ring separates and surrounds the
inputs. The isolation ring comprises a p+ ring or a p+ region, n+ region,
and p+ region formed into adjacent rings.