An improved ESD cell provides in the worst case 2,000 volts HBM ESD protection using an NMOS transistor in a lightly-doped drain process. An NMOS transistor has its source connected to ground, and its drain connected through a polysilicon resistor to a pad of an integrated circuit....http://www.google.com/patents/US5854504?utm_source=gb-gplus-sharePatent US5854504 - Process tolerant NMOS transistor for electrostatic discharge protection
