Patent ID: 7582937

Claim:
An ESD protection circuit, connected to an input pad, comprising: a substrate of a first conductivity type; a diode device, formed in the substrate and having a first end of the first conductivity type and a second end of a second conductivity type, wherein the first end is connected to the input pad; a first snapback device, formed in the substrate and comprising a first doped region of the second conductivity type, a first gate and a second doped region of the second conductivity type, wherein the first doped region is coupled to the second end, the first gate is coupled to the second doped region; a ring structure, formed in the substrate and comprising a third doped region of the second conductivity type located between the diode device and the second doped region; a second snapback device, formed in the substrate and comprising the second doped region, a second gate and the third doped region, wherein the second gate is coupled to the second doped region; and a control circuit, connected to the third doped region for providing an operational voltage to the second snapback device in a normal operation.