Patent ID: 7449750

Claim:
A protection device to protect an internal circuit comprising: a first power source line; a second power source line; a signal line coupled to said internal circuit; a bipolar transistor having its current path between said second power source line and said signal line and its control node coupled to said first power source line; a first parasitic diode coupled between said first power source line and said signal line and having a first breakdown voltage; and a second parasitic diode coupled between said first and second power source line and having a second breakdown voltage lower than said first breakdown voltage; wherein said first parasitic diode has a first diffusion region of a first conductivity type formed over a semiconductor well of a second conductivity type, wherein said second parasitic diode has a second diffusion region of said first conductivity type formed over said semiconductor well and a third diffusion region of said second conductivity type formed between said second diffusion region and said semiconductor well, wherein impurity concentration of said second diffusion region is larger than that of said semiconductor well.