Patent ID: 6919604

Claim:
A silicon controlled rectifier with controlled guard ring structure comprising: a first lightly doped well region of a second conductivity type, a second lightly doped well region of said second conductivity type, and a third lightly doped well region of a first conductivity type in a substrate having said first conductivity type, wherein said third lightly doped well region adjacent to said second lightly doped well region, and said second conductivity type opposites to said first conductivity type; a first node is electrically coupled to a first heavily doped region of said second conductivity type and to a second heavily doped region of said first conductivity type, wherein each said heavily doped region has a concentration is higher than each said lightly doped well region; a switch having a terminal, wherein said terminal is electrically coupled to a fifth heavily doped region; a second node is electrically coupled to said switch, wherein the polarity type of said second node is same as said first node; a third node is electrically coupled to a fourth heavily doped region of said first conductivity type and to a third heavily doped region of said second conductivity type, wherein said polarity type of said third node opposites said first node and said second node; and a control circuit is electrically coupled to said switch.