Input protection circuit for semiconductor integrated circuit device

Claim 1

An input protection circuit formed in a chip in which a semiconductor integrated circuit device is formed, comprising: a semiconductor body of a first conductivity type; a first semiconductor region of a second conductivity type formed in a surface area of said semiconductor body and connected to a first wiring to which a first potential is applied, said first semiconductor region serving as a collector region of a first input protection bipolar transistor; a second semiconductor region of the second conductivity type formed in the surface area of the semiconductor body, separately from said first semiconductor region, and connected to a second wiring to which a second potential is applied, said second potential being different from said first potential, the second semiconductor region serving as a collector region of a second input protection bipolar transistor; and a third semiconductor region of the second conductivity type connected to a signal input pad and formed in the surface area of said semiconductor body, separately from said first and second semiconductor body regions, so as to be located between said first and second semiconductor regions, said third semiconductor region serving as an emitter region common to said first and second bipolar transistors, a portion of said semiconductor body which lies between said first and third semiconductor regions serving as a base region of said first bipolar transistor, a portion of said semiconductor body which lies between said second and third semiconductor regions serving as a base region of said second bipolar transistor, base potentials applied to said first and second bipolar transistors being equal to a potential applied to said semiconductor body.