An apparatus includes: a first SCR device having a first source terminal coupled to a signal terminal, a first body terminal coupled to the first source terminal, a first gate terminal coupled to the signal terminal, and a first drain terminal; a second SCR device having a second drain terminal coupled to the first drain terminal, a second gate terminal coupled to a reference voltage terminal; and a second source terminal coupled to the reference voltage terminal. The apparatus also includes: a third SCR device having a third source terminal coupled to the signal terminal, a third gate terminal coupled to the first gate terminal, and a third drain terminal; a first capacitor coupled between the third drain terminal and the second gate terminal; and a second capacitor coupled between the second gate terminal and the reference voltage terminal.