| 摘要 |
PURPOSE:To prevent breakdown due to an abnormal high voltage applied to an input terminal, by connecting a protection transistor having a gate insulating film thicker than that of a transistor to be protected, to the input side of the transistor to be protected. CONSTITUTION:When an abnormal pulse is applied to an external terminal 1, the pulse reaches a connection point P1 after it is slightly delayed by a diffusion resistor R1 and a diode D1 and a capacitor C1 connected to the resistor, and makes the state of a protection transistor Ts turn on. In this case, the transistor Ts is not broken down by the voltage at the point P1 as it has a thick gate insulating film. Then the voltage at P1 reaches P2 with a delay time due to a diffusion resistor R2 and a capacitor C2. When it reaches at P2, the transistor Ts has already turned on, so that this voltage is absorbed by a capacitor Cs of large capacity connected between drain and ground, and is prevented from applying to the transistor T1 to be protected. |
