| 摘要 |
PURPOSE:To enable the protection of a diode when a reverse bias is applied to the diode and the prevention of the disruption of the gate oxide film of the internal circuit due to the voltage drop of the parasitic resistance by connecting MOS transistors having a thick gate oxide film and a large threshold voltage to the input, thereby forming an overvoltage bypass circuit. CONSTITUTION:As the insulating oxide film is thick, or 10000Angstrom or thicker, first and second Pch MOS transistors 21, 22 have a large threshold voltage Vr and are usually OFF in the power supply voltage range of CMOS ICs. A second diode 23 is formed between a Vss terminal 9 and a Vdd terminal 7(10) by a P<+> diffusion layer 5 as the drain of the second Pch MOS transistor 22 and a N<+> diffusion layer 6. Also to this diode 23, a parasitic resistance 24 is generated in series. When an overvoltage which is negative with respect to the Vss terminal 9 is applied to an input terminal 8, the transistor 21 turns on, making a bypass circuit of the current reaching the transistor 21 through the diode 23. The current at the breakdown time of a diode 25 can be made small, preventing the disruption of the diode 25. |
