| 摘要 |
PURPOSE:To make a filter circuit small in size and low in cost by providing the first MOS diode, which forms an inversion layer consisting of a minority carrier when the forming state of a depletion layer formed in a semiconductor substrate continues for a prescribed time, and the second gate electrode which is adjacent to the first MOS diode on the semiconductor substrate and using the delay of the forming time of the inversion layer due to the MOS diode to eliminate the noise or the like. CONSTITUTION:A surge voltage Vin is applied to a gate electrode 7a of the first MOS diode 7 through an input protecting circuit 5, etc. as a voltage Vin'. At this time, a part lower than a power source voltage like the voltage Vin' of the surge Vin is clamped at a power source voltage Vdd by the input protecting circuit 5, and a negative voltage part lower than an earth potential is clamped at an earth potential Vss, and the surge voltage is applied to the gate electrode 7a of the first MOS diode 7. In this case, the depletion layer is formed under the gate electrode 7a when the voltage Vin' is in the high level, but the inversion layer of a minority carrier is not formed because the time width of formation of the depletion layer is short. Thus, even if the noise such as the surge voltage is applied to an input terminal 15, it does not appear in the output and is eliminated. |
