| 摘要 |
PURPOSE:To make it possible to increase the frequency of an input signal, which can be transmitted, without decreasing the function of an input protecting circuit, by connecting two or more stages of the input protecting circuits, each comprising a resistor and MOS Tr in series. CONSTITUTION:A conventional input protecting circuit comprises an input protecting resistor R1 and an MOS type Tr Q1. The protecting circuits are connected in series in two stages. When a high voltage V1 is applied to an input terminal IN at a time t1, the potential at a node 2 is increased until a time t3 when the MOS Tr Q1 is turned ON as in a conventional device. Then the potential is decreased. With respect to the fluctuation of the potential V2, a potential V3 at a node 3 increases to a time t4 when an MOS Tr Q2 is turned ON from a time t2 when the gate voltage V2 of the Q2 exceeds an ON voltage VT2. Then the potential V3 decreases. By connecting the two stages of the input protecting circuits in series, the maximum voltage, which is applied in the input circuit, becomes smaller than the case of a conventional one-stage input protecting circuit. |
