ELECTROSTATIC DISCHARGE PROTECTION CIRCUIT
An NMOS diode-connected in a backward direction between a power supply terminal and a ground terminal is provided as a protective element. Further, a band-pass blocking filter for blocking the passage of a frequency component of an ESD current is provided between the power supply terminal and an internal circuit. Thus, the inflow of an ESD current having a high frequency component into the internal circuit is blocked by the filter. When a potential VDD at the power supply terminal rises, the NMOS used as the protective element breaks down precedently. Thus, the voltage at the power supply terminal is reduced and hence the internal circuit is protected from the ESD current.
1 . An electrostatic discharge protection circuit for protecting an internal circuit from an electrostatic discharge current applied to a power supply terminal of a semiconductor integrated circuit, comprising:
a protective element which is connected between the power supply terminal and a ground terminal and breaks down when a voltage of a constant value or larger is applied; and
a filter which is provided between the power supply terminal and the internal circuit and blocks passage of a frequency component of the electrostatic discharge current.
2 . The electrostatic discharge protection circuit according to claim 1 , where the filter is a band-pass blocking filter or a low-pass filter.
3 . The electrostatic discharge protection circuit according to claim 2 , wherein the filter comprises resistive and capacitive elements.
4 . The electrostatic discharge protection circuit according to claim 2 , wherein the filter comprises an inductive element and a capacitive element.
5 . The electrostatic discharge protection circuit according to claim 3 , wherein the resistive element is constituted of a MOS transistor.
6 . The electrostatic discharge protection circuit according to claim 3 , wherein the capacitive element is constituted of a MOS transistor.
7 . The electrostatic discharge protection circuit according to claim 4 , wherein the capacitive element is constituted of a MOS transistor.
8 . The electrostatic discharge protection circuit according to any of claim 1 , wherein the protective element is constituted of a MOS transistor, a bipolar transistor or a diode.