| 摘要 |
Electrostatic protection is performed without affecting the transfer of a normal input signal. An electrostatic protection circuit includes an input terminal, aground terminal, an Nch transistor whose gate and source are coupled to the input terminal and the ground terminal, respectively, and an electrostatic protection element connected to a drain and coupled to the gate of the Nch transistor. A discharge current flows into the ground terminal through the electrostatic protection element when an electrostatic discharge is applied to the input terminal. The discharge current flows through a drain-source parasitic resistance in the Nch transistor because the Nch transistor is turned on caused by an applied voltage of the electrostatic discharge to the gate. This leads to an increase in an electric potential at Point B (channel potential) of the Nch transistor. Then, a maximum value of a voltage applied to a gate insulating film reduces lower than the voltage caused by electrostatic discharge.
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