I/o circuit of semiconductor integrated device

Abstract

In addition to first and second control circuits, an I/O circuit has a first MOS transistor which includes a gate electrode connected to a first node to which a first signal is input from at least one of a first power supply and an internal circuit, a first electrode connected to the first power supply, and a second electrode connected to a second node. A second MOS transistor includes a gate electrode connected to a third node, a first electrode, a second electrode connected to a second node, and a substrate connected to a fourth node which is in a floating state. A third MOS transistor includes a gate electrode connected to the third node, a first electrode, a second electrode, and a substrate connected to the fourth node. A fourth MOS transistor includes a gate electrode connected to a fifth node, a first electrode connected to a sixth node to which a signal is either input from an external circuit or from which a signal is output to the external circuit, a second electrode, and a substrate connected to the fourth node. To prevent excess current flow to an output pad, one of the first and second electrodes of the second, third or fourth MOS transistors is in a floating state and is isolated from the fourth node.