Output circuit with high output voltage protection means

摘要

In the case where an external signal line is driven by a circuit other than an output circuit with a voltage higher than an on-chip power-source voltage, if an output transistor is activated in the output state immediately after the driving of the external signal line by the above other circuit was cancelled, a voltage equal to or higher than the breakdown voltage of an oxide film of a transistor composing the output circuit is applied thereto. To prevent this, there is provided a voltage detecting means for detecting a voltage value of the above external signal line being higher than a value in the vicinity of the internal power-source voltage and generating a detection signal, which inhibits the activation of the output transistor. Consequently, in the output circuit of an LSI fabricated using submicron design rules, the application of a voltage equal to or higher than the breakdown voltage of an oxide film of each of the transistors composing the output circuit is prevented, resulting in increased reliability of the output circuit.