Input/output circuit operated by variable operating voltage

A middle level voltage generating circuit, comprising:

• an operating control unit for controlling an operation according to an operating signal;
• and
• a voltage generating unit for generating a middle level voltage by deducting a source-drain voltage of a MOS transistor from a high level operating voltage,
• wherein the operating control unit is coupled to the voltage generating unit via a current mirror using MOS transistors.

A voltage comparison circuit, comprising:

• an input unit for receiving a reference voltage and an external voltage;
• an amplifying unit including a pair of cross-coupled MOS transistors for amplifying and latching a difference between the reference voltage and the external voltage;
• an output unit for outputting a logic value determined by a result of comparing the reference voltage with the external voltage;
• and
• an operating control MOS transistor located at an outflow path of an operating current of the input unit and amplifying unit for controlling a voltage comparison unit by transferring an operating signal through gates.