Input/output buffer

An input/output buffer for receiving an external voltage signal via a resistor and a reference voltage signal, the input/output buffer comprising:

• an input circuit including an n-channel MOS transistor and a comparator connected to the n-channel MOS transistor, the n-channel MOS transistor including:
• a source for receiving the external voltage signal via the resistor;
• a gate connected to the source;
• and
• a drain for receiving reference power, the voltage of which is divided by a divisional resistor;
• wherein the comparator compares the external voltage signal with the reference voltage signal to determine whether the voltage of the external voltage signal is greater than a predetermined threshold voltage from the comparison.

A method for protecting an input/output buffer from a voltage signal that is provided from an external device, wherein the input/output buffer is connected to a high voltage power supply and a low voltage power supply and includes an input/output circuit for transferring data with the external device, the method comprising the steps of:

• decreasing the voltage of the voltage signal to a predetermined voltage with a plurality of MOS transistors, which are connected in series between the high voltage power supply and the low voltage power supply, each MOS transistor having a back gate to generate reference power when the input/output buffer is not supplied with the voltage of the high voltage power supply;
• supplying the input/output circuit with the reference power;
• and
• supplying the back gate of each MOS transistor with voltage that is less than the voltage of the high voltage power supply and greater than the voltage of the low voltage power supply.

An input buffer for receiving an external voltage signal via a resistor and a reference voltage signal, the input buffer comprising:

• an input circuit including an n-channel MOS transistor and a comparator connected to the n-channel MOS transistor, the n-channel MOS transistor including:
• a source for receiving the external voltage signal via the resistor;
• a gate connected to the source;
• and
• a drain for receiving reference power, the voltage of which is divided by a divisional resistor;
• wherein the comparator compares the external voltage signal with the reference voltage signal to determine whether the voltage of the external voltage signal is greater than a predetermined threshold voltage from the comparison.