Patent ID: 7233466

Claim:
An input protection circuit for protecting an internal circuit from an excessive signal originated from static electricity, comprising: input signal conversion section which has at least an input resistor, a feedback resistor and an operational amplifier having an input, and converts a potential of an input signal input from an input terminal in such a way that said potential of said input signal lies in an input range or a range of a signal potential inputtable to said internal circuit; first protection section, connected to a virtual ground node between said input resistor and said operational amplifier and a first power-supply potential, for protecting said internal circuit by allowing an input current of said input signal to flow toward said first power-supply potential when said potential of said input signal excessively exceeds said input range on the said first power-supply potential side; and second protection section, connected to an arbitrary point between said input terminal and said input resistor and a second power-supply potential, for protecting said internal circuit by allowing said input current to flow toward said input terminal from said second power-supply potential when said potential of said input signal excessively exceeds said input range on the second power-supply potential side, wherein the first protection section is connected to a first node that also connects the input of the operational amplifier, the feedback resistor and the input resistor.