Input circuit

Abstract

An input circuit is provided that can identify three states of an external signal without complicated voltage adjustment and that can reduce the power consumption in a standby state. The input circuit includes: four resistor elements serially provided between different fixed potentials; an input terminal connected to a connection point of two of the resistor elements; a switching transistor controlled to turn on and off by a voltage at a connection point of two of the resistor elements; a current supplying circuit outputting a supply current when the switching transistor is on and not outputting the supply current when the switching transistor is off; a constant voltage generating circuit receiving the supply current to output a constant voltage; a constant voltage output buffering circuit that brings its output into a high-impedance state when the switching transistor is off, and that receives the constant voltage to output a prescribed voltage to a connection point of two of the resistor elements when the switching transistor is on; a switching transistor controlled to turn on and off by a voltage between opposing ends of the resistor element; and a combinational circuit outputting identify signals based on combinations of on and off states of the two switching transistors.