| 摘要 |
<p>An input circuit capable of judging a three-valued external signal without requiring troublesome voltage regulation while reducing power consumption when on standby. The input circuit comprises four resistor elements (3-6) connected in series between different fixed potentials, an input terminal (2) connected with the junction of two resistor elements (4, 5), a switching transistor (7) being turned on/off by the voltage at the junction of two resistor elements (5, 6), a current supply circuit (8) outputting a supply current when the switching transistor (7) is turned on but not outputting the supply current when it is turned off, a constant voltage generation circuit (9) outputting a constant voltage by receiving the supply current, a constant voltage output buffer circuit (10) for bringing the output into high impedance state when the switching transistor (7) is turned off and outputting a predetermined voltage to the junction of two resistor elements (3, 4) by receiving the constant voltage when the switching transistor (7) is turned on, a switching transistor (11) being turned on/off by the voltage across the resistor element (4), and a combination circuit (12) outputting a judgment signal based on the combination of on/off of two switching transistors (7, 11).</p> |
