Abstract: An operational amplifier and a digital signal transfer circuit in which an output voltage does not decrease instantly even if an abrupt change of input signal due to noise causes a high-to-low transition to be superposed on an input signal. The operational amplifier includes a differential pair of transistors with a first transistor having a collector that is grounded and a second transistor having an emitter connected to the emitter of the first transistor; a current mirror circuit with a third transistor having a collector connected to an output node of the differential pair of transistors and a fourth transistor having a base connected to a base of the third transistor; a fifth transistor having a collector connected to an output terminal and a base connected to an output node of the current mirror circuit; and a capacitive element connected between the output node of the current mirror circuit and the output terminal.

Abstract: There is disclosed a two-wire input/output device with an object of avoiding that communication becomes impossible when an abnormality occurs on one of two-wire LAN transmission lines. A pair of buses are separately controlled by driver circuits. An abnormality on a transmission line is detected by an abnormality detecting circuit with data supplied to terminals, and driving of only one of the driver circuits which corresponds to the bus having the abnormality is stopped by an output control circuit. When an abnormality occurs on one of the transmission lines, communication is enabled with a driver circuit corresponding to the transmission line having the abnormality being protected.