| 摘要 |
PURPOSE:To prevent the saturation of a receiver circuit and to exactly convert an optical signal to an electric signal by connecting a cathode of a Schottky barrier diode to a collector of a transistor of an emitter ground for constituting an amplifier circuit, and connecting its anode to an input terminal of the amplifier. CONSTITUTION:A current flowing through a feedback resistor 9 usually becomes a small value by only a base current of a transistor TR 2, therefore, a voltage drop caused by the resistor 9 is small, and the potential of an output terminal 11 becomes roughly equal to two folds of a base - emitter voltage VBE of the TR 2. Accordingly, the collector potential of a TR 3 which becomes the cathode potential of a Schottky barrier diode 5 becomes 3VBE being higher by the voltage VBE than the output terminal 11, and the larger an optical input level becomes, the lower the potential drops. In this case, since the anode potential of the diode 5 is the base potential of the TR 2, it becomes 2VBE, and when the collector potential and a forward voltage of the diode 5 are denoted VC and VD, respectively, in a range of VC>2VBE-VD, that is, in a range in which the optical input level is small, the diode 5 does not conduct it is biased in the opposite direction, and accordingly, an optical signal is converted exactly to an electric signal. |
