| 摘要 |
<p>PURPOSE: To obtain an optical output monitor circuit which can be used in a wide dynamic range, by installing a monitor output selection circuit which selects one output, as the monitor output, out of the outputs of a plurality of amplifiers having different gains. CONSTITUTION: A voltage obtained by electrically converting a monitor light in an electricity-light conversion circuit is amplified. A monitor output selection circuit 4 selects and outputs one output, as the monitor output, out of the outputs of a plurality of amplifiers 3a-3c having different gains. For example, when the gains of amplifiers 3a, 3b, and 3c are Ga, Gb, and Gc, respectively, a relation holds as Ga>Gb>Gc. The current Ip of a photodiode 1 for which the outputs of Va, Vb, and Vc of the amplifier 3a, 3b, and 3c become equal to a set voltage Vth is Ia, Ib, and Ic, respectively. In this case, the monitor output selection circuit 4 selects and outputs the voltage as follows in the relation of Vth to the outputs Va, Vb, and Vc. Va is selected for Ip<=Ia, Vb is selected for Ia<Ip<Ib, and Vc is selected for Ip>=Ib.</p> |
