| 摘要 |
PURPOSE:To enable the implementation of the precise judgement of deterioration of an LD by comparing the signal by the backward output of a laser diode with a reference signal, and providing the first comparison circuit transmitting its comparison result to a bias current drive circuit and the second comparison circuit transmitting its comparison result to a deterioration detecting circuit for LDs. CONSTITUTION:An OP-AMP 21 controls a transistor TR1. And, when the transis tor TR1 saturates by the voltage between both ends of resistors RC1 and RE1 with the increase of bias current IB, the bias current IB stops increasing. An OP-AMP 22 controls a transistor TR2. Resistors RC2, RE2 are so selected that the current Ic flowing into the transistor TR2 becomes considerably lower than the bias current IB, and the transistor TR2 is made not to saturate. The value of the current IC sets the base potential of a transistor TR3. And, by comparing this potential with a reference voltage VREF, the deterioration of an LD 20 is judged. |
