| 摘要 |
PURPOSE:To operate an automatic chopping circuit correctly, by giving a hysteresis characteristic to a circuit where the comparison with the reference value of an automatic chopping circuit is made, and keeping the light source in a chopped state even if the input level of the comparison circuit is changed after being chopped once. CONSTITUTION:An LD(semiconductor laser)2 is driven with a driving circuit 1 according to an input signal. Further, it is monitored by a photodiode 3 and an LD level is detected by a peak detecting circuit 5. This level is fed to an APC (automatic output controlling circuit)6 and feedback is given to the circuit 1. On the other hand, the peak value level is inputted to a comparator 8 having hysteresis to be compared with the reference value, and if the peak level is low, the input signal is cut off with a chopping gate 9 and deteriorated LDs are chopped. After that, although the input to the comparator 8 is increased up to a pseudo output level by a protection circuit 10, since the upper-limit threshold level is set higher than the pseudo output level, the output of the comparator 8 is not changed, allowing to complete the automatic chopping of an LD2 smoothly. |
