| 摘要 |
PURPOSE:To decrease the effect of an overload input by supervising an optical output by means of a photodiode, obtaining an average value of the optical output and offsetting the fluctuation of the average value of the change in the average picture level so as to stabilize the optical output. CONSTITUTION:A video input signal is fed to a signal current drive circuit 2, its output is added with an output of a bias current drive circuit 2, modulates positively a laser diode LD3 and an optical signal is outputted from the LD3. Then the photodiode PD4 monitors an optical output, the average value of the optical output is calculated by an average value detecting circuit 5, its signal controls a reference value of a comparator amplifier 6, the fluctuation of the average value of the change in the average picture level is offset, and compared and amplified. The circuit 2 is controlled by the output of the amplifier 6, negative feedback is applied to a bias current of the LD3 and the optical output is stabilized. |
