| 摘要 |
PURPOSE:To stabilize the amplitude of a light signal regardless of variation in differentiation efficiency, by detecing variation in the amplitude of the light signal, amplifying an input signal with a gain corresponding to said detection result and obtaining a modulated current with varied amplitude, and supplying this modulated current to an LD. CONSTITUTION:An output voltae is supplied to an active filter 28 and a control current ICNT corresponding to the output voltage of an OP26 is supplied from the active filter 28 to the AGC circuit 33 of a modulating circuit 31. This AGC circuit 33 is supplied with an input signal IN as a transmitted signal to impose current amplification on the input signal IN with a gain corresponding to the current value of the control current ICNT. The amplification output of the AGC circuit 33, i.e. signal obtained by varying the amplitude of the input signal IN is supplied to the base of a transistor (TR) 15 as a base current for modulation control. Then, the collector current of the TR15, i.e. modulated current is varied according to the base current. |
