| 摘要 |
PURPOSE:To obtain an optical modulation signal having a luminous amount suitable to an external luminous amount by providing a limiter detecting the external luminous amount and changing the current flowing to a light emitting element in response to the change in the external luminous amount. CONSTITUTION:A sensor 9 detects the external luminous amount, outputs a signal in response to the external luminous amount and has an equal spectral sensitivity to that of a luminescent spectral distribution of a light emitting element 1. When a signal from the sensor is received and a signal in response to the signal from the sensor 9 is given to a base of a transistor (TR) 8 by a drive circuit 10 so as to change the resistance value of the TR8. The circuit 10 decreases the resistance value of the TR8 when the external luminous amount is large and increases the resistance value when the external luminous amount is small. A variable current limiter 11 is constituted by the TR8, the sensor 9 and the drive circuit 10. |
