| 摘要 |
PURPOSE:To fixedly hold a bias current and a light modulation degree even when using environment conditions such as an ambient temperature or the like fluctuate by detecting a current value made flow to a light emitting element and controlling the bias voltage of the light emitting element and an input signal level. CONSTITUTION:When a voltage between the base and the emitter of a transistor 2 and the value of a resistor 3 fluctuate due to ambient temperature fluctuation or the like and the bias current value to be supplied to the light emitting element 1 increases, the output of a current value detection means 5 and a DC level detection means 6 increases. A difference voltage detection means 8 obtains the difference of the output of the means 6 and a reference voltage 7, addes it to a bias voltage control means 9, decreases the base voltage of the transistor 2 and absorbs the increased portion of a bias current to be supplied to the element 1. Also, when a signal current value to be supplied to the element 1 increases, the output of a peak detection means 10 and a difference voltage detection circuit 11 increases, a difference voltage with the reference voltage 12 is added through the difference voltage detection circuit 13 to a variable gain amplifier 14 and the increased portion of a signal current to be supplied to the element 1 is absorbed. |
