| 摘要 |
A laser diode 11 performs switching operation with a high speed in response to a digital-modulated electric signal inputted in differential input terminals 10a and 10b. At this time, a voltage detecting portion 14 detects a terminal voltage of the laser diode 11. A peak detecting portion 15 detects a peak value of output of the voltage detecting portion 14. A current control portion 16 controls a drive current of the laser diode 11 in accordance with output of the peak detecting portion 15. The current control portion 16 includes a reference voltage generating portion 16a generating reference voltage, and an error detecting portion 16b detecting an error between the reference voltage generated by the reference voltage generating portion 16a and the output of the peak detecting portion 15. In accordance with an output signal of the error detecting portion 16b, the drive current of the laser diode 11 is controlled. In this way, it is possible to stabilize light output of the laser diode 11 without using a photodiode for monitoring, and thereby to obtain a light emitting device drive circuit with high reliability at low costs. Further, since the current control portion 16 is divided into the reference voltage generating portion and the error detecting portion, required is to change only the reference voltage generating portion 16a when a light emitting device of a different type is used. Further, the reference voltage generating portion 16a generates reference voltage which follows changes of the terminal voltage of the laser diode 11 with respect to temperature changes under the conditions that light output of the laser diode 11 is kept constant, and thereby it is possible to obtain constant light output in a wide range of temperatures. <IMAGE> |
