| 摘要 |
PURPOSE:To provide stable negative feedback control for a laser diode. CONSTITUTION:A driving circuit for a light emitting element is provided with a first voltage/current converting circuit 14 for an input signal voltage, a laser diode 11 which is supplied with the converted current as driving current, a photodiode 12 which receives light from the laser diode 11 and a current/voltage converting circuit 15 which converts monitor current in the photodiode 12 into a voltage. The circuit is constituted of an exponential conversion circuit 21 which applies exponential characteristics to an input signal, a differential amplifier 22 which provides differential output between the input signal voltage with the exponential characteristics and a monitor voltage which corresponds to the monitor current and a second voltage/current converting circuit 23 which converts the differential output into current. Since the input signal is exponentially converted, the input/output characteristics of the input signal and the characteristics of the light emitting quantity and the monitor voltage of the laser diode 11 are permitted to accord and a negative feedback control system for the laser diode 11 is stabilized. |
