Control circuit of light emitting element

摘要

To make compatible low consumption power formation of a control circuit of a light emitting element and high frequency formation of operational frequency band and constituting a variety of usable combination elements of light emitting elements and light receiving elements, bias current is provided to a current mirror for dividing monitor current of a photodiode PD1 by a current source to thereby compensate drive function of a post stage in driving thereof by low current. Reference voltage of a current-voltage conversion portion 4 is set in accordance with an input range of an operational amplifier 51 of a gain adjusting portion 5 at a post stage and input to the operational amplifier 51 is fitted to an input range optimizing amplifying function. A variation of frequency band or phase is restrained by adjusting gain by using a differential amplifier 53 of the gain adjusting portion 5. There are provided switching circuits SW1 and SW2 for selectively supplying monitor current from two photodiodes to respective APC loops of laser diodes LD1 and LD2 to thereby deal with a 2LD-1PD element and two of 1LD-1PD elements.