Patent ID: 7492799

Claim:
A laser diode driver comprising: a photodiode for converting the optical output of a laser diode into current; a first monitor voltage generator that generates a first monitor voltage with a magnitude equal to the product of the current flowing through said photodiode and a first coefficient; a first closed-loop circuit that supplies a bias current to the laser diode such that said monitor voltage becomes equal to a first reference voltage corresponding to the first optical output reference value selected for setting the bias current of said laser diodes; a second monitor voltage generator that generates a second monitor voltage with a magnitude equal to the product of the current flowing through the photodiode and a second coefficient; a second closed-loop circuit that supplies a switching current to the laser diode such that the second monitor voltage becomes equal to a second reference voltage corresponding to the second optical output reference value selected for setting the switching current of said light-emitting element; and a switch circuit for connecting the photodiode to the first monitor voltage generator in a first mode and to the second monitor voltage generator in a second mode.