Patent ID: 7693196

Claim:
A semiconductor laser driving unit controlling driving of a semiconductor laser by performing automatic power control to automatically control a current to be supplied to the semiconductor laser so that a desired amount of light emission is obtained, the semiconductor laser driving unit comprising: a bias current generator circuit part configured to generate a predetermined bias current lower than an oscillation threshold current of the semiconductor laser and constantly output the generated bias current to the semiconductor laser; a switching current generator circuit part configured to generate a first current for causing the semiconductor laser to emit light, and to output the generated first current to the semiconductor laser in accordance with a control signal input to the switching current generator circuit part; an initialization circuit part configured to perform a predetermined initialization operation to detect a light emission characteristic of the semiconductor laser, and to cause the switching current generator circuit part to generate a second current of a value obtained from the detected light emission characteristic; and an offset current setting circuit part configured to cause the switching current generator circuit part to generate the first current in which a set offset current is added to the second current, wherein the bias current generator circuit part detects an amount of light emission of the semiconductor laser, and generates and outputs the bias current so that the amount of light emission of the semiconductor laser produced by a sum of the generated bias current and the first current output from the switching current generator circuit part is a predetermined value, and wherein the offset current is externally set in the offset current setting circuit part.