CURRENT GENERATING CIRCUIT AND METHOD

摘要

A laser drive circuit for generating a level drive current corresponding to any one of three or more laser powers comprises first to third signal producing circuits (110, 120, 130) and a signal synthesizing circuit (140). The first signal producing circuit (110) measures the present output level of a semiconductor laser (50) with reference to a light reception signal (Vp) generated by a light receiving element (51) and generates a first drive current (Ib) corresponding to a bias power. The second signal producing circuit (120) produces a differential current (Ibe) smaller by the first drive current from a second drive current corresponding to an erase power. The third signal producing circuit (130) produces a proportional current (Ibw) by multiplying the differential current (Ibe) by a predetermined factor. This factor is determined by (light power bias power)/(erase power bias power). The signal synthesizing circuit (140) combines the currents (Ib, Ibe, Ibw) according to the operation mode to generate a drive current (Id) of the semiconductor laser (50).