Optical recording/reproducing apparatus having laser diode driver capable of a linear operation responsive to an input signal representative of a laser beam power varying depending on a magneto-optical disk-laser beam spot relative speed

An optical recording/reproducing apparatus having a laser diode and a semiconductor integrated circuit device for driving said laser diode, wherein said semiconductor integrated circuit device comprises:

• a digital-analog converter circuit for converting an input digital signal to an input analog signal, said input digital signal being representative of a laser beam power varying depending on a relative speed between a magneto-optical disk to be mounted on said apparatus and a spot of a laser beam emitted by the laser diode on the optical disk;
• a level shifter circuit connected to receive said input analog signal, said level shifter circuit serving to generate a shift voltage and add said shift voltage to said input analog signal to generate a level-shifted input signal;
• and
• a driver circuit for producing a drive current to be supplied to said laser diode, said driver circuit including a drive current output section for producing said drive current having a non-linear first operation range and a substantially linear second operation range subsequent to said first operation range and connected to receive said level-shifted input signal with a result that an excess output current is produced from said drive current output section for said input digital signal being nil, said driver circuit further including a current suppressing section for supplying to said drive current output section a suppression current for preventing said excess current from being contained in said drive current from said drive current output section.