Patent ID: 8121160

Claim:
A driver circuit to drive a semiconductor laser diode in a differential mode, comprising: a differential unit including a pair of transistors, each transistor coupled with a power supply through a load resistor to configure a differential circuit, said differential unit further including two inputs and two outputs, said two outputs being provided from said pair of transistors, said laser diode being coupled between said two outputs to be provided with a modulation current; a voltage converter configured to provide said power supply to said differential unit; a first detector unit including a pair of resistors to detect a first common mode level of said two outputs of said differential unit, said pair of resistors being connected in series between said two outputs to generate said common mode level from an intermediate node of said pair of resistors; and a second detector unit configured to detect a second common mode level of said two inputs of said differential unit: and a comparing unit configured to compare said first common mode level output from said first detector unit with said second common mode level, to compare said comparison with a reference, and to generate a control signal corresponding to said comparison with said reference, wherein said comparison between said first common mode level and said second common mode level is set equal to said reference by adjusting said power supply by said control signal.