Patent ID: 7301976

Claim:
A semiconductor laser driving circuit, comprising: a light amount detector configured to detect an amount of light emitted by a laser diode, and output a first voltage corresponding to the amount of light; a frequency determiner configured to determine a frequency determining a time period of a detecting operation to detect differential quantum efficiency of the laser diode; a clock signal generator configured to generate a clock signal based on the frequency; a bias current generator configured to generate a bias current having a direct current and output the bias current to the laser diode to cause the first voltage output by the light amount detector to accord with a predetermined target voltage; a logic controller configured to perform the detecting operation in accordance with the clock signal, output a data code signal indicating a current modulation value derived from the differential quantum efficiency of the laser diode to the pulsed current generator and a control signal specifying a second voltage to the bias current generator, and vary the time period of the detection operation according to the clock signal generated based on the frequency determined by the frequency determiner; and a pulsed current generator configured to generate a pulsed current responsive to the data code signal, and output the pulsed current to the laser diode in response to an external control signal.