Patent ID: 7359414

Claim:
A semiconductor laser light emitting circuit, comprising: a semiconductor laser diode configured to emit a laser light by modulating a current supplied to the semiconductor laser diode; a light intensity detection circuit configured to detect the laser light and generate a voltage in accordance with an intensity of the laser light; a voltage-current conversion circuit configured to convert a voltage into a current, said voltage-current conversion circuit supplying the current to the semiconductor laser diode; a sample/hold capacitance configured to store electric charge and output a voltage to the voltage/current conversion circuit; a first operational amplifier configured to output a first current charging the sample/hold capacitance until the voltage detected by the light intensity detection circuit is equivalent to a first reference voltage; and a rapidly charging circuit configured to charge the sample/hold capacitance with a second current while comparing the voltage with a second reference voltage less than the first reference voltage when the semiconductor laser diode is turned on; wherein said rapidly charging circuit terminates charging when the voltage is equal to or more than the second reference voltage, and wherein said sample/hold capacitance stores only the first current charge after the rapidly charging circuit terminates charging.