Patent ID: 7486711

Claim:
An automatic power control filter circuit which outputs a signal corrected to make a laser drive current for driving a laser light emitting element irradiating an optical disc with a laser beam become a desired value, on the basis of a signal obtained by sampling and holding a light emission monitor signal corresponding to an output current of a photodetector for detecting output power of the laser light emitting element, comprising: an offset adjusting circuit which measures and stores an offset voltage of the signal sampled and held when the laser is prevented from emitting light; a first operation circuit which performs offset correction by calculating the offset voltage stored in the offset adjusting circuit and the signal sampled and held when the laser is allowed to emit light; a second operation circuit which calculates an error by comparing a value corrected by the first operation circuit with a value obtained by multiplying a target value by a desired coefficient in order to perform optimum power control; an integrator which integrates the error calculated by the second operation circuit; and a third operation circuit which adds the output of the integrator to a voltage value obtained by multiplying a desired boost voltage value by the coefficient, and outputs the adding result, wherein the target value and the boost voltage value are respectively multiplied by the coefficient at the same timing as the optimum power control is performed.