| 摘要 |
In an optical disc drive, a laser light source emits a laser beam having an intensity changeable with the amount of drive current supplied. A first photodetector receives the laser beam reflected from an optical disc, thereby generating a readout signal. A second photodetector receives the laser beam, generates an electric signal representing the power of the laser beam received, and outputs the electric signal as a light quantity detection signal. A feedback control loop compares the level of the light quantity detection signal with a predetermined target value and regulates the drive current such that the level of the light quantity detection signal approaches the target value. In reading data from the optical disc, the target value is changed so as to compensate for a variation of the sensitivity of the second photodetector, thereby controlling the power of the laser beam emitted from the laser light source.
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