Device for scanning optical discs using phase detection in a system with significant objective lens movement

摘要

Tracking error signal in an optical read/write device, such as a CD ROM, are fine tuned for deviations in the positions of the lens structure normal to the recorded medium to provide more precise tracking control. Track error signal is developed by means of DPD-TE circuitry, using for example, signals from a four quadrant photodetector. Selected pairs of the signals from the photodetector are summed and the sums are differenced to develop an intermediate signal. The intermediate signal is amplified with a gain proportional the reciprocal of the intensity of light received by the photodetector, and thereafter combined with the track error signal to provide a corrected track error signal.