North American Philips Corporation

Keith W Malang

Johannes J Verboom

During recording or reading of data in an optical record carrier such as a disc, focus is optimized by adding a focus offset signal to the focus servo error signal. Each frame contains pre-formatted control marks in a servo field, and reference data marks recorded there at a time of data recording. The focus offset signal is optimized by spacing the reference data marks a distance as close as any data marks between which a zero or non-recorded position must be resolved, and taking samples of the optical readout signal as the optical scanning beam passes over or adjacent the reference marks. Four samples are used, taken between the peaks of the signal corresponding to the two reference data marks.

Focus offset optimization for reading optically recorded data

The present invention provides an apparatus and method for commutating a brushless DC motor that prevents backdriving or spiking, due to energy stored in the coils of the bridge of the brushless DC motor, of a DC power supply providing current to the DC motor.

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Colorado Springs, CO, United States of America

Keith W Malang