Quadrature signal generator using an adaptive length dual arm co

Details Quadrature signal generator using an adaptive length dual arm co Quadrature signal generator using an adaptive length dual arm co

1998-04-03

2000-10-31

Hindi, Nabil

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4434, G11B 700

Patent

active

061413038

ABSTRACT:
A quadrature signal generator for optical disk storage devices is disclosed comprising a differential phase detector (DPD) implemented as an adaptive length dual arm correlator. A photo diode generates a light beam for irradiating the optical disk during read operations, and a pair of diagonal signals S1 and S2 are generated by adding a pair of respective quadrants of a four-quadrant photodetector which detects the light beam reflected from the disk. The phase offset between the diagonal signals represents the centerline offset of the light beam from the centerline of a data track recorded on the optical disk. A first and second position error signals (PES) are generated by computing the difference and sum between a positive and negative correlation of the diagonal signals S1 and S2, otherwise referred to as a dual arm correlation (DAC) ##EQU1## where .DELTA. is the correlation offset and L is the correlation length. In the present invention, the correlation length L is programmably adjusted relative to the t rack crossing velocity such that the correlator outputs a substantially constant number of correlations per track crossing, which facilitates generating a quadrature signal for use in counting track crossings during seek operations.

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