Logarithmic servo error detection for optical disk drive

Details Logarithmic servo error detection for optical disk drive Logarithmic servo error detection for optical disk drive

1989-09-25

1991-03-05

Psitos, Aristotelis M.

Dynamic information storage or retrieval

With servo positioning of transducer assembly over track...

Optical servo system

369 4441, 369124, G11B 700

Patent

active

049982346

ABSTRACT:
An improved focus and tracking error detection circuit for an optical disk servo system. The circuit calculates the logarithm of the signal from each of at least a pair of photodetectors. The difference between two logarithmic signals is then determined to give an error signal. The invention takes advantage of the property of logarithms that the difference between two logarithmic signals is equivalent to the logarithm of the ratio of the two signals. Accordingly, the error signal is a ratio, rather than an absolute difference signal, and is thus insensitive to variations which affect both signals. In addition, the logarithmic circuits inherently minimize variations which affect the photodetectors unequally by performing an AGC-type function. The error signal is inhibited during a write pulse to the laser to prevent saturation of the amplifiers. An automatic, periodic offset adjustment is provided by turning off the laser and varying an offset voltage until the error signal is zero. Peak detectors are used to eliminate the effects of data signals.

REFERENCES:
patent: 4532522 (1985-07-01), Tsunoda
patent: 4547872 (1985-10-01), Henmi
patent: 4556965 (1985-12-01), Tsunoda
patent: 4559622 (1985-12-01), Hazel
patent: 4570251 (1986-02-01), Yokota
patent: 4589103 (1986-05-01), Tajima
patent: 4707648 (1987-11-01), Minami

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