The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Mar. 05, 1991
Filed:
Sep. 25, 1989
Theodore D Rees, Mountain View, CA (US);
Ian Turner, Sunnyvale, CA (US);
William L Harvey, Mountain View, CA (US);
Other;
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.