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Method for Calibrating Focus Error Signal Sensitivity

IP.com Disclosure Number: IPCOM000121282D
Original Publication Date: 1991-Aug-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 67K

Publishing Venue

IBM

Related People

Iwasaki, H: AUTHOR [+3]

Abstract

Disclosed is a method for calibrating a focus error signal sensitivity using a RF signal amplitude in an optical disk drive. In general, the optical disk drive has a large variation in the focus error signal sensitivity because of the tolerances in the optical adjustment or the optical components. The technique corrects the variation electrically and it is widely applicable to any optical disk drive.

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Method for Calibrating Focus Error Signal Sensitivity

      Disclosed is a method for calibrating a focus error
signal sensitivity using a RF signal amplitude in an optical disk
drive.  In general, the optical disk drive has a large variation in
the focus error signal sensitivity because of the tolerances in the
optical adjustment or the optical components.  The technique corrects
the variation electrically and it is widely applicable to any optical
disk drive.

      The basic concept of this method is explained with Fig. 1 and
Fig. 2.  In the optical disk drive, the RF signal amplitude changes
in accordance with the deviation (distance) from the focal point.
The focal point gives the maximum RF signal amplitude, and the
distance from the focal point causes the RF signal amplitude to be
reduced, as shown in Fig. 1. This relationship between the amplitude
and the distance provides the information of the focus error signal
sensitivity.  The three lines, which show the focus error signal with
different sensitivities, are depicted in Fig. 2. When the offset
voltage Voff is put into the focus error signal, a higher sensitivity
in the focus error signal gives a higher RF signal amplitude, as
shown in Figs. 1 and 2.  The result of the RF amplitude with the
offset voltage makes it possible to calibrate the sensitivity by
changing the electrical gain.

      The block diagram for this method is shown in Fig. 3. A
microprocessor gives the offset voltage into the foc...