Dynamic information storage or retrieval – With servo positioning of transducer assembly over track... – Optical servo system
Reexamination Certificate
2000-06-06
2001-10-16
Edun, Muhammad (Department: 2651)
Dynamic information storage or retrieval
With servo positioning of transducer assembly over track...
Optical servo system
C369S044110, C369S124010
Reexamination Certificate
active
06304530
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to an optical data reproduction apparatus for optically reading data signals recorded onto recording media such as CDs and DVDs and more particularly to wiring patterns or terminal arrangement patterns connected to a light-receiving element.
Optical data reproduction apparatus have light-receiving elements for not only optically reading data signals recorded onto recording media but also detecting tracking and focusing errors. Some light-receiving element has light-receiving cells for detecting a tracking error with three beams, for example, in addition to a known quadrifid light-receiving cell, these light-receiving cells being disposed on one chip. The light-receiving element formed of one chip also has output terminals for leading the signals detected by the respective light-receiving cells to an external circuit, a power supply terminal for introducing a power supply to the light-receiving element, a ground terminal and any other proper terminal. An arrangement of these terminals is determined on the part of manufacturers of light-receiving elements. When the light-receiving element is incorporated into such an optical data reproduction apparatus, it has been attempted to make the order of wiring patterns on a flexible printed board for connection to the external circuit or the order of arranging pins of output connectors correspond to the arrangement of terminals of the light-receiving element.
FIG. 5
shows examples of wiring patterns in a related optical data reproduction apparatus. In
FIG. 5
, an optical pickup
40
as the optical data reproduction apparatus is connected to the front end IC
52
of a system board
50
via a wiring pattern
46
formed on a flexible printed board. The optical pickup
40
has a light-receiving element
42
. The light-receiving element
42
has terminals of E, Vcc, Vc, GND and F in this order on one side and terminals of A, RF, B, C, D, F, E and GND in this order on the other. The light-receiving element
42
is packaged on a wiring board in the optical pickup
40
and connected to connectors for use in external connection via a wiring pattern
44
on the board. The wiring pattern
44
has a jumper line
45
and any other alternative pattern, whereby the connectors are arranged in the order of A, RF, B, C, D, F, E and GND.
A system board
50
also has connectors and a wiring pattern
48
extending from the connectors up to the front end IC
52
. An arrangement of connectors on the side of the system board
50
is set conformable to that of connectors on the side of the optical pickup
40
. The wiring pattern
46
such as the flexible printed board is used to electrically connect the connectors on the side of the optical pickup
40
and those on the side of the system board
50
.
The terminals A, B, C and D of the light-receiving element
42
in the example shown in
FIG. 5
are coupled to a quadrifid light receiving cell similar in shape to a quadrifid light-receiving cell
24
of FIG.
2
. Output signals from these terminals are used to generate a phase-difference type tracking error signal. A look at the connectors and the wiring patterns shown in
FIG. 5
reveals that B, C and D out of the signal lines from the quadrifid light-receiving cell are disposed side by side in this order. In other words, crosstalks are easily produced among the signal lines B, C and D; the drawback to the arrangement above is that a precise tracking error signal is hardly easy to obtain from such a phase-difference system.
A general description will now be given of the generation of a tracking error signal of the phase-difference system together with the reason for the difficulty of obtaining a precise tracking error signal because of crosstalks with reference to
FIGS. 6
to
8
.
In
FIG. 6
, reference numeral
54
denotes a quadrifid light-receiving cell. The light-receiving surface of the quadrifid light-receiving cell
54
is divided into four light-receiving cells a, b, c and d. The light-receiving cells a and d, and b and c are orientated in the direction of a track, T, which is equal to the x-axis direction, whereas the light-receiving cells a and b, and c and d are orientated in a direction perpendicular to the direction of the track, which is equal to the y-axis direction. The two light-receiving cells a and c are positioned diagonally, whereas the two light-receiving cells b and d are also positioned diagonally. Outputs of the two diagonal light-receiving cells a and c are added up by an adder
56
as a set so as to obtain an added signal
66
. Outputs of the two diagonal light-receiving cells b and d are also added up by an adder
57
as a set so as to obtain an added signal
68
.
The added signal
66
is subjected to waveform equalization in a waveform equalizer
58
and also waveform shaping in a waveform shaper
60
before being inputted to a phase comparator
62
. Similarly, the added signal
68
is subjected to waveform equalization in a waveform equalizer
59
and also waveform shaping in a waveform shaper
61
before being inputted to the phase comparator
62
. In the phase comparator
62
, the phases of two sets of outputs thus supplied are compared, so that a pulse signal having width equal to the phase difference between the two sets of outputs. The pulse signal is integrated by a low-pass filter
64
and outputted as a tracking error signal.
The principle of detection by the tracking error detector in the phase difference system will now be described.
FIG. 7
refers to a case where a beam spot
70
is moving above the center of the track TC. While the beam spot
70
is related to the pit
72
of a recording medium as shown in
FIG. 7A
, the dark areas
74
and
76
produced from the light diffraction by the pit
72
within a far field are produced in areas equal to the four light-receiving cells a, b, c and d as shown in FIG.
7
B. Therefore, as shown in
FIG. 7C
, output signal waveforms of the light-receiving cells a, b, c and d are equalized and so are output waveform
66
of the adder
56
and the output waveform
68
of the adder
57
as shown in FIG.
7
D. In this state, the phase difference &Dgr;t becomes zero. Here, the variable t is defined by xlv (x: displacement of the beam spot in the track direction T; v: velocity of the beam spot in the track direction T).
Further,
FIG. 8A
refers to a case where the center of the beam spot SC on the recording medium has been displaced by &Dgr;y in the y-axis direction from the center of the track TC. While the beam spot
70
is related to the pit
72
as shown in
FIG. 8A
, the dark areas
74
and
76
within the far field appear as shown in FIG.
8
B and there is produced differences in the dark areas produced in the four light-receiving cells a, b, c and d, whereby a phase difference of &Dgr;t
1
is produced between the output signals of the light-receiving cells a and c and the output signals of the receiving cells b and d, and between the added signals of (a+c) and the added signals of (b+d) as shown in
FIGS. 8C and 8D
. Consequently, a pulse signal having a pulse width of &Dgr;t
1
is produced from the phase comparator
62
. This pulse signal is integrated by the low-pass filter
64
to become an output value corresponding to the amount of displacement &Dgr;y, so that tracking control is performed according to the output value.
In accordance with the tracking error detection of the phase difference system as set forth above, in the case of CD-ROM and DVD-ROM drives at from single speed to double speed, for example, output signal frequencies of the light-receiving cells a, b, c and d become considerably high, namely, ranging from 4.5 MHz to 50 several MHz. Consequently, in a case where terminals and wiring patterns B, C and D for passing signals different in phase therethrough are set adjacent to one another as in the related optical data reproduction apparatus shown in
FIG. 5
, the signal is allowed to leak out of one adjoining wiring pattern and superposed on the signal in the other wiring pattern. Then a so-called cro
Edun Muhammad
Kabushiki Kaisha Sankyo Seiki Seisakusho
Sughrue Mion Zinn Macpeak & Seas, PLLC
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