JP2514427Y2 - Tracking error signal generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a tracking error signal generating device for generating a tracking error signal corresponding to a positional deviation between an information track and an optical spot in an optical information writing or reading device. Is.

[Technical background and problems of the invention]

In an optical information writing / reading device, a tracking servo is added in order to correct the positional deviation (tracking error) between the optical system and the orthogonal direction of the track on the disk.

As a conventional tracking servo control device, there is one shown in FIG.

That is, in FIG. 7, the irradiation light flux from the laser light source 1 enters the recording surface of the recording disk 6 through the lens 2, the beam splitter 3, the quarter-wave plate 4 and the objective lens 5. The incident laser light is converged by the objective lens 5,
It becomes a light spot as a minute information detection point on the recording surface. The reflected light (or transmitted light) from the disk 6 due to this light spot is separated by the beam splitter 3 and is applied to each light receiving surface of the pair of photoelectric conversion elements 9a and 9b. The outputs of both photoelectric conversion elements 9a and 9b are applied to a differential amplifier 12 via amplifiers 10a and 10b and LPFs (low pass filters) 11a and 11b, respectively. This difference output is input to the drive amplifier 14 via the equalizer 13 and becomes a drive signal of the drive coil 8 for moving the objective lens 5 in the direction orthogonal to the track.

As shown in FIG. 8, a pair of photoelectric conversion elements 9a and 9b are attached such that their light-receiving surfaces are divided by a single dividing line 9c, and the dividing line 9c is attached in the recording track tangential direction (arrow Y).
It is shown in. ), And these elements 9a, 9b are provided symmetrically with respect to the optical axis 7'of the reflected light of the light spot. In addition, 7 is an incident light optical axis, and
Indicates a spindle motor for rotating the disk.

FIG. 9 shows a photoelectric conversion element when a light spot S is incident on a pit P which constitutes a recording track on the disk 6.
The light intensity distributions on 9a and 9b and their outputs are schematically shown.

That is, (b) in FIG. 9 (a) shows a state in which the light spot S is located at the center with respect to the pit P, and at this time, the pair of photoelectric conversion elements 9a and 9b has (b) As shown by the diagonal lines in (b), a substantially symmetrical light irradiation can be obtained. As a result,
The outputs of the photoelectric conversion elements 9a and 9b are symmetrical as shown in (c) (b), the output of the differential amplifier 12 becomes substantially zero, and the tracking servo output becomes substantially zero.

On the other hand, (a) or (c) of FIG.
The light spots S are respectively displaced upward or downward on the paper surface with respect to the pits P, and the photoelectric conversion elements 9a and 9a are shown.
b is subjected to asymmetric light irradiation as shown in (a) or (c) of (b), and has an output as shown in (a) or (c) of (c). As a result, the differential amplifier
Positive or negative output is generated from 12, and the drive coil 8 drives the objective lens 5 to control the light beam spot S to be positioned at the center of the pit P.

In the above description, the case where the shape of the pit P is an ideal shape conforming to the standard is taken as an example. However, in an actual disc, the pit shape such as the pit depth and the pit width is within the allowable error range for each disc. It's different. Therefore, it is known that the asymmetry of the light intensity distribution on the photoelectric conversion elements 9a and 9b changes from disk to disk due to the change in the pit shape. Therefore, in the conventional tracking error signal generation device, when the pit shape of the disc changes, even if the tracking shift amount is the same, the magnitude of the tracking error signal corresponding to this changes. In addition, the optimum value of the tracking servo gain changes, and there is a drawback that stable tracking servo cannot be realized.

[Purpose of device]

The present invention has been made to eliminate the above-mentioned drawbacks, and is a device for generating a tracking error signal capable of always performing optimum and stable tracking servo even if the asymmetry changes due to a change in the pit shape of a disc. Is to provide.

[Outline of device]

In order to achieve the above-mentioned object, in the present invention, in addition to a set of photoelectric conversion elements dividedly installed at positions corresponding to the information track in a substantially orthogonal direction, the information track is divided into positions corresponding to a substantially parallel direction in the information track. It is characterized by including a set of installed photoelectric conversion elements, and controlling the amplitude of the asymmetric output of the former photoelectric conversion element by the asymmetric output of the latter photoelectric conversion element.

[Example of device]

The present invention will be described below based on the embodiment shown in FIGS.

FIG. 1 shows only the tracking error signal generating device portion of the present invention in which the optical system and the tracking drive coil corresponding to the reference numerals 1 to 8 in FIG. 7 are deleted. In the figure, the photoelectric conversion element for receiving the light spot S is provided on the recording surface at a position corresponding to a substantially parallel direction of the information track and at a position corresponding to a substantially orthogonal direction of the information track. Split line 9D
Is divided into four parts.

That is, the group of 9E, 9H and 9F, 9G is divided and installed at the position corresponding to the information track substantially orthogonal direction by the dividing line 9C, and the group of 9E, 9F and 9H, 9G is divided by the dividing line 9D. Are installed at positions corresponding to the direction substantially parallel to.

Of these, the outputs of the former groups 9E, 9H and 9F, 9G are applied to the adders 10c and 10d, respectively, and the outputs thereof are applied to the low-pass filters 11a and 11b, and the difference output is derived by the differential amplifier 12. Is configured. The output from the differential amplifier 12 is the same tracking error signal as the output from the differential amplifier 12 of the conventional example shown in FIG. 3, and is input to the variable gain amplifier 20.

On the other hand, the latter combination of photoelectric conversion elements, that is, 9E, 9
The outputs of F, 9H, and 9G are applied to the adders 17b and 17a, respectively, and the respective outputs are applied to the differential amplifier 18.

The amplitude detector 19 detects the amplitude level of the output of the differential amplifier 18, and the detected output is applied to the variable gain amplifier 20 as a gain control signal. The output of the differential amplifier 12 whose amplitude is controlled by the variable gain amplifier 20 is amplified by the drive amplifier 14 via the equalizer 13,
Similar to the conventional one shown in FIG. 3, it is used as a drive signal for the drive coil 8 for moving the objective lens 5 in the direction orthogonal to the track.

FIG. 2 is a schematic diagram for explaining the operation of the servo gain control system including the adders 17a and 17b, the differential amplifier 18, and the amplitude detector 19 described above, and the operation will be described below. 2 (a) shows the positional relationship between the pit P and the light spot S as an information detection point, and FIG. 2 (b) shows the light intensity distribution on the photoelectric conversion element at that time. For example, the shaded portion indicates the portion with high strength.

(B) of FIG. 2 (a) shows a state in which the light spot S is scanning the center of the pit P, and the light intensity distribution on the photoelectric conversion element at this time is shown in (b) of (b). That's right.
At this time, the outputs of the adders 17a and 17b are substantially equal to each other, so that the output of the differential amplifier 18 is substantially zero. On the other hand, FIG. 2 (a)
As shown in (a) or (c) of FIG. 5, when the light spot S scans the edge portion on the pit P, the light intensity distribution on the photoelectric conversion element is (b) in FIG. As shown in. Therefore, in the case of (a), the adder
The output of the adder 17b increases more than the output of 17a,
18 generates a negative voltage according to the difference output. Also, (C)
In this case, the output of the adder 17a becomes lower than the output of the adder 17b, and the differential amplifier 18 generates a positive voltage according to the difference output.

In this way, the differential amplifier 18 has (a) in FIG. 2 (a).
Outputs based on the asymmetry are generated each time when passing through the edge portion of the pit S in (c) and (c) of FIG.
No output is generated when passing through a portion other than the edge of the pit, such as (b). Therefore, the output of the differential amplifier 18 becomes a signal indicating the degree of asymmetry at the edge portion of the pit of the disc. As described above, the degree of asymmetry at the edge portion of the pit changes depending on the shape of the pit (for example, pit depth, pit width, etc.). It represents.

The magnitude of the amplitude of the output of the differential amplifier 18 obtained as described above is detected by the amplitude detector 19 and applied to the variable gain amplifier 20 as a gain control signal. The variable gain amplifier 20 has its gain variably controlled in inverse proportion to the magnitude of the gain control signal. As a result, the gain of the variable gain control amplifier 20 is changed to an optimum value according to the pit shape of the disc at that time, and the output change due to the pit shape of the disc is canceled and the optimum tracking error signal is output.

The principle of controlling the gain of the variable gain amplifier 20 will be described in more detail below.

As described above, when the pit shape such as the pit depth and pit width of the disc changes, the asymmetry of the light intensity distribution on the photoelectric conversion elements 9E and 9H, 9F and 9Ga that detects the tracking error signal is as shown in FIG. It will be exactly the same.
Therefore, taking the pit depth as an example of the change in the pit shape, the difference with respect to the change in the depth of the pit P when the light spot S is in the state of (a) or (c) of FIG. The change in the output of the dynamic amplifier 12 is obtained as shown in FIG.

On the other hand, when the light spot S is located at the edge portion of the pit P as shown in (a) or (c) of FIG. 2A, the light intensity distributions on the photoelectric conversion elements 9E and 9F, 9H and 9G The asymmetry is the same as in the case of (a) or (c) of FIG. 9 (a) in that it is caused by optical diffraction at the edge portion, and therefore the light spot S is changed to that of FIG. 2 (a). When the change in the output of the differential amplifier 18 (and thus the amplitude detector 19) with respect to the change in the depth of the pit S in the case of (a) or (c) is obtained, it becomes as shown in FIG.
The curve is very similar to that of FIG.

From FIG. 3 and FIG. 4 above, the differential amplifier 12 and the amplitude detector 19 are shown.
The output relationship is graphed as shown in Figure 5 (the vertical axis and horizontal axis are different in scale), and it is extremely strong between both the differential amplifier 12 and the differential amplifier 18 (and thus the amplitude detector 19). It can be seen that there is a correlation.

As is clear from FIG. 5, when the output of the amplitude detector 19 tends to increase due to the change in the pit shape of the disc, the output of the differential amplifier 12 also tends to increase. When the output of the amplitude detector 19 tends to decrease due to the change, the output of the differential amplifier 12 also tends to decrease. Therefore, as shown in FIG. 6, if the gain of the variable gain amplifier 20 is variably controlled in inverse proportion to the magnitude of the output of the amplitude detector 19, the pit shape of the disk changes, and the differential amplifier 12 has a different shape. Even if the output changes, the change in the output of the differential amplifier 12 due to this pit shape can be changed by the variable gain amplifier.
You can cancel at 20.

The present invention has been made based on the above-described principle. As shown in FIG. 1, a variable gain amplifier 20 is connected behind a differential amplifier 12 that outputs a tracking error signal. The gain of 20 is variably controlled in inverse proportion to the magnitude of the output of the amplitude detector 19. With such a configuration, even if the pit shape changes for each disc, it is possible to automatically cancel the fluctuation of the tracking error signal due to the change of the pit shape, and even if the pit shape changes for each disc. Tracking control can always be performed with the optimum tracking servo gain.

Although the above description is based on the embodiment of FIG. 1,
This invention is not limited to the embodiment of FIG. For example, in the embodiment shown in FIG. 1, the photoelectric conversion element is divided by two dividing lines that are substantially orthogonal to each other, but these dividing lines do not necessarily have to be orthogonal, and the point is that the two dividing lines must be parallel. , The tracking error signal and the gain control signal can be extracted.

Further, in the embodiment shown in FIG. 1, one dividing line for dividing the photoelectric conversion element is parallel to the track direction.
It is not always parallel, and detection is possible even if there is some deviation.

Further, in the above-mentioned embodiment, among the photoelectric conversion elements divided, the asymmetry in the track parallel direction is detected by the difference signal of the sum of 9E and 9F and the sum of 9G and 9H, but the difference between 9E and 9G,
The initial purpose can be achieved even by detecting the difference between 9E and 9H, the difference between 9F and 9G, and the difference between 9F and 9H.

[Effect of device]

As described above, according to the present invention, the gain of the variable gain amplifying means is made variable according to the change of the pit shape, so that the fluctuation of the tracking error signal based on the change of the pit shape is automatically canceled. Even if the pit shape changes for each disk, tracking control can always be performed with an optimum tracking servo gain.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a schematic diagram showing a relationship between a light spot scanning a pit and a photoelectric conversion element in the present invention, and FIG. 3 shows an output characteristic of an operational amplifier 12. Fig. 4 is a diagram showing the output characteristics of the amplitude detector 19, Fig. 5 is a diagram showing the correlation between the outputs of the operation amplifier 18 and the amplitude detector 19, and Fig. 6 is a gain control of the variable gain amplifier 20. FIG. 7 shows a characteristic, FIG. 7 is a block diagram of a conventional example, FIG. 8 is a front view of a photoelectric conversion element in the conventional example, and FIG. 9 is a photoelectric conversion element corresponding to a conventional relationship between a pit and a light spot and its It is a schematic diagram which shows an output. 9E ~ 9H ... photoelectric conversion element, 9C, 9D ... dividing line, 10a ~ 10d
…… Adder, 11a, 11b …… Low pass filter, 12 …… Differential amplifier, 13 …… Equalizer, 14 …… Drive amplifier, 17a,
17b ... Adder, 18 ... Differential amplifier, 19 ... Amplitude detector, 20 ... Variable gain amplifier.

Claims (1)

(57) [Scope of utility model registration request] 1. A tracking error signal generation device for generating a tracking error signal corresponding to a positional deviation between an information track and a light spot in an optical information writing or reading device, wherein light from a light source irradiated on the information track is used. The reflected light or the transmitted light of the spot is received by a set of photoelectric conversion elements divided and installed at positions corresponding to the direction substantially orthogonal to the information track, and the asymmetry of the output intensity from the set of photoelectric conversion elements is detected. And a reflected light or a transmitted light of the light spot from the light source is received by a set of photoelectric conversion elements dividedly installed at positions corresponding to the substantially parallel direction of the information track, and this set is detected. Second detection circuit for detecting the asymmetry of the output intensity from the photoelectric conversion element, and the tracking circuit for amplifying the output of the first detection circuit. Variable gain amplifying means for outputting the error signal and controlling the amplification gain thereof by the output of the second detection circuit. The variable gain amplification means is inversely proportional to the magnitude of the output of the second detection circuit. A tracking error signal generating device characterized in that the gain of a variable gain amplifying means is increased or decreased.