JP2580593B2 - Tracking error signal detection device - Google Patents

Description

The present invention relates to an apparatus for detecting a tracking error signal of an optical pickup.

2. Description of the Related Art Conventionally, in order to constantly track the irradiation light from an optical pickup at the center of a track formed by a signal pit row of an optical disc, a signal representing the deviation between the center of the track and the irradiation light, that is, a tracking error A signal has been detected. This tracking error signal is detected by, for example, the following configuration in a tracking error signal detection device for a reflective optical disk shown in FIG.

(I) Output from laser diode LD, beam splitter BS, collimator lens CL, objective lens (laser light)
The focus of the irradiation light (laser light) through the OL in order is focused on the optical disk OD.

(Ii) The spot SP of the laser beam reflected from the optical disk OD, traced back through the objective lens OL and the collimator lens CL, and reflected by the beam splitter BS, as shown in FIG. The photodiode PD is formed on a two-division photodiode PD including the detection unit PDB.

(Iii) A detection unit intensity of spot SP on PDA and B detection unit
A tracking error signal is detected based on a difference from the intensity of the spot SP on the PDB.

[Problems to be Solved by the Invention] However, according to the above-described conventional technology, when the tracking of the objective lens OL and the like is controlled by a servo system (not shown) based on the tracking error signal, the spot SP on the two-division photodiode PD is reduced In some cases, the tracking error signal was not accurately detected.

This is because the focus on the optical disk OD is moved by a distance Δ in the radial direction by moving the objective lens OL and the like by tracking control.
χ When moved (see Fig. 5), the spot SP itself is divided into two parts as shown by the dotted line in Fig. 6.
A distance Δχ ′ on the PD in the direction of one detecting unit (here, PDB)
It is because it shifts. That is, the shift of the spot SP itself causes a change in brightness on the two-division photodiode PD, which is output as a tracking error signal.

An object of the present invention is to detect an accurate tracking error signal by solving the above problems.

[Means for Solving the Problems] The present invention made to achieve the above object is to provide a light reflected from a track on which a signal pit row is formed and converged in a spot shape by a lens or the like to the track. A plurality of photodetectors arranged in a radial direction perpendicular to the tracking direction along the photodetectors, and an error signal generating means for generating a tracking error signal from a difference in received light intensity detected by each of the photodetector detectors And a tracking error signal detection device comprising: a detection unit that detects at least one of a light irradiation area and a light irradiation area based on an output of the detection unit. The irradiation area is divided into approximately two parts based on the specified detection part, and two parts arranged in the radial direction are specified. Selecting means for dividing the detection unit into blocks to define blocks; and for each of the detection units divided by the selection means, a detection signal from the detection unit is added to obtain a light receiving intensity for each block. And a tracking error signal generated from the difference in the received light intensity obtained for each block by the adding means.

[Operation] In the tracking error signal detection device of the present invention, the photodetector reflects light reflected from the track on which the signal pit row is formed and converged into a spot by a lens or the like in the tracking direction along the track. Light is received by three or more detectors arranged in a vertical radial direction.

Then, in the error signal generation unit, the selection unit specifies the detection unit in the light irradiation region based on the output of the detection unit, and based on the specified detection unit, divides the irradiation region into approximately two parts and The detection unit is divided into blocks to define two blocks arranged in the radial direction. For example, if the number of the detection units specified as being in the light irradiation area is an even number, the specified detection units are divided into blocks so that each block includes the same number of the detection units, and the number of the specified detection units is an odd number. Then, the detection unit located in the middle of the irradiation area,
If the blocks are divided so that the same number of the remaining detectors are included in each block without being assigned to any block,
Irradiation regions having substantially the same area are allocated to each block. Thereafter, the adding means adds the detection signals from the detecting sections for each of the detecting sections divided into blocks by the selecting means, and obtains the light receiving intensity for each block.

The error signal generating means generates a tracking error signal from a difference in received light intensity obtained for each block, that is, for each irradiation area divided into substantially equal areas in the radial direction.

[Embodiment] Next, an embodiment of the tracking error signal detecting device of the present invention will be described with reference to FIG.

In FIG. 1, a laser beam (here, a wavelength of 780 nm) output from a laser diode 3 is reflected by a beam splitter 5, converted into a parallel beam by a collimator lens 7, and reflected by a total reflection mirror 9. The reflected laser light enters the objective lens 11. Objective lens
The laser light incident on 11 focuses on a signal pit row (not shown) formed along the circumferential direction of the reflective optical disk 15. The laser light focused on the optical disk 15 is reflected by the optical disk 15 and the objective lens 11
Come back to. At this time, the intensity of the reflected light that returns is
It is small when there is a signal pit at the focal point, and large when there is no signal pit. The reflected light returning to the objective lens 11 follows the incident optical path in reverse, is reflected by the total reflection mirror 9, and is converged by the collimator lens 7,
The beam returns to the beam splitter 5. Beam splitter 5
Reflects about half of the reflected light from the disk 15 toward the laser diode 3 and transmits the remaining reflected light. The reflected light transmitted through the beam splitter 5 generates astigmatism by a cylindrical lens 13 arranged at 45 ° to the radial direction Yr of the optical disk 15, and the optical disk 15
A spot SP is formed on a six-division photodiode 19, which is a photodetector divided into six in the radial direction Yr.

The six-division photodiode 19 in which the spot SP is formed,
As shown in FIG. 2, the first, second, third, fourth, fifth, and sixth detectors
21,23,25,27,29,31. The six-division photodiode 19 includes a tracking error signal output device 33.
And the tracking error signal output device.
33 is a first, second, third, fourth, fifth, sixth adder 35, 37, 39, 41, 4
3, 45, first and second changeover switches 47 and 49, first and second changeover switch controllers 51 and 53 for switching control of the first and second changeover switches 47 and 49, a differential amplifier 55 and the like. Have been.

Based on the output of the first detection unit 21 input to the A1 terminal and the output of the fifth detection unit 29 input to the B1 terminal, the first changeover switch controller 51 performs the first
The changeover switch 47 is controlled to one of the positions 1, 2, and 3.

In Table 1, "low level L" indicates that the spot area on the detector corresponding to the divided photodiode 19 is smaller than a predetermined value, and "high level H" indicates that the spot area is larger than the predetermined value.

The second changeover switch controller 53 that controls the second changeover switch 49 includes a first changeover switch according to the following Table 2.
Similarly to 47, the second changeover switch 49 is controlled to one of the positions 1, 2, and 3 based on the outputs of the second detection unit 23 and the sixth detection unit 31 input to the A2 terminal and the B2 terminal.

First changeover switch 47 controlled based on Table 1 above
And the output side of the first adder 35 to which the first and second detectors 21 and 23 are connected are connected to the second adder 37. The output side of the second adder 37 and the position 3 of the second switch 49 controlled based on Table 2 correspond to the third adder.
Connected to 39. The output side of the third adder 39 is a differential amplifier 55 that finally outputs a tracking error signal.
Is connected to the “+” side of the The third and fourth detectors 2
Position 2 of the first and second changeover switches 47, 49 connected to 5, 27 is a neutral position.

Fourth adder 41 to which fifth and sixth detectors 29 and 31 are connected
And the position 1 of the first changeover switch 47 are connected to the fifth adder 43. The output side of the fifth adder 43 and the position 1 of the second switch 49 are connected to the sixth adder 45. The output side of the sixth adder 45 is connected to the “−” side of the differential amplifier 55 in which the output side of the third adder 39 is connected to the “+” side.

Tracking error signal output device 33 having such a configuration
Are calculated based on the outputs of the respective detectors of the six-division photodiode 19 and the calculated values of the first to sixth adders 35 to 45 and
Depending on the switching state of the second changeover switches 47 and 49, the detection unit of the six-division photodiode 19 that outputs to the “+” side of the differential amplifier 55 and the detection unit that outputs to the “−” side are selected. The output difference of the detection unit is output by the differential amplifier 55 as a tracking error signal.

Next, an operation example will be described. For example, as shown by a two-dot chain line in FIG.
Are formed almost at the center of the detection section 21, there is no spot SPs in the detection sections 21 and 31 (here, the A1 terminal and the B2 terminal become "low level L"), and the detection sections 23, 25, 27, 29, No spot
Because of the presence of SPs (here, the B1 terminal and the A2 terminal become “high level H”), the first changeover switch 47 is controlled to the position 3 based on Tables 1 and 2, and the second changeover switch 49
Is controlled to position 1. As a result, the outputs of the first, second, and third detectors 21, 23, and 25 are added to the “+” side of the differential amplifier 55, and the fourth, fifth, and fifth to the “−” side. 6 The outputs of the detection units 27, 29, 31 are added.

On the other hand, as shown by the dotted line in the spot SPs, the fourth detection unit 2
When moving above 7 to form spot SPd,
The detection units 21, 23, and 31 have no spot SPs (here, the A1, A2, and B2 terminals are at “low level L”).
Since there is a spot SPd at 25, 27, and 29 (here, the B1 terminal becomes “high level H”), the first changeover switch 47 is controlled to the position 3 based on Tables 1 and 2, Second
The odd changeover switch 49 is controlled to the position 2. Thus, the first, second, and third detection units are provided on the “+” side of the differential amplifier 55.
The outputs of 21, 23 and 25 are added, and the outputs of the fifth and sixth detectors 29 and 31 are added to the “−” side. That is, spot SPd
Is not applied to the differential amplifier 55.

Further, when the light spot moves in the radial direction (in this case, no spot is formed on the detection units 21, 23, 25, and there is a spot on the detection units 27, 29, 31), the same as above is performed. Based on Tables 1 and 2, the first changeover switch 47 and the second changeover switch 49 are both controlled to the position 3. Thus, the outputs of the first, second, third, and fourth detectors 21, 23, 25, and 27 are added to the “+” side of the differential amplifier 55, and the fifth , The outputs of the sixth detectors 29 and 31 are added.

As described above, according to the first embodiment, the differential amplifier 55 that finally outputs the tracking error signal detects the combination in which the area on the outer circumference side and the area on the inner circumference side of the spot are almost equal. The output from the section is added.
As a result, even if the spot moves on the six-division photodiode 19 in the radial direction, the tracking error signal hardly fluctuates due to this movement. Therefore,
There is an extremely excellent effect that the accuracy of the tracking error signal is improved. In addition, according to the present embodiment, it is not necessary to accurately match the position of the spot with the position of the six-division photodiode 19, so that the number of steps in assembling is reduced. Further, since the tracking error signal can be accurately output even if there is a positional shift due to a change with time, there is an effect that reliability is improved.

The tracking error signal output device 61 of the second embodiment
As shown in FIG. 3, adders 68 and 71, a changeover switch 73,
A three-divided photodiode 89 comprising a changeover switch controller 75 for controlling the changeover switch 73 and differential amplifiers 77, 79, 81 and the like, and comprising first, second, and third detection units 83, 85, 87. Are input to the differential amplifier 81 in the same way as in the first embodiment. Here, the changeover switch controller 75 inputs the output of the differential amplifier 77 to the A3 terminal, inputs the output of the differential amplifier 79 to the B3 terminal, and moves the changeover switch 73 to the position 1, as shown in Table 3 below. 2,3
Control to either.

Tracking error signal output device 61 having such a configuration
Outputs a tracking error signal in the same manner as in the first embodiment, based on the output of each detector of the three-division photodiode 89.

Next, an operation example will be described. For example, as shown by a two-dot chain line in FIG.
, The spot area on the second detector 85 is larger than that on the first and third detectors 83 and 87, so that both of the differential amplifiers 77 and 79 are “low level L”. "become. As a result, the changeover switch 73 is controlled to the position 2 (neutral position) based on Table 3, and the differential amplifier 81
A tracking error signal is output according to the output difference between the third detection units 83 and 87. That is, when the spot SPs is located substantially at the center (on the second detection unit) on the center three-division photodiode 89, the other first and third detection units 83 and 87 excluding the output of the second detection unit 85 , A tracking error signal is output.

On the other hand, as shown by the dotted line in the spot SPs, the first detector 8
When moving up to 3 to form spot SPd,
The output of the differential amplifier 77 becomes “high level H”, and the output of the second differential amplifier 79 becomes “low level L”. As a result, the changeover switch 73 is controlled to the position 3 based on Table 3, and the differential amplifier 81 is connected to the output of the first detector 83 and the second detector 85.
And outputs a tracking error signal based on the sum output of the third detector 87. That is, the output of the second detection unit 85 at the center is added to the output of the detection unit on the opposite side to the direction in which the spot has moved.

As described above, according to the second embodiment, the differential amplifier 81 that finally outputs the tracking error signal detects the combination in which the area on the outer peripheral side and the area on the inner peripheral side of the spot are almost equal. The output from the section is added.
Thus, even if the spot moves on the three-division photodiode 89 in the radial direction, the tracking error signal does not change as in the first embodiment. Therefore, there is an excellent effect that the accuracy of the tracking error signal is improved. In addition, the present embodiment has substantially the same effect as the first embodiment, and also has an excellent effect that the number of components is reduced.

Note that the present invention is not limited to the above embodiment,
For example, the present invention can be applied to all optical pickups that perform tracking control by a push-pull method in a transmission optical disk system or the like. Also, as shown in FIG.
The division photodiode 89 may be divided along the radial direction Yr, and may be used in combination with a configuration in which the sum of the detection units in the diagonal directions is compared to detect a focus error signal.

[Effects of the Invention] The tracking error signal detection device of the present invention specifies a detection unit located in a light irradiation area (spot) and, based on the specified result, divides a spot into which each block has an approximately equal area. The detection unit is divided into blocks to include
A tracking error signal is generated from a difference in received light intensity for each block. For this reason, even if the spot moves in the radial direction by the tracking servo, the area of the divided spot included in each block does not greatly deviate, and the tracking error signal is hardly affected by the movement of the spot. There is no. As a result, there is an extremely excellent effect that the accuracy of the tracking error signal is improved. In addition, there is an excellent effect that the adjustment of the position of the spot is facilitated and the tracking error signal can be accurately detected even if the spot is displaced due to aging.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a tracking error signal detecting device according to the present invention, FIG. 2 is a block diagram of a photodiode and a tracking error signal output device of the first embodiment, and FIG. FIG. 4 is a configuration diagram of a tracking error signal output device, FIG. 4 is a configuration diagram of a modified example of the photodiode of the second embodiment, and FIGS. 5 and 6 are explanatory diagrams of a conventional example. 3 Laser Diode 5 Beam Splitter 7 Collimator Lens 11 Objective Lens 13 Cylindrical Lens 15 Optical Disc 19 Six-Division Photodiode 33,61 Tracking Error Signal Output Device 89 3 Split photodiode

Claims (1)

(57) [Claims] 1. A light reflected from a track on which a signal pit row is formed and converged into a spot by a lens or the like.
A photodetector that receives light by a plurality of detectors arranged in a radial direction perpendicular to the tracking direction along the track, and an error that generates a tracking error signal from a difference in light reception intensity detected by each detector of the photodetector. A tracking error signal detection device comprising: a signal generation unit; and the photodetector includes three or more detection units; and the error signal generation unit includes a light irradiation area based on an output of the detection unit. Selecting means for specifying a detection unit in the above, and based on the specified detection unit, dividing the irradiation area into approximately two and dividing the detection unit into blocks to define two blocks arranged in the radial direction; and , For each of the detection units divided into blocks by the selection unit,
Adding means for respectively adding the detection signals from the detection unit to obtain the received light intensity for each block; and generating a tracking error signal from the difference in the received light intensity obtained for each block by the adding means. Characteristic tracking error signal detection device.