JPS6113447A - Detecting device for tracking error - Google Patents

Abstract

PURPOSE:To obtain a tracking error signal having no offset error by decomposing the tracking error signal into a part generating at a land part and a part generated at a pit part, and detecting an offset quantity from the tracking error signal generated at the land part. CONSTITUTION:An RF signal 13 outputted by an operational amplifier 16 is inputted to a comparator 18 and a comparator 19. An error signal (DFT signal) outputted by an operational amplifier 17 is branched to gate circuits 20 and 21; the gate circuit 20 samples the input according to the output of the comparator 18 and the gate circuit 21 samples the input according to the output of the comparator 19. Their outputs are smoothed by LPFs 22 and 23 and inputted to a differential amplifier 9. The output of an LPF22 contains the tracking error signal and the offset quantity due to a slant of a disk, and the output of an LPF23 is a signal part picked up from the land part, so it contains only the offset quantity due to the disk slant. Consequently, the difference between the outputs of the LPFs 22 and 23 is amplified by an operational amplifier 9 to obtain the tracking error signal 10 having a small offset quantity.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to an optical disc player.
disk-shaped recording medium (
Recording pits (hereinafter referred to as disks) recorded on
The present invention relates to an optical pickup that optically reads information from ), and more particularly to a tracking error detection device that detects an error signal for tracking the optical pickup.

In order to read the information recorded in the recording pits, similar to the relationship between a magnetic disk and a magnetic head, relative movement is required between the light pickup point of the optical pickup and each pit, and magnetic Similar to tracking in a disk device, the point at which the optical pickup picks up the light must always be kept accurately on the line along which the center point of each pit moves.

Such an error signal for tracking is detected from the light itself picked up by the optical pickup.

[Prior art]

FIG. 1 is a drawing showing a conventional tracking error detection device for this Yuzu, and in the figure, j is a semiconductor laser, (2
1 is a beam splitter, 13) is a collimator lens, (
4) is the objective lens, (5) is the disk, (6) is the pit, (7a) and (7b) are the diffracted lights, respectively; 8) is the photodetector, which consists of two parts (8a) and (8b). (9
) is a differential amplifier, ll01 is a tracking error signal, f
lv is actuator, (2) is amplifier, α score is RF
(radio frequency) signal.

Normally, the recording signal is obtained by limiting the amplitude of the high frequency FM signal using a limiter, so an amplifier (2
) is an RF multiplied signal.

In Figure 1, III, 121, 13), 14
1, (8a), (8b) are fixed, and the disk (5
) rotates, the vicinity of the focal position of the +81a light beam, that is, the focused spot, moves in a direction perpendicular to the plane of the paper.

'The light emitted from the semiconductor laser (1) passes through the beam splitter 12j1 and the collimator lens (3), enters the objective lens (41), and is focused onto the pit 161 by the objective lens (41. The light focused on the pit (6) separates the diffracted light (7a) and the diffracted light (7
b) and they are reflected. The reflected diffracted light (7a) and diffracted light (7b) go back through the objective lens (41) and the collimator lens (3), have their optical paths bent by 90 degrees by the beam splitter (21), and enter the photodetector 181.

FIG. 2 is an explanatory diagram illustrating the configuration and operation of the photodetector (8) in FIG. 1, and the same reference numerals as in FIG. 1 indicate the same parts. The light receiving surface Jd is divided into two as shown in (8a) and (8b),
Independent photodetectors (8a) that are electrically isolated from each other
, (8b). In this specification, (8a) is referred to as the right side photodetector, and (8b) is referred to as the left side photodetector.

E1) In the example shown in the figure, the focused spot of the light beam is a pit (
6) (with respect to the horizontal direction in the drawing), there is K, that is, there is no tracking error. In this case, the diffracted light (7a) generated by the pit (6) and the diffracted light (7
b) is symmetrical with respect to the optical axis, and the amounts of light reflected and incident on the photodetectors (8a) and (8b) are equal to each other. Therefore, the voltages at both input terminals of the differential amplifier (9) become equal to each other, the tracking error signal du which is the output voltage of the differential amplifier (9) becomes 0, and the actuator dυ does not operate. In the amplifier (2), the output voltages of the photodetectors (8a) and (8b) are added together and amplified to output an RF multiplied signal 3).

FIG. 3 is a diagram showing a case where a tracking error occurs in the apparatus shown in FIG. 1, where the same reference numerals as in FIG. This shows the case where it is shifted to the left (on the drawing). The diffraction effect of the laser beam incident on the left side of the pit is reduced and the diffracted light (7
b) and the diffracted light (7a) are asymmetrical, and the reflected light becomes stronger on the left side. Therefore, the amount of light incident on the photodetector 9 (8b) becomes greater than the amount of light incident on the photodetector (8a), and as a result, the tracking error signal 1)01 becomes negative.

Conversely, when the focal point of the light beam is shifted to the right from the center of the pit (6), the tracking error signal Q[m becomes positive.

By the way, as shown in FIGS. 1 and 3, the pits (6) are aligned in the radial direction of the disk (5) (a direction perpendicular to the direction of movement of the pits; in this specification, this direction is temporarily referred to as the left-right direction). Therefore, when the focal position of the light beam moves in the radial direction of the disk (5) (relatively, when the pit position moves in the radial direction of the disk (51)), the tracking error signal II[lI changes as shown in Fig. 4. That is, the tracking error signal Q
l becomes 0 when the focus of the light beam is at the center of one pit (6) and at the center between the pit (61) and the pit (6) (referred to as a land).Using this phenomenon, Feedback control can be performed via the actuator αυ to keep the focus of the light beam at the center of the pit (6).

The conventional device as described above has a drawback in that tracking accuracy becomes poor when the disk (5) is tilted.

FIG. 5 shows a conventional device in which the disk (51) is tilted from a plane perpendicular to the optical axis. In FIG. 5, the same reference numerals as in FIG. 3 indicate the same parts. In the case shown in FIG. Diffracted light (7a') diffracted by the pit (6),
(7b) has almost the same amount of light, but is not symmetrical with respect to the optical axis and is reflected at an angle. Therefore, the diffracted light (7
In a), there is a portion that deviates from the outer periphery of the objective lens (4) and protrudes to the outside, so that the amount of light passing through the objective lens (4) decreases.

On the other hand, in the case of diffracted light (7b), all the light is reflected by the objective lens (
41, so there is no decrease in the amount of light. Therefore, the amount of light incident on the photodetector (8a) is smaller than the amount of light incident on the photodetector (8b), and even if the focal position of the light beam is correctly located at the center of the pit (6), the signal f101 does not become zero.

FIG. 6 is a diagram showing the tracking error signal alJl when the disk (5;) is tilted. i16 Figure 1bl shows a case where the disk is tilted in the opposite direction to that in Figure 5, resulting in a positive offset.

The conventional device has the drawback that an offset occurs in the error signal as shown in Fig. 6, resulting in a decrease in tracking accuracy.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above.In this invention, the tracking error signal is divided into a part generated in the land part and a part generated in the pit part, and the tracking error signal is divided into the part generated in the land part and the part generated in the pit part. A tracking error signal free of offset error was obtained by detecting the offset roughness from the tracking error signal and subtracting the detected offset amount from the tracking error signal generated at the pit portion.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

The off-line diagram shows the situation that changes between the RF double signal land and the pit in the device shown in Figure 1. (b) shows the change in the intensity of the RF signal 13, and (cl) is the output of the comparator 1 that extracts a region larger than the average value of the intensity shown in (b), which is referred to as the second rectangular wave in this specification. , in the same figure (dl is the output of the comparator 2 which extracts the region whose intensity is smaller than the average value of the same figure (b). In this specification, this is called the first rectangular wave. When the focused spot of the light beam hits the land, tl The objective lens (4
; However, when it hits the pit (6), it is diffracted and a part of it does not enter the objective lens (4), so the RF multiplied signal 3 becomes weak at the pit part, and as shown in the off diagram (bl) Off figure (off figure 1cl from bl, (d)
It is possible to generate a signal and separate the tracking error signal +101 into pit portions and land portions.

FIG. 8 is a block diagram showing an embodiment of the present invention, in which the same reference numerals as in FIG. 1 indicate the same or corresponding parts, and (81
is a four-part photodetector consisting of photodetectors (8c), (8d), (8e), and (8f). a→, αi, a*
, wholesalers are each an operational amplifier, a photodetector (8c), (
The outputs of 8d) are added by operational amplifier a4, and the outputs of photodetector (
Since the outputs of 8e) and (8f) are added by the operational amplifier (2), the output of the operational amplifier Q4 and (1!li) is the photodetector (8a) in FIG.

(8b), respectively. Figure 8 Nioni 2nd
The reason why a 4-split photodetector (81) is used, which is different from the one shown in the figure, is that in the actual device, focus control of the light beam, etc. is performed by the signal from the photodetector +81, and it is not directly related to this invention, so please explain it. omitted.

The outputs of (14, (16) in Fig. 8 are (8a), (
8b), the a* and outputs in FIG. 8 correspond to *'21 and +91 in FIG. 1, respectively.

Also, in FIG. 8, u81. (20) and (21) Ia and soh are gate circuits, and (22) and (23) are low-pass filters (hereinafter abbreviated as LPF), respectively.

The RF multiplied signal 13) of the output of the operational amplifier (ill) is input to the comparator 1) 81 and the comparator α9, and the off diagram (C) is shown.

(Generates first and second rectangular wave voltages shown at dl.

The error signal (hereinafter referred to as DFT signal) which is the output of the operational amplifier u9 is divided into the gate circuit (2θ) and (21). Then, the output of comparator 1) is sampled and each LPF (22)
, (23) and input to the differential amplifier (9).

The output of the LPF (22) includes a tracking error signal and an offset amount due to the disk tilt, and the output of the LPF (
Since the output of 23) is the signal portion picked up from the land portion, it contains only the offset amount due to the disk tilt, so it is applied to the operational amplifier (9) by the LPF.
By amplifying the difference between the outputs of (22) and LPF (23), it is possible to obtain a tracking error signal [1 with a small amount of offset.

FIG. 9 is a waveform diagram explaining the operation of each part in FIG. Figure 9 (bl is the RF output of the operational amplifier (IQ)
Signal 1) 3, Fig. 9 1cl is the DFT signal that is the output of the operational amplifier (171), Fig. 9 (d) is the output of the gate circuit (4), Fig. 9 (e) is the output of the LPF (22), Figure 9 (fl is the output of the gate circuit (21), Figure 9 (g) is L
The output of PF' (23) in FIG. 9 (hl is the tracking error signal d01).

As explained earlier, the DFT signal in FIG. 9 (cl) includes an offset amount in addition to the tracking error signal.
LPF (21) that smoothes the output of the gate circuit (21)
Since only the offset amount is extracted from the output (Fig. 9-)), the tracking error signal plane (Fig. 9 (h)) from which the offset amount has been removed can be obtained using the differential amplifier (9). .

FIG. 10 is a block diagram showing another embodiment of the present invention, in which the same reference numerals as in FIG. 8 indicate the same or corresponding parts, and (
24) is a π/2 phase shifter, (25) and (26) are each zero cross detection circuit, (25) is when the input voltage rises and crosses zero, (26) tj input voltage falls and crosses zero. A pulse is generated in each case.

Therefore, the zero cross detection circuit (25) is
A pulse (referred to as the second pulse in this specification) is generated at the maximum point of the RF multiplied signal (corresponding to when the focused spot is at the center of the land) shown in 1, and the zero cross detection circuit (26
) generates a pulse (referred to as the first pulse in this specification) at the RF multiplied signal minimum point (corresponding to when the focused spot is at the center of the pit), so these outputs are used to generate a gate circuit (20).

(21) By performing k control, the same effect as the circuit shown in FIG. 8 can be obtained.

In addition, the gate circuit (20) in FIGS. 8 and 10 #
A sample and hold circuit may be provided to sample and hold the output of (21).

〔Effect of the invention〕

As described above, according to the present invention, the tracking error signal is obtained by subtracting the signal of the land portion where no pit exists from the signal of the portion of the recording medium where the pit exists, thereby correcting the offset amount due to the disk tilt. can be obtained. Note that the VC deflection of the present invention also eliminates the offset that occurs when the objective lens is axially misaligned.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a conventional device, Fig. 2 is an explanatory diagram showing the configuration and operation of the photodetector shown in Fig. 1, and Fig. 3 shows a case where a tracking error occurs in the device shown in Fig. 1. diagram showing,
Figure 4 shows the change in tracking error in the case of Figure 3, Figure 5 shows the case when the disc is tilted from a plane perpendicular to the optical axis, and Figure 6 shows the tracking error in the case of Figure 5. The OFF diagram is a diagram showing the RF multiplication signal change in the case of FIG. 1, FIG. 8 is a block diagram showing an embodiment of the present invention, and FIG. Waveform diagram to explain,
FIG. 10 is a block diagram showing another embodiment of the invention. (8c), (8d)--Right side photodetector, (8e), (
8f) - Left side photodetector, (9)...Differential amplifier, 1
)01...Tracking error signal, ([3)...f
(F signal, 1) 81, (19... each comparator, (20), (21)... each gate circuit, (24)... π/2 phase shifter, (25), (
26)...Zero cross detection circuit respectively. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (3)

[Claims] (1) Information is recorded in the form of a pit row on an information recording medium, and a focused spot of a light beam is irradiated onto the pit row, and the relative position between the focused spot and the pit irradiated by this focused spot is determined. When moving in the direction of the pit row and reading information from the pit row, control is performed to keep the focused spot correctly on the axis of the pit row.
In a tracking error detection device that detects a deviation of the focused spot from on the axis to a direction perpendicular to the axis (hereinafter referred to as the left-right direction), the reflected light to the right half of the focused spot is a right photodetector into which light is input via an optical system; a left photodetector into which reflected light from the left half of the focused spot is input via the predetermined optical system; and an output from the left photodetector and the right light means for outputting a difference signal between the output of the detector, and converting the difference signal into a first difference signal when the focused spot is on the pit portion and a second difference signal when the focused spot is on the land portion; A tracking error detection device comprising: difference signal separation means for separating the second difference signal from the first difference signal; and means for subtracting the second difference signal from the first difference signal to obtain a tracking error signal. (2) The difference signal separation means generates a first rectangular wave in a portion where the amplitude of the signal obtained by adding the output of the right photodetector and the output of the left photodetector is smaller than the average level of the signal, and A second rectangular wave is generated in a portion where the amplitude of the signal is larger than the average level of the signal, the difference signal between the first rectangular waves is used as the first difference signal, and the difference signal of the second rectangular wave is 2. A tracking error detection device according to claim 1, further comprising means for converting a difference signal between them into a second difference signal. (3) The difference signal separation means separates the phase of the alternating current component of the signal obtained by adding the output of the right photodetector and the output of the left photodetector by 90°.
A first pulse is generated at a zero-crossing point where the phase-shifted signal changes from negative to positive, a second pulse is generated at a zero-crossing point where the phase-shifted signal changes from positive to negative, and the difference signal is converted to the first pulse.
Claim 1, characterized in that it is provided with means for determining a first difference signal by sampling the difference signal with the second pulse, and determining a second difference signal by sampling the difference signal with the second pulse. 1) Tracking error detection device described in section 1).