JPH06168471A - Tracking control circuit - Google Patents

Abstract

PURPOSE:To obtain a tracking control circuit capable of reading a tracking error signal without including a pre-pit signal and easily obtaining an accurate offset compensation value and a gain compensation value. CONSTITUTION:A tracking loop part 18 and a peak/bottom calculating means 24 are connected by means of a changeover means 20 and, when a pre-pit signal included in a light receiving signal is detected by a pre-pit signal detecting means 22 by inserting an optical disk, a changeover deciding means 23 decides wether the time from inputting of the pre-pit signal until a light beam passes through the sector formatting area of the optical disk elapses or not. By outputting a changeover signal to the changeover means 20 and stopping the output of the tracking error signal to the peak/bottom calculating means 24 in every lapse of the time, the tracking error signal without including a pre-pit signal is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking control circuit used in an optical disk device or the like.

[0002]

2. Description of the Related Art Generally, a tracking control circuit of an optical disk device forcibly swings a light beam as an optical disk is inserted, and based on an average value of peak and bottom values of a track error signal for one rotation, a track error signal is generated. An offset correction value for correcting the offset value included in the signal and a gain correction value for making the sensitivity level of the track error signal constant are obtained, and thereafter, tracking is performed using these correction values. Such a tracking control circuit will be described below.

FIG. 7 is a schematic configuration diagram of a conventional tracking control circuit. In the figure, the light receiving section 1 converts the light beam reflected from the disk surface into an electric signal and outputs it as a light receiving signal. The track error signal generation circuit 2 generates and outputs a track error signal based on the light receiving signal. The variable gain amplifier 3 amplifies the track error signal with a predetermined gain and outputs it. The subtracter 4 outputs the difference between the amplified track error signal and the correction signal to the objective lens controller 5 as a tracking signal. The objective lens controller 5 moves the objective lens based on the tracking signal to perform tracking.

Low-pass filter (hereinafter referred to as LPF) 1
0 inputs the tracking signal through the subtractor 4 and removes the high frequency component contained in the tracking signal. The peak / bottom detection circuit 11 inputs the tracking signal via the LPF 10 and detects the peak and bottom values from the tracking signal. The A / D 12 converts the peak and bottom values from the peak / bottom detection circuit 11 into a digital signal. The microcomputer 13 determines at least a correction value (hereinafter referred to as an offset correction value) for correcting the offset included in the track error signal based on the peak and bottom value data of the tracking signal, and
A correction value (hereinafter referred to as a gain correction value) for correcting the gain of the variable gain amplifier 3 is obtained.

A digital-analog converter (hereinafter referred to as D / A) 14 converts the offset correction value into an analog signal and outputs it to the subtractor 4. The D / A 15 converts the gain correction value to analog and outputs it to the variable gain amplifier 3. The adjustment when determining the tracking offset and the tracking loop gain using the tracking control circuit configured as described above will be described below.

To adjust the offset, a tracking loop consisting of the objective lens section, the light receiving section 1, the track error signal generating section 2, the gain variable amplifier 3, the subtractor 4, and the objective lens control section 5 is used to adjust the track error correction value and the gain correction value. Set to the state where the signal is not fed back (hereinafter referred to as the tracking loop open state). In this state, the LPF 10 inputs the track error signal from the light receiving unit 1, the track error signal generating unit 2, the variable gain amplifier 3, and the subtractor 4, and removes the high frequency component contained in the track error signal as noise to make a peak. Output to the bottom detection circuit 11. Then, the peak-bottom detection circuit 11 detects the peak and bottom values of the input track error signal,
Input to the microcomputer 13 via / D12. Next, the microcomputer 13 reads the peak and bottom values of the track error signal for at least one rotation, calculates the average of the peak and bottom values, and offsets so that the difference between the calculated average value and the reference value becomes zero. The value is obtained and the offset value is used as the offset correction value.

Further, a gain correction value that makes the amplitude constant is calculated based on the calculated average value of the peak and bottom values. Then, those values were fed back to the tracking loop via D / A14 and D / A15.

[0008]

In the conventional tracking control circuit, the light beam is forcibly struck along with the insertion of the optical disk, and the average of the peak and bottom values of the track error signal for one rotation at that time. Based on the value, an offset correction value that corrects the offset value included in the track error signal and a gain correction value that makes the level of the track error signal constant are obtained, and thereafter, tracking is performed using these correction values. .

However, since the optical disc has an eccentricity, the sector format formed on the track shown in FIG. 8 is irradiated with a light beam, and as shown in FIG. 9, the track error signal and the signal in the pre-pit area ( (Hereinafter referred to as pre-pit signal) will be included as noise. This noise is removed by the LPF,
If it is attempted to be removed by the LPF, a phase delay occurs and the gain is lowered, and the amplitude of the track error signal itself is lowered, so that the prepit signal cannot be removed.

Therefore, even if the peak and bottom values are obtained from the track error signal via the LPF, the accurate peak and bottom values cannot be obtained because the pre-pit signal is included. Further, there are JP-A-3-1057733 and JP-A-2-285523 as methods for performing such tracking control, but neither of them obtains a peak and a bottom value from which the pre-pit signal is removed. The present invention has been made to solve the above problems, and obtains a tracking control circuit capable of reading a track error signal that does not include a prepit signal and obtaining accurate peak and bottom values of the track error signal. The purpose is to

[0011]

A tracking control circuit according to the present invention causes a light beam to follow a track center of an optical disk by a track error signal based on a light receiving signal from a light receiving section which receives a reflected beam from the optical disk. In a tracking control circuit having at least a tracking loop unit and a peak / bottom detection means for calculating an average value of a peak and a bottom value of a track error signal for one rotation of an optical disk, the tracking control circuit is formed on a track included in a light reception signal from the light reception unit. Pre-pit detection means for detecting the signal of the pre-pit area of the sector format as a pre-pit signal, and when the pre-pit signal is detected, it is determined whether or not the light beam has passed through the area of the sector format, and a switching signal is output. Input the switching determination means and the switching signal, and It is obtained by a switching means for stopping the output of the track error signal to Kubotomu detection means.

[0012]

In the present invention, when the light receiving section detects the reflected light from the optical disk, the prepit signal detecting means detects the prepit signal included in the light receiving signal and the track error signal obtained based on the light receiving signal. Is input to the switching means connected to the tracking loop section and the peak bottom calculating means. Then, the switching determination means determines whether or not the light beam has passed through the sector format area of the optical disk based on the input of the prepit signal from the prepit signal detection means, and outputs the switching signal to the switching means.

[0013]

1 is a block diagram showing the concept of the present invention. In the figure, the tracking loop unit 18 is composed of at least the light receiving unit 1, the track error generation circuit, the gain variable amplifier 3, the subtractor 4, and the objective lens control circuit 5 at least as described above, and the track of the optical disc is irradiated with the light beam, When the light receiving section 1 receives the reflected light of the light beam, the light beam is caused to follow the center of the track based on the track error signal of the received light signal.

The switching means 20 is a tracking loop section 18
The track error signal is input from the subtractor 4, and the output of the track error signal is stopped each time the switching signal is input. When the light receiving section 1 receives the light beam, the pre-pit detecting means 22 detects the signal of the pre-pit area formed in the track included in the received light signal. When the pre-pit signal is detected along with the rotation of the optical disc, the switching determination means 23 determines whether or not the time when the light beam has passed through the sector format area a predetermined number of times has passed, and after the passage, the switching signal is sent to the pre-pit area. It outputs to the switching means 20 only during.

The peak / bottom detection means 24 is a switching means 20.
When the track error signal is input from, the peak and bottom values are calculated and averaged each time the track error signal is input, at least during one rotation of the optical disc.
The offset value correction means 25 obtains an offset correction value for correcting the offset included in the track error signal based on the average value of the peak and bottom values, and applies it to the subtractor 4 of the tracking loop unit 18. Gain correction means 26
Calculates a gain correction value for correcting the gain of the tracking loop unit 18 based on the average value of the peak and bottom values, and applies the gain correction value to the variable gain amplifier 3 of the tracking loop unit 18.

The concept of the present invention is configured as described above, and will be described below with reference to specific examples. FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention. In the figure, 1 to 15
Is the same as above. The analog switch 30 corresponds to the switching means 20. In the initial state, the contact is closed (hereinafter referred to as ON state), and when the switching signal is input, the contact is opened (hereinafter referred to as OFF state),
The track cross signal from the subtractor 4 is output to the peak / bottom detection circuit 11. The pre-pit signal creation circuit 31, the reproduction signal processing circuit 32, and the sector mark detection circuit 33 correspond to the pre-pit signal detection means 22, and the pre-pit signal generation circuit 31 irradiates a track of the optical disk with a light beam and reflects the reflected light beam. When the light receiving section 1 detects the prepit signal of the sector format of the disk of the present apparatus which is set in advance, the light receiving signal component corresponding to the set prepit signal is output as the detected prepit signal.

This pre-pit signal generating circuit 31 is used when a light beam is applied to the track of the optical disk of this apparatus.
The area up to the address section and the flag section of the sector format on that track is a prepit area, and a signal when the area is irradiated is set in advance. The reproduction signal processing circuit 32 binarizes the pre-pit signal, converts it into a digital signal, and outputs it. Sector mark detection circuit 33
Detects the sector mark indicating the beginning of the sector format written in the address section of the sector format,
The detection period is output as a sector mark signal. In order to make it easy to distinguish this sector mark from other areas (flag section, data section, etc.), the sector mark is detected especially when the mark length is lengthened or when it has a pattern that is not found elsewhere. Output as a signal.

The microcomputer 35 is provided with a program including at least a switching determination means 20, a peak bottom value calculation means 24, a gain correction means 25, and an offset correction means 26 in a ROM area (not shown) so as to insert an optical disk. Accordingly, when the pre-pit signal is detected,
It is judged whether or not the light beam has passed a sector format area a predetermined number of times, and after that, a switching signal is output to the switching means only during the prepit area, and a track error signal to the peak bottom value calculating means is output. Stop the output of. In addition, the microcomputer 35 has an irradiation time for irradiating the pre-pit area with the light beam (hereinafter referred to as pre-pit area time), an irradiation time for an area other than the pre-pit area of the sector format (hereinafter referred to as pre-pit area time), and an analog signal. Switch 30 ON / OF
The time for F is set in advance. Next, the structure of the sector format will be described.

FIG. 3 is an explanatory view for explaining the structure of the sector format. In this case, it is assumed that the CAV method is used, the rotation speed is 1800 rpm, and the sector format is divided into 17 on one track (final SM is not shown). As shown in the figure, the address part has an SM (Sector) indicating that it is the beginning of the sector format.
Mark), VFO which is a continuous repetitive data pattern for surely reproducing data even if there is a change in the rotation of the optical disc, AM (Address Mark) indicating a code read position (synchronization position), and the like. . In addition, the flag portion includes a flag gap, VFO, and a synchronization byte portion that enable detection of a data error.
This prepit area has small irregularities as shown in FIG. Further, the data section includes a data area and a buffer.

The sector format is 5 bytes for the SM and 650 bytes for the data part, for a total of 7 bytes.
It is 46 bytes. In the figure, the rotation speed is 18
In the case of 00 rpm, assuming that SM to the synchronous byte is the pre-pit area, the time for which the light beam is irradiated to this pre-pit area is 213 μs, the irradiation time for the area outside the pre-pit area is 1748 μs, and one sector format is irradiated. The total time is 1961 μs. Such a time is stored in advance, and the same signal as that of each part when light is received in the prepit area is set in the prepit signal generation circuit in advance.

The operation of the tracking control circuit configured as described above will be described below. In this case, in order to remove the pit pit signal of the track error signal, the microcomputer 35 is not feedback controlled. That is, since no signal is output to the variable gain amplifier 3 and the subtractor 4 in order to remove the prepit signal, the tracking loop is opened. Next, the light beam is forcibly shaken as the optical disc is inserted. At this time, the objective lens unit is controlled to perform tracking. When the light receiving unit 1 detects the light beam from the optical disc and outputs it as a light receiving signal, the track error signal obtained by the track error signal generating circuit 2 is as shown in FIG.
The waveform is shown in.

The track error signal including the pre-pit signal is input to the analog switch 30 via the variable gain amplifier 3 and the subtractor 4. Also, the light receiving unit 1
When the light beam from the optical disc is detected and output as a light reception signal, the pre-pit generation circuit 31 inputs the light reception signal. The pre-pit generating circuit 31 compares the received light signal with a pre-pit signal of a preset sector format of the present optical disc in response to the input of the received light signal, and processes a reproduction signal as a received pre-pit signal at a portion corresponding to the pre-pit signal. Output to the circuit 32. Next, the pre-pit signal is digitally converted by the reproduction processing circuit 32, and only the sector mark is detected by the sector mark detection circuit 33 and output to the microcomputer 35.

At this time, if the microcomputer 35 closes the contact of the analog switch 30, the track error signal is input to the peak bottom detection circuit 11, and the peak bottom detection circuit 11 includes the track error signal including the pit pit signal. In this case, the microcomputer 35 does not close the contact of the analog switch 30 and performs the processing described below, and then closes the contact of the analog switch. Next, the operation of the microcomputer according to the present invention will be described. In this case, the analog switch 30 is assumed to be ON in the initial state. 4 and 5
Is a flow chart for explaining the operation of the microcomputer according to the present invention.

First, the microcomputer 35 determines whether a sector mark signal is input (S401),
When the sector mark is input, the timer 1 is started (S403). When this sector mark signal is input, since the analog log switch 30 is in the ON state, the track error signal including the prepit signal is input to the peak / bottom detection circuit 11 to detect the peak value and the bottom value of the track error signal. Then, it is input to the microcomputer 35 via the A / D 12. However, in the initial stage, the microcomputer 35 may have small peaks and bottom waves of the track error signal depending on the amount of eccentricity of the optical disc. May fall on the first peak part, so that the peak and bottom values detected by the peak / bottom detection circuit 11 are not read when the sector format associated with the first rotation is irradiated.

Next, the microcomputer 35 reads the timer 1 (S405) and determines whether the timer 1 has reached 1956 μs (S507). This 1956 μs
This is the total time that the light beam irradiates the above-mentioned sector format, and the fact that the timer 1 has counted 1956 μs means that it is the time when the sector format was irradiated at the initial rotation of the optical disk. Next, when it is determined that the timer 1 has reached 1956 μs, the timer 2 is started (S409).
Then, the analog switch 30 is turned off (S41
1). Here, turning off the analog switch after 1956 μs means that the prepit signal is included in the bottom waveform of the track error signal, and therefore the track error signal at this time is not input to the peak bottom detection circuit 11. Become. Next, the value of the timer 2 is read (S413), and it is determined whether the timer 2 has reached 225 μs (S415). This 225 μs is in the pre-pit area in the sector format (213 μs)
The processing time and the rotation jitter for turning on / off the analog switch 30 after reading the sector mark signal which is the synchronization signal are taken into consideration. Next, when the microcomputer 35 determines that the timer 2 has counted 225 μs, it turns off the timer 2 and clears the timer 2 (S417).

Then, as shown in FIG. 5, the analog switch 30 is turned on (S501). As a result, only the track error signal other than the prepit area of the sector format is input to the peak bottom detection circuit. next,
The microcomputer 35 starts the timer 2 (S503). Then, the timer 2 is read (S505),
It is determined whether the timer 2 has reached 1736 μs (S507). The value of 1736 μs is a value slightly corrected because the jitter and the ON / OFF time of the analog switch 30 are taken into consideration in advance. next,
If the timer 2 reaches 1936 μs, the timer 2 is turned off and the value is cleared (S509). Then, it is determined whether or not the track error signal for one rotation is detected, and if not detected, the control proceeds to step S409 in FIG. 4 (S511).

That is, since the sector format is divided into 17 on one track, the track error signal excluding the prepit signal is read 17 times, and the offset correction value and gain correction value are calculated based on the average of the peak and bottom values. Is calculated and applied to the tracking loop. Such processing will be described with a timing chart. FIG. 6 is a timing chart for explaining the operation of the present invention. Also in this case, similarly, the CAV system in which one track is followed by the tracks of the optical disk divided into the 17-sector format and the rotation speed of the optical disk is constant. Further, the analog switch is assumed to be ON in the initial state. When following such an optical disc, a track error signal as shown in (a) is obtained due to the eccentricity of the optical disc or the like. At this time, when the light beam passes through the pre-pit area of the sector format of the track, the pre-pit signal from the pit area is added to the track error signal. This means that if the irradiation time of one sector format is 213 μs in the pyretite region and 1748 μs in the region other than the prepit region, the prepit signal of the next sector format will be added to the track error signal after 1961 μs.

In this pre-pit signal, for example, when the first pre-pit signal rides on the peak side waveform, the next pre-pit signal rides on the bottom side waveform. To prevent this pre-pit signal from being input to the peak bottom detection circuit 11,
As shown in (b), when the pre-pit signal is first detected, the sector mark of the pre-pit signal is detected to be a sector mark signal, which is output every 1961 μs. With the output of the sector mark signal, the timer 1 is started as shown in (c), and 1956 μs is counted in consideration of the switching time of the analog switch 30, the jitter, and the like.
F Then, as the timer 1 is turned off, (d)
Start timer 2 as shown in
225 μs is counted in consideration of 0 switching time, jitter, etc., and after counting 225 μs, timer 2 is set to 1936 μs.
The operation of turning off only s is repeated.

With the start of the timer 2,
As shown in (e), the analog switch 30 is turned off, and after the timer 2 has counted 225 μs, the operation of turning on the analog switch 30 based on the count count of the timer 2 is repeated. When the timer 2 is started, the analog switch 30 is turned off. Depending on how the light beam traverses, the prepit area may not be illuminated, and noise may not be included in the track error signal. . Therefore, the generation cycle of the pre-pit signal is almost constant regardless of whether the pre-pit signal is included in the track error signal or not. Therefore, the timer 2 outputs the track error signal to the peak-bottom detection circuit 11 every 1936 μs. It has stopped.

To repeat the operation of turning on the analog switch 30 based on the count of the timer 2 is repeated 17 times because one track has a 17-sector format. In the above embodiment, the sector mark is detected, but other prepit areas may be used as long as the sector mark can be clearly detected as a prepit signal. Further, although the analog switch is turned on / off by the timer of the microcomputer in the above embodiment, a hardware timer circuit may be provided to turn on / off the analog switch. Further, in the above-described embodiment, the tracking method using the objective lens is shown, but tracking control not using the objective lens may be used.

[0031]

As described above, according to the present invention, the tracking loop portion and the peak bottom value calculating means are connected by the switching means, and the pre-pit signal included in the light receiving signal is detected as the optical disk rotates. When the pre-pit signal is input, it is determined whether or not the time for the light beam to pass through the sector format area of the optical disc has elapsed, and a switching signal is output to the switching means for each elapsed time to calculate the peak bottom. By stopping the output of the track error signal to the means, it is possible to obtain the track error signal that does not include the prepit signal. Further, since the track error signal that does not include the pre-pit signal can be obtained, accurate peak and bottom values can be obtained, and the offset correction value that corrects the offset included in the track error signal can be accurately obtained. Since the offset contained in can be accurately removed and an accurate gain correction value can be obtained, the effect that the level of the tracking error signal can be accurately set to a constant level is obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a concept of the present invention.

FIG. 2 is a schematic configuration diagram showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating a configuration of a sector format.

FIG. 4 is a flowchart explaining the operation of the microcomputer according to the present invention.

FIG. 5 is a flowchart explaining the operation of the microcomputer according to the present invention.

FIG. 6 is a timing chart explaining the operation of the present invention.

FIG. 7 is a schematic configuration diagram of a conventional tracking control circuit.

FIG. 8 is an explanatory diagram of a typical track form.

FIG. 9 is a waveform diagram of a track error signal.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Light receiving part 2 Track error signal generation circuit 3 Gain variable amplifier 10 LPF 11 Peak bottom detection circuit 20 Switching means 22 Pre-pit detection means 23 Switching determination means 24 Peak bottom detection means 25 Offset value correction means 26 Gain correction means 30 Analog switch 31 Pre-pit Signal creation circuit 33 Sector mark detection circuit 35 Microcomputer

Claims (1)

[Claims] 1. A tracking loop unit that causes a light beam to follow the track center of the optical disc by a track error signal based on a light reception signal from a light receiving unit that receives a reflected beam from the optical disc;
In a tracking control circuit having at least a peak / bottom detection means for calculating an average value of the peak and bottom values of a track error signal for rotation, a sector format of the sector format formed in the track included in the light reception signal from the light receiving unit is used. Pre-pit detecting means for detecting a signal in the pre-pit area as a pre-pit signal; and a switching judging means for judging whether the light beam has passed through the area of the sector format when the pre-pit signal is detected and outputting a switching signal. And a switching means for inputting the switching signal and stopping the output of the track error signal to the peak-bottom detection means.