JP3439139B2 - Tracking servo circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking servo circuit for controlling the position of a pickup with respect to a disc type recording medium.

[0002]

2. Description of the Related Art A compact disc (CD) used for digital audio is also utilized as a read-only memory (CD-ROM) for storing various digital data that can be read by a computer device. In a disc reproducing apparatus for reproducing such a CD,
A servo mechanism is provided to control the relative position of the disc and the pickup so that the pickup can correctly trace the spiral recording track recorded on the disc.

FIG. 4 is a block diagram showing an outline of a disk reproducing apparatus including a servo mechanism.

The disc 1 has a spiral recording track formed on at least one surface thereof, and digital data according to a predetermined format is recorded along the recording track. For example, in the case of a CD, as shown in FIG. 5, according to an EFM signal obtained by EFM modulating digital data,
A convex portion (pit) having a predetermined length is formed on the recording track. The spindle motor 2 rotationally drives the disk 1 at a predetermined speed in response to a drive signal SD supplied from a servo control unit 6 described later. Pickup 3
It includes a laser light source and a sensor, and is arranged so as to face the recording track surface of the disc 1 and to be movable in the radial direction of the disc 1. As shown in FIG. 5, the pickup 3 has a main reading light P for reading the presence or absence of pits on the recording track surface and a pair of auxiliary reading lights T1, T for detecting the positional deviation of the pickup 3 with respect to the recording track.
Have two. These reading lights P, T1, and T2 are weakly reflected to the sensor side when irradiated onto the pits of the disk 1, and strongly reflected to the sensor side when reflected outside the pits. Then, in the sensor that receives each reflected light, the intensity of each reflected light is extracted as a voltage value. The actuator 4 supports the pickup 3 and moves the pickup 3 in the radial direction of the disc 1 in response to a drive signal TD described later.

The signal processor 5 receives the voltage value extracted from the pickup 3 based on the main reading light P,
An EFM that repeats high / low corresponding to the unevenness on the recording track of the disk 1 by performing processing such as waveform shaping and binarization.
Generate a signal. Further, the signal processing unit 5 generates the tracking error signal TE from the difference between the two voltage values based on the auxiliary reading lights T1 and T2, and generates the off-track signal OT from the low frequency component of the EFM signal. When the pickup 3 is at the correct position on the recording track of the disc 1, the voltage values based on the auxiliary reading lights T1 and T2 become equal to each other, and therefore the tracking error signal TE based on the difference therebetween.
Is maintained at the "0" level. Then, when the pickup 3 is displaced toward the inside of the recording track, for example, the voltage value based on the auxiliary reading light T1 becomes smaller than the voltage value based on the auxiliary reading light T2, and the tracking error signal TE becomes negative. Conversely, when the pickup 3 is displaced to the outside of the recording track, for example, the auxiliary reading light T
The voltage value based on 2 becomes smaller than the voltage value based on the auxiliary reading light T1, and the tracking error signal TE becomes positive. Further, when the pickup 3 is correctly tracing the recording track of the disc 1, the EFM signal is continuously extracted, so that the EFM signal does not include a low frequency component, and the off-track signal OT is maintained at a low level. To be done.

The servo control unit 6 receives the EF from the signal processing unit 5.
The spindle motor drive signal SD is received by receiving the tracking error signal TE and the off-track signal OT together with the M signal.
And an actuator drive signal TD. That is, E
The frequency of the FM signal is maintained at a predetermined value to generate the drive signal SD for driving the spindle motor 2, the tracking error signal TE is brought close to the “0” level, and the off-track signal OT is maintained at the low level. Then, the drive signal TD for driving the actuator 4 is generated. As a result, spindle servo and tracking servo are realized.

FIG. 6 is a waveform diagram of each signal that appears when a so-called track jump is performed in which the pickup 3 is moved across the recording track of the disc 1. In this figure, the horizontal axis represents time, and shows the case where the pickup 3 moving at a predetermined speed is decelerated.

The tracking error signal TE exhibits a sinusoidal waveform by repeating the inversion of the polarity every time the pickup 3 crosses one recording track. Therefore, with the level "0" as the threshold value, the tracking error signal TE
Is binarized, a track jump signal TJ having a rising or falling edge can be obtained when the center of the pickup 3 is at the center of the recording track. Also, EF
The M signal has a predetermined amplitude when the pickup 3 is on the recording track, and maintains a constant value when the pickup 3 deviates from the recording track. Therefore, the off-track signal OT is
When the center of the pickup 3 is near the end of the pit, it has a rising or falling edge. Normally, the off-track signal OT has a phase difference of ± 90 ° with respect to the tracking error signal TE. Therefore,
Tracking error signal TE or off-track signal O
By counting T, the number of recording tracks skipped by the pickup 3 is detected, and the moving direction of the pickup 3 is detected from the phase difference between the tracking error signal TE and the off-track signal OT. The movement of the pickup 3 is controlled based on these detection results.

[0009]

When the pickup 3 is moved in the radial direction of the disk 1 and stopped at the target position, the pickup 3 is accelerated at the start of the movement, and the pickup 3 is decelerated from before the stop position. Then, the drive signal TD is generated. The stop control of the pickup 3 is usually configured to take out either the positive polarity or the negative polarity of the tracking error signal TE and apply a starting force in the direction opposite to the moving direction according to the value. For example, when the pickup 3 is moving toward the outer periphery of the disc 1, the tracking error signal TE is taken out during the high level period of the track jump signal TJ, and the reverse starting force, that is, the braking force is given according to the taken out value. . When the moving direction of the pickup 3 is opposite (from the outer circumference to the inner circumference), the tracking error signal TE is taken out during the low level period of the track jump signal TJ.

When the tracking error signal TE is taken out on the basis of the track jump signal TJ, if the phases are deviated from each other, the tracking error signal TE cannot be biased to a specific polarity, so that the moving pickup 3 is sufficiently moved. You cannot slow down. For example, as shown in FIG. 7, when the track jump signal TJ is delayed with respect to the tracking error signal TE, the tracking error signal T extracted in response to the track jump signal TJ.
Since E ′ includes the period of negative polarity, the pickup 3 may be accelerated. The horizontal axis of FIG. 7 represents the moving distance of the pickup 3. As a result, there is a possibility that so-called slippage occurs, in which the pickup 3 does not stop even if it exceeds the target position. In addition, since the actuator 4 itself has a difference in operation characteristics due to a difference in structure, manufacturing variations, and the like, even if the same processing is performed on the circuit in generating the drive signal TD, the reproducibility of the operation is improved. Sometimes you can't get it.

Therefore, according to the present invention, the moving pickup 3 is used.
The purpose is to give an accurate braking force to the vehicle so as to surely stop at the target position.

[0012]

The present invention has been made to solve the above problems, and is characterized in that a disk type recording medium having a spiral recording track and recording of the recording track are provided. The relative position with respect to the pickup that reads information is controlled based on a tracking error signal that changes to a positive polarity when the pickup shifts to one side of the recording track and changes to a negative polarity when the pickup shifts to the other side. A tracking servo circuit, an A / D converter for digitizing the tracking error signal obtained when the pickup is moved in the radial direction of the disk type recording medium to generate error data, and the error data On the other hand, the first and second multipliers that give the first and second gains respectively, and the output of the first multiplier or the second multiplier. A selector that selects and extracts one of the outputs of the multiplier, a selection control unit that determines the selection operation of the selector based on the sign bit indicating the polarity of the error data, and a selection output of the selector. In response, a drive signal generation unit that generates a drive signal that brakes the pickup that moves in the radial direction of the disk-type recording medium,
Is equipped with.

According to the present invention, the tracking error signal is digitized to generate error data, and the error data is selected based on the sign bit thereof. At this time, since the selection control means can be configured by a small number of logic gates, it is possible to reduce the delay amount and prevent the displacement timing of replacement of error data. At the same time, the gains to be given to the first and second multipliers can be individually set, so that fine setting according to the movement mechanism of the pickup can be performed and the movement of the pickup can be controlled more accurately. it can.

[0014]

1 is a block diagram showing an embodiment of a tracking servo circuit of the present invention, and FIG.
FIG. 7 is a waveform chart of each signal for explaining the operation. This tracking servo circuit corresponds to the servo control unit 6 which constitutes the disc reproducing apparatus shown in FIG. 4, and has a tracking error signal TE and an OFF signal supplied from a signal processing unit that performs a predetermined process on the output of the pickup. It operates based on the track signal OT.

The tracking servo circuit of the present invention is
D converter 11, first and second multipliers 12a, 12b,
The selector 13, the direction determination unit 14, the EXOR gate 15, and the drive signal generation unit 16 are included.

The A / D converter 11 samples the tracking error signal TE represented by an analog value at a cycle shorter than that of the tracking error signal TE, standardizes the sampling value, and digitizes it into a proper number of bits. The error data ER is generated. This error data ER is
It is generated so that the most significant bit represents the polarity of the tracking error signal TE and the remaining bits represent the amplitude of the tracking error signal TE. In the normal circuit operation of the A / D converter 11, since the value is determined between the ground potential and the power supply potential, the tracking error signal is referenced with the intermediate potential between the ground potential and the power supply potential as a reference. TE
Is determined. Here, the intermediate potential that serves as a reference for polarity determination is set so as to match the threshold value when the tracking error signal TE is binarized to generate the track jump signal TJ.

The first and second multipliers 12a and 12b are
First and second multipliers A1 and A that can be individually set
2 and multiplies the error data ER input from the A / D converter 11 by the first and second multipliers A1 and A2, respectively, and outputs the first and second multiplication data MP1 and MP2.
To generate. Here, when the first multiplier A1 is set to a positive value, the second multiplier A2 is set to a negative value,
The second multiplication data MP obtained from the second multiplier 12b
In No. 2, the polarity is inverted with respect to the error data ER. The first and second multipliers A1 and A2 can be individually set, and are set according to the operating characteristics of the mechanism for moving the pickup. Selector 13
Selects one of the first and second multiplication data MP1 and MP2 obtained from the first and second multipliers 12a and 12b and supplies the selected one to the drive signal generation unit 16 described later.

The direction determining section 14 is a track jump signal TJ obtained by binarizing the tracking error signal TE.
And the off-track signal OT are received, the moving direction of the pickup is determined based on the phase difference between them, and a direction indicating signal DR indicating the moving direction of the pickup is output. For example, the off-track signal OT is the track jump signal T
When the phase is delayed by 90 ° with respect to J, it is determined that the pickup is moving from the inner circumference side to the outer circumference side of the disc, and the direction indicating signal DR is fixed to the high level. vice versa,
When the off-track signal OT leads the track jump signal TJ by 90 ° in phase, it is determined that the pickup is moving from the outer circumference side to the inner circumference side of the disc, and the direction indicating signal DR is fixed to the low level. The direction determination unit 14 has the same determination result until the pickup reaches the target position. Therefore, the track jump signal TJ
The timing deviation between the tracking error signal TE and the tracking error signal TE does not matter.

The EXOR gate 15 takes the exclusive OR of the sign bit ER ₀ of the tracking error signal TE and the direction designating signal DR and supplies the output to the selector 13 as the selection signal SL. As a result, as shown in FIG. 2, when the direction indicating signal DR is at the high level, the sign bit ER ₀
Inverted by the select signal SL, and the first multiplier data MP1 selected period sign bit ER ₀ indicates a positive polarity, the second multiplication data M during the sign bit ER ₀ indicates negative polarity
Select P2. The polarity of the second multiplication data MP2 is inverted with respect to the error data ER, and the tracking error signal TE 'exhibits a positive polarity in all periods. Further, when the direction indicating signal DR is at the low level, the code bit ER ₀ is directly used as the selection signal SL, the first multiplication data MP1 is selected in the period in which the code bit ER ₀ exhibits the negative polarity, and the code bit ER ₀ has the positive polarity. The second multiplication data MP2 is selected during the period indicated by. As mentioned above,
Since the polarity of the second multiplication data MP2 is inverted with respect to the error data ER, the tracking error signal T
E'becomes negative in all periods. In the actual circuit, the tracking error signal TE 'is
It is represented by digitized error data ER and inverted error data IER.

The drive signal generator 16 controls the control data AC from a control system (not shown) that instructs the movement of the pickup.
In response to the error data ER or the fixed data CV extracted from the selector 13, a braking signal is generated, and these signals are combined to generate a drive signal TD. The drive signal TD generated by the drive signal generation unit 16 is based on the sign bit,
The braking signal is generated so as to limit the error data ER to only one polarity. For this reason, when the pickup moves in the radial direction on the recording surface of the disc, as shown in FIG. 3, the tracking error signal TE exhibits a positive polarity, between the approximate center of the pit gap and the approximate center of the next pit. Then, the first deceleration will be performed. Then, the second deceleration is performed between the approximate center of the pit and the approximate center of the next pit gap in which the tracking error signal TE exhibits a negative polarity. Regarding the first and second deceleration processing, the first and second multipliers 12a and 12a, respectively.
It is determined by the first and second multipliers A1 and A2 set to b, and independent control is possible. The horizontal axis of FIG. 3 represents the moving distance of the pickup. Further, the stop position of the pickup is preferably at the center of the pit, but even if the pickup is stopped with some deviation, the servo moves when the disc starts to rotate, so the pickup moves to the center of the pit.

In the above embodiment, the selection control signal SL for controlling the switching of the selector 13 and the error data ER.
The difference in timing between and is only due to the delay of the EXOR gate 15, and the selector 13 operates correctly as in the first embodiment. In addition, it can be controlled independently while the pickup moves in the radial direction of the disc.
More precise control is possible because different types of deceleration processing are performed.

In the above embodiment, the case where the deceleration processing is continuously performed for the movement of the pickup is illustrated. However, one of the first and second multipliers A1 and A2 is " By setting it to "0", it is possible to decelerate the pickup only between the approximate center of the pit gap and the approximate center of the next pit.

[0023]

According to the present invention, only one polarity of the tracking error signal can be taken out at an accurate timing, and a braking force is applied to the pickup based on the taken tracking error signal, so that the radial direction of the disc is increased. The pickup that moves to can be stopped exactly. Further, since the braking force can be set individually in the two periods, the braking force can be finely set according to the configuration of the moving mechanism of the pickup, and as a result, the time required for the pickup to move between tracks can be reduced. It can be shortened and the response speed can be expected to improve.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a tracking servo circuit of the present invention.

FIG. 2 is a waveform diagram of each signal for explaining the operation of the embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between movement of a pickup and a tracking error signal.

FIG. 4 is a block diagram showing a configuration of a disc reproducing device.

FIG. 5 is a plan view showing a structure of a recording track of a disc type recording medium.

FIG. 6 is a diagram showing a relationship between a tracking error signal and an off-track signal.

FIG. 7 is a diagram showing a relationship between movement of a pickup and a tracking error signal.

[Explanation of symbols]

1 disc 2 spindle motor 3 pickups 4 actuators 5 Signal processor 6 Servo control unit 11 A / D converter 12a, 12b multiplier 13 selector 14 Direction determination unit 15 EXOR gate 16 Drive signal generator 18 Inverter

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G11B ^7/ 08-7/10 G11B 21/10

Claims (3)

(57) [Claims] 1. A relative position between a disc type recording medium having a spiral recording track and a pickup for reading recorded information on the recording track is changed to a positive polarity when the pickup is displaced to one side of the recording track, A tracking servo circuit that controls based on a tracking error signal that changes to a negative polarity when deviated to the other side, wherein the tracking error obtained when the pickup is moved in the radial direction of the disk type recording medium. An A / D converter that digitizes a signal to generate error data, and a first and a second for the error data, respectively.
And a selector that selects and outputs either the output of the first multiplier or the output of the second multiplier, and the polarity of the error data. Selection control means for determining the selection operation of the selector based on the indicated sign bit, and a drive signal for braking the pickup moving in the radial direction of the disk type recording medium in response to the selection output of the selector And a drive signal generation section for performing the tracking servo circuit. 2. The second gain provided by the second multiplier has an opposite polarity to the first gain provided by the second multiplier. Tracking servo circuit. 3. A direction detecting section for detecting a moving direction of the pickup is further provided, and the selection control means, in response to a detection result of the direction detecting section, selects a sign bit of the error data and the selector. The tracking servo circuit according to claim 2, wherein the correspondence with the operation is reversed.