JP3851004B2 - Pickup movement control circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pickup movement control circuit for controlling the position of a pickup with respect to a disk type recording medium.
[0002]
[Prior art]
A compact disk (CD) used for digital audio is also used as a read-only memory (CD-ROM) for storing various digital data that can be read by computer equipment. In such a disk reproducing apparatus for reproducing a CD, a servo mechanism is provided to control the relative position between the disk and the pickup so that the pickup can correctly trace the spiral recording track recorded on the disk. .
[0003]
FIG. 6 is a block diagram showing an outline of a disk reproducing apparatus including a servo mechanism.
[0004]
On the disk 1, a spiral recording track is formed on at least one surface, and digital data according to a predetermined format is recorded along the recording track. For example, in the case of CD, as shown in FIG. 7, in accordance with the EFM signal obtained by the digital data by EFM modulation, concave portion having a predetermined length on the recording track (pit) is formed. The spindle motor 2 rotates the disk 1 at a predetermined speed in response to a drive signal SD supplied from a servo control unit 6 described later. The pickup 3 includes a laser light source and a sensor, and is disposed so as to face the recording track surface of the disk 1 and be movable in the radial direction of the disk 1. As shown in FIG. 7, 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 and T2 for detecting a positional deviation of the pickup 3 with respect to the recording track. These reading lights P, T1, and T2 are weakly reflected to the sensor side when irradiated onto the pits of the disk 1, and are strongly reflected to the sensor side when reflected from other than the pits. And in the sensor which receives each reflected light, the intensity | strength of each reflected light is taken out as a voltage value. The actuator 4 supports the pickup 3 and moves the pickup 3 in the radial direction of the disk 1 in response to a drive signal TD described later.
[0005]
The signal processing unit 5 receives a voltage value extracted from the pickup 3 based on the main reading light P, performs processing such as waveform shaping and binarization, and corresponds to the unevenness on the recording track of the disk 1 to high / low. To generate an EFM signal. Further, the signal processing unit 5 generates a tracking error signal TE from a difference between two voltage values based on the auxiliary reading lights T1 and T2, and generates an off-track signal OT from a low frequency component of the EFM signal. When the pickup 3 is at the correct position on the recording track of the disk 1, the voltage values based on the auxiliary reading lights T1 and T2 are equal to each other, and therefore the tracking error signal TE based on the difference is maintained at the “0” level. . When the pickup 3 is displaced to 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. On the contrary, when the pickup 3 is shifted to the outside of the recording track, for example, the voltage value based on the auxiliary reading light T2 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 correctly traces the recording track of the disk 1, the EFM signal is continuously taken out, so the low frequency component is not included in the EFM signal, and the off-track signal OT is maintained at the low level. Is done.
[0006]
The servo control unit 6 includes a tracking servo circuit , receives the tracking error signal TE and the off-track signal OT together with the EFM signal from the signal processing unit 5, and generates a spindle motor drive signal SD and an actuator drive signal TD. That is, the drive signal SD for driving the spindle motor 2 is generated by maintaining the frequency of the EFM signal at a predetermined value, the tracking error signal TE is brought close to the “0” level, and the off-track signal OT is maintained at the low level. so as to drive signal TD for driving the actuator 4 is generated. Thereby, spindle servo and tracking servo are realized.
[0007]
FIG. 8 is a waveform diagram of each signal appearing when a so-called track jump is performed in which the pickup 3 is moved across the recording track of the disk 1 by opening the tracking servo loop . In this figure, the horizontal axis represents time, and the case where the pickup 3 moving at a predetermined speed is decelerated is shown.
[0008]
The tracking error signal TE repeats polarity inversion every time the pickup 3 crosses one recording track, and shows a sinusoidal waveform. Therefore, when the tracking error signal TE is binarized using the level “0” as a threshold value, 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. The EFM signal has a predetermined amplitude when the pickup 3 is on the recording track, and maintains a constant value when the pickup 3 is off the recording track. Therefore, the off-track signal OT has a pit at the center of the pickup 3. It has a rise or fall when it is near the edge. Normally, the off-track signal OT has a phase difference of ± 90 ° with respect to the tracking error signal TE. Therefore, by counting the tracking error signal TE or the off-track signal OT, the number of recording tracks skipped by the pickup 3 is detected, and the movement direction of the pickup 3 is determined from the phase difference between the tracking error signal TE and the off-track signal OT. To detect. Based on these detection results, the movement of the pickup 3 is controlled.
[0009]
[Problems to be solved by the invention]
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 movement, and the drive signal TD is generated so as to decelerate the pickup 3 before the stop position. . 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 give 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 disk 1, the tracking error signal TE is extracted during the high level period of the track jump signal TJ, and a reverse starting force, that is, a braking force is applied according to the extracted value. . When the movement direction of the pickup 3 is reverse (from the outer periphery toward the inner periphery), the tracking error signal TE is extracted during the low level period of the track jump signal TJ.
[0010]
When the tracking error signal TE is extracted based on the track jump signal TJ, if the phase is shifted, the tracking error signal TE cannot be biased to a specific polarity, so that the moving pickup 3 cannot be sufficiently decelerated. . For example, as shown in FIG. 9, when the track jump signal TJ is delayed with respect to the tracking error signal TE, the tracking error signal TE ′ extracted in response to the track jump signal TJ includes a negative polarity period. In some cases, the pickup 3 is accelerated. The horizontal axis in FIG. 9 represents the moving distance of the pickup 3 , and the concave portion represents a pit . As a result, there is a possibility that a so-called slip that does not stop even if the pickup 3 exceeds the target position may occur.
[0011]
Accordingly, an object of the present invention is to apply an accurate braking force to the moving pickup 3 and to reliably stop the pickup at the target position.
[0012]
[Means for Solving the Problems]
The present invention has been made to solve the above-mentioned problems. The first feature is a pickup movement control circuit that accelerates and decelerates a pickup in a predetermined direction to stop a target position. The relative position of the disk-type recording medium having a spiral recording track and the pickup for reading the recording information of the recording track changes to positive polarity when the pickup is shifted to one side of the recording track, and the other side Obtained when the pickup servo is moved in the radial direction of the disk-type recording medium, and the tracking servo circuit is controlled based on a tracking error signal that changes to a negative polarity when shifted and opens a servo loop at the time of track jump. An A / D converter that digitizes the tracking error signal to generate error data, and the error data or A selector taking out by selecting one of the fixed data indicating a predetermined value, the off-track signal generated from the low-frequency component of the EFM signal, the moving direction of the pickup from the phase difference between the tracking error signal Responding to the direction detection unit to detect, the sign bit indicating the polarity of the error data, the selection control means for determining the selection operation of the selector based on the detection result of the direction detection unit, and the selection output of the selector And a drive signal generator for generating a drive signal for braking the pickup that moves in the radial direction of the disk type recording medium.
[0013]
The second feature is a pickup movement control circuit for accelerating and decelerating the pickup in a predetermined direction to stop the target position, and includes a disc type recording medium having a spiral recording track and a recording track. Controls the relative position of the pickup that reads recorded information based on a tracking error signal that changes to positive polarity when the pickup is shifted to one side of the recording track and changes to negative polarity when the pickup is shifted to the other side. A tracking servo circuit that opens a servo loop at the time of track jump, and an A / D that generates error data by digitizing the tracking error signal obtained when the pickup is moved in the radial direction of the disk type recording medium A converter, an inverter for inverting the error data to generate inverted error data, A selector for retrieving the error data, or by selecting one of the inverted error data, and the off-track signal generated from the low-frequency component of the EFM signal, the moving direction of the pickup from the phase difference between the tracking error signal Responding to the direction detection unit to detect, the sign bit indicating the polarity of the error data, the selection control means for determining the selection operation of the selector based on the detection result of the direction detection unit, and the selection output of the selector And a drive signal generator for generating a drive signal for braking the pickup that moves in the radial direction of the disk type recording medium.
[0014]
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 and the detection result of the moving direction of the pickup . At this time, since the selection control means can be composed of a small number of logic gates, the amount of delay can be reduced, and displacement of the replacement timing for error data can be prevented. Therefore, the digital data indicating the positive polarity period and the digital data indicating the negative polarity period of the tracking error signal can be correctly distributed.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing a first embodiment of the pickup movement control circuit of the present invention, and FIG. 2 is a waveform diagram of each signal for explaining the operation thereof. This pickup movement control circuit corresponds to the servo control unit 6 constituting the disk reproducing apparatus of FIG. 6, and includes a tracking error signal TE supplied from a signal processing unit that performs predetermined processing on the output of the pickup, and It operates based on the off-track signal OT.
[0016]
The pickup movement control circuit of the present invention includes an A / D converter 11, a register 12, a selector 13, a direction determination unit 14, an EXOR gate 15, and a drive signal generation unit 16.
[0017]
The A / D converter 11 samples the tracking error signal TE represented by an analog value at a shorter cycle than the tracking error signal TE, normalizes the sampling value, and digitizes error data ER with an appropriate number of bits. Is generated. The error data ER 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 based on the intermediate potential between the ground potential and the power supply potential. The polarity of TE is determined. Here, the intermediate potential serving as a reference for polarity determination is set so as to coincide with the threshold value when the tracking error signal TE is binarized to generate the track jump signal TJ.
[0018]
The register 12 stores fixed data CV having the same number of bits as the tracking error signal TE. The fixed data CV is set to match the error data ER corresponding to the tracking error signal TE when the amplitude is “0”, for example. The register 12 only needs to be able to fix each bit of the fixed data CV to either the high level or the low level. Therefore, the register 12 can be configured to be constantly connected to the power supply potential or the ground potential. The selector 13 selects either the error data ER input from the A / D converter 11 or the fixed data CV input from the register 12 and supplies it to the drive signal generation unit 16 described later.
[0019]
The direction determination unit 14 receives the track jump signal TJ obtained by binarizing the tracking error signal TE and the off-track signal OT obtained from the low frequency component of the EFM signal, and the moving direction of the pickup based on the phase difference between them. And a direction instruction signal DR indicating the moving direction of the pickup is output. For example, when the phase of the off-track signal OT is delayed by 90 ° with respect to the track jump signal TJ, it is determined that the pickup is moving from the inner circumference side to the outer circumference side of the disc, and the direction indication signal DR is set to the high level. Fix it. On the other hand, when the off-track signal OT is advanced in phase by 90 ° with respect to the track jump signal TJ, it is determined that the pickup is moving from the outer peripheral side of the disc to the inner peripheral side, and the direction indicating signal DR is set to the low level. Fix it. In this direction determination unit 14, since the same determination result is obtained until the pickup reaches the target position, the timing shift between the track jump signal TJ and the tracking error signal TE does not matter.
[0020]
The EXOR gate 15 takes an exclusive OR of the sign bit ER ₀ of the tracking error signal TE and the direction indication signal DR and supplies the output to the selector 13 as a selection signal SL. Thereby, as shown in FIG. 2, when the direction indication signal DR is at the high level, the sign bit ER ₀ is inverted to be the selection signal SL, and the fixed data CV is selected and output during the low level period of the selection signal SL. Thus, the error data ER is replaced with the fixed data CV during the period in which the sign bit ER ₀ is negative. As a result, the tracking error signal TE ′ has a negative amplitude of “0”. When the direction indication signal DR is at a low level, the sign bit ER ₀ is used as it is as the selection signal SL, and the fixed data CV is selected and output during the low level period of the selection signal SL, so that the sign bit ER ₀ exhibits positive polarity. During the period, the error data ER is replaced with the fixed data CV. As a result, the tracking error signal TE ′ has a positive polarity of “0”. In an actual circuit, the racking error signal TE ′ is represented by digitized error data ER and fixed data CV. Here, the timing difference between the selection control signal SL for controlling the switching of the selector 13 and the error data ER is only the delay of the EXOR gate 15, and the EXOR gate 15 is longer than the sampling period of the A / D converter 11. If the delay time is set to be short, the selector 13 operates correctly.
[0021]
The drive signal generation unit 16 generates an acceleration signal in response to control data AC from a control system (not shown) instructing movement of the pickup, and generates error data ER or fixed data CV extracted from the selector 13. In response, a braking signal is generated, and these signals are combined to generate a drive signal TD. The drive signal TD generated in the drive signal generation unit 16 includes a braking signal generated so as to limit the error data ER to only one polarity based on the sign bit. For this reason, as shown in FIG. 3, when the tracking servo loop is opened and the pickup moves in the radial direction on the recording surface of the disk, a period during which the tracking error signal TE is positive, that is, the pit gap The pickup is decelerated only between approximately the center and approximately the center of the pit. The horizontal axis in FIG. 3 represents the movement distance of the pickup , and the concave portion represents a pit . Although the pickup stop position is preferably at the center of the pit, the tracking servo operates when the disk starts to rotate even when the pickup stops, so that the pickup moves to the center of the pit.
[0022]
FIG. 4 is a block diagram showing a second embodiment of the pickup movement control circuit of the present invention, and FIG. 5 is a waveform diagram of each signal for explaining its operation. The second embodiment is different from the first embodiment shown in FIG. 1 in that the register 12 is replaced with an inverter 18.
[0023]
For example, the inverter 18 includes a plurality of inverters, is connected to the A / D converter 11, inverts each bit of the error data ER input from the A / D converter 11, and outputs the inverted error data IER. Output. This inversion error data IER is supplied to the selector 13 in the same manner as the fixed data CV in FIG. In the selector 13, either the error data ER input from the A / D converter 11 or the inverted error data IER input through the inverter 18 is selected in response to the selection control signal SL and driven. The signal is supplied to the signal generator 16. The generation of the drive signal TD in the drive signal generator 16 is the same as that of the first embodiment shown in FIG.
[0024]
In the above-described pickup movement control circuit, as shown in FIG. 5, when the direction indication signal DR is at a high level, the sign bit ER0 is inverted to become the selection signal SL, and error data is displayed during the period in which the sign bit ER0 is negative. ER is replaced with inversion error data IER. As a result, the tracking error signal TE ′ becomes positive in all periods. When the direction indication signal DR is at a low level, the sign bit ER0 is used as it is as the selection signal SL, and the error data ER is replaced with the inverted error data IER during the period when the sign bit ER0 is positive. As a result, the tracking error signal TE ′ becomes negative in all periods. In an actual circuit, the tracking error signal TE ′ is represented by digitized error data ER and inverted error data IER. Also in this embodiment, the timing difference between the selection control signal SL for controlling the switching of the selector 13 and the error data ER is only the delay of the EXOR gate 15, and, similarly to the first embodiment, the selector 13 will operate correctly.
[0025]
In the above embodiment, the case where the fixed data CV is supplied from the register 12 to the selector 13 and the case where the inversion error data IER is supplied from the inverter 18 to the selector 13 are exemplified. Data for replacement may be generated (substantially a multiplier) and supplied to the selector 13 together with the error data ER. In this case, processing equivalent to that of the first embodiment can be realized by setting the gain of the amplifier to “0”, and processing equivalent to that of the second embodiment can be realized by setting the gain to “−1”. .
[0026]
【The invention's effect】
According to the present invention, it is possible to extract only one polarity of the tracking error signal at an accurate timing, and by applying a braking force to the pickup based on the extracted tracking error signal, the pickup moving in the radial direction of the disk can be obtained. It can be stopped accurately. Therefore, the time required for the pickup to move between the tracks can be shortened, and the response speed can be improved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a first embodiment of a tracking servo circuit of the present invention.
FIG. 2 is a waveform diagram of signals for explaining the operation of the first embodiment.
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 second embodiment of the tracking servo circuit of the present invention.
FIG. 5 is a waveform diagram of signals for explaining the operation of the second embodiment.
FIG. 6 is a block diagram showing a configuration of a disc playback apparatus.
FIG. 7 is a plan view showing the structure of a recording track of a disk type recording medium.
FIG. 8 is a diagram illustrating a relationship between a tracking error signal and an off-track signal.
FIG. 9 is a diagram showing a relationship between movement of a pickup and a tracking error signal.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Disc 2 Spindle motor 3 Pickup 4 Actuator 5 Signal processing part 6 Servo control part 11 A / D converter 12 Register 13 Selector 14 Direction determination part 15 EXOR gate 16 Drive signal generation part 18 Inverter

Claims (2)

A pickup movement control circuit that accelerates and decelerates the pickup in a predetermined direction and stops the target position,
The relative position of the disk-type recording medium having a spiral recording track and the pickup that reads the recording information of the recording track changes to a positive polarity when the pickup is shifted to one side of the recording track, and shifts to the other side. A tracking servo circuit that controls based on a tracking error signal that changes to negative polarity when the
An A / D converter that digitizes the tracking error signal obtained when the pickup is moved in the radial direction of the disk-type recording medium to generate error data;
A selector for selecting and retrieving either the error data or fixed data indicating a predetermined value;
A direction detection unit that detects a moving direction of the pickup from a phase difference between an off-track signal generated from a low-frequency component of the EFM signal and the tracking error signal ;
A selection control means for determining a selection operation of the selector based on a sign bit indicating the polarity of the error data, and a detection result of the direction detection unit;
A drive signal generator for generating a drive signal for braking the pickup that moves in a radial direction of the disk-type recording medium in response to a selection output of the selector;
A pickup movement control circuit comprising: A pickup movement control circuit that accelerates and decelerates the pickup in a predetermined direction and stops the target position,
The relative position of the disk-type recording medium having a spiral recording track and the pickup that reads the recording information of the recording track changes to a positive polarity when the pickup is shifted to one side of the recording track, and shifts to the other side. A tracking servo circuit that controls based on a tracking error signal that changes to negative polarity when the
An A / D converter that digitizes the tracking error signal obtained when the pickup is moved in the radial direction of the disk-type recording medium to generate error data;
An inverter that inverts the error data to generate inverted error data;
A selector for selecting and retrieving either the error data or the inverted error data;
A direction detection unit that detects a moving direction of the pickup from a phase difference between an off-track signal generated from a low-frequency component of the EFM signal and the tracking error signal ;
A selection control means for determining a selection operation of the selector based on a sign bit indicating the polarity of the error data, and a detection result of the direction detection unit;
A drive signal generator for generating a drive signal for braking the pickup that moves in a radial direction of the disk-type recording medium in response to a selection output of the selector;
A pickup movement control circuit comprising:

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