JPH1153740A - Focusing servo device and optical recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely pull in a focusing servo by allowing a focus lens to detect the inclinations of positions more approaching a focsing point than a position where a focus error expresses the extreme value and closing a focusing servo loop when the inclinations are within a preliminarily set range. SOLUTION: After an inclination detecting circuit 12 detects a peak position from a signal S11 in which a focus error signal FE is subjected to an A/D conversion, it outputs a signal in which inclinations are calculated with a prescribed time interval. When a dicision circuit 13 discriminate that inclinations of the signal FE from signal S12 are within the preliminarily set range, it outputs a start signal S13. An input register 14 which inputted the start signal S13 becomes an operating state to apply the signal S11 to a drive signal generating circuit 16 via a servo filter 15 to turn a a focusing servo on. Thus, the focusing servo is surely pulled in with a simple circuit without being affected by a disk and light receiving elements or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a CD (Compact Dis
c) A focus servo device used for an optical disk device such as a player and a magnetic recording / reproducing device using the same.

[0002]

2. Description of the Related Art Optical disc players such as CDs
The player generates a so-called RF signal based on the reflected light of the laser light applied to the disk surface. This RF
The signal is a signal generated by converting the intensity of the reflected light into a voltage through a light receiving element such as a photodetector, the reflected light of the light applied to the disk surface. When the pit on the disk surface is irradiated with light, the RF signal
The reflected light is attenuated to a low level, and when a portion other than the pits is irradiated with light, most of the light is reflected so that the level is high.

The RF signal is generated by an RF amplifier. The RF amplifier generates a focus error signal FE used for driving a focus actuator and a tracking error signal TE used for driving a tracking actuator. And these RF signals,
The focus error signal FE and the tracking error signal TE are supplied to a servo circuit, which controls the driving of the focus actuator and the tracking actuator.

An optical pickup for irradiating a laser beam onto a disk surface is provided with a focus lens for converging the laser beam to a desired position on the disk, and a servo circuit connects the focus lens and the disk to a predetermined position. A focus servo system circuit for turning on / off the focus servo to maintain the distance is provided.

As this type of focus servo device,
Generally, the one disclosed in Japanese Patent Publication No. 63-13261 is known. This focus servo device has the same polarity as the focus error signal FE as shown in FIG. 5 and is generated when the focus lens is located at a point farther from the disc than the in-focus position. The reference voltage Vref having a small absolute value is compared with the focus error signal FE, and the state is changed from one state to another state.
Alternatively, a comparator that generates an output signal that changes from another state to one state, and a comparator at a position where the focus lens is closer to the in-focus position than when the focus error signal FE indicates one extreme value. And a switch for detecting a point at which the output signal changes and outputting a control signal, and a switch for closing the focus servo loop in accordance with the control signal.

According to the focus servo device having such a configuration, the time when the focus servo loop is started, that is, when the focus servo is turned on, is determined by the focus error signal FE itself having a so-called S-shaped characteristic and the comparator. Nearby points that are slightly further away from the disk are detected and determined. For this reason, it is possible to suppress the influence of the disk, the light receiving element, and the like, and perform the pull-in to the focus servo.

[0007]

However, in the above-described focus servo device, the focus error signal F
Since the focus servo is turned on by detecting a point near the in-focus position based on the result of comparison between E and the reference voltage Vref, the focus servo always has an S-shaped characteristic due to the influence of the fluctuation of the focus error signal FE and the like. It may not be possible to detect a point near the focal point that follows the focus error signal FE, and there may be variations in the detection of a point near the focal point. As a result, it is difficult to say that the focus servo can be accurately drawn. Also,
Although a circuit for compensating the variation can be provided, this has disadvantages such as a complicated circuit and an increase in circuit scale.

The present invention has been made in view of the above circumstances, and an object of the present invention is to reliably focus without being affected by a disk, a light receiving element, and the like without inviting a complicated circuit and an increase in circuit scale. It is an object of the present invention to provide a focus servo device and an optical recording / reproducing device that can perform servo pull-in.

[0009]

In order to achieve the above object, the present invention relates to a focus servo device for converging light emitted from a light source to a recording medium surface via a focus lens. Becomes zero when the focus lens is at the in-focus position, and when the focus lens is positioned before and after the in-focus position, signals having different polarities are generated, and the signals having the different polarities pass through one extreme value. Means for generating a focus error signal having a characteristic of approaching zero as the distance from the in-focus position increases, and wherein the focus lens is closer to the in-focus position than the position when the focus error signal indicates the one extreme value. A tilt detecting means for detecting a tilt at at least one position, and a tilt detected by the tilt detecting means. When it is within the range set beforehand, and a means for closing the focus servo loop.

In the present invention, the one extreme value at which the inclination detecting means starts the inclination detection is a peak value of a focus error signal.

Further, according to the present invention, a focus error signal obtained in accordance with a reflected light level of light applied to a recording medium surface via a focus lens is input to a servo filter in a servo-on state, and the focus error signal A focus servo device for obtaining a drive output for maintaining a predetermined distance from a recording medium surface, comprising: an analog / digital converter for converting an analog focus error signal into a digital focus error signal; A tilt detecting circuit for detecting, at a predetermined time interval, a tilt at a position where the focus lens is closer to the in-focus position than a position at which the focus error signal indicates one extreme value, and the tilt detecting means detects the tilt. Outputs a start signal when the inclination falls within the preset range. A judging circuit, and inputs the digital focus error signal by the analog / digital converter receiving the activation signal, and an input register at a predetermined timing causes input to the servo filter.

The present invention is also an optical recording / reproducing apparatus for performing at least a reproducing operation of data recording and reproducing by converging light emitted from a light source to a recording medium surface via a focus lens. When the focus lens is at the in-focus position, it becomes zero. When the focus lens is located before and after the in-focus position, signals having different polarities are generated, and the signals having different polarities represent one extreme value. Means for generating a focus error signal having a characteristic of approaching zero as the distance from the in-focus position increases, and wherein the focus lens is located closer to the in-focus position than the position when the focus error signal indicates the one extreme value. A tilt detecting means for detecting a tilt at at least one approached position, and a tilt detected by the tilt detecting means; When it is within the range set in advance, and a focus servo device having a means for closing the focus servo loop.

The present invention also relates to an optical recording / reproducing apparatus for performing at least a reproducing operation of recording and reproducing data by converging light emitted from a light source onto a recording medium surface via a focus lens, It becomes zero when the focus lens is at the in-focus position according to the reflected light level of the light applied to the recording medium surface via the lens, and has a polarity when the focus lens is located before and after the in-focus position. An RF amplifier for generating an analog focus error signal having a characteristic in which different signals are generated and each of the signals having different polarities approach zero as the distance from the focus position increases through one extreme value; An analog / digital converter for converting a signal into a digital focus error signal; A tilt detection circuit that receives a focus error signal and detects at a predetermined time interval a tilt at a position where the focus lens is closer to the in-focus position than a position when the focus error signal indicates one extreme value; A determination circuit for outputting a start signal when the inclination detected by the inclination detection means falls within a predetermined range; and a digital focus error signal from the analog / digital converter receiving the start signal and receiving a start signal. And a servo circuit having an input register which is inputted to the servo filter at the timing described above and keeps the focus lens and the recording medium surface at a predetermined distance.

According to the present invention, according to the reflected light level of the light emitted from the light source and applied to the recording medium surface via the focus lens, the value becomes zero when the focus lens is at the in-focus position. Focus signals having different polarities are generated when they are positioned before and after the in-focus position, and the respective signals having different polarities approach zero as the distance from the in-focus position increases through one extreme value. An error signal is generated and input to the inclination detecting means. In the inclination detecting means, the focus lens outputs a focus error signal of one extreme value,
For example, an inclination at at least one position closer to the in-focus position than the position at which the peak value is shown is detected. Then, when the detected inclination falls within a preset range, the focus servo loop is closed. Thereby, the focus lens and the recording medium surface are adjusted so as to maintain a predetermined distance (focus distance).

[0015]

FIG. 1 is a system block diagram showing a configuration example of an optical disc player to which a tracking servo circuit according to the present invention is applied.

In FIG. 1, the information recorded on the disk 1 is
It is read by the optical pickup 2. The optical pickup 2 includes a focus actuator that drives a focus lens (objective lens) in the optical axis direction so as to converge a light beam irradiating the disk 1 on the disk surface, and a light beam spot converged on the disk surface. And a photodetector that receives a reflected light beam from the disk surface based on the three light beams irradiated on the disk 1 and the like, and is provided so as to be movable in the radial direction of the disk 1. I have.

The photodetector built in the optical pickup is shown in FIG.
As shown in the figure, of the three light beams, four integrated photodiodes A to D for receiving the reflected light beam based on the main beam, and receiving the reflected light beams based on the two light beams on both sides thereof And a pair of photodiodes E and F. Each output of the four photodiodes A to D and each output of the pair of photodiodes E and F are supplied to the RF amplifier 3.

The RF amplifier 3 outputs focus error signals FE and R used for driving a focus actuator based on the outputs of the four photodiodes A to D.
An F signal is generated, and a tracking error signal TE used for driving the tracking actuator is generated based on each output of the pair of photodiodes E and F. Then, these RF signal, focus error signal FE and tracking error signal TE are
Output to Note that the RF signal is also output to a reproduction processing system (not shown) and used for demodulation of digital data.

For example, as shown in FIG. 5, the focus error signal FE becomes zero when the focus lens is at the focal point, and has different polarities when the focus lens is located before and after the focal point of the focus lens. Each signal has a characteristic of approaching zero as it goes away from the focal point through one extreme value.

The digital servo circuit 4 generates a signal FOK indicating that the RF signal generated by the RF amplifier 3 has exceeded a certain level based on the reflected light, and supplies the signal FOK to the tracking servo system and the focus servo system. Signal F
OK is set to a high level when the RF signal exceeds a certain level, and is set to a low level when reflected light cannot be obtained for some reason and the RF signal becomes below a certain level. In the focus servo system, the signal FOK is used to confirm that reflected light from the disk surface is obtained to a certain extent when performing a focus search operation. Further, in the tracking servo system, it is used for correction control of imbalance such as the sensitivity of the photodiodes E and F. Specifically, when the signal FOK is at the low level, the correction operation is stopped.

The focus servo system converts a focus error signal FE, which is an analog signal, into a digital signal,
On the basis of this digital signal, a portion from a position indicating one extreme value of the focus error signal (a position where the inclination is zero) to at least a focus position (a position where the inclination is the maximum in the negative direction) is divided into a plurality on the time axis. For each division unit, the slope of the focus error signal is calculated, and when the calculated slope is within a preset range, it is recognized as a near-focus point area and a focus servo loop is started, that is, the focus servo is turned on. To drive the focus actuator to perform focus adjustment.

The system controller 5 is composed of a microprocessor and controls the entire system such as the control of the digital servo circuit 4.

FIG. 3 is a block diagram showing an embodiment of the focus servo circuit of the optical disk player according to the present invention, and constitutes a part of the digital servo circuit 4. That is, the focus servo circuit 10 controls the A / D
It comprises a converter 11, a tilt detection circuit 12, a determination circuit 13, an input register 14, a focus servo filter 15, and a drive signal generation circuit 16.

The A / D converter 11 converts the focus error signal FE, which is an analog signal from the RF amplifier 3, into a digital signal, and converts it into a signal S11 as a signal S11.
2 and input register 14.

The inclination detecting circuit 12 is provided with the A / D converter 1
1, one extreme value of the focus error signal, specifically, a peak position is detected on the time axis, and as shown in FIG. 4, the focus error signal is detected at a predetermined unit time interval from the peak position. (Minus slope), and outputs the result to the determination circuit 13 as a signal S12. Note that this inclination calculation is performed at least up to the in-focus position where the inclination is maximum.

The determination circuit 13 receives the signal S12 from the inclination detection circuit 12, and determines whether or not the inclination of the focus error signal obtained for each division unit is within a preset inclination range. If the obtained inclination is within the set range, it is recognized as a point near the focal point, and the focus servo loop is activated, that is, a pulse-like activation signal S13 for turning on the focus servo is output to the input register 14. I do.

The input register 14 is kept in the clear state when the start signal S13 by the determination circuit 13 is inactive, and the clear terminal is turned off in response to the start signal S13 to be in the operating state. The output 8-bit digital signal S11 (focus error signal) is captured, and the captured digital signal is output to the servo filter 15 in synchronization with a clock.

Next, the operation of the focus servo system in the above configuration will be described. Laser light emitted from the optical pickup 2 via the focus lens is applied to the disk 1, and the reflected return light is received by the photodetector of the optical pickup 2. The outputs of the four integrated photodiodes A to D and the outputs of the pair of photodiodes E and F are supplied to the RF amplifier 3.

In the RF amplifier 3, based on each output of the four photodiodes A to D, a focus error signal FE used for driving the focus actuator is driven.
And an RF signal are generated, and a tracking error signal TE used for driving the tracking actuator is generated based on each output of the pair of photodiodes E and F. Then, the RF signal, the focus error signal FE, and the tracking error signal TE are output to the digital servo circuit 4. The RF signal is also output to a reproduction processing system (not shown) and used for demodulating digital data.

In the digital servo circuit 4, the input register 14 is in a clear state. The focus error signal FE, which is an analog signal, is output from the A / D converter 1
1, where it is converted to a digital signal S11 and output to the inclination detection circuit 12 and the input register 14.

The inclination detecting circuit 12 detects the peak position of the focus error signal on the time axis based on the digital signal S11 from the A / D converter 11, and from the peak position, the inclination of the focus error signal at a predetermined unit time interval. (Negative slope) is obtained, and the result is signal S1.
2 is output to the determination circuit 13.

In the determination circuit 13, the inclination detection circuit 1
In response to the signal S12 of step S2, it is determined whether or not the inclination of the focus error signal obtained for each division unit is within a preset inclination range. As a result of this determination, if the obtained inclination is within the set range, it is recognized as a near focus point area, and a pulse-like start signal S13 for starting the focus servo loop is generated, and the input register 14 Is output to

In the input register 14 which has received the start signal S13 from the determination circuit 13, the clear terminal is turned off to be in an operating state, and the output signal from the A / D converter 11
Bit digital signal S11 (focus error signal)
Is taken in. Then, the captured digital signal is output to the servo filter 15 in synchronization with the clock, and a drive output is obtained by the drive signal generation circuit 16 based on the output signal of the servo filter 15. As a result, drive control of the focus actuator is performed, and the position of the focus lens is adjusted to the in-focus position.

As described above, according to the present embodiment, the peak position which is one extreme value of the focus error signal is detected on the time axis based on the digital signal S11 from the A / D converter 11, and this peak is detected. In response to a signal S12 from the tilt detection circuit 12 for obtaining the tilt of the focus error signal at predetermined unit time intervals from the position, the tilt of the focus error signal obtained for each division unit is set to a predetermined slope. It is determined whether it is within the range or not, and when the obtained inclination is within the set range, it is recognized as a near-focus point area and a start signal S13 for starting a focus servo loop is output. When the activation signal S13 by the circuit 13 and the determination circuit 13 is inactive, the activation signal S13 is held in the clear state.
In response to the signal 13, the clear terminal is turned off to be in an operation state, the 8-bit digital signal S11 (focus error signal) output from the A / D converter 11 is fetched, and the fetched digital signal is synchronized with a clock to perform a servo filter. Since the input register 14 is provided to output the data to the point 15, the timing for starting the focus servo loop, that is, for turning on the focus servo is determined by detecting a point near the disk slightly away from the focal point position. Since the focus servo is turned on by detecting the gradient of the focus error signal having the S-characteristics instead of comparing with the reference voltage and detecting the point near the focus position, the influence of the fluctuation of the focus error signal FE and the like is obtained. Thus, the detection of the point near the focus position following the focus error signal FE can be performed without variation. As a result, there is an advantage that the focusing servo can be accurately performed without being affected by the disk, the light receiving element, and the like, and the circuit can be simplified and the circuit scale can be reduced.

[0035]

As described above, according to the present invention,
There is an advantage that the focus servo can be reliably pulled in without being affected by the disk, the light receiving element, and the like. Further, there is an advantage that the circuit can be simplified and the circuit scale can be reduced.

[Brief description of the drawings]

FIG. 1 is a system block diagram showing a configuration example of an optical disc player to which a focus servo device according to the present invention is applied.

FIG. 2 is a layout diagram of photodiodes in the optical pickup of FIG. 1;

FIG. 3 is a block diagram showing one embodiment of a focus servo circuit of the optical disc player according to the present invention.

FIG. 4 is a diagram for explaining a function of a tilt detection circuit according to the present invention.

FIG. 5 is a waveform chart for explaining a focus error signal.

[Explanation of symbols]

1 disk, 2 optical pickup, 3 RF amplifier,
4: Digital servo circuit, 5: System controller,
10 focus servo circuit, 11 A / D converter, 12 tilt detection circuit, 13 determination circuit, 14 input register, 15 servo filter, 16 drive signal generation circuit.

Claims (5)

[Claims] 1. A focus servo device for converging light emitted from a light source to a recording medium surface via a focus lens, wherein the focus servo device becomes zero when the focus lens is at a focal point, and A focus error having such characteristics that signals having different polarities are generated when the signal is located before and after the in-focus position, and that the signals having different polarities approach zero as the distance from the in-focus position increases through one extreme value. Means for generating a signal; inclination detection means for detecting an inclination at at least one position where the focus lens is closer to the in-focus position than a position when the focus error signal indicates the one extreme value; When the inclination detected by the inclination detection means falls within the preset range, the focus sensor A focus servo device having means for closing a volo loop. 2. The focus servo device according to claim 1, wherein the one extreme value at which the inclination detection means starts inclination detection is a peak value of a focus error signal. 3. A focus error signal obtained in accordance with a reflected light level of light applied to a recording medium surface via a focus lens is input to a servo filter in a servo-on state. A servo output device for obtaining a drive output for holding a digital focus error signal at a predetermined distance, comprising: an analog / digital converter for converting an analog focus error signal into a digital focus error signal; A tilt detection circuit for detecting, at predetermined time intervals, a tilt at a position closer to the in-focus position than a position at which the focus error signal indicates one extreme value, and a tilt detected by the tilt detecting means is preset. A determination circuit that outputs a start signal when the distance falls within the range of A focus servo device comprising: an input register that receives the start signal and inputs a digital focus error signal from the analog / digital converter and inputs the digital focus error signal to the servo filter at a predetermined timing. 4. An optical recording and reproducing apparatus for performing at least a reproducing operation of data recording and reproducing by converging light emitted from a light source onto a recording medium surface via a focus lens, wherein the focus lens is When the focus lens is located at the focal position, it becomes zero. When the focus lens is located before and after the in-focus position, signals having different polarities are generated, and the signals having the different polarities pass through one extreme value. Means for generating a focus error signal having the property of approaching zero as the distance from the position increases;
An inclination detecting means for detecting an inclination at at least one position where the focus lens is closer to the in-focus position than a position at which the focus error signal indicates the one extreme value, and an inclination detected by the inclination detecting means And a focus servo device having means for closing the focus servo loop when the value falls within a preset range. 5. An optical recording / reproducing apparatus for performing at least a reproducing operation of data recording and reproducing by converging light emitted from a light source to a recording medium surface via a focus lens, wherein According to the reflected light level of the light applied to the recording medium surface, the focus lens becomes zero when the focus lens is at the in-focus position, and signals having different polarities are generated when the focus lens is located before and after the in-focus position. An RF amplifier that generates an analog focus error signal having a characteristic that each signal having a different polarity approaches zero as the distance from the in-focus position passes through one extremum; and digitally focuses the analog focus error signal. An analog / digital converter for converting to an error signal and the digital focus An inclination detection circuit for receiving an error signal and detecting, at a predetermined time interval, an inclination at a position where the focus lens is closer to the in-focus position than a position at which the focus error signal indicates one extreme value; A determination circuit for outputting a start signal when the inclination detected by the detection means falls within a preset range; and a digital focus error signal from the analog / digital converter receiving the start signal and receiving a predetermined timing. An optical recording and reproducing apparatus comprising: a servo circuit having an input register for inputting the signal to the servo filter and holding the focus lens and the recording medium surface at a predetermined distance.