JP2013131260A - Optical disk drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk drive capable of reducing the processing time of actuator control finely adjusting the position of the objective lens of an optical pickup in an optical disk drive.SOLUTION: The optical disk drive: restricts bandwidth by a servo compensator to digital signals of a tracking error signal and a focus error signal calculated and formed from a signal read out from an optical disk to provide predetermined response characteristics to the digital signal; converts the digital signals into a PWM signal in a PWM converter; and supplies the PWM signal to a driver part without passing through a DAC to perform actuator control. Signal processing clocks having a frequency relation of integral multiple respectively and phase-synchronized are supplied to the servo compensator and the PWM converter on the basis of a sampling frequency of the digital signals. A carrier frequency of the PWM signal formed in the PWM converter is equal to the sampling frequency of the digital signals.

Description

  The present invention relates to an optical disc apparatus, and more particularly to an optical disc apparatus with reduced servo control processing time.

  In an optical disk device (ODD; Optical Disk Drive) using an optical disk such as a CD (Compact Disk), a DVD (Digital Versatile Disk), or a BD (Blu-ray Disk) as a recording medium, Tracking control and focus control techniques for accurately irradiating a laser beam with an optical pickup (OPU) are important. The ODD performs a predetermined calculation on the signal read from the optical disk by the OPU to generate a tracking control signal and a focus control signal. The OPU objective lens in the radial direction (tracking direction) and the vertical direction (focus direction) with respect to the optical disk When generating an actuator driving signal for finely adjusting the position, a processing process including analog signal processing is used.

  In Patent Document 1, an example of a method for generating the tracking control signal and the focus control signal described above is disclosed. In Patent Document 2, an example of a method for processing a tracking control signal and a focus control signal is further disclosed.

JP 2003-162824 A JP 2009-146488 A

First, the servo control unit of the optical disc apparatus will be described.
The objective lens of the OPU is mounted on a tracking actuator that finely adjusts the position in the radial direction with respect to the recording track of the optical disk and a focus actuator that finely adjusts the position in the vertical direction. Hereinafter, when referring to both actuators at the same time, they may be simply referred to as actuators. The OPU has a plurality of photoelectric conversion elements arranged in a grid pattern, and each photoelectric conversion element converts a read signal included in light reflected from the optical disk into an electric signal and outputs the electric signal.

The servo control unit first calculates a plurality of electrical signals output from each photoelectric conversion element, for example, as shown in the patent document, and calculates an error from a predetermined position of the objective lens in the radial direction of the recording track of the optical disk ( A TE signal (tracking error signal) indicating an error) and an FE signal (focus error signal) indicating an error from a predetermined position of the objective lens in the vertical direction are generated. Hereinafter, when both error signals are indicated simultaneously, they may be simply referred to as error signals or error signals. Conventionally, these error signals are analog signals, and operations for generating them are often performed by analog signal processing.
Each of the error signals is subjected to AD (Analog to Digital) conversion to be converted into a digital signal, and given a band limit and a predetermined response characteristic via a digital filter (also referred to as a compensator circuit). Focus actuator control signal (when both are indicated simultaneously, it may be simply referred to as an actuator control signal).

Until now, the actuator control signal has been DA (Digital to Analog) converted into an analog signal and supplied to a PWM (Pulse Width Modulation) converter. Therefore, the signal processing after the PWM conversion unit is performed by analog signal processing as described below.
The PWM conversion unit compares the actuator control signal converted into an analog signal with a level of a triangular wave signal having a predetermined amplitude and period, and converts the actuator control signal into a PWM signal having a pulse width based on the comparison result. The PWM signal is supplied to an actuator driving circuit, also called an H-bridge circuit, which drives each of the two actuators described above so that the position of the objective lens with respect to the recording track of the optical disk is set to a predetermined position. Control position and vertical position.

However, in the control method described above, a DA converter is necessary, and in the method of generating a PWM signal by analog signal processing, there is a problem that there is a limit in reducing the processing time generated by servo control.
In view of the above problems, an object of the present invention is to provide an optical disc apparatus in which the processing time of servo control is reduced.

In order to solve the above problems, the present invention is an optical disc apparatus for reading an information signal from an optical disc as a recording medium,
An objective lens that irradiates a recording track of the optical disc on which the information signal is recorded and receives reflected light of the laser light, and the information that is reflected by the reflected light received by the objective lens and included in the reflected light A photoelectric converter for converting a signal into an electrical signal, a tracking actuator for finely adjusting a radial position of the objective lens in the optical disc with respect to the recording track, and a vertical position of the objective lens in the optical disc with respect to the recording track An optical pickup (OPU) having a focus actuator for fine-tuning,
The electric signal output from the photoelectric converter is supplied to calculate the electric signal, and a tracking error signal indicating an error in a position of the objective lens in the radial direction of the optical disc with respect to the recording track, and the objective with respect to the recording track. An OPU signal processing unit for generating both error signals, and a focus error signal indicating an error in the position of the lens in the vertical direction of the optical disc;
A servo compensator having a digital filter that supplies the error signal output from the OPU signal processing unit as a digital signal having a predetermined sampling frequency and gives a band limitation and a predetermined response characteristic to the digital signal;
A PWM converter that converts the digital signal output by the servo compensator into a PWM signal having a carrier frequency equal to the sampling frequency of the error signal;
An actuator drive circuit for generating an actuator drive signal for finely adjusting the position of the objective lens with respect to the recording track based on the PWM signal generated by the PWM converter, and supplying the actuator drive signal to the tracking actuator and the focus actuator;
A sampling clock for generating a digital signal of the error signal is generated, and further, a phase-synchronized signal processing clock having an integer multiple frequency with respect to the sampling clock is generated to generate the servo compensator, and the PWM It is characterized by having a clock generator for supplying to the converter.

  According to the present invention, it is possible to provide an optical disk device with a reduced servo control processing time, and there is an effect that it is possible to contribute to improvement of the basic performance of the optical disk device.

1 is a block diagram of an optical disc device in one embodiment. It is a block diagram of the optical disk apparatus in a prior art example. It is a block diagram of the clock generation part in one Example. It is a figure which shows an example of the frequency of the clock which the clock generation part of FIG. 3 supplies. It is a block diagram of the servo compensator in one Example. It is a block diagram of the digital filter which the servo compensator of FIG. 5 has. It is a circuit diagram of the actuator drive circuit in one Example. It is a truth table of operation in the actuator drive circuit of FIG. It is a time chart of the signal in one Example. It is a figure which shows the PWM conversion characteristic in one Example. It is a figure which shows the general PWM conversion characteristic in a prior art example. It is a block diagram which shows the PWM conversion part and its periphery in one Example.

Embodiments of the present invention will be described below with reference to the drawings.
In this embodiment, after the two error signals obtained by analog operation of the electric signal output from the OPU are converted into digital signals by the AD converter, the PWM signal supplied to the actuator drive circuit is generated. Up to this point, one feature is that it is performed by digital signal processing. As a result, higher integration of the circuit in the semiconductor device is advanced, the DA converter is not required, and the processing time in the servo control unit is reduced. Further, simply digitizing the signal processing causes a problem that a newly required processing time is generated and a folding signal is generated as described later. There is an effect of improving the control performance.

First, regarding the optical disk apparatus, the operation of the entire apparatus including the servo control unit will be described.
FIG. 1 is a block diagram of an optical disc apparatus 1 according to an embodiment. An optical disc 101 as a recording medium is, for example, a DVD or a BD. Of course, any of write-once type such as DVD-R and BD-R that can be written only once, rewritable type such as DVD-RAM and BD-RE, and read-only type such as DVD-ROM. good. The optical disk 101 is mounted on a disk tray type or slim slot type loading mechanism (not shown), guided to the inside of the optical disk apparatus 1 as the loading motor 123 rotates, and mounted on an extension of the shaft of the spindle motor 105. .

The mounted optical disk 101 is rotationally driven by a spindle motor 105 so as to have a predetermined rotational speed (for example, a rotational speed that provides a predetermined linear speed at a position where data is recorded / reproduced). A spindle motor drive signal 115 for that purpose is generated by a servo unit 113 included in an SOC (System On a Chip) 109, power amplified by the driver unit 108, and then supplied to the spindle motor 105. In order for the servo unit 113 to generate the spindle motor drive signal 115, a rotation speed detection circuit 106 is provided, and a signal indicating the rotation speed of the spindle motor 105 generated by the rotation speed detection circuit 106 is supplied to the SOC 109. Yes.
In FIG. 1, only the components related to the tracking control and the focus control described above are shown for the components of the driver unit 108 and the servo unit 113 in order to avoid complication of the drawing. The components related to the rotational drive of the motor 123 and the thread motor 103 to be described later are not shown.

The optical pickup 102 irradiates the recording surface of the optical disc 101 with a laser beam through the objective lens 104 to record or reproduce data.
The optical pickup 102 is mounted on a sled mechanism, and moves in the radial direction of the optical disc 101 with the rotation of the sled motor 103 to record and reproduce data at a predetermined track position. A sled motor drive signal 118 for this purpose is generated by the servo unit 113, power amplified by the driver unit 108, and supplied to the sled motor 103.
The objective lens 104 is mounted on a tracking actuator 119 and a focus actuator 120 using electromagnetic force (in FIG. 1, 119 and 120 show only directions for driving the objective lens 104 to avoid complication).

The tracking actuator 119 is supplied with a tracking actuator drive signal 116 obtained by processing the first PWM signal generated by the servo unit 113 by the actuator drive circuit 108A of the driver unit 108. Based on this, the position of the objective lens 104 in the radial direction (tracking direction) with respect to the optical disc 101 is finely adjusted so that the laser beam correctly traces on a predetermined recording track of the optical disc 101.
The focus actuator 120 is supplied with a focus actuator drive signal 117 obtained by processing the second PWM signal generated by the servo unit 113 by the actuator drive circuit 108A of the driver 108. Based on this, the position of the objective lens 104 in the vertical direction (focus direction) with respect to the optical disc 101 is finely adjusted so that the laser beam is correctly focused on a predetermined recording track of the optical disc 101.

  A photodetector 121 included in the optical pickup 102 detects the reflected light from the optical disk 101 of the laser beam, detects an information signal recorded on the optical disk 101, and converts it into an electrical signal. The detected information signal is supplied to the OPU signal processing unit 107 included in the SOC 109. The OPU signal processing unit 107 has a circuit block called an AFE (Analog Front End) circuit, and the AFE circuit performs processing of the information signal at a stage that should be handled as an analog signal even in digital recording. . That is, the OPU signal processing unit 107 performs arithmetic processing on the information signal to generate, for example, a tracking error signal and a focus error signal, and supplies them to the servo unit 113.

The servo unit 113 converts the supplied tracking error signal and focus error signal into digital signals in the ADC (113A). The two error signals converted into digital signals are given a band limit and predetermined response characteristics by a servo compensator 113B having a digital filter, and are used as a tracking actuator control signal and a focus actuator control signal. Each of the two actuator control signals is converted into a PWM signal corresponding to the signal value by the PWM converter 113C. The two PWM signals are supplied from the SOC 109 to the driver unit 108, and based on this, the actuator drive circuit 108A generates the tracking actuator drive signal 116 and the focus actuator drive signal 117, and sends them to the tracking actuator 119 and the focus actuator 120. Supply. Thereby, the objective lens 104 of the OPU 102 is subjected to predetermined tracking servo control and focus servo control.
Note that in the path from the servo unit 113 to the driver unit 108, only one signal path is indicated by an arrow. However, as described above, in reality, two signals related to tracking servo control and focus servo control are used. There is a system.

Further, the OPU signal processing unit 107 equalizes the frequency characteristics of the amplitude and phase when data is recorded on and reproduced from the optical disc 101, and supplies the equalized data to the encoding / decoding unit 112 included in the SOC 109. . The encode / decode unit 112 performs reproduction processing of the information signal recorded on the optical disc 101. For example, the information signal is demodulated according to the modulation method applied when recording on the optical disc 101 and decoded according to the encoding method. Further, error correction processing using an error correction code added to the information signal at the time of recording is performed. As a result, the original information signal is decoded. The decoded information signal is temporarily stored in the memory 114.
The operation of the optical disc apparatus 1 described above is performed based on the control signal generated by the control unit 111. The control unit 111 has a microcomputer, for example.

Further, for example, an operation command from the user is generated by a host computer (not shown) which is a host device of the optical disc apparatus 1. The command signal generated by the host computer is transmitted when the IF (interface) unit 110 included in the SOC 109 mediates communication between the host device and the optical disc apparatus 1.
The information signal temporarily stored in the memory 114 is supplied to the host computer via the IF unit 110. Conversely, the information signal supplied from the host computer via the IF unit 110 is temporarily stored in the memory 114, and then the error correction code, for example, is given by the encoding / decoding unit 112, and a predetermined recording is performed. Encoding and modulation processing are performed, the power is amplified to a value suitable for supply to the OPU 102 by the OPU signal processing unit 107, and further recorded on the recording track of the optical disc 1 through the laser beam generated by the optical pickup 102. . Note that an optical disc apparatus having only a signal reproduction function that does not have these signal recording functions is also in the category of this embodiment.

The memory 114 not only stores information signals to be recorded and reproduced, but also stores a number of OSs (Operating Systems) and applications for operating the control unit 111. Accordingly, not only a readable / writable RAM (Random Access Memory) or flash memory but also a programmable flash ROM (Read Only Memory), for example, may be included.
The clock generation unit 122 generates a clock having a predetermined frequency, multiplies or divides the frequency, and supplies the operation clock in the SOC 109 to each block that requires it.
Although FIG. 1 shows a case where many components excluding the driver unit 108 are integrated on the SOC 109 which is a large integrated semiconductor element, it goes without saying that the components may be integrated into a plurality of semiconductor chips. .

Further, FIG. 1 shows a method of generating a tracking error signal and a focus error signal by performing an analog operation in the OPU signal processing unit 107 when reproducing an information signal, and supplying it to the ADC 113A recently. Different methods have been developed. For example, there is a method in which the output signal of the photodetector 121 of the OPU 102 is directly input to an ADC that operates at high speed to generate a digital signal, and the above two error signals are generated by digital calculation. The operation of equalizing the frequency characteristics of the amplitude and phase of the reproduction information signal is also performed by digital processing. The generation of the two error signals does not require a sampling frequency as high as the information signal is processed. For this reason, the band is limited in the error signal generation process, the sampling period is thinned, and an error signal having a predetermined sampling frequency (corresponding to CK3 described later, for example, about 400 kHz) is generated in the servo system.
As will be understood from the following description, the present embodiment can be applied to the case where two error signals are generated by digital calculation, and is in that category.

Next, the difference between the configuration of the optical disc apparatus 1 shown in FIG. 1 and the conventional configuration will be clarified.
FIG. 2 is a block diagram of an optical disc apparatus in a conventional example. In FIG. 2, unlike FIG. 1, the servo unit 113 of the SOC 109 has a DAC (113D), and the PWM conversion unit 113C has the driver unit 108, not the SOC 109. Note that there is an example in which the driver unit 108 includes a DAC (113C) in order to use a digital interface between the driver unit 108 and the SOC 109. Accordingly, the two actuator control signals output from the servo compensator 113B are converted into analog signals by the DAC (113D) and then supplied to the PWM converter 113C. That is, the servo unit 113 and the PWM conversion unit 113C perform signal processing independent of each other.

On the other hand, in the embodiment of FIG. 1, the DAC (113D) is not required, and the error signal is AD-converted by the ADC (113A) and then supplied as an actuator control signal to the actuator drive circuit 108A. In the meantime, it is exchanged with digital signals. That is, the difference is that an actuator control signal, which is a digital signal, is directly converted into a PWM signal.
At this time, the clock frequency used in each block of the servo unit 113 and the frequency of the PWM signal are phase-synchronized, that is, the phase is synchronized with the frequency as a predetermined integer multiple, thereby reducing the servo control processing time. There is a feature that obtains many effects such as. This will be described in more detail below.

  FIG. 3 is a block diagram of the clock generator 122 in one embodiment. The reference clock is generated by, for example, the oscillation unit 122B having an inverter element based on the natural vibration frequency of the crystal oscillator 122A, for example. Further, the frequency is multiplied and divided by the multiplier / divider 122C to be a clock having a plurality of frequencies whose phases are synchronized with each other, and supplied to each block in the SOC 109 that requires an operation clock. Here, an oscillator having a stable oscillation frequency represented by the crystal oscillator 122A is used, and the generated reference clock is multiplied or divided to obtain a stable clock and a timing signal having a predetermined frequency.

FIG. 4 is a diagram showing an example of the frequency of the clock supplied by the clock generator 122 of FIG.
CK1 is a reference clock, and the frequency is a natural vibration frequency of the crystal oscillator 112A, and is 25 MHz as an example here.
CK2 is a clock obtained by the clock generator 122 multiplying CK1 by 2 and has a frequency of 50 MHz. CK2 is used for digital signal processing in the servo compensator 113B.

CK3 is a clock obtained by the clock generator 122 dividing CK1 by 64 and has a frequency of 390.625 kHz. CK3 is used as a sampling clock of the ADC 113A in the servo unit 113, for example. Therefore, the clock (CK2) in the servo compensator 113B is 128 times the sampling clock (CK3) of the data digitally converted by the ADC 113A. For this reason, the time delay generated in the digital filter processing in the servo compensator 113B can be suppressed to be small with respect to the cycle of the input data. This will be clearly shown later in FIG.
The reason why the frequency of CK3 is set to about 400 kHz is that, when the servo control frequency band of the optical disk apparatus 1 is required to be, for example, 5 kHz or more, performance degradation due to the influence of sampling is eliminated.

  CK4 is a clock obtained by the clock generator 122 multiplying CK1 by 16 and has a frequency of 400 MHz. CK4 is used as a signal processing clock when the PWM converter 113C generates a PWM signal, and has a frequency 1024 times that of CK3. CK4 determines the resolution of the generated PWM signal as described below. In this case, a PWM signal having a resolution of 10 bits, that is, a resolution of 1024 can be generated, which contributes to an improvement in servo performance.

Next, the configuration of the servo compensator 113B will be described.
FIG. 5 is a block diagram of the servo compensator 113B in one embodiment.
In tracking control and focus control for the objective lens 104 of the OPU 102, control of each actuator is generally performed by feedback control. The two digitized error signals output from the ADC (113A) are supplied from the input terminal 113B01 to the servo compensator 113B. Next, in the addition circuit 113B03, a correction signal is added so as to correct the offset of the ADC (113A) detected by the offset correction circuit 113B02.

  The two error signals output from the addition circuit 113B03 are input to the proportional circuit 113B04, the integration circuit 113B05, and the differentiation circuit 113B06. The control of each actuator by the feedback control described above is performed by PID control including proportional control (P control), integral control (I control), and differential control (D control). Correspondingly, the error signal includes an adder circuit 113B07 and an adder circuit 113B08 that are an output multiplied by a constant by the proportional circuit 113B04, an output integrated by the integrator circuit 113B05, and an output differentiated by the differentiator circuit 113B06. Are added as shown in FIG. Next, the output of the addition circuit 113B07 is added with a correction signal for correcting the shift between the target control center detected by the operation point correction circuit 113B10 and the operation center point of the servo unit 113B in the addition circuit 113B09.

Through the above process, the actuator control signal described above can be obtained as the output of the adder circuit 113B09, and the control signal is supplied to the PWM converter 113C via the output terminal 113B11.
FIG. 6 is a block diagram of a digital filter included in the servo compensator 113B of FIG. The integrating circuit 113B05 and the differentiating circuit 113B06 in FIG. 5 can be basically realized by the configuration shown in FIG. Note that the proportional circuit 113B04 is not shown because it can be easily realized by a multiplication circuit.

In FIG. 6, including the coefficient circuits (proportional circuits) 601, 603 and 604, the inverse Z conversion circuit 605, and the addition circuits 602 and 606, the transfer function F from the input terminal 113B01 to the output terminal 113B11 is
F = a × (1 + cZ ⁻¹ ) / (1-bZ ⁻¹ ) (Formula 1)
It is expressed as

When a = 1 and b = 0, the transfer function F is
F = 1 + cZ ⁻¹ ≈cZ ⁻¹ (ABS (cZ ⁻¹ ) >> 1) (Formula 2)
That is, the integration circuit is determined by the coefficient c of the coefficient circuit 604.
When a = 1 and c = 0, the transfer function F is
F = 1 / 1−bZ ⁻¹ ≈ (−1 / b) × Z (ABS (bZ ⁻¹ ) >> 1) (Expression 3)
That is, the differential circuit is determined by the coefficient b of the coefficient circuit 603.
As long as the digital filter shown in FIG. 6 performs a linear operation, when all of a, b, and c are not 0, the outputs of the integrating circuit and the differentiating circuit are added and output to the output terminal 113B11. 5 is realized.

Next, the configuration of the actuator drive circuit 108A will be described.
FIG. 7 is a circuit diagram of the actuator drive circuit 108A in one embodiment. The drive circuit having this configuration is also called an H-bridge circuit.
Four switches 701A to 701D are connected as shown in the figure between a power supply (corresponding to a logic high level in the case of positive logic) and ground (corresponding to a logic low level in the case of positive logic). An output terminal 702N is provided at a common contact point between the switches 701A and 701B, and an output terminal 702P is provided at a common contact point between the switches 701C and 701D. An actuator coil 703 is connected between the output terminal 702N and the output terminal 702P.

The actuator coil 703 is a component included in the OPU 102. If the actuator coil 703 is a coil included in the tracking actuator 119, the objective lens 104 is positioned in one direction (for example, the inner circumferential direction of the optical disc 101) in the tracking direction if a current flows in the direction indicated by E in the drawing. On the other hand, if a current flows in a direction indicated as F direction in the drawing, the objective lens 104 is finely adjusted in the tracking direction in the remaining direction (for example, the outer peripheral direction of the optical disc 101).
If the actuator coil 703 is a coil included in the focus actuator 120, the objective lens 104 can be slightly adjusted in the focus direction position in one direction (for example, the direction approaching the optical disc 101) when a current flows in the direction indicated by the E direction in the drawing. On the contrary, if a current flows in a direction indicated as F direction in the drawing, the objective lens 104 is finely adjusted in the focus direction position in the remaining direction (for example, the direction away from the optical disc 101).
Note that the switches 701A to 701D often use CMOS transistors that are characterized by a small ON resistance and a large OFF resistance.

FIG. 8 is a truth table of operations in the actuator drive circuit 108A of FIG. No indicates four states. PWM + indicates the level of the PWM signal output to the output terminal 702P, and PWM− indicates the level of the PWM signal output to the output terminal 702N. A, B, C, and D indicate the states of the switches 701A to 701D.
No. No. 2 passes a current in the direction F of FIG. 3 is a state in which a current is passed in the direction E of FIG. 7 to finely adjust the position of the objective lens 104 of the OPU 102. No. 1 and No. Reference numeral 4 denotes a state in which no current flows through the actuator coil 703.

Next, a time chart of signals related to actuator control will be described.
FIG. 9 is a time chart of signals in one embodiment, and the horizontal axis indicates the time axis direction.
(1) in FIG. 9 indicates an analog tracking error signal or focus error signal output from the OPU signal processing unit 107.
(2) shows the sampling timing of the error signal in the ADC (113A), that is, the sampling timing of the actuator control system. As described above, the sampling signal in the ADC (113A) is CK3 in FIG. 4, and the frequency is, for example, 390.625 kHz. Needless to say, the sampling frequency for operating the structure is sufficiently high.

The following (3) to (6) are enlarged between the sampling signals of four consecutive periods for convenience of illustration.
(3) shows the digital data of the error signal obtained by sampling with the ADC (113A), and the codes are given in the order of generation. The digital data is supplied to the servo compensator 113B.
(4) shows an actuator control signal obtained by giving a band limitation and a predetermined response characteristic to the digital data by the servo compensator 113B, and the codes are given in the order of generation. The numbers in parentheses correspond to the magnitude of the positional deviation of the objective lens 104 in the OPU 102, and the sign represents the direction of deviation. As described above, the signal processing clock in the servo compensator 113B is CK2 in FIG. 4 and the frequency is, for example, 50 MHz, which is a sufficiently high value of 128 times the sampling frequency in the ADC (113A).

Here, the time indicated as Top in the figure indicates a time delay generated in the servo compensator 113B. The time delay is mainly caused by arithmetic processing such as product operation and sum operation in the digital filter shown as an example in FIG. In general, the time delays associated with these processing times are preferably as small as possible because they are related to the performance and stability of actuator control.
In this embodiment, an object is to reduce the processing time of servo control. For this purpose, first, the digital filter processing in the servo compensator 113B is performed at a clock frequency sufficiently higher (for example, 128 times) than the sampling frequency in the ADC (113A) to reduce the time delay.

In this case, since the frequency of the signal processing clock subsequent to the servo compensator 113B including the PWM converter 113C is different from the sampling frequency in the ADC (113A), signal components related to the sum signal and difference signal of both frequencies are generated. To do. In the conventional example, the servo unit 113 needs a band limiting circuit called an anti-folding filter for removing this. This not only causes an increase in circuit scale, but also has a problem that a new time delay occurs due to the anti-aliasing filter.
However, in this embodiment, the frequency of the signal processing clock subsequent to the servo compensator 113B including the PWM converter 113C is a predetermined integer multiple of the sampling frequency in the ADC (113A) and is phase-synchronized. Therefore, one feature is that a new anti-folding filter is not required. Therefore, there is an effect of reducing the servo control processing time. Furthermore, the frequency band to be controlled can be widened, and there is an effect that the stability of servo control is improved and the performance is improved. This is also the effect of performing digital processing including the servo compensator 113B and the PWM converter 113C in the same SOC 109 in FIG. 1 (ADC 113A) and including the PWM converter 113C.

(5) and (6) in FIG. 9 show PWM signals generated in the PWM converter 113C based on the actuator control signal supplied from the servo compensator 113B. Each corresponds to the PWM signal shown in FIG. 8, and as shown in FIG. 7, a drive current is supplied to the actuator coil 703 via the actuator drive circuit 108A.
At this time, the carrier frequency of the generated PWM signal is equal to the sampling frequency for actuator control shown in (2) of FIG.

For both the tracking actuator and the focus actuator, according to the position of the objective lens 104 of the OPU 102 with respect to the recording track of the optical disc 101, the PWM signal keeps the carrier frequency constant and the duty (high period for one period). Ratio) changes. This will be described in detail later with reference to FIG.
The duty of the two PWM signals reflects the actuator control information as it is, and if the average potential is obtained by power amplification and band limitation, it can be used as it is as an actuator drive signal. Therefore, actuator control can be performed by supplying the PWM signal generated by the PWM converter 113C to the actuator drive circuit 108A that is an H-bridge circuit as it is, and a DAC can be eliminated. This is also due to the fact that the PWM converter 113C is taken into the servo unit 113, that is, the SOC 109, and the sampling frequency of the two error signals and the carrier frequency of the PWM signal are the same.
For the signal processing clock in the PWM conversion unit 113C, for example, 400 MHz having a multiple relationship with other clock frequencies is selected as previously indicated by CK4 in FIG. In this case, as in the case described above, there is one feature that a new anti-folding filter is not required because the clock frequencies have a predetermined multiple relationship in which the phases are synchronized with each other.

FIG. 10 is a diagram illustrating PWM conversion characteristics in one embodiment. The horizontal direction indicates a data code, and corresponds to the number shown in parentheses in the signal shown in (4) of FIG. In the present embodiment, as described above, there are 1024 data codes corresponding to the resolution of the PWM signal based on the frequency relationship between CK3 and CK4 in FIG. The vertical axis represents the duty of the generated PWM signal, the broken line represents the PWM + signal of (5) in FIG. 9, and the solid line represents the PWM-signal of (6) in FIG.
As shown in FIG. 9, at least one of the PWM signals is Low and the duty is 0%. As the position of the objective lens 104 shifts, the duty of any PWM signal increases toward 100% in accordance with the direction of deviation. The matter to be noted here is that this embodiment does not have a duty of 50% as a control center, and the duty at the control center is 0% for any PWM signal. Of course, the control characteristic may be reversed to design the duty at the control center as 100%. This matter will be described in comparison with a conventionally used example.

FIG. 11 is a diagram showing typical PWM conversion characteristics in the conventional example shown in FIG. That is, the control center is at a position with a duty of 50%, and the PWM signal is a rectangular wave signal having a predetermined period even at the control center. In this case, even if the position of the objective lens 104 is at a predetermined position (duty 50%), the period of the PWM signal until the information of the actuator control signal supplied from the servo compensator 113B is reflected in the PWM signal. There is a problem that a time delay occurs as much as half.
On the other hand, in this embodiment shown in FIG. 10, if the data code is fixed when the actuator control signal is processed by the signal processing clock CK4 in the PWM converter 113C, it can be immediately reflected in the duty of the PWM signal. There is an effect of reducing the servo control processing time.

Next, the configuration of the PWM conversion unit 113C will be described.
FIG. 12 is a block diagram showing the PWM converter 113C and its periphery in one embodiment, including the servo compensator 113B at the front stage and the actuator coil 703 from the driver part 108 at the rear stage.
The actuator control signal supplied from the servo compensator 113B is input to the gain / operating point correction circuit 1202. In actual ODD, it is difficult to avoid fluctuations in the power supply voltage. Servo control characteristics may be deteriorated due to fluctuations in the gain and operating point of the PWM converter 113C due to fluctuations in the power supply voltage. In FIG. 12, the power supply voltage detection circuit 1201 detects the voltage and provides it to the gain / operating point correction circuit 1202 so as to reduce the fluctuation of the gain and the operating point of the PWM converter 113C.

The actuator control signal via the gain / operating point correction circuit 1202 is supplied to the two PWM conversion circuits 1203 and 1204, which respectively generate the PWM + and PWM− PWM signals shown in FIG. To do. The driver unit 108 has the configuration shown in FIG. 7, for example, and supplies a drive current to the actuator coil 703 via the output terminals 702P and 702N.
In general, when the power supply voltage decreases, the high level of the PWM signal generated by the PWM conversion circuits 1203 and 1204 also decreases, and the drive current supplied to the actuator coil 703 decreases below a predetermined value. Of course, the reverse phenomenon occurs when the power supply voltage rises. In order to solve this problem, the gain / operating point correction circuit 1202 according to the present embodiment may perform the following operation using the characteristics of the PWM signal. That is, the power supply voltage detection circuit 1201 detects a difference in power supply voltage from a predetermined value, and supplies a control signal including the difference value to the gain / operating point correction circuit 1202. The gain / operating point correction circuit 1202 changes the gain and operating point of the actuator control signal supplied from the servo compensator 113B in accordance with the control signal.

As a result, the duty of the PWM signal generated by the PWM conversion circuits 1203 and 1204 is changed. For example, when the power supply voltage decreases by 5%, the duty of the PWM signal is increased by, for example, 5%. Thereby, the dependence with respect to the power supply voltage of an actuator control characteristic can be reduced. In other words, it is possible to obtain a characteristic compensation method for the power supply voltage that takes advantage of the feature that the actuator drive signal is a PWM signal.
There is also a method of improving the fluctuation of the power supply voltage by using a regulator. However, in recent electronic circuits, the power supply voltage used is low, and the efficiency of the regulator tends to decrease. For this reason, the improvement by this example is superior.
The embodiments described so far are merely examples, and do not limit the present invention. While different embodiments can be considered based on the spirit of the present invention, all fall within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 1: Optical disk apparatus (ODD), 101: Optical disk, 102: Optical pick-up (OPU), 104: Objective lens, 107: OPU signal processing part, 108: Driver part, 108A: Actuator drive circuit, 109: SOC, 113: Servo 113A: ADC, 113B: servo compensator, 113C: PWM converter, 119: tracking actuator, 120: focus actuator, 121: photodetector, 122: clock generator, 601, 603, 604: coefficient circuit, 602 604: addition circuit, 605: inverse Z conversion circuit, 701A to D: switch, 703: actuator coil, 1201: power supply voltage detection circuit, 1202: gain / operating point correction circuit, 1203, 1204: PWM conversion circuit.

Claims (4)

An optical disk device for reading an information signal from an optical disk as a recording medium,
An objective lens that irradiates a recording track of the optical disc on which the information signal is recorded and receives reflected light of the laser light, and the information that is reflected by the reflected light received by the objective lens and included in the reflected light A photoelectric converter for converting a signal into an electrical signal, a tracking actuator for finely adjusting a radial position of the objective lens in the optical disc with respect to the recording track, and a vertical position of the objective lens in the optical disc with respect to the recording track An optical pickup (OPU) having a focus actuator for fine-tuning,
The electric signal output from the photoelectric converter is supplied to calculate the electric signal, and a tracking error signal indicating an error in a position of the objective lens in the radial direction of the optical disc with respect to the recording track, and the objective with respect to the recording track. An OPU signal processing unit for generating both error signals, and a focus error signal indicating an error in the position of the lens in the vertical direction of the optical disc;
A servo compensator having a digital filter that supplies the error signal output from the OPU signal processing unit as a digital signal having a predetermined sampling frequency and gives a band limitation and a predetermined response characteristic to the digital signal;
A PWM converter that converts the digital signal output by the servo compensator into a PWM signal having a carrier frequency equal to the sampling frequency of the error signal;
An actuator drive circuit for generating an actuator drive signal for finely adjusting the position of the objective lens with respect to the recording track based on the PWM signal generated by the PWM converter, and supplying the actuator drive signal to the tracking actuator and the focus actuator;
A sampling clock for generating a digital signal of the error signal is generated, and further, a phase-synchronized signal processing clock having an integer multiple frequency with respect to the sampling clock is generated to generate the servo compensator, and the PWM An optical disc apparatus comprising a clock generation unit for supplying to a conversion unit.   2. The optical disk apparatus according to claim 1, wherein a duty of a PWM signal generated by the PWM converter is approximately 0% or approximately 100% at a control center of a position of the objective lens with respect to the recording track. An optical disk device.   2. The optical disk apparatus according to claim 1, wherein a frequency of a clock generated by the clock generation unit is 128 times a signal processing clock supplied to the servo compensator on the basis of a sampling frequency of the error signal, and the PWM conversion unit. An optical disc apparatus characterized in that a signal processing clock to be supplied to is 1024 times. The optical disc apparatus according to claim 1,
A power supply voltage detection circuit for detecting a power supply voltage supplied to the actuator drive circuit;
Based on the detection result of the power supply voltage by the power supply voltage detection circuit, the servo compensator corrects the gain and operating point of the digital signal supplied to the PWM converter, and the PWM signal generated by the PWM converter is generated. An optical disc apparatus comprising a gain / operating point correction circuit for changing a duty.

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