JPH10269596A - Optical disk device and automatic gain servo circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand a dynamic range of a servo error signal when an automatic gain servo circuit is constituted of a digital servo circuit. SOLUTION: This circuit is provided with a switching means 10 provided with switches SF1, ST1, SR1 turning on/off detected focus error signal FE, tracking error signal TE and pull-in signal (RF signal) Pi showing a level of reflection light from a disk and an integration circuit 20 provided with capacitors CF, CT, CR in feedback circuits of three pieces of differential amplifiers OP (1, 2, 3), and its outputs are converted to digital signals by A/D converters 30 (A, B, C) to be supplied to an IC circuit 40. By turning on/off respective switches of the switching means 10 by a PWM signal outputted from the differential amplifier OP4 comparing the integrated value of the pull-in signal integrated by the integrating capacitor CR of the integration circuit 20 with a reference voltage Ereff, the servo error signal applied with AGC is generated as the terminal voltage of the integrating capacitors CF, CR, and the signal is taken in the IC circuit 40 at prescribed timing through the A/D converter to supply servo signals for driving an optical head 50.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device capable of recording and reading information on and from an optical disk, and particularly to automatically giving an appropriate servo gain to a disk mounted on the optical disk device. The present invention relates to an automatic gain servo circuit that is useful in this case.

[0002]

2. Description of the Related Art Information is recorded on tracks of an optical disk,
Or, an apparatus for recording or reproducing an optical disk capable of reading this information can record and reproduce a large amount of information by irradiating a fine track with a light beam by using a laser light source. It has been. However, a tracking servo device and a focus servo device having at least high responsiveness are required in order to reliably irradiate a light beam on a track of a rotating optical disk. These servo devices are usually constructed by a servo circuit that detects light reflected from an optical disc by a divided light receiving surface, detects a tracking error signal or a focus error signal, and feeds it back to an actuator of an optical head. .

[0003] Such a feedback servo circuit,
It is configured by a transmission circuit having an appropriate servo band and servo gain.
In an apparatus capable of reproducing, recording, and erasing, the light amount of the beam irradiated on the optical disk is controlled to a different value during recording, reproducing, and erasing, so that a servo error detected from the reflected light from the optical disk is In order to provide a signal detection level with a different value and provide an appropriate servo characteristic, first, it is necessary to provide a servo circuit in which a loop gain is always constant regardless of the amount of irradiation beam.

FIG. 3 shows the principle of an automatic gain servo circuit in which the level of a tracking error signal or a focus error signal supplied to an actuator of an optical head becomes constant even when the amount of light reflected from an optical disk changes. Numeral 1 denotes divided light receiving surfaces A, B, C, and D for detecting reflected light, and light receiving surfaces E and F for tracking.
From the electric signal output from the detector Pd having
An arithmetic circuit that calculates and generates a tracking error signal, an RF signal (hereinafter referred to as a pull-in signal), and a focus error signal.
The pull-in signal Pin corresponding to the light receiving amount of d is output as a sum signal of the divided light receiving surfaces A, B, C, and D. The tracking error signal is obtained by EF, and the focus error signal is obtained by (A + D)-(B + C).

Reference numeral 2 denotes a division circuit for dividing the focus error signal FE by the pull-in signal Pin, and 3 denotes a tracking error signal TE by the pull-in signal Pin.
Is a division circuit. The output of the division circuit 2 is supplied to a focus actuator Lf of an optical head 6 composed of, for example, a two-axis mechanism via a focus error signal servo system circuit 4, and the tracking output from the division circuit 3 The error signal is similarly supplied to the tracking actuator Lm of the optical head 6 via the servo system circuit 5 for tracking.

The above-described automatic gain servo circuit shown in FIG. 3 can keep the tracking servo signal TE and the focus servo signal FE constant irrespective of a change in the light amount of the detector Pd. This will be described below. When the power of the laser light source is increased in order to put the optical disk device in the recording mode, the amount of light received by the detector Pd increases, the pull-in signal Pin increases, and the levels of the detected tracking error signal TE and focus error signal FE also increase. I do. However, since the focus error signal FE and the tracking error signal TE are divided by the pull-in signal Pin by the divider circuits 2 and 3, the output focus error signal FE and tracking error signal TE are gained here. AGC is performed so that the level of the error signal fed back to the servo system is constant.

The above-described automatic gain servo circuit is also often constituted by a digital servo circuit. FIG. 4 shows an outline of digitally adjusting the gain of a servo signal, and the same parts as those in FIG. 3 indicate the same functional circuits. In this conventional example, signals output from the detector Pd are output as a pull-in signal Pi, a focus error signal FE, and a tracking error signal TE by an arithmetic circuit 1 similar to that shown in FIG. The signal is directly converted into a digital signal by the / D converter 7 (A, B, C), converted into an analog signal by the software of the digital servo signal processing circuit 8 having an automatic gain function, and The signals are supplied to the tracking actuator Lt and the focus actuator Lf.

[0008]

The automatic gain servo circuit constituted by an analog circuit as shown in FIG. 3 can be a servo circuit having a wide dynamic range depending on the circuit design. However, since two division circuits 2 and 3 are required for the tracking error and for the focus error, there is a problem that the cost is increased and at the same time, the division circuits are susceptible to the aging. Also, as shown in FIG. 4, the method of digitally processing the signal processing of the servo system has an advantage that the servo characteristics can be set according to the characteristics of the disk or the optical pickup by software of the digital servo signal processing circuit unit. On the other hand, it is difficult to increase the dynamic range unless the number of bits of data to be handled is increased, and the load on the digital signal circuit becomes too large in order to perform quick sampling control according to the disk rotation speed. As a result, there arises a problem that a high IC circuit is required.

[0009]

SUMMARY OF THE INVENTION An optical disk apparatus and an automatic gain servo circuit according to the present invention have been made in order to solve such a problem, and an optical disk apparatus constituting the first invention of the present invention is an optical disk apparatus. For detecting reflected light of the light beam applied to the detector, an arithmetic circuit for forming a pull-in signal and a servo signal from a detection signal of the detector, and a PWM signal having a pulse width modulated by the level of the pull-in signal Signal generating means for outputting a signal, an integrating means for integrating the servo error signal and the pull-in signal intermittent by the PWM signal, and an A / D converting means for sampling the output of the integrating means and converting it into a digital signal And a digital signal for outputting a control signal for controlling the optical head from the output of the A / D conversion means. Comprising a Le signal processing unit writes data to the disk by the optical head, so that it is possible to read the data written from the disk.

According to a second aspect of the present invention, there is provided an arithmetic means for forming a pull-in signal, a focus error signal, and a tracking error signal from a detection signal of a detector, and a PWM signal having a pulse width modulated by the level of the pull-in signal. PWM signal generating means for outputting, switching means for intermittently switching the focus error signal and tracking error signal by the PWM signal, tracking for integrating the output of the switching means and sampling at a predetermined timing, and generation of the focus error signal. An automatic gain servo circuit is constituted by sampling means and digital signal processing means for outputting a focus servo signal for controlling the head of the optical disk from the output of the sampling means and a tracking servo signal.

In the present invention, the level of the RF signal is detected in accordance with the timing of the digital servo signal processing circuit, and the integrated value is sampled while integrating the servo signal for which the intermittent ratio is set by the level of the detected signal. Since a constant level of servo error signal is obtained, even when the reflectivity of the disk or the like changes, the servo gain for one cycle can be kept constant and the dynamic range of the input servo error signal can be reduced. It becomes easy to widen. Further, since the servo error signal extracted at a certain level is converted into a control signal for driving the actuator by an IC circuit for digital signal processing, its characteristics can be easily set.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing an outline of a servo circuit applicable to an optical disk apparatus according to the present invention. A drive mechanism of an optical disk and a circuit for recording / reproducing are conventionally known. Therefore, the detailed description is omitted. In this figure, reference numeral 10 denotes a switch SF1 for intermittently switching the focus error signal FE, the tracking error signal TE detected by the arithmetic circuit 1, and the pull-in signal (RF signal) indicating the level of the reflected light from the disk.
Switching means including ST1 and SR1, 20 is a capacitor CF, CF in the feedback circuit of the three differential amplifiers OP (1, 2, 3).
This is an integrating circuit provided with CT and CR, and resetting switches SF2 and S are provided in integrating capacitors CF, CT and CR.
T2 and SR2 are provided.

A / D converters 30A, 30B and 30C have their digital outputs supplied to an IC circuit 40 which is a digital servo processor. The IC circuit 40 for the digital servo processor, based on a focus error signal, a tracking error signal, and a pull-in signal input as digital signals, supplies a tracking servo signal, a track jump control signal, and a focus servo signal to be supplied to the optical head. And a comprehensive digital signal processing circuit that can output a search signal for pulling in a focus and the like.

The servo signal and the control signal as described above are provided with a laser light source, various optical elements, and a light receiving element for detecting an error signal, and an optical head for controlling an objective lens by a biaxial mechanism or the like. 50. In the case of the present invention, a PWM signal generator 60 is provided to make the levels of the input focus error signal FE and tracking error signal TE constant irrespective of the intensity of the laser light irradiated on the optical disk. That is, the integrating capacitor CR of the integrating circuit 20
The integrated value of the pull-in signal integrated by
And a differential amplifier OP4 for comparing the signal with a pulse width modulated signal (PWM signal) corresponding to the level of the pull-in signal at its output. The switch is configured to be intermittent.

Hereinafter, the circuit of the automatic gain servo system according to the present invention will be described with reference to the waveform diagram of FIG. When each switch of the switching means 10 is turned on by a reset signal PR output from the digital servo IC circuit 40, as shown in FIG. 2 (a), a pull-in signal is supplied to a differential amplifier via an integrating resistor r. The signal is input to OP4 to obtain an integrated signal SRF. This signal is equal to the reference voltage E of the PWM signal generation circuit 60.
reff is compared as a threshold level Th, and the comparison output Pagc is output from each switch ST1,
Turn off SF1 and SR1.

As a result, the focus error signal and the tracking error signal taken in via the switches SF1 and ST1 are integrated during this switch-on period as indicated by ER, and the sampling of the integration end point indicated by SP is performed. In the area, the voltage is converted into a digital signal by the A / D converters 30A and 30B, and the signal is taken into the digital servo IC circuit 40 immediately before the next reset signal PR. Note that the timing of this capture is based on the comparison output P
AGC low level IC circuit 40 or A / D converter 3
Data may be fetched by controlling so that 0 (A, B, C) is enabled. Therefore, when the level of the pull-in signal reproduced from the disk increases, the level of the error signal taken into each integration circuit decreases. That is, when the reflected light of the laser beam applied to the disk becomes stronger, first, as shown in FIGS. 2B and 2C, the time required for the integrated value of the pull-in signal to reach the reference threshold level Th. Has a shorter TRF and P
AGC pulse width becomes narrow. As a result, the acquisition time (integration time) of the focus error signal and the tracking error signal is shortened, and the integrated values of these error signals are automatically controlled to be reduced as indicated by levels e1, e2, and e3. You.

As described above, according to the circuit configuration of the present invention, the tracking error signal input to the digital servo processor IC circuit 40 by the analog circuit.
, And the focus error signal is controlled so as to be always at a constant level even when the pull-in signal changes. A digital IC circuit processes the frequency and phase characteristics of the servo error signal, which has been converted into a digital signal at a predetermined timing, so that a division function for automatic gain control is required. This makes it possible to use a simple arithmetic circuit that does not require the use of a general microprocessor. The level of the tracking error signal and the level of the focus error signal become optimum values even when the reflectivity of the disk changes by adjusting the time constant of each of the integrating capacitors and the integrating resistors constituting the integrating circuit 20. It can be determined as follows.

[0018]

As described above, the optical disk device of the present invention and the automatic gain servo circuit adapted to this optical disk device are provided with a servo set to a predetermined level by an automatic gain circuit constituted by an analog circuit. Since an error signal is taken in at the timing of a digital IC circuit having a microprocessor function for signal processing, a servo circuit having a wide dynamic range can be constructed with a relatively inexpensive circuit configuration. is there.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an outline of an automatic gain servo circuit applied to an optical disc of the present invention.

FIG. 2 is a waveform chart showing an operation of the circuit shown in FIG.

FIG. 3 is an explanatory diagram of a servo circuit composed of an analog circuit.

FIG. 4 is an explanatory diagram of a servo circuit having a digital configuration.

[Explanation of symbols]

10 switching means, 20 integrating circuit, 30 (A,
B, C) A / D converter, 40 I for digital servo
C circuit, 50 optical head

Claims (5)

[Claims] 1. A detector for detecting reflected light of a light beam applied to an optical disc, an arithmetic circuit for forming a pull-in signal and a servo signal from a detection signal of the detector, and a level based on the level of the pull-in signal. PWM signal generating means for outputting a PWM signal with a modulated pulse width; integrating means for integrating the servo error signal and the pull-in signal intermittent by the PWM signal; and a digital signal obtained by sampling the output of the integrating means. A / D conversion means for converting the data into a digital signal, and digital signal processing means for receiving an output of the A / D conversion means and outputting a control signal for controlling the optical head; ,
Alternatively, an optical disk device comprising a mechanism for reproducing recorded data. 2. The apparatus according to claim 1, wherein said integration means is configured to be reset by a predetermined reset signal output from said digital signal processing means.
An optical disk device according to claim 1. 3. The optical disk apparatus according to claim 2, wherein said PWM signal generating means comprises a comparison circuit for comparing a pull-in signal integrated by said integrating means with a reference signal. 4. The optical disk apparatus according to claim 3, wherein the servo error signal is a focus error signal and a tracking error signal of the optical disk. 5. A calculating means for forming a pull-in signal, a focus error signal and a tracking error signal from a detection signal of a detector, and a PWM signal generating a PWM signal having a pulse width modulated by a detection level of the pull-in signal. Means for switching the focus error signal and the tracking error signal by the PWM signal; tracking for integrating an output of the switching means and sampling at a predetermined timing; and sampling means for the focus error signal; An automatic gain servo circuit comprising digital signal processing means for outputting a focus servo signal for controlling a head of an optical disk from an output of a sampling means and a tracking servo signal.