JPS63271730A - Automatic gain controller - Google Patents

Abstract

PURPOSE:To always keep a servo-gain of a tracking servo constant, and to execute a stable tracking servo, by providing a means for synthesizing the tracking error amplitude and the reflected light quantity sum. CONSTITUTION:A control signal of an AGC circuit 16 of a tracking servo becomes a signal which has added and synthesized an output of a light quantity sum detecting amplifier 15, and a signal which is outputted from a D/A converter 31 by adding a prescribed weight, after having inputted an output of a tracking error amplitude detecting circuit 24 for detecting the amplitude of a tracking error signal, to a microcomputer 30 from an A/D converter 39. By such a signal which has synthesized the reflected light quantity sum and the modulation degree, a servo-gain is controlled. In such a way, even in the case of a disk whose modulation degree is different, the servo-gain of the tracking servo is kept constant irrespective of magnitude of the modulation degree, and a stable tracking servo can be executed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an automatic gain control device (hereinafter referred to as an AGC device) that controls the gain of a servo loop.

2. Description of the Related Art In recent years, optical discs such as CDs (compact discs) and video discs have become rapidly popular.

Also, today, write-once type optical discs and date-replaceable type optical discs are also attracting attention.

By the way, such optical disk devices have technologies unique to optical disk devices, such as a focus servo that irradiates the optical disk with a light beam such as a laser beam and focuses the light beam on a track on the disk, and a light beam There is a tracking servo that controls the spot to follow the track.

Hereinafter, an example of the conventional focus servo and tracking servo mentioned above will be explained with reference to the drawings.

FIG. 5 is a simple block diagram showing a conventional focus servo and tracking servo. The configuration and operation will be explained below. Note that the AGC device will be explained separately into an AGC circuit and a detection section for a control signal that controls the AGC circuit.

The disk 1 is rotationally driven by a disk motor 19. A light beam is irradiated onto the signal recording surface of the disk 1 through an objective lens 3 attached to a pickup 20, and the reflected light is split and incident on a focus detector 6 and a tracking detector. The output of the focus detector 6 passes through a focus error detection circuit 8 and an AGC circuit 9, and then is applied to a switch 1o and a focus position detection circuit 13. When the output of the AGC circuit 9 reaches a predetermined level, the output of the focus detector 6 is applied to a switch 1o and a focus position detection circuit 13. It is configured to close ゜. Further, the output of the switch 1° passes through a phase compensation circuit 11 and a drive amplifier 12, and then is applied to a voice coil 4 for driving the objective lens 3 in the vertical direction in the drawing.

In this way, the focus servo receives the reflected light from the disk 1 with the focus detector 6, detects the focal position error of the light beam, and adjusts the objective lens 3 so that the focus of the light beam always matches the signal recording surface of the disk 1. This means to control the vertical direction of the drawing.

Further, the output of the tracking detector 7 is transmitted to a tracking error detection circuit 14, an AGC circuit 16, a phase compensation circuit 17,
After passing through the drive amplifier 18, the light beam is applied to a tracking coil that drives the objective lens 3 in the radial direction of the disk 1, so that the spot of the light beam follows the track on the disk 1. Furthermore, the feed motor 5
is for moving the pickup 20 in the radial direction in order to stably follow the track when the optical beam robot moves from the inner circumference to the outer circumference or from the outer circumference to the inner circumference of the disk 1 while following the track.

Further, the output of the light quantity sum detection amplifier 6 of the control signal detection section that controls the AGC circuits 9 and 16 detects the sum of the reflected light quantities of the light beam from the disk 1, and detects changes in the reflectance of the disk 1 and changes in the light intensity of the light beam. is applied to the AGC circuits 9 and 16, respectively, so that the servo loop gains of the focus servo and tracking servo remain constant even when this occurs.

A specific example of the AGC circuit is a variable gain OP amplifier. Figure 4 shows a simple configuration.

Components with the same reference numerals as those in FIG. 6 are the same components.

The OP amplifier 21 is a general OP amplifier whose gain is determined by a fitback resistor, and R1, R2 and R3 are resistors. The output v0 of the OP amplifier 21 has a variable gain y O
It is fed back to the OP amplifier 21 via the P amplifier 22. The amplifier gain A of the variable gain 10P amplifier 22 is proportional to the VC of the light quantity sum detection amplifier 16 output.
It is expressed as A=kVc (k is a constant). Therefore, due to the tracking error detection port, vo changes in inverse proportion to the sum signal of the light amount, and vo is controlled to be constant. In addition, there is a method using an FET introduced in Japanese Patent Laid-Open No. 60-22746, which has a similar effect.

Problems to be Solved by the Invention However, the AGC device configured as described above is insufficient in tracking servo. That is,
This is because the degree of modulation is an important factor that determines the gain of the tracking servo.

The degree of tracking modulation is the value obtained by dividing the amplitude of the tracking error signal by the sum of the amount of reflected light from the disk or the sum of the amount of reflected light from a mirror surface with a predetermined reflectance, and the larger this value is, the more likely tracking error is detected. This means that the sensitivity is good.

Fig. 3 briefly shows the degree of modulation. As shown in FIG. 3, the modulation degree is defined by the output T'' of the two-divided tracking detector, T-yoshi, the ratio of the amplitude a of the tracking error signal to the amplitude s of the light quantity sum signal.

Therefore, even if the sum of the light amounts is constant, the amplitude of the tracking error signal may be small due to differences in the groove width and depth of the disk, the wavelength and spot shape of the light beam, etc.
Not only is it impossible to accurately adjust the gain, but the tracking servo also becomes unstable.

In view of the above-mentioned problems, the present invention provides a highly reliable AGC device in which the tracking servo always operates stably even if the reflectance and degree of modulation differ from disk to disk.

Means for Solving the Problems In order to solve the above problems, the AGC device in the tracking servo of the present invention is configured to control the servo gain using a signal that combines the sum of the amount of reflected light and the degree of modulation. .

Function: With the above-described configuration, the present invention can maintain the servo gain of the tracking servo constant and perform stable tracking servo, regardless of the magnitude of the modulation degree, even on discs with different modulation degrees. An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of an AGC device in an embodiment of the present invention, and the same reference numerals as in FIG. 5 are the same components.

This configuration and operation will be explained below. focus detector 6, focus error detection circuit 8, AGC circuit 9,
Focus position detection circuit 13, switch 1o, phase compensation circuit 1
1, a drive amplifier 12, and a voice coil 4. As a control signal for the AGC circuit 9 of the focus servo, the output signal of the light amount sum detection amplifier 16 is conventionally used. Further, the tracking detector 7, the AGC circuit 16, the phase compensation circuit 17, the drive amplifier 18, and the objective lens 3 are arranged so that the spot of the light beam follows the track.
It is composed of a tracking coil and the like for driving the disk 1 in the radial direction of the disk 1.

Further, the control signal for the AGC circuit 16 of the tracking servo is obtained by connecting the output of the light amount sum detection amplifier 15 and the output of the tracking error amplitude detection circuit 24 for detecting the amplitude of the tracking error signal to the A/D converter 29 and the microcontroller 30. This signal is obtained by adding and synthesizing the signal and the signal output from the D/A converter 31 with a predetermined weight applied thereto.

In this way, in this embodiment, the AGC circuit in the tracking servo and the means for detecting its control signal are used.
In the C device, the control signal is obtained by the sum of the amount of light reflected from the disk and the amplitude of the tracking error signal.

Also, as a method of importing the tracking error amplitude from the A/D converter 29 to the microcomputer 30, the tracking error amplitude can be detected only when the tracking servo is OFF.
When the system is started, track jumps are performed at least once per rotation on the inner, middle, and outer circumferences of the disk, and the tracking error amplitudes at the inner, middle, and outer circumferences are captured. There is a method of taking the average value of the values, a method of changing the capture position when the level is extremely high or low, and a method of recording the information signal at least once per revolution before starting to record information signals on the disc in the case of recordable optical discs. There is a method of performing the above track jump and capturing the tracking error amplitude.

Next, an embodiment for detecting the amplitude of a tracking error signal will be described with reference to the drawings.

FIG. 2 [A1 stage is a simple block diagram of a tracking error amplitude detection circuit, and FIG. 2 [A1 stage] shows signal waveforms at various parts of FIG. In general, the track shapes of optical discs are either concentric or spiral. In the case of the spiral disc shown in Figure 2, the light beam spot performs one track jump per rotation and is on the same track. This is a description of a tracking error amplitude detection circuit when tracking the following. Since the optical beam spot jumps once per rotation, the tracking error signal waveform becomes as shown in C of the CBI stage in Figure 2, According to the second
Figure [30 steps d and e, the peak value of ■ and ○
The peak value of is detected.

The reason why the output of the hold circuit has a sawtooth shape is due to the charging/discharging time constant of the hold circuit, and the timing at which the output is actually taken into the microcomputer 30 in FIG. 1 is a certain period of time after the jump timing.

Next, the output d of the peak hold circuit from the differential amplifier 27
and (2) The output e of the peak hold circuit is combined to form f, which then passes through the low-pass filter 28 and is output as the tracking error amplitude signal at stage q in FIG. 2 [B].

Furthermore, in this embodiment, the method for detecting the tracking error amplitude when the optical beam spot jumps once per revolution on a spiral disk was explained, but it is also possible to detect the tracking error signal using a diode when the tracking servo is OFF. According to this method, the tracking error amplitude can be detected regardless of whether the disk is concentric or spiral. Furthermore, in the above embodiment, the case where the sum of the amount of reflected light and the tracking error amplitude are added and synthesized is explained.
When the amount of change in the tracking error amplitude value is large, it is also effective to input the sum of reflected light amounts and the trunking error amplitude value into a microcomputer, and then perform product synthesis to control the AGC circuit.

Effects of the Invention As described above, the present invention provides a means for synthesizing the tracking error amplitude and the sum of the amount of reflected light in a tracking servo AGC device. It is possible to always keep the servo gain of the tracking servo constant and perform stable tracking servo.

Furthermore, the present invention requires a track for recording or reproducing signals, such as an optical card, not just a disk.
There is also a great effect when tracking servo of a light beam spot is performed using a tracking error signal obtained when the light beam spot crosses a track.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an automatic gain control device according to an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining the tracking error amplitude detection operation in FIG. 1, and FIG. 3 is for explaining the degree of modulation of the tracking error. FIG. 4 is a circuit diagram of an example of the AGC circuit, and FIG. 5 is a circuit diagram of a conventional AGC device. 15... Light quantity sum detection amplifier, 16...
AGC circuit, 24... Tracking error amplitude detection circuit, 29... A/D converter, 3o...
...Microcomputer, 31...Song D/A converter. Name of agent: Patent attorney Toshio Nakao and one other person
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Claims (2)

[Claims] (1) A means for rotationally driving a disk, and a focus servo means for irradiating a light beam onto a track provided in advance for recording or reproducing a signal on the disk and focusing the light beam on the track. , a tracking servo means for detecting the relative position of the light beam with respect to the track and causing the light beam to follow the track; and an amplitude of a relative position signal with respect to the track when the light beam crosses the track. An automatic gain control device comprising: tracking error amplitude detection means for detecting the tracking error amplitude; and means for controlling the servo gain of the tracking servo means based on the level of the tracking error amplitude value. (2) The first aspect of the present invention is characterized by comprising: a light amount sum detection means for detecting the sum of the amounts of reflected light from the disk; and a synthesizing means for synthesizing the amplitude of the relative position signal and the sum of the reflected light amounts. Automatic gain control device as described in Section.