JPS58188339A - Optical reproducer - Google Patents

Abstract

PURPOSE:To attain required characteristics at accessing, by switching the frequency characteristics at an audible band of a servo system at the reproduction and accessing, reducing the gain at the reproduction and decreasing noisy audible noise. CONSTITUTION:A servo error signal is given to a noninverting input of an amplifier 29 through a resistor R1, and the output is given to a servo device driving circuit 28. The output of the operational amplifier 29 is fed back to an inverting input via an LPF comprising resistors R2-R4 and a capacitor C1, resulting in that the feedback amount at a frequency lower than the cutoff frequency (e.g., 1kHz) is increased and the gain at the low frequency is reduced as shown in chainned lines in a figure. Since a switch 30 is turned off with a mode signal at the accessing, the frequency characteristics are shown in solid lines in the figure. Thus, the noisy audible oscillation at the reproduction is reduced, the required frequency band at the accessing is attained, and the deterioration in the operation is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical playback device, and more particularly to a focus control device for a disc player in which audio signals, video signals, etc. are recorded in the form of bits, and a playback signal is extracted from a nine-disc disc using a laser beam. It is most suitable for use in a navigation system or a tracking servo system.

In this type of disc player, a 7-orcus nervo system and a track are used to keep the laser spot in a focused state 111 with respect to one disc surface in order to accurately follow a spiral track formed by a column of pits with a width of 1βm or less. The optical system is provided with a tracking servo system that deflects the laser spot in the width direction. 7 Orcus napo system is equipped with a moving magnet or moving coil type electromagnetic drive device that controls the objective lens in the optical axis direction. The focus error signal is generated by converting the change in the focusing state of the reflected beam due to the change in the height of the disk reflecting surface into the shape of the convergence by the cylindrical lens, and by converting the change in the focusing state of the reflected beam due to the change in the height of the disk reflecting surface into the shape of the convergence by the cylindrical lens. Detected with a photodiode.

The tracking servo system is equipped with an electromagnetic drive device that moves the optical axis of the objective lens in the width direction of the track, or a galvano-electric device that deflects the light beam incident on the objective lens in the width direction of the track. In a well-known optical system, a reading laser beam is divided into 93 beams by slightly shifting the position in each of the longitudinal and width directions of the tractor using a diffraction grating.
'Aso spot is formed, each reflected beam 6 pieces07
The tracking error is detected by the difference in the amount of light received by the two inner and outer diodes.

In addition to the above-mentioned focus servo and tracking servo, a laser beam is swung in the tangential direction of the track to round off the reproduced signal to remove time axis fluctuations.

Each of these servo systems is designed to prevent the reproduction signal from deteriorating mainly due to disk surface runout, eccentricity, and rotational fluctuations of the spindle motor.
Regarding frequency components of ~8 Hz (25 to 60 Hz for video recorders), it is necessary to have a speed gain of 60 dB or more.

Furthermore, when a desired position on the disk is accessed and then reproduced, a jump pulse signal of a constant width is sometimes applied to the tracking servo system to move the beam in large steps. In this case, each servo system needs to have a response band from DC to more than ten KHz in order to stably control the jump and the transient response after the jump, and to strengthen the player's vibration resistance.

For focus servo systems other than tracking servo,
It has a small-mass body vice (objective lens and galvanometer), and has a structure similar to a speaker (tweeter) consisting of a diaphragm and a voice coil. Therefore, the servo device vibrates in the audible range of several KH2, and the mechanical noise may become audible, especially when playing music. In particular, playback audio information (gFM) is added to servo error information.
The low-frequency components of the signal (NRZ encoded PCM signal) are superimposed, or the noise caused by the finger prints on the disc is superimposed, causing the focusing device or tracking device to make unnecessary movements. mechanical noise is likely to occur. Since this type of S-G system is generally a second-order lag system, the 1-frequency-gain characteristic is often increased around 1 to 3KH2 in order to compensate for the phase, and mechanical noise is particularly important in this frequency band. In view of the above-mentioned problems, the present invention is designed to reduce mechanical noise during playback without degrading performance of systems other than tracking servo or focus servo. Now, the present invention will be explained based on examples. FIG. 1 is a block diagram of an optical system and a servo system of an optical distractor player to which the present invention is applied. On a disk (tl), information is recorded as columns of concave or convex phase structures (bits) along a spiral track. The reproduced signal is generated by a radar (2) in the pickup, which guides nine beams through an optical system to a nine-phase structure along the track of the disk (fl), and the reflected light modulated by this zero-phase structure is sent to a photodiode. It is obtained by converting it into an electrical signal using an array.

The optical system includes mirrors (3) (4), a diffraction grating (5),
Magnifying lens (6), polarizing beam splitter (7), λ/
It consists of a 4-wavelength plate (Mihu Ze (9), a focusing lens OI, and a cylindrical lens (11). The beam emitted from the laser (2) passes through Dentsu (3) and (4) and enters the diffraction grating (5). The nine beams are further expanded by a magnifying lens (6), passed through a beam splitter (7), and converted into circularly polarized beams by a λ/4 wavelength plate (8). A focusing lens 01 (t or objective lens) K is provided from the 2 (9).The focusing lens α is a tracking direction (track width direction), a focusing direction (beam optical axis direction), and a focusing direction (beam optical axis direction). The bottle is attached to a servo device that can control the position with respect to the O two axes.

The laser beam is focused on the disk (1
) is controlled so that the reading spot is connected on the track of the surface. This reading spot consists of 93 minute spots that are slightly shifted along the track direction and in the track width direction.The beam for the central minute spot is modulated by the bits in the disk and reflected. The direction of rotation of circularly polarized light is reversed. This reflected beam is focused by a focusing lens O
It is picked up at I, goes back along the optical path 7'j and returns to
/4 wavelength [i (8), it is converted into linearly polarized light, is further reflected by a polarizing beam sinter (7), passes through a cylindrical lens aυ, and reaches a 7-otodiode array (a). Also 6
The outer two of the two fine spots pass through the same return path as the first one and pass through the photodiode ClIc,!
It reaches υ.

The 7 photodiode array (to) is divided into four parts and consists of a nine-fold array, and the outputs of two pairs of photodiodes on each opposite side are added by an adder a'a (131), and an adder a'a (131)
By adding the outputs of 4 with an adder 041, an RF signal as reproduction information is obtained. This reproduced RF signal is sent from terminal - to a demodulation circuit (not shown).

The focus error f is detected by adding the outputs of each opposing side of the photodiode array with an adder (1 and α4, and calculating the difference between the two circled signals with a subtractor aQ.9) racking error. ttL is detected by calculating the difference between the outputs of the two photodiodes αHυ using a subtractor aη.

Focus error signal f and tracking error signal t
are the two-axis deflection device (2) (c) of the Suto lens IlG, respectively.
, thereby controlling the focusing lens Ql in the seven orcus directions (arrow A direction) and the tracking direction (arrow B direction). Note that it is also possible to use the construction two (9) as a galpanon two and to give the ratification two signal to this.

When accessing any track on the disk (1) twice before starting playback, a jump pulse j is generated from the access control circuit (to), and this jump pulse j
is added to the tracking error signal t by an adder (to) and provided to the deflection device @. As a result, the reading beam is stepped towards the access target position, for example over a width of 100 tracks.

Note that the entire pickup optical system is moved by a linear transport motor that moves it in accordance with the step transport of the beam in another NAPO system.

Next, Fig. 2 is a plotter circuit diagram of the focus servo system or tossing napo system shown in Fig. 1.
The phase characteristics are shown respectively.

As shown in the solid line in Figure 5, the frequency-gain characteristics of the servo system electric-mechanical (servo system) Funsdeena have a gain of 60 dB or more at disk rotation frequencies of 13 to 8 H2, and 1
1 shows the transfer characteristic of a second-order lag system so that at frequencies above the resonance point existing in the range 0 to 50H1K, the frequency is attenuated toward the high range. The phase characteristic has a band in which the phase rotates by 1180 degrees or more, as shown by the solid line in FIG. 3C.

In order to obtain a phase margin and avoid unstable operation at high frequencies, as shown in Figure 2, the focus effect signal ft or tracking error signal t detected by the subtractor Q or Qη in Figure 1 is , drive circuit @ through the phase compensation circuit Qη tube
given to. In the phase compensation circuit (2), as shown in the frequency-gain characteristic diagram in FIG.
The frequency characteristics in the 1 to 6- band around t (+-Po system open loop gain is OdB) are improved. Therefore, the frequency-gain characteristic of the K-l loop is as shown by the dotted line in Fig. 6 (A) < KfkD, and the frequency-phase characteristic is the point l in Fig. 6
iI.

It will be improved as follows.

According to an embodiment of the present invention, the phase compensation (b) path (
The constant that determines the gain of the product is switched between normal playback (including Bose) and access. As the switching signal, a command signal M generated from the access control circuit (c) in FIG. 1 at the time of access is used.

FIG. 5 shows a specific circuit of the phase compensation circuit of this embodiment, and FIG. 6 shows its frequency-gain characteristics. Figure 5 - Boe 2 - The signal is given to the non-inverting input of the operational amplifier (to) through a resistor, and its output is given to the drive circuit (to) in Figure 2. The output of the operational amplifier (21 is the resistor - ~
It is fed back to the inverting input via a low pass filter consisting of R4 and capacitor C4. As a result, the amount of feedback in the lower range becomes larger than the cutoff frequency (for example, I KM, ), and the fourth
The Jllll characteristic as shown in the figure can be obtained.

A resistor, a capacitor C1, and a switch (to) are connected in series between the non-inverting input of the operational amplifier (to) and the ground point, and this switch (to) is turned off by the mode signal M at the time of access. ◇ During normal playback, the switch (to) is on during pause, and the operational amplifier (2)
A low-pass filter consisting of a resistor, a capacitor, and a capacitor C2 is coupled to the input of the circuit to ensure that it is in good condition.

−11 control−1 This low-pass filter has a frequency of 2”Cx (& +
Rs) (e.g. 200H1) or more, it exhibits attenuation characteristics,
Frequency] I~. A certain amount of attenuation is reached at -2- (for example, 1st).

Therefore, the overall frequency-gain characteristic of the phase compensation circuit @ during reproduction is as shown by the dashed line in FIG.

That is, the audible band component of the servo error signal is attenuated. As a result, the overall frequency characteristics of the servo loop, as shown by the dashed-dot line in Figure 6 (■), decreases the gain in the audible band of 200 Hz or higher, which attenuates the harsh mechanical vibration sound of the servo device. can be done.

During access, the mode signal MK turns off the switch, so the frequency characteristics of the phase compensation circuit @ are as shown by the solid line in Figure 6, and the required response frequency band is as shown by the dotted line in Figure S. is ensured.

Note that during playback, the servo gain in the low range (near the disc rotation period) is not changed and is maintained at 60 dB or more, so that there is no effect on the tracking performance of focusing and cooking with respect to surface runout and eccentricity of the disc.

Next, Fig. 7 shows a modification of the phase compensation circuit shown in Fig. 5, and Fig. 8 shows its frequency-gain characteristics. To further reduce the range gain, connect a capacitor C in parallel with the resistor.
3 is connected. As a result, the high frequency gain of the phase compensation circuit (5) during normal reproduction is further reduced as shown by the dashed line in FIG. This reduces the audible vibration noise of the servo device in higher frequencies (for example, 5 degrees or higher).

FIG. 9 shows yet another modification of the phase compensation circuit, and FIG. 10 shows its frequency-gain characteristics. In this modification, the phase characteristics are improved during playback (when the switch is turned on). , as shown in Figure 6 (■), the cutoff frequency decreases as fc', and the phase margin at this point decreases. A new capacitor C4 is connected in parallel.

The frequency-gain characteristics of the phase compensation circuit shown in FIG.
As shown by the dashed line in the figure, the frequency of the gain enhancement portion for phase compensation is shifted to the lower frequency side by the amount of the capacitor C4. Therefore, the phase characteristic of the servo system is such that the peak part is in the low range (
A phase margin is secured at the cutoff frequency fc' of movement L1 in FIG. 3, and the stability of the servo system when the switch is turned on is improved.

In the above-described embodiment, since the level of vibration noise differs depending on each servo device, it is preferable that the amount of attenuation of the servo gain in the audible band is determined according to the noise level. In some cases, the present invention can be applied to only one of the focus servo system and the tokki servo system to obtain a noise reduction effect.
May be applied to both.

Furthermore, in each of the embodiments shown in FIGS. 5, 7, and 9, the servo gain switching switch (to) and the time constant circuit (C2
, R5, etc.) may be inserted into the feedback circuit of the operational amplifier (c), or may be provided on the output side of the operational amplifier (to).

As described above, the present invention switches the gain in the listening band of the servo system that controls the reading beam between playback and access so that the gain is reduced during playback fC4.
It is. Therefore, according to the present invention, the harsh audible vibration noise of the servo device during playback can be reduced, and the required frequency response band can be secured during access.

[Brief Description of the Drawings] Fig. 1 is a block diagram of the optical system and servo system of an optical disc player to which the present invention is applied, Fig. 2 is a block circuit diagram of the optical servo system, and Fig. 3 is a servo system. Figure 3 shows the frequency-gain characteristic diagram, and Figure 4 shows the frequency-phase characteristic diagram.
The figure is a frequency-gain characteristic diagram of the phase compensation circuit in Figure 2,
FIG. 5 is a circuit diagram of a phase compensation circuit showing an embodiment of the present invention;
FIG. 6 is a frequency-gain characteristic diagram of the ag5 diagram, FIGS. 7 and 9 are circuit diagrams showing modified examples of the phase compensation circuit of FIG. 5, and FIGS. 8 and 10 are diagrams of the diagram shown in FIG. and a frequency-gain characteristic diagram corresponding to FIG. 21) ... Photodiode (2(1)
-7 Otoguiode array operation q ... Knee deflection device (Koji) ... Atassess control circuit (to) ... Switch. Agent: Katsutsune Ueya, Yoshio Sugiura, Figure 5 6 Figure 8m Figure 10 ＼On

Claims (1)

[Claims] In an optical reproducing device in which pressure information recorded on a track of an information recording medium is retrieved by a reading beam, a time constant circuit and a changeover switch are provided to change the frequency gain characteristics of a servo system that controls the track scanning state of the reading beam. The changeover switch is changed during access and playback to move the reading beam at high speed to a desired playback track, and during playback, the gain of the servo system is set to the gain at the time of access in a predetermined portion of the audible frequency band. Nine optical playback devices configured to reduce damage.