JPH0441417B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention is applicable to CDs (compact discs) and VDs.
The present invention relates to an optical disc playback device for playing back optical discs such as video discs, and more particularly to an automatic focus pull-in circuit that automatically focuses a light beam emitted from an optical pickup onto the signal recording surface of the disc.

[Technical Background of the Invention] Conventionally, for example, in the case of a CD type optical disc playback device (hereinafter referred to as a CD playback device),
An automatic focus drawing circuit is provided to automatically draw the focus of the light beam emitted from the optical pickup onto the signal recording surface of the disk. FIG. 4 shows the configuration of a conventional automatic focus pull-in circuit.

That is, in the figure, 11 is a semiconductor laser, 12 is an optical system, and 13 is a photodetector, which constitute an optical pickup. irradiated onto the signal recording surface,
The reflected light changes depending on the presence or absence of pits formed on the disk 14. This reflected light passes through the optical system 12 again and is irradiated onto the photodetector 13. As shown in the figure, this photodetector 13 is of a four-segment type, with each light receiving area A
-D output signals a to d corresponding to the amount of incident light (frequency signals corresponding to the presence or absence of pits), respectively.

Of these, signals a and c output from the light receiving areas A and C and signals b and d output from B and D are respectively added to become a+c and b+d, which are respectively supplied to the differential amplifier circuit 15. This differential amplifier circuit 15 receives (b+d)-(a+) from the above input signal.
c) A signal is generated, amplified, and outputted as a focus error signal FE. The signal is supplied to the focus actuator coil 19 via the signal. This focus actuator coil 19 works with a magnet (not shown) to move the objective lens 121 that focuses the laser beam in the direction of the arrow in the figure, and a closed loop of the focus servo is configured here. The focus of the laser beam is always on the signal recording surface of the disk 14 (focus point).

On the other hand, the focus error signal FE extracted by the differential amplifier circuit 15 is supplied to the zero cross detector 20. This zero cross detector 20 detects that the focus error signal FE is
[V] level is detected, and a trigger signal T is output at that zero-crossing point, and this trigger signal T is sent to the reset priority flip-flop circuit 21.
is supplied to the set terminal S of. Further, the current addition signal a+ of the outputs a to d of the photodetector 13 is
c, b+d are added by an adder circuit 22, high frequency components are removed by a low pass filter (LPF) 23, and converted into a voltage signal V23, which is then compared with a reference voltage V _S by a level comparison circuit 24. This level comparison circuit 24 is at H (high) level when V23>V _S ;
Signal V24 becomes L (low) level when V23<V _S
This signal V24 is supplied to the inverting reset terminal of the flip-flop circuit 21. This flip-flop circuit 21 sets and outputs a state setting signal Q1 to H or L level according to the input signals of the set terminal S and the inverted reset terminal, and this state setting signal Q1 is supplied to the control input terminal of the switch circuit 16. be done. This switch circuit 16 connects a and b when the control input is at H level, and connects between b and c when the control input is at L level.
The terminal is connected to the output end of a focus search signal generator (OSC). This focus search signal generator 25 outputs a triangular wave voltage signal of about 1 [Hz].

In other words, the focus error signal FE is
As shown in FIG. 5a, the voltage signal corresponds to the magnitude and direction of the error when the distance between the disk 14 and the objective lens 121 is based on the in-focus position, but when the distance is significantly different from the in-focus position, Since the reflected light that should be incident on the photodetector 13 is diffused, each light receiving area A~ of the photodetector 13 is
The outputs a to d of D become almost zero, and thereby the focus error signal FE also becomes zero. At this time, the output of the zero cross detector 20 is in an undefined state as shown in FIG. The output of this adder circuit 22 is supplied to a level comparison circuit 24 via a low-pass filter 23 and compared with _a reference voltage _VS.
and the objective lens 121 are significantly different from the focal length, the low-pass filter 23
The output voltage V23 is set higher than the output voltage V23 of the output voltage V23. Therefore, the output V24 of the level comparison circuit 24 is
Since the state setting signal Q1 outputted from the flip-flop circuit 21 becomes L level as shown in FIG. Therefore, the output of the focus search signal generator 22 is supplied to the actuator coil 19 via the switch circuit 17, the phase compensation circuit 17, and the actuator drive circuit 18, and the output of the focus search signal generator 22 is supplied to the actuator coil 19 via the switch circuit 17, the phase compensation circuit 17, and the actuator drive circuit 18. 121 will start moving. This operation is called focus search.

By this focus search operation, objective lens 1
When the lens 21 approaches the in-focus position, the diffused reflected light gathers on the photodetector 13, and a focus error signal FE is generated. Its polarity is determined by whether the objective lens 121 is close to or far from the disk 14. Furthermore, since the output of the adder circuit 22 also gradually increases, the output V23 of the low-pass filter 23 comes to exceed the reference voltage _VS. Then, the output V24 of the level comparison circuit 24 is inverted to the H level, so at this point the flip-flop circuit 21 becomes ready for setting.

When the objective lens 121 further moves and reaches the focused position, the focus error signal FE crosses the zero potential, so the zero cross detector 20 detects this and outputs the trigger signal T. As a result, the flip-flop circuit 21 is set and the state setting signal Q1 is set to H level. Then, the switch circuit 16 connects between a and b, thereby supplying the focus error signal FE to the actuator coil 19, so that the actuator coil 19 always keeps the objective lens 121 connected. The movement is now controlled to the in-focus position, and the focus servo described above is applied.
In this state, the disk 14 is rotated, a well-known tracking servo is applied, and the signals recorded on the disk 14 are read out.

By the way, when the disk 14 rotates, even if the focus servo is correctly controlled and in focus, the output of the adder circuit 22 fluctuates depending on the signal component (focus signal component) of the disk 14, and instantaneously changes to the reference value. It is possible that the voltage will be lower than V _S. In this case, if the output terminal of the adder circuit 22 is connected to the (+) input terminal of the level comparison circuit 24, the flip-flop circuit 21 will be reset and the servo operation will be turned off, resulting in a focus search mode. Undesirable. In order to prevent such malfunction, the adder circuit 2
A low-pass filter 23 is interposed between the disc 2 and the level comparison circuit 24 to remove signal components from the disc 14.

[Problems in the Background Art] However, in the automatic focus retrieval circuit of the optical disc playback device as described above, when performing a focus search, the faster the displacement speed of the objective lens 121 is, the longer it takes to find the in-focus point. On the other hand, when the servo operation is turned on at the focused point while moving at a certain speed, the servo loop operates to bring the speed of the objective lens 121 to zero. Therefore, at this time, the input of the actuator coil 19 is supplied with the voltage necessary for the above speed change from the drive circuit. This voltage becomes higher as the displacement speed of the objective lens 121 becomes faster in the ON state of the servo operation.
In other words, objective lens 1 during focus search operation
Since the displacement speed of 21 is limited by the voltage value that can be output by the actuator drive circuit, focus search becomes impossible at a displacement speed exceeding this value.

Furthermore, when the output of the switch circuit 16 is switched from the focus search signal to the focus error signal FE, the voltage supplied to the actuator coil 19, the displacement of the objective lens 121, and the change in the focus error signal FE are each As shown in FIGS. 6a to 6c, as can be seen from these figures, the objective lens 121 passes the in-focus position and the amount of overshoot increases, and it takes time to achieve complete focus.

[Objective of the Invention] This invention was made in consideration of the above circumstances, and it is possible to increase the actuator displacement speed that allows focus search to be faster than the conventional one, provided that the output voltage value of the actuator drive circuit is the same. In addition, if the actuator speed during focus search is kept the same, the voltage range that can be output by the actuator drive circuit can be reduced.
Another object of the present invention is to provide an automatic focus pull-in circuit for an optical disc playback device that can reduce focus error overshoot.

[Summary of the Invention] That is, the automatic focus pull-in circuit of the optical disc playback device according to the present invention uses an objective lens for a disc on which information signals are recorded in a plurality of pit rows, and this objective lens is used as an input signal. An optical disk that reads out the information signal by tracing it with an optical pickup having a focus actuator and a multi-segmented light receiving section that are driven and controlled in accordance with the direction to move the signal recording surface of the disk in a direction perpendicular to the signal recording surface of the disk. In the reproducing device, a focus search signal generator generates a linearly increasing voltage signal for moving the objective lens to a focused position, and a focus search signal generator generates a voltage signal having at least a polarity opposite to the focus search signal. a brake signal generator for generating a focus error control signal for controlling the movement of the objective lens to a focused position based on each detection signal of the multi-division light receiving section; A zero cross detector detects the point at which the focus error control signal passes through the zero level, and a sum signal is generated from each detection signal of the multi-division light receiving section, and the signal level is compared with a reference level to detect the objective lens. a level comparison means for detecting that the control range of the focus error control signal has been reached; and a state is set in the detection state of the level comparison means and in the detection state of the zero cross detector, and in the non-detection state of the level comparison means. a first state holding means whose state setting is canceled; and a second state holding means whose state is set according to the detection state of the level comparison means and whose state setting is canceled by the state setting of the first state setting means. a first switching circuit that derives the focus search signal when the state setting of the second state setting means is canceled and derives the brake signal when the state is set; and a first switching circuit that derives the focus search signal when the state setting of the second state setting means is canceled; a second switching circuit that derives the signal selected by the first switching circuit and derives the focus error control signal when setting the state;
Focus actuator drive control means for automatically pulling the objective lens to a focused position by driving and controlling the focus actuator based on the signal selected by the switching circuit. That is.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. However, in Fig. 1, the same parts as in Fig. 3 are indicated with the same reference numerals.
Only the different parts will be described here.

FIG. 1 shows its configuration, in which the output V24 of the level comparison circuit 24 is supplied to the inverting reset terminal of the reset priority flip-flop circuit (hereinafter referred to as the first flip-flop circuit) 21, and also to the second reset terminal. It is applied to the set terminal S of the priority flip-flop circuit 26. Also,
Output Q1 of the first flip-flop circuit 21
is supplied to the control input terminal of the switch circuit (hereinafter referred to as the first switch circuit) 16, and is also supplied to the reset terminal R of the second flip-flop circuit 26. The state setting signal Q2 output from the second flip-flop circuit 26 is
The signal is supplied to the control input terminal of the switch circuit 27.
The fixed terminal b of this second switch circuit 27 is connected to the output terminal of the focus search signal generator 25, and the fixed terminal c has at least the opposite polarity of the voltage signal generated by the focus search signal generator 25. The state setting signal Q2 is connected to the output terminal of the brake signal generator 28 which generates the voltage signal Q2.
A movable terminal a whose drive is controlled in accordance with the above is connected to an input terminal c of the second switch circuit 16.

The operation of the above configuration will be described below with reference to FIGS. 2 and 3.

Figure 2 shows each signal output waveform generated when the objective lens 121 is moved in the direction of the arrow in the figure with respect to the signal recording surface of the disk 14. Figure a shows the focus error signal FE, and Figure b shows the focus error signal FE. The output T and c of the zero cross detector 20 are the low pass filter 23
Figures d and d represent the output V24 of the level comparison circuit 24, Figures e and g represent the output Q2 of the second flip-flop circuit 26, respectively, and Figures f and h represent the waveforms of the output Q1 of the first flip-flop circuit 21. It shows.

First, in the initial state, that is, when the distance between the disk 14 and the objective lens 121 is significantly different from the in-focus point, the reflected light that should be incident on the photodetector 13 is diffused as described above, so the focus error signal FE is also The output V23 of the low-pass filter 23 also becomes almost zero. low pass filter 2
3's output V23 is the reference voltage in the level comparison circuit 24.
This reference voltage V _S is compared with V S , and this reference voltage V _S is set to V23<V _S in the above state. therefore,
Since the output V24 of the level comparison circuit 24 becomes L level, the first flip-flop circuit 21 maintains the reset state. At this time, since the state setting signal Q1 is at L level, the first switch circuit 16 is
Connect between c. At the same time, the second flip-flop circuit 26 is not set and its output Q2
is at L level, the second switch circuit 27 connects a and b. As a result, the focus search mode is set, and the output of the focus search signal generator 25 is guided to the focus actuator coil 19 and the objective lens 12 is outputted from the focus search signal generator 25.
1 in the direction of the focal point.

When the objective lens 121 approaches the in-focus position, the diffused reflected light is transmitted to the photodetector 1.
3, and both the focus error signal FE and the output V23 of the low-pass filter 23 increase. And low pass filter 2
When the output V23 of the first flip-flop circuit 2 becomes equal to or higher than the reference voltage _VS , the output V24 of the level comparator circuit 24 becomes H level.
1 is in the reset release state, and the second flip-flop circuit 26 is in the set state. Then, the output Q2 of the second flip-flop circuit 26 becomes H level, so the second switch circuit 27 becomes a-
The output of the brake signal generator 28 is thereby led to the focus actuator coil 19. Since the brake signal supplied to the actuator coil 19 is a voltage signal having a polarity opposite to that of the focus search signal, a force is applied to the objective lens 121 in a direction opposite to the moving direction, and the objective lens 121 is decelerated.

Further, when the objective lens 121 reaches the in-focus position, the focus error signal FE passes through the zero point, so the zero-cross detector 20 outputs the trigger signal T. Therefore, the first flip-flop circuit 21 enters the set state and sets the state setting signal Q1 to H level. Therefore, the first switch circuit 16 connects a and b, and outputs the focus error signal FE to the focus actuator coil 19. As a result, the objective lens 121 is subjected to focus servo and is always controlled to move to the in-focus position.
When the focus servo operation is started, the second flip-flop circuit 26 is reset by the state setting signal Q1 and becomes ready for the next focus search.

Here, when the output of the switch circuit 16 switches from the focus search signal to the focus error signal FE, the voltage supplied to the actuator coil 19, the displacement of the objective lens 121, and the change in the focus error signal FE are respectively As shown in FIGS. 3a to 3c. In other words, when the objective lens 121 reaches the in-focus position, the objective lens 121 has already
is decelerated, and the amount of overshoot is considerably smaller than that of the conventional one.

Therefore, the automatic focus pull-in circuit of the optical disc playback device configured as described above can make the objective lens movement speed during focus search even faster than the maximum speed range in which servo focusing is possible. This allows the focus search time to be shortened. Furthermore, if the focus search speeds are the same, the focus servo can be set to the ON state with a lower output voltage value of the actuator drive circuit 18. It is very effective for equipment, etc.

[Effects of the Invention] As detailed above, according to the present invention, if the output voltage value of the actuator drive circuit is the same, the actuator displacement speed that allows focus search can be made faster than that of the conventional method, Furthermore, if the actuator speed during focus search is kept the same, the voltage range that can be output by the actuator drive circuit can be reduced, and the overshoot of the focus error can be reduced. A focus retraction circuit can be provided.

[Brief explanation of drawings]

FIG. 1 is a block circuit configuration diagram showing an embodiment of an automatic focus pull-in circuit of an optical disc playback device according to the present invention, and FIGS. 2 and 3 are operational explanations for explaining the operation of the same embodiment, respectively. 4 are block circuit diagrams showing the configuration of a conventional automatic focus pull-in circuit, and FIGS. 5 and 6 are operation explanatory diagrams for explaining the operation of the conventional automatic focus pull-in circuit, respectively. 11... Semiconductor laser, 12... Optical system, 13
...Photodetector, 14...Disc, 15
... Differential amplifier circuit, 16 ... First switch circuit, 17 ... Phase compensation circuit, 18 ... Actuator drive circuit, 19 ... Focus actuator coil, 20 ... Zero cross detector, 21 ... First reset priority flip-flop circuit, 22...
...Addition circuit, 23...Low pass filter, 24...
... Level comparison circuit, 25 ... Focus search signal generator, 26 ... Second reset priority flip-flop circuit, 27 ... Second switch circuit, 2
8... Brake signal generator.

Claims (1)

[Claims] 1. An objective lens for a disk on which information signals are recorded in a plurality of pit rows, and this objective lens is driven and controlled according to an input signal to move in a direction perpendicular to the signal recording surface of the disk. In an optical disc playback device in which the information signal is read out by tracing by an optical pickup having a focus actuator and a multi-segmented light receiving section, a linearly increasing voltage is used to move the objective lens to a focused position. a focus search signal generator that generates a signal; a brake signal generator that generates a voltage signal having at least the opposite polarity to the focus search signal; a focus error control signal generation means for generating a focus error control signal for controlling the movement of the focus error control signal to a focused position; a zero cross detector for detecting a point at which the focus error control signal passes through a zero level; level comparison means for detecting that the objective lens has reached the control range of the focus error control signal by generating a sum signal from each detection signal of the divided light receiving section and comparing the signal level with a reference level; a first state holding means whose state is set in the detection state of the level comparison means and the detection state of the zero-cross detector, and whose state setting is canceled in the non-detection state of the level comparison means; and a detection state of the level comparison means. a second state holding means whose state is set and the state setting is canceled by the state setting of the first state setting means; and a second state holding means for deriving the focus search signal when the state setting of the second state setting means is canceled. a first switching circuit that derives the brake signal when setting the state; and a signal selected by the first switching circuit when canceling the state setting of the first state holding means to control the focus error when setting the state. a second switching circuit that derives a signal; and a focus actuator that automatically pulls the objective lens into a focused position by driving and controlling the focus actuator based on the signal selected by the second switching circuit. An automatic focus pull-in circuit for an optical disc playback device, characterized in that it is equipped with a cast actuator drive control means.