JPH06105505B2 - Optical playback device - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical reproducing device, and more particularly to a CD player and
The present invention relates to an optical reproducing device capable of adjusting a focus offset caused by imbalance between the A and C sides and the B and D sides of an optical pickup in a CD-V player or the like.

[Prior Art] A CD player is provided with a focusing servo system for always focusing a beam of an optical pickup on a signal surface of a disc.

Specifically, as shown in FIG. 5, an optical pickup 14 is provided on the lower surface side of a disk 12 which is rotatable by driving a motor 10, and a signal recorded on the disk 12 is detected.
The optical pickup 14 has a focus coil 16 provided on a focusing actuator (not shown),
By driving the focusing coil 16, the objective lens can be moved in the direction (focus direction) perpendicular to the signal surface of the disk 12.

Further, the optical pickup 14 is provided with a four-divided photodetector 20, and outputs two detection signals of A + C and B + D.

On the output side of the photodetector 20, two current-voltage converters 11, 13 are provided.
Are connected, and the focus error detection circuit 22 and the RF detection circuit 26 are connected to these output sides, and the subtractor RD of the focus error detection circuit 22 uses (A + C)-(B +
D) is performed to detect the focus error signal (FE signal), and the adder AD3 of the RF detection circuit 26 performs A + B + C + D to detect the RF signal.

The output side of the focus error detection circuit 22 is connected to the focus system amplifier circuit 34. The output side of the amplifier circuit 34 is connected to the focus coil 16. Therefore, the FE signal indicating the deviation between the disc signal surface and the beam focus is amplified by the amplifier circuit 34 and then output to the focus coil 16 as a focus coil drive signal, so that the objective lens is focused on the disc signal surface. Amplifier circuit 34
Has a predetermined frequency-gain characteristic and frequency-phase characteristic.

By the way, the photodetector 20 has (A + C) side and (B +
Even if there is a focus offset between the two systems on the D) side and the beam is focused on the signal surface of the disc (A +
C)-(B + D) does not become zero. Therefore, even if the servo control is simply performed by the output of the focus error detection circuit 22, accurate focusing cannot be performed.

Therefore, the focus offset adjusting circuit 23 has been conventionally used.
The output of one of the two current-voltage converters 11 and 13,
For example, the level-variable focus offset adjustment DC voltage V _FO is superimposed on the (A + C) signal so that the FE signal becomes zero when the beam is focused on the disk signal surface (so-called injection method).

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technique, the optical pickup
When the beam from 14 passes through the scratches and spots on the disc, the beam reflected from the disc 12 is lost and
No signal of A, B, C, D is detected, and the diagonal signal (A
+ C) and (B + D) become zero. At this time, the sixth
As shown in a of FIG. 1A, the RF signal of the RF detection circuit 26 disappears and the focus error detection circuit 22 outputs V
Only _FO is multiplied by the gain of the subtractor RD and output as the FE signal, and this FE signal is further multiplied by the gain of the amplifier circuit 34 and output. Therefore, as shown in b of FIG. During passing, an abnormal DC voltage is generated in the focus coil drive signal, which causes the objective lens to largely deviate in the focus direction from the normal position immediately before the scratch. In the worst case, playback is no longer possible beyond the focus pull-in range of the focus servo system, and even if it does not go beyond the focus pull-in range, it will take some time until the disc returns to the normal focus position after the scratches on the disc have disappeared. To wake up. In addition, a large displacement of the objective lens adds a disturbance to the tracking error signal of the tracking servo system and adversely affects the tracking servo system.

In view of such a problem, an object of the present invention is to provide an optical reproducing device in which the stability of a focusing servo system against a disc scratch is improved.

[Means for Solving Problems] In the present invention, the (A + C) signal and the (B +) signal from the photodetector are used.
D) A focus error detection unit that obtains a focus error signal from the difference between two diagonal line signals, an amplification unit that drives the focus coil based on the focus error signal, and a level-adjustable focus offset adjustment voltage for one diagonal line signal. In an optical reproducing apparatus having a focus offset adjusting unit for superimposing and sending to a focus error detecting unit, a defect unit for detecting a disc scratch, and the focus offset adjusting voltage is set to zero while the defect unit detects the scratch. It is characterized by including a focus offset adjustment canceling unit that is close to.

[Embodiment] An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the main part of the CD player.

An optical pickup 14 is provided on the lower surface side of a disk 12 which is rotatable by the drive of a motor 10, and a signal recorded on the disk 12 is detected. The optical pickup 14 has a focus coil 16 provided on a focusing actuator (not shown), and moves the objective lens in a direction (focus direction) perpendicular to the signal surface of the disk 12.

Further, the optical pickup 14 is provided with a four-divided photodetector 20, and outputs two detection signals of A + C and B + D.

On the output side of the photodetector 20, two current-voltage converters 11, 13 are provided.
Are connected, and the focus error detection circuit 22 and the RF detection circuit 26 are connected to the output side thereof, and the subtracter RD of the focus error detection circuit 22 uses (A + C)-(B +
D) is performed to detect the focus error signal (FE signal), and the adder AD3 of the RF detection circuit 26 performs A + B + C + D to detect the RF signal.

The output side of the focus error detection circuit 22 is connected to a focus system amplification circuit 34 via a switch 33. The output side of the amplifier circuit 34 is connected to the focus coil 16.

The switch 33 is closed during playback, so that the FE signal indicating the deviation between the disc signal surface and the beam focus is transmitted to the amplifier circuit.
After being amplified by 34, it is output to the focus coil 16 as a focus coil drive signal, and the objective lens is focused on the disc signal surface. The amplifier circuit 34 is
It has a predetermined frequency-gain characteristic and frequency-phase characteristic.

A comparator CM for automatic focus detection is connected to the output side of the focus error detection circuit 22. The beam is focused on the signal surface of the disk 12 and is used to move the objective lens within a range where focusing servo is possible. That is, the comparator CM compares the FE signal when the objective lens is UP / DOWN with a predetermined threshold level before starting reproduction, and
When the signal is high, it outputs the FZC signal which becomes "H". This F
At the falling timing of the ZC signal, the "H" level servo-on signal SO is output to the switch 33 and the like.

A focus offset adjustment circuit 23 is connected to the focus error detection circuit 22. The focus offset adjusting circuit 23 includes a resistor R1, a volume VR, and a resistor R2 that are connected in series between + V _cc and −V _cc.
Output as the focus offset adjustment voltage V _FO (A
The focus error signal FE is calculated from the difference between the (A + C) signal and the (B + D) signal after being superimposed on the + C) signal.

By superimposing V _FO on the focus offset adjusting circuit 23, the FE signal becomes zero when the beam is focused on the disc signal surface.

A focus offset adjustment release circuit 25 is connected to the focus offset adjustment circuit 23, and V
_FO is designed to approach zero. The focus offset adjustment cancel circuit 25 includes a transistor Q1 connected between the VR and the ground, R1 connected between the base of Q1 and the ground, and a diode D connected between the base of Q1 and the defect input terminal IN _DF. And resistor R2, the base of Q1 and + V
resistor R3 and transistor Q2 connected between _cc and Q2
A resistor provided between the base of the and the servo-on input terminal IN _SO
It consists of R4, and when "H" is input to the defect input terminal IN _DF or "L" is input to the servo-on input terminal IN _SB , Q1 turns on and V _FO becomes zero.

The output side of the RF detection circuit 26 is connected to the defect circuit 28, which performs envelope detection on the RF signal to detect the loss of the beam reflected light due to a scratch on the disk, and outputs the defect signal (DF signal) of "H" level to the above. Output to the focus offset adjustment cancel circuit 25.

Next, the overall operation of the above embodiment will be described.

The VR of the focus offset adjustment circuit 23 is adjusted in advance so as to remove the imbalance between A, C and B, D of the optical pickup 14.
Has been adjusted.

First, during playback, switch 33 is closed, and during playback of anything other than scratches, Q1 is off, so V _FO adjusted with VR
Is directly superimposed on the (A + C) signal. Therefore, from the focus error detection circuit 22, the offset adjusted
The FE signal is formed and output to the amplifier circuit 34 via the switch 33. Then, the FE signal is amplified by the amplifier circuit 34 and output to the focus coil 16 as a focus coil drive signal, so that the objective lens is accurately focused on the signal surface of the disc.

When the beam from the optical pickup 14 passes through the disc scratch in the state where the focusing servo is applied in this way, the beam reflected light from the disc 12 is lost and the photodetector 20 detects A, B, C, and D Neither signal is detected, and the diagonal signals (A + C) and (B + D) become zero. On this occasion,
As shown in c of FIG. 2 (1), the RF detection circuit 26
The RF signal disappears.

Then, the defect circuit 28 detects the disc scratch and outputs the DF signal to the defect input terminal IN _DF . In the focus offset adjustment cancel circuit 25, Q1 turns on immediately after IN _DF becomes “H”, and V _FO becomes zero (d in FIG. 2 (3)).
reference). Therefore, the FE signal output of the focus error detection circuit 22 also becomes zero, and the output of the amplifier circuit 34 remains unchanged.
Therefore, during the passage of the flaw, the focus coil drive signal level immediately before the flaw is continuously input to the focus coil 16 (see e in FIG. 2 (2)), and the position of the objective lens in the focal direction is immediately before the flaw. It will be fixed in position and will not move carelessly.

After the optical pickup 14 has passed through the scratch, the photodetector 20 again
The A, B, C, D signals are output normally from (A + C),
The (B + D) diagonal signal and the RF signal are not zero (second
See (f) of FIG. At the same time, the defect circuit 28 is DF
Stops signal output and stops focus offset adjustment circuit 25
Q1 turns off and V _FO output is restarted (see g in FIG. 2 (3)). Therefore, the focus error detection circuit 22 outputs the FE signal whose offset has been adjusted again, and the normal focus servo is restarted (see h in FIG. 2 (2)).

When the focus servo is restarted, the disc signal surface is usually at almost the same position before and after the scratch, so the deviation between the focus of the objective lens and the disc signal surface is minimized, and quick focusing can be performed. Out-of-focus blurring is suppressed.

Separately from this, when performing a focus search before the start of reproduction, the servo-on signal SO (which is initially "L") is previously set to the switch 33 and the focus offset adjustment cancel circuit.
Output to 25, open switch 33, turn on Q1, and keep V _FO at zero. Then, the objective lens is moved so as to gradually approach from a predetermined position away from the disk 12. At this time, the focus error detection circuit 22 outputs an FE signal as shown in FIG.
As shown in (2) of the figure, the comparator CM outputs the "H" level FZC signal when the FE signal exceeds the threshold level. This FZC signal falls to "L" when the beam focus of the optical pickup 14 comes almost to the signal surface of the disk 12 and the FE signal falls below the threshold level, and is urged by the fall of this FZC signal. The servo-on signal SO becomes "H". Thus, the switch 33 is closed and, Q1 is the focus servo is applied based on the offset-adjusted FE signal by V _FO off.

Here, V _{FO is set} to zero during the focus search for the following reason.

That is, when the objective lens is moved while _VFO is superposed, the FE signal is shown in Fig. 4 (1) instead of Fig. 3 (1).
In some cases, the FE signal is caught at the threshold level of the comparator CM when the objective lens is still far from the disc, and the FZ as shown in Fig. 4 (2) is generated.
The C signal is output, and the servo is turned on incorrectly at the first falling point A. On the other hand, as described above, the servo can be turned on at an accurate position by setting _VFO to zero during the focus search.

According to this embodiment, when the defect circuit 28 detects a disc scratch, the focus offset adjustment cancel circuit 25
By setting the offset adjustment voltage V _FO to zero, the error signal becomes zero even if the optical signal output of the optical pickup 14 is lost due to a scratch on the disk, and the focus coil drive signal immediately before the scratch is maintained and the objective lens The position of becomes constant. Therefore, unlike the conventional method, the position of the objective lens is not displaced unnecessarily large due to an abnormal error signal output, and it is held at the normal position immediately before the scratch, and the normal state is promptly obtained after passing the scratch. Since the stability of the focusing servo system is increased, an unnecessary change in the optical signal in the tracking direction does not occur, and the adverse effect on the reproduced sound and the reproduced image due to the disc scratch can be reduced.

In the above embodiment, when a disc scratch is detected,
Although V _{FO is set} to zero, the present invention is not limited to this, and in consideration of the electric offset of the focus error detection circuit 22, V _FO is set to a predetermined value other than zero that can stabilize the system. You may make it switch.

[Advantages of the Invention] According to the optical reproducing device of the present invention, the defect of the disk is detected in the defect portion, and the focus offset adjustment canceling portion brings the focus offset adjustment voltage close to zero while the scratch is detected. As a result, the focus coil does not move while passing through the disc scratch, and the objective lens can be held in the state immediately before the scratch, and the control error when control is restarted after passing the scratch is minimized. It is possible to quickly return to the normal control state and obtain stable servo characteristics.

[Brief description of drawings]

FIG. 1 is a block diagram showing an essential part of a CD player according to an embodiment of the present invention, FIG. 2 is a waveform diagram showing the operation of FIG. 1 during reproduction, and FIG. 3 is FIG. 1 during focus search. FIG. 4 is a waveform diagram showing the operation of FIG. 4, FIG. 4 is a reference waveform diagram showing an example of bad operation, FIG. 5 is a block diagram showing the main part of a conventional CD player, and FIG. 6 is the operation of FIG. 5 during reproduction. It is a waveform diagram showing. 12: Disc, 14: Optical pickup 16: Focus coil 22: Focus error detection circuit 23: Focus offset adjustment circuit 25: Focus offset adjustment release circuit 28: Defect circuit 34: Amplification circuit

Claims (1)

[Claims] 1. A focus error detection unit for obtaining a focus error signal from a difference between two diagonal line signals of A + C signal and B + D signal from a photodetector, an amplification unit for driving a focus coil based on the focus error signal, and In an optical reproducing apparatus having a focus offset adjustment unit that superimposes a level-adjustable focus offset adjustment voltage on the diagonal signal of, and sends the focus offset detection voltage to the focus error detection unit, a defect unit that detects a disc scratch and a defect unit that detects the scratch An optical reproducing apparatus, comprising: a focus offset adjustment canceling unit that brings the focus offset adjustment voltage close to zero during detection.