JPH0516651Y2 - - Google Patents

Description

[Detailed explanation of the invention] [Industrial application field] This invention relates to an optical playback device, especially for CDs.
An optical playback device that can prevent focus pull-in mistakes in devices such as players and CD-V players that have a focus offset adjustment section that cancels out the imbalance between the A, C side and the B, D side of an optical pickup. Regarding.

[Prior Art] A CD player is equipped with a focusing servo system that keeps the beam of an optical pickup always focused on the signal surface of the disc.

Specifically, as shown in FIG. 3, an optical pickup 14 is provided on the underside of a disk 12 which is rotatable by the drive of a motor 10, and the signals recorded on the disk 12 are detected. Light pick up 1
4 has a focus coil 16 provided in a focusing actuator (not shown),
By driving this focusing coil 16, the objective lens is moved in a direction perpendicular to the signal plane of the disk 12 (focal direction).

Further, the optical pickup 14 is equipped with a photodetector 20 divided into four parts, and has two photodetectors A+C and B+D.
Two detection signals are output.

Two current-voltage converters 11 and 13 are connected to the output side of the photodetector 20, and a focus error detection circuit 22 and an RF detection circuit 26 are connected to these output sides. (A+C) - (B+D) in the subtracter RD of the error detection circuit 22
The focus error signal (FE signal) is calculated by
is detected, and the adder AD3 of the RF detection circuit 26
+B+C+D calculation is performed to detect the RF signal.

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

During playback, the switch 33 is closed, thus indicating the deviation between the disk signal plane and the beam focus.
After the FE signal is amplified by the amplifier circuit 34, it is output as a focus coil drive signal to the focus coil 16, and the objective lens is focused on the disk signal surface.

A comparator CM for automatic focus detection is connected to the output side of the focus error detection circuit 22. When this comparator CM starts playback, it
It is used to focus the beam approximately on the signal plane and move the objective lens within the range where focusing servo is possible. That is, before starting playback, the comparator CM compares the FE signal when the objective lens is UP/DOWN with a predetermined threshold level,
Outputs the FZC signal which becomes "H" when the FE signal is high. At the falling timing of this FZC signal, an "H" level servo-on signal SO is output to the switch 33, etc.

[Problems to be solved by the invention] By the way, in the photodetector 20, there is a focus offset between the two systems on the (A+C) and (B+D) sides, and the beam is focused on the disk signal surface. Even if (A+C)-(B+D) does not become zero. Therefore, simply focus error detection circuit 2
Even if servo control is performed with output 2, accurate focusing cannot be achieved.

For this reason, a focus offset adjustment circuit 23 has conventionally been provided, and two current-voltage converters 11,
13, for example, the (A+C) signal,
Focus offset adjustment DC voltage with variable level
The V _FO was superimposed so that when the beam was focused on the disk signal plane, the FE signal was zero (so-called injection method).

On the other hand, in focus search before starting playback, the objective lens is moved and gradually approached from a predetermined position away from the disk 12, but at this time,
Good balance between (A+C) side and (B+D) side,
When the focus offset adjustment voltage _VFO is close to zero, the focus error detection circuit 22 outputs an FE signal that rises from a point close to the zero level as shown in FIG. 41 over time. Then,
In order for the comparator CM to detect the in-focus position without error, it is sufficient to set a threshold level that is relatively close to zero, and the FZC signal is set at a threshold level (see Figure 4), as shown in Figure 2. (See the dashed line in 2)
When the beam focus of the optical pickup 14 comes to almost the signal surface of the disk 12, and the FE signal falls below the threshold level, it becomes "L", and this FZC becomes "H". The servo-on signal SO is activated by the falling edge of the signal.
becomes "H". This closes the switch 33 and activates the focus servo based on the FE signal.

However, the (A+C) side and (B
+D) side is unbalanced and a large focus offset adjustment DC voltage V _FO is superimposed,
When the objective lens is moved to perform focus pull-in, the focus error detection circuit 22 outputs an FE signal that rises from a position slightly away from the zero level as shown in FIG. 4 as time passes. Therefore, when compared at a threshold level that is relatively close to zero, when the objective lens is still far from the disk, the fluctuations in the FE signal (see Figure 4B) are at the threshold level of the comparator CM. 4.
The FZC signal is output, and the servo is turned on incorrectly at the first falling point A, causing focus pull-in to fail.

To prevent this focus pull-in failure, when a large focus offset adjustment DC voltage V _FO is superimposed, it is possible to raise the threshold level of the comparator CM accordingly (see Figure 4). (see double-dashed line in 3), comparator
A variable level reference voltage generator ER is connected to the reference side input terminal of the CM, and the threshold level is adjusted to match the focus offset adjustment DC voltage V _FO for each set. On the other hand, in order to match the upper limit of the variation of the unbalance between (A+C) and (B+D) of the photodetector 20, the adjustment is complicated and troublesome. If the setting is fixed at the threshold level, when the photodetector 20 is originally well-balanced and the focus offset adjustment DC voltage V _FO is set to almost zero, the focal position of the objective lens is originally set to the disk signal plane. Even though it is possible to turn on the servo when the lens reaches point C, the focal position of the objective lens turns on slightly in front of the disk signal surface, as shown at point C in Figure 4, and it takes a long time until the focus is achieved. There was a drawback that it took a while.

In view of these problems, this invention eliminates the focus pull-in error, eliminates the need for troublesome threshold level adjustment of the in-focus point detection section, and, in the case of a well-balanced light detection section, allows the focus to be focused at a position closer to the ideal position. The object of the present invention is to provide an optical reproducing device that can turn on a cass servo.

[Means for solving the problem] In this invention, the A+C signal and B signal from the photodetector are
a focus error detection unit that obtains a focus error signal from the difference between two diagonal signals of the +D signal;
a focus offset adjustment section that superimposes a level-variable focus offset adjustment voltage on one diagonal signal and sends it to a focus error detection section;
In an optical reproducing device, the optical reproducing device includes a focused point detection unit that compares a focus error signal with a predetermined threshold level and outputs a focus zero cross signal when the focus is pulled in, The present invention is characterized in that it includes a focus offset adjustment canceling section that changes the focus offset to a predetermined value close to zero.

[Example] An embodiment of this invention will be described based on the drawings.

FIG. 1 shows a block diagram showing the main parts of a CD player.

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

Further, the optical pickup 14 is equipped with a photodetector 20 divided into four parts, and has two photodetectors A+C and B+D.
Two detection signals are output.

Two current-voltage converters 11 and 13 are connected to the output side of the photodetector 20, and a focus error detection circuit 22 and an RF detection circuit 26 are connected to these output sides. (A+C) - (B+D) in the subtracter RD of the error detection circuit 22
The focus error signal (FE signal) is calculated by
is detected, and the adder AD3 of the RF detection circuit 26
+B+C+D calculation is performed to detect the RF signal.

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

During playback, the switch 33 is closed, thus indicating the deviation between the disk signal plane and the beam focus.
After the FE signal is amplified by the amplifier circuit 34, it is output as a focus coil drive signal to the focus coil 16, and the objective lens is focused on the disk signal surface.

A comparator CM for automatic focus detection is connected to the output side of the focus error detection circuit 22. It is used to focus the beam almost on the signal surface of the disk 12 and move the objective lens to a range where focusing servo is possible. That is, the comparator CM is
Before starting playback, compare the FE signal when the objective lens is UP/DOWN with a predetermined threshold level that is relatively close to zero, and when the FE signal is large, it is set to "H".
Outputs the FZC signal. At the falling timing of this FZC signal, an "H" level servo-on signal SO is output to the switch 33, etc.

A focus offset adjustment circuit 23 is connected to the focus error detection circuit 22.
This focus offset adjustment circuit 23 has +V _cc
It includes a resistor R1, _a volume VR, and a resistor R2 connected in _series between
C) The focus error signal FE is calculated from the difference between the (A+C) signal and the (B+D) signal after superimposition.

This focus offset adjustment circuit 23 adjusts V _FO
By superimposing , the FE signal becomes zero when the beam is focused on the disk signal surface.

A focus offset adjustment cancellation circuit 25 is connected to the focus offset adjustment circuit 23, so that _VFO can be switched to a predetermined value (zero in this embodiment) as necessary. This focus offset adjustment canceling circuit 25 consists of a switch 35 provided between the output side of the volume VR and the ground, and is controlled to open and close by the servo-on signal SO.

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

It is assumed that the VR of the focus offset adjustment circuit 23 has been adjusted in advance so as to eliminate the imbalance between A, C and B, D of the optical pickup 14.

First, during playback, the switch 33 is closed and the switch 35 is open, so the V _FO adjusted by VR is directly superimposed on the (A+C) signal. Therefore, the focus error detection circuit 22 generates an offset-adjusted FE signal.
The signal is outputted to the amplifier circuit 34 via the switch 33. The FE signal is amplified by the amplifier circuit 34 and output as a focus coil drive signal to the focus coil 16, thereby accurately focusing the objective lens on the disk signal plane.

Separately, when performing a focus search before starting playback, the servo-on signal SO (initially set to "L") is output to the switch 33 and the focus offset adjustment cancellation circuit 25, and the Open the switch 35 to turn off the focus servo, and close the switch 35 to make the V _FO zero. Then move the objective lens and
Start from a predetermined position far away and gradually approach it.

At this time, (A+C) and (B+) of the photodetector 20
D) is unbalanced, and the focus offset adjustment DC voltage V _FO is increased by adjusting the volume VR.
While the adjustment is being made, the focus error detection circuit 22 outputs the signal shown in FIG.
A vertically asymmetric FE signal like
The first fluctuation of the signal never exceeds the threshold level, and from the time when the FE signal exceeds the threshold level, the FZC signal of "H" level is output from the comparator CM as shown in Figure 2. Output.

This FZC signal falls to "L" when the beam focus of the optical pickup 14 approaches the signal surface of the disk 12 and the FE signal falls below the threshold level, and is energized by the fall of this FZC signal. The servo-on signal SO becomes "H".
Therefore, the switch 33 is closed and the switch 3
5 is open and the FE with offset adjustment by V _FO is opened.
Focus servo is applied based on the signal.

On the other hand, when the balance between (A+C) and (B+D) of the photodetector 20 is good and the volume VR is adjusted so that the focus offset adjustment DC voltage _VFO is almost zero, the focus error occurs. As time passes, the detection circuit 22 outputs a vertically symmetrical FE signal as shown in FIG. As shown in FIG. 4, the comparator CM outputs an "H" level FZC signal from the time when the FE signal exceeds the threshold level at the subsequent rise.

Since the FE signal is vertically symmetrical, this FZC signal goes to "L" when the beam focus of the optical pickup 14 almost reaches the signal surface of the disk 12 and the FE signal falls below the threshold level. energized by the falling edge of this FZC signal, the servo-on signal SO becomes "H".

As a result, the switch 33 is closed and the switch 35 is opened, and the focus servo is applied based on the FE signal whose offset has been adjusted by the _VFO , but since the beam focus is already almost on the signal surface of the disk 12 when the servo is turned on. , it does not take much time to focus, and the recorded signal on the disk 12 can be read immediately.

According to this embodiment, during focus search,
By setting the offset adjustment voltage V _FO to zero in the focus offset adjustment cancellation circuit 25, even if the threshold level of the comparator CM is fixed near zero, the objective Attach the lens to disk 12 from a distance.
When the photodetector 20 (A
Regardless of the magnitude of the unbalance between +C) and (B+D), fluctuations in the FE signal initially occur near the zero level, so this fluctuation in the FE signal may exceed the threshold level and cause the in-focus position to be incorrectly detected. In the case of a well-balanced photodetector 20 that does not have the risk of being damaged, the servo can be turned on when the beam focus almost reaches the disk signal surface.
After the servo is turned on, the servo system is quickly stabilized and reading of the disc recording signal can be started immediately.

In addition, in the above embodiment, during the focus search,
Although the focus offset adjustment DC voltage V _FO was set to zero, this invention is not limited to this in any way, and considering the stability of the focus search system, etc.
It may be a predetermined value other than zero at a small level.

[Effect of the invention] According to the optical reproducing device according to the invention, during focus search, the focus offset adjustment voltage is changed to a predetermined value close to zero in the focus offset adjustment canceling section, so that the optical reproduction device (A+) of the detection part
Regardless of the size of the unbalance between the C) side and the (B+D) side, when the objective lens is brought close to the disk for focus search, the FE signal will initially fluctuate near zero, so the threshold of the focus detection section By fixing the field level close to the zero level, there will be no focus pull-in mistakes even if no adjustment is made, and the focus servo can be turned on at a position closer to the in-focus point for a light detection section that is already well-balanced. This excellent effect can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the main parts of a CD player according to an embodiment of this invention, Fig. 2 is a waveform diagram showing the operation of Fig. 1 during focus search, and Fig. 3 is a diagram of a conventional CD player. FIG. 4 is a block diagram showing the main parts, and a waveform diagram showing the operation of FIG. 3 during focus search. 12...Disk, 14...Light pickup,
22...Focus error detection circuit, 23...Focus offset adjustment circuit, 25...Focus offset adjustment cancellation circuit, 33, 35...Switch, CM...Comparator.

Claims (1)

[Claims for Utility Model Registration] A focus error detection unit that obtains a focus error signal from the difference between two diagonal signals, A+C signal and B+D signal from a photodetector, and a focus-off device whose level is variable for one of the diagonal signals. A focus offset adjustment section that superimposes the set adjustment voltage and sends it to the focus error detection section, and a focusing point that compares the focus error signal with a predetermined threshold level and outputs a focus zero cross signal when the focus is pulled in. An optical reproducing device comprising: a detecting section; and a focus offset adjustment canceling section that changes the focus offset adjustment voltage to a predetermined value close to zero when the focus is pulled in. .