JPH0227530A - Bias adjusting circuit - Google Patents

Abstract

PURPOSE:To always obtain an appropriate focusing bias by using the output of a level detection circuit to which signal reproducing output is supplied and an inversion amplifier to which the output of the circuit is supplied as bias for a focusing error signal. CONSTITUTION:The title circuit is provided with a peak hold circuit 1 which becomes the level detection circuit, the inversion amplifier 2 to which the output of the peak hold circuit 1 is supplied, and a variable resistor device 3 on which the output from the level detection circuit 1 and that from the inversion amplifier 2 are applied, and adds the output via the variable resistor device 3 on the focusing error signal. And the focusing bias is set at a level in which the level difference of the level of the signal reproducing output detected by the level detection circuit 1 and the level in which the level of the signal reproducing output is inverted by the inversion amplifier 2 is voltage-divided with a prescribed ratio by the variable resistor device 3, and changes corresponding to the change of the level of the signal reproducing output. In such a way, it is possible to always adjust the focusing bias at the appropriate level corresponding to the change of the level of the signal reproducing output.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of Application The present invention is applied to a bias adjustment circuit that adjusts the bias of a focus error signal in, for example, an optical pickup used to read information signals recorded on an optical disk. .

B0 Summary of the Invention The present invention relates to a bias adjustment circuit used in an optical pickup used for reading information signals recorded on an optical disk, and which includes a level detection circuit to which a signal reproduction output is supplied, and an output of the level detection circuit. By using the output of the inverting amplifier that is supplied with this as a bias for the focus error signal via a variable resistance device, the bias amount corresponds to the level of the signal reproduction output, thereby eliminating dirt on the optical disk or lens system. Even if the level of the signal reproduction output changes due to factors such as the above, an appropriate focus bias can always be obtained and good focus servo can be performed.

C2 Prior Art Conventionally, when reading information signals recorded on an optical disk using an optical pickup device, a focus error is detected based on the signal reproduction output (so-called RF multiplied signal) obtained by the optical pickup device, and a focus servo control is performed. It is carried out.

This focus servo drives a focus adjustment mechanism of an optical pickup device based on a detected focus error, so that a light beam irradiated from the optical pickup device onto the signal recording surface of the optical disk is directed to the signal recording surface. This allows the light to be accurately focused on the top.

The focus adjustment mechanism is configured such that the movement of an optical device such as an objective lens is controlled by a predetermined drive device.

In order to detect the focus error, the optical pickup device uses an optical device such as a cylindrical lens that applies astigmatism to the light beam that is irradiated onto the optical disk and reflected by the signal recording surface. As shown in FIG.
, 101d configured to receive light by a light receiving device 101 has been proposed. In this optical pickup device, the focus error detection circuit 102 adds together the signal reproduction outputs of the light receiving elements that are arranged to face each other across the center of the light receiving device 101. The two outputs are subtracted from each other and output as a focus error signal indicating the amount of focus error. That is, the levels of the signal reproduction outputs of the four light receiving elements 101a, 101b, 1o1c, and 101d are respectively a, b, c,
d, the focus error signal SF is Sp =
(a+c)-(b+d) If this focus error signal SF is zero,
Focus error is zero.

However, in the optical pickup device, due to errors in position adjustment of the optical devices constituting the optical pickup device, a focus error occurs when focus servo is performed so that the focus error signal SF becomes zero. The light beam may not become zero and the light beam may not be accurately focused on the signal recording surface.

Therefore, focus servo is performed based on a signal obtained by adding the focus bias e to the focus error signal Sp.

The focus bias e is the reference voltage +Vw.

Focus bias adjustment volume 1 with Vm applied
03 to adjust to a predetermined level. This focus bias e is sent to the adder 104 and added to the focus error signal SF. A focus error signal S to which the focus bias e is added. is connected to the actuator drive circuit 106 via the phase compensation circuit 105.
sent to. This actuator drive circuit 106 drives and controls an actuator 107 that controls the movement of an objective lens and the like based on the sent focus error signal Ss. In this way, by performing focus servo so that the focus error signal Ss to which the focus bias e is added becomes zero, the focus error can be made zero.

D1 Problem to be Solved by the Invention By the way, as mentioned above, the focus bias e adjusted to a predetermined level by the focus bias adjustment volume 103 is always kept at a constant level even if the level of the signal reproduction output changes. It will be done.

Therefore, the level of the signal reproduction output decreases due to a decrease in the optical output due to changes over time in the light emitting elements such as laser diodes built into the optical pickup device, or dirt on the optical devices or optical disks that make up the optical pickup device. When this happens, the focus bias e is not at an appropriate level, and there is a problem that good focus servo is not performed and so-called out-of-focus occurs.

Conventionally, in order to solve this problem, techniques for adjusting the focus bias have been proposed.
In the technology described in Publication No. 143439,
Increase (or decrease) focus bias in steps when reading information signals recorded on optical discs
The focus bias is set at an optimal level by stopping the change in the focus bias at the step where the level of the signal reproduction output reaches its maximum.

However, this technique requires a predetermined circuit for changing the focus bias in steps, which complicates the device configuration and makes it difficult to miniaturize the device and facilitate manufacturing.

In addition, since the focus bias is not set to an appropriate level when reading the information signal, it takes a certain amount of time from the start of reading the information signal until the focus bias is set to the appropriate level. Become.

Furthermore, in the technique described in Japanese Patent Application Laid-Open No. 61-177646, prior to reading an information signal recorded on an optical disk, the focus al1 mechanism is driven over almost the entire adjustable range. At a so-called focus search stage in which the focus position is searched, the bias level applied to the focus adjustment mechanism when the level of the signal reproduction output reaches the maximum is stored. While reading the information signal, a focus bias at an appropriate level is obtained by setting a level with the opposite polarity of the stored bias level as a force bias.

In this technique, the focus bias during reading of the information signal is set based on the bias level stored at the focus search stage. Therefore, if the level of the signal reproduction output changes while reading the information signal, for example when a part of the optical disc is dirty, the focus bias will not follow this level change and change. Therefore, there is a problem that the focus bias is no longer at an appropriate level, resulting in so-called out-of-focus.

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above-mentioned circumstances, and it is possible to constantly adjust the focus bias to an appropriate level according to changes in the level of the signal reproduction output without complicating the configuration. Means for Solving the 81 Problems In order to solve the above-mentioned problems and achieve the above objects, a bias adjustment circuit according to the present invention provides a bias adjustment circuit capable of A bias adjustment circuit that adjusts the bias of an error signal includes a level detection circuit to which a signal reproduction output is supplied, an inverting amplifier to which the output from this level detection circuit is supplied, and an output from the level detection circuit and the inverting amplifier. and a variable resistance device to which an output from the variable resistance device is applied, and the output via the variable resistance device is added to the focus error signal.

As the level detection circuit, a so-called peak hold circuit, a low pass filter, etc. can be used.

F1 action In the bias adjustment circuit according to the present invention, the focus bias is determined by the variable resistance device between the level of the signal reproduction output detected by the level detection circuit and the level obtained by inverting the level of the signal reproduction output by the inverting amplifier. The level difference is set to a level obtained by dividing the voltage at a predetermined ratio, and changes in accordance with changes in the level of the signal reproduction output.

G. Examples Specific examples of the present invention will be described below with reference to the drawings.

This example is an example in which the present invention is applied to an optical pickup device configured to perform focus error detection using a so-called astigmatism method.

As shown in FIG. 1, the bias adjustment circuit according to the present invention includes a peak hold circuit 1 serving as a level detection circuit, and an inverting amplifier 2 to which the output of the peak hold circuit 1 is supplied.
It has the following.

The peak hold circuit 1 is configured to maintain an output corresponding to the maximum value of the supplied signal level for a predetermined period of time when a signal whose level changes is supplied. The output of the inverting amplifier 2 is designed to have a level that is inverse to the level of the supplied signal.

The output of the peak hold circuit 1 and the output of the inverting amplifier 2 are applied to one end and the other end of a resistor 3a constituting the variable resistance device 3, respectively. Therefore, the output of the variable resistance device 3 can be set to a desired level between the output level of the peak hold circuit 1 and the output level of the inverting amplifier 2.

In the optical pickup device to which the bias adjustment circuit according to the present invention is applied, the peak hold circuit 1 is supplied with a signal reproduction output (so-called RF multiplied signal) from the light receiving device 4 of the optical pickup device.

The light receiving device 4 includes first to fourth light receiving elements 4a, 4b.
, 4c, and 4d. The light beam irradiated onto the optical disk from the optical pickup device and reflected by the signal recording surface of the optical disk is transmitted to the light receiving device 4 through an optical device such as a cylindrical lens that imparts astigmatism to the light beam. It is incident on the ground.

The first to fourth light receiving elements 4a, 4b, 4c.

The respective outputs of 4d are sequentially added to each other by the first to third adders 5, 6.7 to form the signal reproduction output, which is sent to the peak hold circuit 1 and connected to this optical pickup device. The signal is sent to the signal processing circuit 8. This signal processing circuit 8 is configured to reproduce an information signal from the signal reproduction output by subjecting the signal reproduction output to a predetermined demodulation process or the like.

Further, a focus error signal Sp is generated from the output of the light receiving device 4 by a focus error detection circuit 9 serving as a focus error detection section. That is, the outputs of the first and third light receiving elements 4a and 4c facing each other across the center of the light receiving device 4 are added together by the fourth adder 10, and similarly, the center of the light receiving device 4 is The outputs of the second and fourth light-receiving elements 4b and 4d facing each other are the fifth light-receiving elements.
The output of the fourth adder lO and the output of the fifth adder 11 are added to each other by the adder 11 of the subtracter 1.
A focus error signal SF is generated by subtracting 2 from each other.

The focus error signal Sp generated by the focus error detection circuit is sent to the sixth adder 13.

The output of the variable resistance device 3 is supplied to the sixth adder 13 as a focus bias e, and added to the focus error signal SF.

The focus error signal Ss to which the focus bias e has been added is sent to the focal point 11 node device 14 of this optical pickup device. In this focus iJ node device 14, a focus error signal S is supplied. is sent to the actuator drive circuit 16 via the phase compensation circuit 15. This actuator drive circuit 16 drives and controls an actuator 17 configured to control the movement of a predetermined optical device such as an objective lens based on the sent focus error signal Se, so that the focus error signal se becomes zero. Focus servo is performed so that The phase compensation circuit 15 is a circuit for compensating for a phase shift between the focus error signal Se and the operation of the actuator 17, which is caused by the mechanical characteristics of the actuator 17.

As described above, in the optical pickup device to which the bias adjustment circuit according to the present invention is applied, the focus bias e can be adjusted by adjusting the variable resistance device 3 to adjust the level of the output of the peak hold circuit 1 and the inverting amplifier. The level difference between the level of the second output and the second output level is a level obtained by dividing the voltage at a predetermined ratio. In this optical pickup device, the optical output of the light emitting element of the optical pickup device, such as a laser diode, is adjusted to the standard output, and the signal is picked up while each optical device that makes up the optical pickup device is free of dirt, scratches, etc. The variable resistance device 3 is adjusted so that the signal reproduction level obtained from a so-called reference optical disk from which a reference level of reproduction output is obtained is maximized.

If the optical output of the light emitting element is maintained at the standard output, each of the optical devices is free of dirt, scratches, etc., and the optical disc to be played has the same light reflection characteristics as the reference optical disc, then the signal The reproduction output is at the above reference level. At this time, the focus bias e is set to an optimal level that has been adjusted in advance from the beginning of reading the information signal.

In addition, when the level of the signal reproduction output changes due to a decrease in optical output due to aging of the light emitting element, dirt on each of the optical devices, dirt on the optical disc, or differences in light reflection characteristics of the optical disc, the focus bias e The level changes in response to the change in the level of the signal reproduction output.

Therefore, the focus bias e is always set at an optimal level corresponding to the level of the signal reproduction output,
There is no occurrence of so-called out-of-focus.

Note that the bias adjustment circuit according to the present invention is not limited to the above-mentioned embodiments, and can be modified as appropriate.
The level detection circuit is not limited to the peak hold circuit as shown in the above-described embodiments, and a low-pass filter can also be used. In this case as well, the level of the focus bias e changes in accordance with the change in the level of the signal reproduction output, and the same effect as in the above embodiment can be obtained.

Further, the present invention is applicable not only to an optical pickup device configured to detect a focus error by the so-called astigmatism method as shown in the above-mentioned embodiments, but also to, for example, the so-called Knifezi method, the critical angle method, or the push-pull method. The present invention can be used in an optical pickup device configured to detect focus errors by various means such as the pull method.

Furthermore, the present invention is applicable not only to an optical pickup device configured to obtain a signal reproduction output and a focus error signal based on the output from the same light receiving device as shown in the above-described embodiments, but also to a signal reproduction device. The present invention can also be applied to an optical pickup device configured to obtain an output and a focus error signal based on the outputs of separately provided light receiving devices.

H9 Effects of the Invention As described above, in the bias adjustment circuit according to the present invention, the focus bias is determined by the variable resistance device, and the level of the signal reproduction output detected by the level detection circuit and the level of the signal reproduction output detected by the inverting amplifier. The level difference from the inverted level is set to a level divided at a predetermined ratio.

Therefore, the focus bias changes in response to changes in the level of the signal reproduction output around a preset level, and is always set at an optimal level corresponding to the level of the signal reproduction output.

That is, the present invention can provide a bias adjustment circuit that can always adjust the focus bias to an appropriate level according to changes in the level of the signal reproduction output with a simple configuration.

FIG. 1 is a block circuit diagram showing the configuration of a main part of an optical pickup device to which a bias adjustment circuit according to the present invention is applied.

FIG. 2 is a block circuit diagram showing the configuration of the main parts of a conventional optical pickup device in which the focus bias is set at a constant level.

1...Peak hold circuit 2...
・・Inverting amplifier 3・・・・・・・Variable resistance device

Claims (1)

[Claims] A bias adjustment circuit that adjusts the bias of a focus error signal from a focus error detection section, comprising: a level detection circuit to which a signal reproduction output is supplied; and an inverting amplifier to which the output from the level detection circuit is supplied. and a variable resistance device to which an output from the level detection circuit and an output from the inverting amplifier are applied, and a bias adjustment circuit configured to add the output via the variable resistance device to the focus error signal.