JPH09270137A - Lens position detecting device for optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the number of pieces of circuit elements and to simplify a circuit by sampling and holding a push-pull signal at the passage timing of a mirror part. SOLUTION: Reflection light from an optical disk is made incident on a quadripartite photodetector 7 through a convergence lens. The photodetector 7 divides it to light receiving areas Pa-Pd, and further divides them in the radial, tangential directions, and supplies them to amplifiers 8, 9 for obtaining respective difference signals. At this time, respective push-pull signal and tangential push-pull signal are generated. The tangential push-pull signal between them is inputted to a timing generation circuit 10, and a zero cross of rise is detected, and a timing signal is obtained. Then, the timing signal is inputted to a sample and hold circuit 11, and the push-pull signal from the amplifier 8 is sampled and held at the timing. Thereafter, a noise component is removed by a low-pass filter 12. Thus, the number of pieces of the circuit elements are reduced, and the circuit is simplified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens position detecting device for reducing a DC offset in a push-pull method in an optical disk device.

[0002]

2. Description of the Related Art In an optical disc apparatus, in order to precisely irradiate a laser beam spot on a track of an optical disc, a focusing servo system of an optical head which is an objective lens is provided, and a tracking servo of an optical head or an optical pickup. Equipped with a system.

Here, the tracking servo corrects the position in the radial direction of the optical disk and compensates for a tracking error due to eccentricity of the track.
The causes of the tracking error include not only the eccentricity of the track to be compensated by the above tracking servo, but also the deviation of the optical axis (mechanical neutral point) of the objective lens when the tracking servo is applied and the deviation due to the optical system and skew. Yes, in this case a DC offset occurs.

Various types of DC offset detection have been proposed in the past, and a push-pull method using a two-division or four-division photodetector (hereinafter referred to as 2D-PD, 4D-PD) has been proposed. In this case, for example, a method of obtaining a lens position offset from a low frequency difference signal by 2D-PD and a low frequency signal by a high frequency envelope (Japanese Patent Laid-Open No. 6-58242).
1-71423), a method of obtaining a DC offset from the difference between the peak hold and the bottom hold of a push-pull signal (Japanese Patent Laid-Open No. 3-286430), a first division region on both sides of a center division line of a photodetector. And a method for obtaining a lens position signal in the second divided area outside thereof (Japanese Patent Laid-Open No. 5-159328) and a tracking error by extracting a high frequency zero cross of the tracking error signal (push-pull signal) from the 4D-PD. There is a method of extracting the DC offset of the signal (Japanese Patent Laid-Open No. 63-291224).

[0005]

However, in each of the DC offset detection methods described above, a push-pull signal is processed to obtain a DC offset, and a lens position signal is obtained by using a special photodetector. is there.

In particular, when a zero-cross timing signal is extracted from the push-pull signal and a DC offset is extracted from the push-pull signal, circuits such as a high-pass filter, zero-cross, sample and hold are required, and a signal required for timing is created. This requires an increase in the number and complexity of circuit elements.

As a result, there are problems that the number of circuits is increased, the circuit is complicated to obtain a necessary signal, and a special photodetector is used.

The present invention has been made in view of the above problems, and an object thereof is to provide a lens position detection for an optical disk apparatus which has a small number of circuits and can be simplified.

[0009]

The present invention that achieves the above object has the following matters specifying the invention.

(1) Means for obtaining the timing at which the laser beam spot from the optical head passes through the mirror section of the optical disk, and sample and hold the push-pull signal based on the laser beam spot at this timing to obtain the lens position signal. And means.

(2) In the above (1), the push-pull signal is sampled and held at a rising zero cross of the tangential push-pull signal.

Focusing on the laser beam reflected and returned from the optical disc, at the moment when the laser beam spot passing through the mirror surface of the optical disc, which is the moment when there is no influence of the pits of the optical disc, is detected from the photodetector at that time. The push-pull signal is a DC offset itself.
It is possible, for example, to obtain the zero-cross timing by obtaining this mirror plane passage with, for example, a dangential push-pull signal, only with a comparator and zero-cross detection, and at this timing, the push-pull signal can be switched very easily. As a result, it is possible to obtain a lens position signal by simplifying the DC offset with a small number of circuit elements.

[0013]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will now be described with reference to FIGS. First, an outline of the apparatus will be described with reference to FIG. 2. In FIG. 2, an optical disc 1 and a reflection type optical pickup are shown. The optical pickup includes a laser diode 2 which is a light source, a coupling lens 3,
Half mirror 4 which is a beam splitter, objective lens 5
The laser beam spot is irradiated onto the optical disc 1 by the system consisting of the following, and the reflected beam from the optical disc 1 is bent by the half mirror 4 and detected by the four-division photodetector (4D-PD) 7 via the condenser lens 6. It is supposed to do.

Here, the 4D-PD 7 is a photodetector as shown in FIG. 3, which has four light receiving regions Pa,
It is divided into Pb, Pc, and Pd, and is bisected by the projection line of the pit tangent line of the optical disc to be divided in the radial direction, and further bisected by a line which intersects with the projection line of the pit tangent line at a right angle. The photodetector structure is divided into four parts and divided into four parts.

In these four areas, an area Pa is a position where the radial direction is the inner circumference side of the disk and a dangling direction is the position where the pit edge precedes, and the inner circumference side is the next pit edge. Area Pb at the position where the pit edge precedes on the outer peripheral side of the disk
d, and the area Pc at the position where the pit edge comes next on the outer peripheral side of the disk.

FIG. 1 shows a circuit for obtaining a DC offset,
The four areas Pa, Pb, Pc, and Pd of the 4D-PD7 are connected to amplifiers 8 and 9 for obtaining a difference signal, of which the terminals of the amplifier 8 for generating a push-pull signal are connected to the optical disc of the optical disc. Areas Pa and Pb that are bisected in the radial direction and areas Pc and Pd are respectively connected,
Amplifier 9 for generating tangential push-pull signal
2 to each terminal in the tangential direction of the optical disc.
The equally divided areas Pa and Pd are connected to the areas Pb and Pc, respectively.

When the outputs of the areas Pa, Pb, Pc and Pd are Sa, Sb, Sc and Sd, the push-pull signal of the amplifier 8 becomes PP = (Sa + Sb)-(Sc + Sd) and the tangential of the amplifier 9 is obtained. The push-pull signal is TTP = (Sa + Sd)-(Sb + Sc).

Of these, the tangential push-pull signal from the amplifier 9 is input to the timing generation circuit 10 to detect a rising zero cross and obtain a timing signal. That is, the push-pull signal (RF signal) output from the amplifier 8 is a signal difference between areas divided into two in the optical disc radial direction as shown in FIG. 4A, and is a signal including a DC offset and a tracking error. On the other hand, the dangling push-pull signal TPP output from the amplifier 9 is a discrimination signal between the pit portion and the mirror portion including the pit edge component shown in FIG. 4B. That is, the rising zero cross of the signal TPP represents passing through the mirror section.

Therefore, as shown in FIG. 4C, FIG.
By forming a timing signal based on the above, and taking the rising zero cross, it is possible to obtain the timing of passing through the mirror portion.

The timing signal from the timing generation circuit 10 is input to the sample hold circuit 11 to sample and hold the push-pull signal from the amplifier 8 at this timing. That is, the push-pull signal shown in FIG. 4 (d) is sampled and held at the rising zero-cross timing shown in FIG. 4 (c) to obtain the stepwise sample-hold signal shown in FIG. 4 (e).

After that, the noise component is removed by the low-pass filter 12, and a DC offset signal of the push-pull signal is obtained as shown in FIG. 4 (f), which becomes a lens position signal.

FIG. 5 is a concrete example of the block diagram shown in FIG. 1. In this figure, 8 surrounded by a chain line is an amplifier for obtaining a push-pull signal, 9 is an amplifier for obtaining a tangential push-pull signal, and 10 is an amplifier. A timing generation circuit, 11 is a sample hold circuit, and 12 is a low-pass filter.
Here, the amplifiers 8 and 9 are differential amplifiers, and the timing generation circuit 10 waveform-shapes the tangential push-pull signal into a rectangular wave by the comparator 101 in order to detect the rising zero cross of the tangential push-pull signal. , Its output is a low-pass filter 102
The DC component is extracted by multiplying the
We are feeding back to the comparison level. As a result, the rising zero cross of the tangential push-pull signal can be reliably detected. Then, EX-O of a rectangular wave in which the tangential push-pull signal is shaped and a waveform obtained by delaying this rectangular wave by applying the filter 103
By taking R104, a pulse-like timing signal in which the rising zero cross of the tangential push-pull signal is detected is generated (FIG. 4 (c)).

The sample-hold circuit 11 is turned on when the timing signal is "H", and the capacitor 11 is turned on.
The voltage value of the push-pull signal is charged to 1. This voltage value is output by the next buffer 112. Immediately, the timing signal turns off and the signal is sampled and held.

FIG. 6 is another specific example of the block diagram shown in FIG. 1, and the same parts as those in FIG. 5 are designated by the same reference numerals. 6, in order to detect the rising zero crossing of the tangential push-pull signal, the timing generation circuit 10 waveform-modifies the tangential push-pull signal into a rectangular wave by the comparator 101 as in FIG. The low-pass filter 102 is applied to extract the DC component and the feedback is made to the comparator level of the first-stage comparator 101, and the timing signal in which the rising zero cross of the tangential push-pull signal is detected can be reliably generated, but the output is 1st stage inverter 1
I got it from 05. Further, in the sample hold circuit 11, the push-pull signal is A /
The D-exchanged data is latched, and the A / D exchanged data at that moment is D / A converted and output at the rising edge of the timing signal. The output is held until the next timing signal rises. That is, this sample hold circuit 11
Samples and holds at the rising edge of the timing signal,
The hold value is output with a delay of 1/2 pulse.

[0025]

As described above, according to the present invention, the number of circuit elements can be reduced and simplified by sample-holding the push-pull signal at the passage timing of the mirror section, thereby forming a special photodetector. Is unnecessary and the lens position signal can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram of an example of an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of an optical disc and an optical pickup.

FIG. 3 is an explanatory diagram of a quadrant photodetector.

FIG. 4 is a waveform diagram of each part in FIG.

FIG. 5 is a configuration diagram of a first specific example.

FIG. 6 is a configuration diagram of a second specific example.

[Explanation of symbols]

 7 Photodetector (4D-PD) 8, 9 Amplifier 10 Timing generation circuit 11 Sample and hold circuit 12 Low pass filter

Claims (2)

[Claims] 1. A means for obtaining a timing at which a laser beam spot from an optical head passes through a mirror portion of an optical disk, and a means for obtaining and holding a lens position signal by sample-holding a push-pull signal based on the laser beam spot at this timing. A lens position detecting device for an optical disk device, comprising: 2. The lens position detecting device according to claim 1, wherein the timing of sampling and holding the push-pull signal is performed at a rising zero cross of the tangential push-pull signal.