JPH0589491A - Servo circuit for optical disk device - Google Patents

Abstract

PURPOSE:To provide a servo circuit which is inexpensive and does not receive the influence of a preformat part by using the switching signal of the preformat part and a data area from a drive controller. CONSTITUTION:A track error signal in form that discontinuity generated in the preformat part is removed by switching gain by a gain converter 32A is inputted to a phase compensation circuit 31A, and an objective lens driving device 25, 26 is operated by a driver circuit 40, and track follow-up is executed by moving an objective lens. This result is detected by a photodetector 27, and is turned into the track error signal by a signal processing circuit 33A. A closed loop is formed in this way, and is made the servo circuit 30A, and the smooth track follow-up is executed in the form that the influence at the preformat part is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo circuit for performing focus servo and track servo of an optical disk device for optically recording / reproducing recorded information.

[0002]

BACKGROUND OF THE INVENTION An optical disc has a recording film formed by vapor deposition or the like on a substrate having a track (guide groove) having a width of about the wavelength of laser light and a depth of about ⅛ of the wavelength.

The optical disk device focuses laser light on the disk and reads or writes information on a recording film.

FIG. 4A shows a cross section of the optical disk. Reference numeral 11 is a track, 12 is a pre-format portion (pre-bit) in which addresses and the like are recorded, and 13 is a data area in which information is recorded.

The optical disk device guides a light focusing spot from the optical head along the track 11 of the optical disk 10 to record predetermined information, and irradiates the light spot along the track 11 during reproduction, and reflects light quantity. Is made to read. The optical disk device follows the surface deflection of the optical disk 10 by moving the objective lens up and down, and also follows the track 11 by moving the objective lens left and right.

FIG. 4B is an explanatory view of the configuration of an optical disk device which follows the surface wobbling of the optical disk 10 and tracks the track 11.

In the figure, 21 is a laser light source, 22 is a beam splitter, 23 is a reflecting prism, 24 is an objective lens, 2
Reference numerals 5 and 26 are drive units for moving the objective lens 24 in the vertical and horizontal directions, and 27 is a light receiving element including a plurality of divided light receiving units.

The light beam emitted from the laser light source 21 is reflected by the beam splitter 22, further reflected by the reflection prism 23, and then focused by the objective lens 24 to illuminate the optical disk 10 surface as a light spot. The emitted reflected light passes through the objective lens 24, is reflected by the reflecting prism 23, and then passes through the beam splitter 22, and is irradiated onto the light receiving element 27. An electric signal is output from the light-receiving element 27 in accordance with the applied irradiation state, and the electric signal drives the driving devices 25 and 26 via the servo circuit 30 and the driver circuit 40.

However, the optical disk 10 has a pre-format 12 for each sector, and the reflectance of the pre-format 12 is significantly different from the reflectance of other groove portions. There is a problem that this affects the servo system that follows the above.

Conventionally, the servo gain is constant, and the gain has not been changed especially by pre-formatting. However, this method has the following drawbacks. In order to explain this drawback, description will be given based on the track servo.

FIG. 5 is a track error signal obtained by crossing a track. The servo circuit is shown in Figure 5.
If it deviates upward from the point A, the force acts on the objective lens 24 by returning to the point A, and conversely, if it deviates downward, the opposite force acts on the objective lens 24 so as to return to the point A. As a result, when the track servo state is set, the track error signal matches the servo target value. However, this is an ideal case, and a deviation actually occurs as shown in FIG. FIG. 6A shows a track error signal in the case where there is no preformatted portion. If there is a preformatted portion between them, the amount of light is reduced in the preformatted portion even if the track shift amount is the same before and after the preformatted portion. Therefore, the track error signal as shown in FIG. 6B is obtained.

FIG. 7 shows a conventional servo circuit. In order to apply the servo stably, the track error signal passes through a phase compensation circuit, and the driver circuit drives the objective lens by the objective lens driving device to follow the track. The result of the movement of the objective lens is detected by the photo detector (light receiving element 27), and the signal processing circuit causes a track error. In this way, a closed loop is formed to form a track servo circuit.

FIG. 8 shows the circuit characteristics of the above-mentioned phase compensation circuit, and FIG. 8 (a) shows the gain characteristics.
(B) shows the phase characteristic. As is clear from this gain function, the gain in the high range is increased. Therefore, if a step-like input as shown in FIG.
An output waveform as shown in (b) will be obtained. For example, assuming that the track error signal as shown in FIG. 6A has been output in the state where there is no preformat, and there is preformat in the middle, the preformat portion does not change the track error amount. Regardless of the output, the output as shown in FIG. 9B is added,
The servo system becomes unstable.

Therefore, conventionally, the following two methods have been adopted in order to prevent such a phenomenon. The servo circuit of the first method is one in which a divider is provided before the phase compensation circuit as shown in Fig. 10. The total light amount is added to the denominator and the track error signal is added to the numerator and the result is input to the phase compensation circuit. Things have been done. By providing a divider, even if the level of the track error signal goes down after passing through the preformat section, the total amount of light also goes down, so the divided value becomes almost constant in the area with and without preformatting. Will be stable.

In the servo system of the second method, as shown in FIG. 11, an A / D circuit and a D / A circuit are provided prior to the phase compensation circuit, and division is performed in the same manner as the first method. Then, the track error signal is input to the input of the A / D conversion circuit, the total amount of light is input to the reference, and the output D / A conversion circuit restores the analog signal so that the same effect as the first method can be obtained. It is a thing.

[0016]

SUMMARY OF THE INVENTION With respect to the conventional servo circuit described above,
The method that does not change the servo gain has a drawback that the servo system becomes unstable in the preformat section. Further, in order to prevent this phenomenon, the conventional method has required an expensive IC such as a divider and an A / D conversion circuit.

An object of the present invention is to obtain a servo circuit for an inexpensive optical disk device having a servo system that is not affected by preformat.

[0018]

The above object is characterized in that it has a detecting means for detecting a preformatted portion from a signal from the drive controller and has a servo system for changing the gain of the preformatted portion. This is achieved by a servo circuit of an optical disk device, which has a detecting means for detecting a preformatted portion from a signal, and the preformatted portion has a servo system for holding an error signal before the preformatted portion.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, since the drive controller has the ability to read data, the preformatted portion and the data area can be distinguished from each other by utilizing the distinction between the preformatted portion and the data area. FIG. 1 shows a servo circuit 30A showing the first invention, in which a switching signal is output and an unstable factor generated when passing through the preformat section is removed by using the switching signal. ..

In the servo circuit 30A, a gain converter 32A is provided prior to the phase compensation circuit 31A, and a switching signal between the preformat section and the data area from the drive controller is input to the gain converter 32A. The servo is operated stably by switching the gain between the format section and the data area.

A concrete circuit example of the gain converter 32A is shown in FIG.
Shown in (a) and (b). Circuit 32A shown in FIG. 2 (a)
(I) is a signal from the drive controller for the feedback resistors R ₂ and R ₃ of the operational amplifier.
(A) and 322 (A) are used to change the gain. The circuit 32A (II) shown in FIG. 2 (b) converts the track error signal into a D / A conversion circuit 32.
Input to the reference of 3 (A), and from the bus data switch 324 (A) to D / A by the signal from the drive controller.
The data value of the bus to the conversion circuit 323 (A) is changed.

This is because the gain of the track error signal input to the reference changes when the value of the data bus of the D / A conversion circuit 323 (A) is changed.

The gain is switched by the gain converter 32A, the track error signal is input to the phase compensation circuit 31A with the discontinuity generated in the preformat section removed, and the driver circuit 40 operates the objective lens driving devices 25 and 26. The objective lens 24 is moved to follow the track. The result of the movement of the objective lens 24 is detected by the photo detector (light receiving element 27), and the signal processing circuit 33 causes a track error. In this way, a closed loop is formed and the servo circuit 30A is formed, and smooth track following is performed while the influence of the preformat section is removed.

Although the track-following servo system has been described above, track-following with respect to surface wobbling can be performed in exactly the same manner.

FIG. 3 shows a servo circuit 30B showing the second invention.

Instead of changing the gain of the preformat section described above, the preformat section is a method of sampling and holding the track error signal immediately before the preformat section. In the figure, the sample hold circuit 321 (B) is operated during the pre-format section by switching the analog switches 322 (B) and 323 (B). Similar to the invention, smooth track following is performed with the influence removed by the preformat section.

[0027]

According to the present invention, by using the switching signal between the preformat section and the data area from the drive controller, it is possible to obtain the servo circuit of the optical disk device which is inexpensive and is not affected by the preformat section. It was

[Brief description of drawings]

FIG. 1 is a circuit block diagram of a first invention.

FIG. 2 is an embodiment (a) of the gain converter of the first invention,
It is (b).

FIG. 3 is a circuit block diagram of a second invention.

FIG. 4A shows a cross section of an optical disc,
(B) is an explanatory view of the configuration of the optical disk device.

FIG. 5 shows a track error signal.

6A and 6B show track error signals when a servo system operates, where FIG. 6A shows a case without a preformatted portion and FIG. 6B shows a case with a preformatted portion.

FIG. 7 is a circuit block diagram showing a conventional servo system.

FIG. 8 shows characteristics of a phase compensation circuit, (a) showing a gain characteristic and (b) showing a phase characteristic.

FIG. 9 shows (a) a step-like input waveform to the phase compensation circuit and (b) a waveform after passing through.

10 is a conventional circuit block diagram in which the servo system of FIG. 7 is improved.

FIG. 11 is another circuit block diagram in which the servo system of FIG. 7 is improved.

[Explanation of symbols]

 10 Optical disc 11 Track 12 Pre-format section 13 Data area 24 Objective lens 25, 26 Driving device 27 Light receiving element (detector) 30A, 30B Servo circuit 31A, 31B Phase compensation circuit 32A Gain converter 33A, 33B Signal processing circuit 40 Driver circuit 321 (B) Sample and hold circuit 322 (B), 323 (B) Analog switch

Claims (2)

[Claims] 1. A servo circuit for an optical disk device, comprising a detecting means for detecting a preformatted portion from a signal from a drive controller, and having a servo system for changing a gain of the preformatted portion. 2. A servo circuit for an optical disk device, comprising a detection means for detecting a preformatted portion from a signal from a drive controller, and the preformatted portion has a servo system for holding an error signal before the preformatted portion. ..