JP2000182239A - Optical disk drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical disk drive which can complete an acquiring operation for cutting off the DC component of a signal read out of an optical disk normally even if the signal has abrupt level variation. SOLUTION: When an HPF 16 cuts off the DC component of the output signal of an optical head 13 which is different in DC level between a header area and a data area, the time constant of the HPF 16 is set to a specific value only for a certain period from the point of time of switching between the header area and data area. When a defect detecting circuit 21 detects a defect at this time, a pulse control circuit 22 makes the period, wherein the HPF 16 is set to the specific time constant, longer than the certain period corresponding to the defect detection period.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention relates to an improvement in an optical disk device that writes and reads data to and from an optical disk such as a RAM (Random Access Memory).

[0002]

2. Description of the Related Art As is well known, a wobble land-groove system is adopted as a physical format of a DVD-RAM. In the wobble land-groove method, as shown in FIGS. 4 and 5, when viewed from the side irradiated with the laser light, a convex groove track 101 and a concave land track 102 recorded on the optical disk surface are provided. Each is a method of recording marks.

[0003] The groove track 101 and the land track 102 are data areas in which user data is recorded. Each of the groove tracks 101 and the land track 102 has a small undulation called a wobble 103 at a predetermined frequency. The optical disk device is capable of performing a rough read channel PLL pull-in based on a frequency signal obtained by detecting the wobble 103.

The groove track 101 and the land track 102 are divided into units called sectors 104, and a header area 105 is provided at the head of each sector 104. In the header area 105, sector address information is recorded in the form of a pit string at the time of manufacturing. Therefore, in the wobble land / groove system, the sector address can be detected by reading the pit string in the header area 105.

[0005] In the header area 105, the pit row is divided into two in the track direction, and each pit row is formed in a CAPA (Complementary Allocated Pit Address).
s), that is, each track 101, 10
2 are arranged so as to be alternately offset in the radial direction of the optical disk at intervals of half the track width (pitch).

FIG. 6 shows an optical disk apparatus for reproducing this type of optical disk. That is, the optical disk 11
Is read by the optical head 13 while being rotated by the spindle motor 12. First, in the optical head 13, the laser light generated from the laser diode 13a is
3b and the optical disk 11 through the objective lens 13c.
Is irradiated on the data recording surface of the.

[0007] The laser beam reflected from the optical disk 11 travels backward through the objective lens 13c, is reflected at a substantially right angle by the beam splitter 13b, is received by the optical detector 13d, and is photoelectrically converted. This light detector 13d is
The light receiving area is divided into two in the track row on the optical disk 11 so as to correspond to the radial direction and the tangential direction, respectively, to be divided into a total of four light receiving areas.

Each electrical signal obtained from the four light receiving areas of the photodetector 13d is I / V (current / current).
Voltage) after passing through the conversion amplifiers 14a to 14d.
A sum signal is generated by level addition at 5.

This sum signal is, as shown in FIG.
The DC level obtained in the header area 105 is higher than the DC level obtained in the data area (tracks 101 and 102). The reference level L1 shown in FIG. 7A is a DC level obtained from the adder 15 when there is no reflected light from the optical disk 11, and is lower than the bottom level of the sum signal obtained in the data area. .

The reason why the DC level of the sum signal in the data area is low is that the reflected light of the two tracks 101 and 102 is mixed because of the difference in height between the groove track 101 and the land track 102. This is because lights having different phases with respect to the wavelength cause interference and weaken each other.

Therefore, in the optical disk device, the adder 1
5 is output to the HPF (High Pass Filte
r) The DC component is cut off through 16 to absorb the difference in DC level between the header area 105 and the data area.

The sum signal from which the difference in the DC level has been eliminated by the HPF 16 is subjected to waveform equalization processing by an equalizer circuit 17, converted into digital data clock-normalized by a data slice circuit 18, and then required by a decoder 19. Various decoding processes are performed, and each data in the header area 105 and the data area is reproduced here.

By the way, the HPF 16 determines when the DC level of the sum signal changes, that is, when the sum signal in the data area changes to the sum signal in the header area 105, or when the sum signal in the header area 105 changes from the sum signal in the header area 105 to the data area. At the time when the sum signal is changed, the time constant of the operation needs to be set short in order to quickly absorb the DC level of the changed sum signal.

On the other hand, if the time constant of the operation of the HPF 16 is set to be short, there is a disadvantage that distortion occurs in a low-frequency component of input data (modulation code).

For this reason, in the optical disk device, the sum signal is supplied to the pull-in pulse generation circuit 20, and as shown in FIG. 7B, when the DC level of the sum signal changes, the H (High) level is maintained for a certain period of time. , And is supplied to the HPF 16. The HPF 16 is switched between a state where the time constant of the operation is short and a state where the time constant is long during the H level period and the L (Low) level period of the pull-in pulse.

Thus, as shown in FIG. 7C, the HPF 16 can quickly pull in the sum signal after the DC level has changed to the state where the DC level is cut off, and can add the sum signal after the pull-in. Signal distortion can be prevented.

The H level period of the pull-in pulse is as follows:
In consideration of the time constant of the HPF 16, the time is set so as to sufficiently correspond to the time required from when the DC level of the sum signal changes to when the sum signal is completely pulled into the state where the DC level is shut off. ing.

However, in the above-mentioned conventional optical disk device, as shown in FIG.
The level of the sum signal obtained in step (b) is reduced to the reference level L1 during the H level period of the pull-in pulse shown in FIG. In this case, the following problem occurs.

That is, at time T1, the sum signal switches from the data area to the header area 105, and at time T2 when the pull-in pulse is in the H-level period, the sum signal level drops to the reference level L1 due to a defect. Consider a case where the sum signal level returns to a normal value due to the end of the defect at time T3 during which the pulse is in the H level period.

In this case, after time T1, the HPF 16
Since the operation of pulling the sum signal into a state where the DC level is interrupted is started, the level of the sum signal is controlled in a direction where the DC level becomes 0, that is, as shown in FIG. However, at time T2, the output level of the HPF 16 sharply decreases to the negative side because the sum signal level sharply decreases.

Then, after time T2, the HPF 16 controls its output level to the positive side, that is, to the upper right in the figure, in order to reduce the DC level of the sum signal to zero. Therefore, when a normal sum signal is obtained after passing through the defect at the time T3, the output level of the HPF 16 becomes higher than the time T2 in the positive direction from the time T2 to the time T3 by an amount Δ
Appears raised by L.

Then, from this state, the HPF 16 operates to set the DC level of its output to 0. However, the DC level is completely set to 0 since the pull-in pulse is inverted to L level due to timeout. Without, that is,
The pull-in operation ends with the DC offset remaining.

Therefore, the data in the header area 105 cannot be correctly sliced by the data slice circuit 18 at the subsequent stage, and a problem arises in that the address data cannot be correctly reproduced. This problem also occurs when the sum signal is switched from the header area 105 to the data area.

[0024]

As described above, in the conventional optical disk device, if a sudden level change occurs in the sum signal during the pull-in operation for cutting off the DC component from the sum signal, the pull-in operation is normally performed. There is a problem that the process may be completed before the process is completed, which may cause inconvenience in data reproduction in a subsequent stage.

Therefore, the present invention has been made in view of the above circumstances, and even when a signal read from an optical disk has a sudden level fluctuation, the pull-in operation for cutting off the DC component of the signal is normally performed. It is an object of the present invention to provide a very good optical disk device that can be completed.

[0026]

According to the present invention, there is provided an optical disk apparatus comprising: a header area in which address data is recorded;
It is intended for an optical disc having a light reflectance different from that of the header area and having a data area in which user data is recorded, at least reproducing data using an optical head.

A filter for cutting off the DC component of the output signal obtained from the optical head, and the time constant of this filter are changed for a certain period from the time of switching between the header area and the data area of the output signal obtained from the optical head. Setting means for setting a specific value, detecting means for comparing a level of an output signal obtained from the optical head with a predetermined detection level to detect a defect, and control means for setting a filter to a specific time constant. When a defect is detected by the detection unit in the set state, the control unit extends the period in which the filter is set to a specific time constant in correspondence with the detection period, beyond a predetermined period. ing.

Further, the optical disk device according to the present invention comprises:
In the above object, a filter for blocking a DC component of an output signal obtained from an optical head, and a time constant of the filter, for a certain period from a point in time when an output signal obtained from the optical head is switched between a header area and a data area Setting means for setting a specific value, detecting means for comparing a level of an output signal obtained from the optical head with a predetermined detection level to detect a defect, and control means for setting a filter to a specific time constant. When a defect is detected by the detection unit in the set state, the control unit stops setting the filter to a specific time constant during the detection period.

According to the above configuration, when a defect is detected, the period in which the filter is set to a specific time constant corresponding to the detection period is extended beyond a certain period, or the defect is detected. When detected,
During the detection period, setting the filter to a specific time constant is stopped, so even if the signal read from the optical disk has a sudden level fluctuation, the pull-in for cutting off the DC component of the signal is performed. The operation can be completed normally.

[0030]

Embodiments of the present invention will be described below in detail with reference to the drawings. In FIG. 1, the same parts as those in FIG. 6 are denoted by the same reference numerals. That is, the sum signal output from the adder 15 is equal to the HP signal.
F16 and the pull-in pulse generation circuit 20 and also to the defect detection circuit 21.

The defect detection circuit 21 is provided in the circuit shown in FIG.
As shown in FIG. 2A, the level of the input sum signal is compared with a preset defect detection level DL. During the period when the sum signal level is lower than the defect detection level DL, FIG. As shown, a defect detection pulse which becomes H level is output.

The defect detection level DL corresponds to the bottom level of the sum signal obtained in the data area and the reference level L.
If it is set between 1 and 1, defects obtained in any area can be detected. FIG. 2 (b)
Indicates a pull-in pulse.

The defect detection pulse output from the defect detection circuit 21 is supplied to a pulse control circuit 22. When the defect detection pulse is inverted from the H level to the L level, that is, when the defect detection pulse has passed the defect, the pulse control circuit 22 shown in FIG.
As shown in (d), a pull-in pulse is generated in the pull-in pulse generation circuit 20 and supplied to the HPF 16.

That is, at time T4 when the sum signal is switched from the data area to the header area 105, the HPF 16 is supplied with the H-level pull-in pulse, and from that point onward, as shown in FIG. From the time T5 at which the signal has passed through, the pull-in pulse which is at the H level for a certain period of time is newly supplied. In short, the H-level period of the pull-in pulse is substantially extended.

As a result, the HPF 16 can sufficiently complete the pull-in operation for cutting off the DC component of the sum signal from time T5 as shown in FIG. 2 (f). During the pull-in operation for cutting off the DC component from, the pull-in pulse times out and the DC offset is prevented from remaining.

FIG. 3 shows a modification of the above embodiment. That is, the header area 10 shown in FIG.
In the state where the H-level pull-in pulse is generated as shown in FIG.
Assume that an H level defect detection pulse is output at the timing shown in FIG.

In this case, the pulse control circuit 22 sets the pull-in pulse to the L level during the H level period of the defect detection pulse, as shown in FIG.
To supply. This means that the HPF 16 is controlled to stop the pull-in operation for cutting off the DC component of the sum signal during the defect period.

By doing so, the output level of the HPF 16 during the defect period is kept constant as shown in FIG. 3E, and does not increase by ΔL as shown in FIG. 8C. Therefore, after passing through the defect, the pull-in can be performed continuously from the level before the defect. For this reason, as described with reference to FIG. 2, it is not necessary to extend the H-level period of the pull-in pulse, so that quick pull-in can be performed.

It should be noted that the present invention is not limited to the above-described embodiment, and can be variously modified and implemented without departing from the scope of the invention.

[0040]

As described in detail above, according to the present invention,
It is possible to provide an extremely good optical disk device that can normally complete a pull-in operation for cutting off a DC component of a signal read from an optical disk even when a sudden level change occurs in the signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical disk device according to the present invention.

FIG. 2 is a waveform chart shown for explaining the operation in the embodiment.

FIG. 3 is a waveform chart for explaining a modification of the operation in the embodiment.

FIG. 4 is a view for explaining a physical format of a wobble / land-groove optical disk.

FIG. 5 is a view for explaining a configuration of a header area in a physical format of the optical disk of the wobble land groove system.

FIG. 6 is a block diagram showing a conventional optical disk device.

FIG. 7 is a waveform chart for explaining the operation of the conventional optical disc device.

FIG. 8 is a waveform chart for explaining a problem of the conventional optical disc device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Optical disk, 12 ... Spindle motor, 13 ... Optical head, 14a-14d ... I / V conversion amplifier, 15 ... Adder, 16 ... HPF, 17 ... Equalizer circuit, 18 ... Data slice circuit, 19 ... Decoder, 20 ... Pull-in pulse generation circuit, 21: defect detection circuit, 22: pulse control circuit

Claims (3)

[Claims] 1. An optical head having at least a header area in which address data is recorded, and a data area in which user data is recorded, having a different light reflectance from the header area, using an optical head. In an optical disc device for reproducing data, a filter for cutting off a DC component of an output signal obtained from the optical head; and a time constant of the filter, the header area and the data area of an output signal obtained from the optical head. Setting means for setting to a specific value for a certain period from the time point of switching to, and a detecting means for detecting a defect by comparing a level of an output signal obtained from the optical head with a predetermined detection level, While the filter is set to a specific time constant by the control means, the detection means detects a defect. When optical disk apparatus characterized by comprising and a control means for a period which is set the filter in correspondence with the detection period specified time constant, stretching than the predetermined period. 2. The apparatus according to claim 1, wherein the control unit sets the time constant of the filter to a specific value for a certain period of time again from the time when the defect is no longer detected by the detection unit. Optical disk device. 3. An optical head having at least a header area for recording address data and a data area for recording user data, having a different light reflectance from the header area, using an optical head. In an optical disc device for reproducing data, a filter for cutting off a DC component of an output signal obtained from the optical head; and a time constant of the filter, the header area and the data area of an output signal obtained from the optical head. Setting means for setting to a specific value for a certain period from the time point of switching to, and a detecting means for detecting a defect by comparing a level of an output signal obtained from the optical head with a predetermined detection level, While the filter is set to a specific time constant by the control means, the detection means detects a defect. When optical disk apparatus characterized by comprising and a control means for stopping the setting during the detection period, the filter to a specific time constant.