JPH06139700A - Disk reproducing device - Google Patents

Abstract

PURPOSE:To accurately reproduce data by a simple constitution independent of the kind of an optical disk (ROM disk) and a magneto-optical disk (RAM disk). CONSTITUTION:When the ROM disk is detected by a disk discriminating circuit 14, a switch 13 is changed over to the side of contact point (b), besides it is changed over to the side of contact point (a) when the RAM disk is detected. By this procedure, the demodulation taking a specified threshold as the reference is performed by a level demodulator 16 in the case of ROM disk, and a viterbi decoding is performed in the case of RAM disk.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc reproducing device suitable for use in, for example, a magneto-optical disc device.

[0002]

2. Description of the Related Art Audio data is recorded digitally on compact discs that are already on the market. Similar to this compact disc, a magneto-optical disc device capable of digitally recording or reproducing audio data on a magneto-optical disc is about to be commercialized.

In this magneto-optical disk, a magnetic field corresponding to recording data and laser light are irradiated to record digital data. At the time of reproduction, the magneto-optical disk can be irradiated with laser light and the recorded data can be reproduced from the reflected light. That is, the optical head used for reproduction may basically have the same structure as that for the magneto-optical disk and that for the optical disk. Therefore, the magneto-optical disk device is configured to be able to reproduce not only a recordable and reproducible magneto-optical disk (RAM disk) but also a read-only optical disk (ROM disk).

It is theoretically possible to record data on a magneto-optical disk and use it for reproduction only. However, it is costly to manufacture a large number of read-only magneto-optical disks. On the other hand, an optical disc on which data is recorded by forming physical pits is relatively easy to mass-produce. Therefore, the read-only optical disc is often formed as an optical disc instead of a magneto-optical disc.

[0005]

In the conventionally proposed magneto-optical disk device, when reproducing either the RAM disk (magneto-optical disk) or the ROM disk (optical disk), for example, Viterbi decoding is performed.
The same demodulation method is used. This Viterbi decoding is advantageous for accurately reproducing high density recorded data.

However, in the case of a ROM disk, R
It often has asymmetry compared to AM discs. That is, FIG. 7 shows an example of an eye pattern of a signal reproduced from a disc. However, when the reference central level is a ROM disc, it often shifts up and down from the reference position. It is theoretically possible to design a Viterbi decoding demodulator in consideration of this shift. However, doing so has a problem that the configuration becomes extremely complicated and expensive.

The present invention has been made in view of such circumstances, and it is an object of the present invention to realize a device having a simple structure and low cost.

[0008]

A disc reproducing apparatus of the present invention comprises a level demodulator 16 as first demodulating means for demodulating a digital signal reproduced from a ROM disc as a first disc dedicated to reproduction. Viterbi demodulator 15 as a second demodulation means for demodulating a digital signal reproduced from a RAM disk as a second disk capable of both recording and reproduction, and disk discrimination as discrimination means for discriminating the type of disc. Circuit 14 and disk discriminating circuit 1
4 is provided with a switch 13 as a selection means for selecting one of the level demodulator 16 and the Viterbi demodulator 15.

The level demodulator 16 performs demodulation based on the level of the digital signal reproduced from the ROM disc, and the Viterbi demodulator 15 Viterbi-decodes the digital signal reproduced from the RAM disc.

[0010]

In the disc reproducing apparatus having the above structure, the RO
The level demodulator 16 is used when an M disk is detected, and the Viterbi demodulator 15 is used when a RAM disk is detected. Therefore, different types of disks can be accurately read by a low-cost device with a simple configuration.

[0011]

1 is a block diagram showing the configuration of an embodiment of a magneto-optical disk device to which the disk reproducing device of the present invention is applied. The spindle motor 2 rotates the disk 1 at a predetermined speed. The disc 1 is a magneto-optical disc (RAM disc) capable of both recording and reproduction.
Then, one of the read-only optical discs (ROM discs) in which data is previously formed as physical pits (recesses or protrusions) is selectively mounted and driven.

A magnetic head 3 is arranged above the disk 1 and an optical head 4 is arranged below it. The magnetic head 3 is used when a magneto-optical disk is mounted as the disk 1 and data is recorded on this magneto-optical disk. On the other hand, the optical head 4 is used regardless of whether a magneto-optical disc or an optical disc is mounted, and during recording or reproduction.

The analog audio signal to be recorded is supplied to the recording data generating circuit 5 from a circuit (not shown). The recording data generation circuit 5 converts the analog audio signal into a digital signal and modulates it in a predetermined method.
Output to the pre-encoder 6. For this modulation method,
Partial response class IV NRZI or interleaved NRZI is used. The pre-encoder 6 performs encoding for partial response. The laser drive circuit 7 drives a laser diode or the like built in the optical head 4 in response to a signal output from the pre-encoder 6. That is, in this embodiment, the optical modulation method is used,
It is also possible to adopt a magnetic field modulation method in which the magnetic head 3 is driven corresponding to the recording data and a magnetic field corresponding to the recording data is applied to the magneto-optical disk.

The RF amplifier 8 outputs R output from the optical head 4.
The F signal is amplified and output to the PLL circuit 9 and the A / D converter 11. The PLL circuit 9 generates a clock and outputs it to the recording data generation circuit 5 and the delay circuit 10. The delay circuit 10 delays the input clock by a predetermined time, adjusts the timing, and then outputs the clock to the A / D converter 11.

The data output from the A / D converter 11 is supplied to the Viterbi demodulator 15 or the level demodulator 16 via the equalizer 12 and the switch 13. The disc discrimination circuit 14 is the A / D converter 1
The type of the mounted disk is discriminated from the output of 1, and when the magneto-optical disk is detected, the switch 13 is set to the contact a.
When the optical disk is detected, the switch 13 is switched to the contact b side. The threshold value setting circuit 17 sets a predetermined threshold value from the output of the equalizer 12 and outputs it to the level demodulator 16.

FIG. 2 shows a sector format of the disk 1. That is, the disk 1 is divided into a plurality of sectors on one circumference, and each sector is composed of a plurality of segments. A servo area is provided at the beginning of each segment, and a clock pit for generating a clock and a wobbled pit for generating a tracking error signal are formed in this servo area. These servo pits are formed as physical pits by, for example, embossing.

A data area is formed next to the servo area. In the case of a magneto-optical disk, this area is formed by a magneto-optical recording layer. Therefore, the user can record and reproduce data magneto-optically in this data area. On the other hand, in the case of an optical disc, data is pre-formed in the data area with physical pits. Therefore, the user can only reproduce the data from this data area.

At least in the case of an optical disc, the data area of the first segment of a sector is a reference area. As shown in FIG. 3, this reference area is divided into three types of areas R _a , R _b , and R _c .
Then, no pits are formed in the area Ra, and the area Ra is _a mirror surface area. In the region R _b , a plurality of pits for defining an intermediate level for setting a threshold value described later are formed. The logic of this pit is, for example, 0101010
For example, 101 is repeated 0 and 1. Further, in the region _Rc , long pits that define the lowest level for setting the threshold value are formed.
The pit logic is such that 1 is repeated, for example, 1111111111. In the figure,
Adjacent logic 1 pits are joined and represented as one long pit overall.

A reference area can also be provided in the data area of the first segment of the sector of the magneto-optical disk as in the case described above. However, as will be described later, in the case of the magneto-optical disk, this reference area is set. Since it is not used, it is possible to set this as a normal data area.

Next, the operation of the embodiment shown in FIG. 1 will be described. When a magneto-optical disk is used as the disk 1, the recording mode can be set. At this time, the analog audio signal is supplied to the recording data generating circuit 5, and N
It is converted into digital data modulated by a method such as RZI. The recording data output from the recording data generating circuit 5 is encoded by the pre-encoder 6 for a partial response, and is supplied to the optical head 4 via the laser driving circuit 7.

The optical head 4 modulates a built-in laser diode in accordance with input recording data. As a result, the data area of the magneto-optical disk is irradiated with the laser light turned on or off corresponding to the recording data.
At this time, a magnetic field in a predetermined direction is applied to the magneto-optical disk via the magnetic head 3. As a result, magnetic domains corresponding to the recording data are formed in the data area of the magneto-optical disk, and the data is recorded magneto-optically.

In this recording mode, the optical head 4 outputs a signal corresponding to the light reflected from the magneto-optical disk in the servo area of each segment. This reproduction signal is amplified by the RF amplifier 8 and supplied to the PLL circuit 9. The PLL circuit 9 generates a clock synchronized with the clock pit in this servo area. This clock is supplied to the recording data generating circuit 5, and the recording data generating circuit 5 generates recording data in synchronization with this clock.

Although not shown, the RF amplifier 8
The tracking error signal and the focus error signal are generated from the output of, and the tracking servo and the focus servo are performed. Further, a spindle motor drive signal is generated from the output signal, and the spindle motor 2 is rotated at a predetermined speed.

When reproducing data from a magneto-optical disk, a reproduction mode is set. At this time, the optical head 4
The magneto-optical disk is continuously irradiated with laser light.
Then, the recorded data is reproduced from the reflected light. The reproduction signal output from the optical head 4 is amplified by the RF amplifier 8 and then supplied to the PLL circuit 9. The PLL circuit 9 is
A clock is generated in the same manner as described above and is output to the delay circuit 10.

The delay circuit 10 delays this clock by a preset time and outputs it to the A / D converter 11. The A / D converter 11 performs A / D conversion on the signal input from the RF amplifier 8 in synchronization with the clock supplied from the delay circuit 10, and outputs the signal to the equalizer 12. The equalizer 12 converts the signal input from the A / D converter 11 into
It is equalized to have a predetermined frequency characteristic and output to the switch 13.

The disc discriminating circuit 14 includes an A / D converter 1
From the output of 1, it is determined whether the magneto-optical disc or the optical disc is currently being reproduced. That is, in the case of a magneto-optical disc, the reproduction RF
The signal level decreases. So disc discriminating circuit 1
4 compares the data output from the A / D converter 11 with preset reference data (reference level), and A / D
When the output of the converter 11 is higher than the reference level, it is determined to be an optical disk, and when it is low, it is determined to be a magneto-optical disk. Since the magneto-optical disk is being reproduced now, the switch 13 is switched to the contact a side by the disk discrimination circuit 14. Therefore, the signal output from the equalizer 12 is supplied to the Viterbi demodulator 15 via the contact a of the switch 13 and is Viterbi-decoded.

That is, the partial response PR (1,
In the case of 1), the state transition diagram between logic 1 and logic -1 is as shown in FIG. The trellis diagram corresponding to it is as shown in FIG.

The level Y of the reproduced signal at a predetermined time k
_k can be expressed by the following equation, where A _k (+1 or −1) is an input bit and S is an expected level. _Yk = (S * _Ak + S * _Ak-1 ) / 2 + _Nk Here, _Nk is noise according to a Gaussian distribution.

In the trellis diagram of FIG. 6, each point represents the state A _k at each time, and each branch shows the transition of the new state at the next time. The formula shown beside each branch expresses the probability of the transition using square error.

Here, the possibility that A _k is +1 (likelihood)
L _k ⁺ can be expressed by the following equation, because the one with the higher probability can be selected from the two branches that enter it. L _k ⁺ = max {L _k-1 ⁺ + [− (Y _k −S) ² ], L _k−1 ⁻ +
[− (Y _k −0) ² ]} Similarly, the possibility (likelihood) that A _k is −1 can be expressed by the following equation. ^{_{L k - = max {L k}} -1 + + [- (Y k -0) 2], L k-1 - +
[-(Y _k + S) ² ]}

[0031] Therefore, the L _k ⁺ and L _k ^- by determining the larger of the computation, the Viterbi decoding is performed. Since the principle of this Viterbi decoding is well known, its details are omitted.

Therefore, when the magneto-optical disk is reproduced,
The reproduced data is output from the Viterbi demodulator 15.

Next, the operation for reproducing the optical disc will be described. In this case, the disc discrimination circuit 14 switches the switch 13 to the contact b side. Therefore, the signal output from the equalizer 12 is the level demodulator 16
Is supplied to.

On the other hand, the threshold setting circuit 17 includes the equalizer 1
A predetermined threshold value is set based on the signal input from 2. That is, the Reference lance area of the first segment of a sector of the optical disc, as shown in FIG. 3, three regions R _a,
R _b and R _c are formed, and a mirror surface portion, a relatively small pit and a long pit are formed therein.
The level of the reproduction RF signal in each area is shown in FIG.
It changes as shown in. In the region R _a, since a mirror surface portion, the reproduction level is the largest constant level L _a. In contrast, the reproduction level of the region R _c in which logic 1 pit are consecutive becomes smallest constant level L _c.

On the other hand, the reproduction level of the region R _b is
Level substantially intermediate level L _a and L _c mentioned above L _b (= (L _a
+ L _c ) / 2) (However, since a pit is formed in this region R _b , its level changes depending on the presence or absence of this pit). Therefore, the level in this region R _b changes as shown in FIG. Threshold setting circuit 17
Calculates two thresholds L _H and L _L from the following equation. L _H = (L _a + L _b ) / 2 L _L = (L _b + L _c ) / 2

The two threshold values L _H thus generated
And L _L are supplied to the level demodulator 16. The level demodulator 16 compares the level of the reproduction signal supplied from the contact b of the switch 13 with these two thresholds L _H and L _L. When the level of the reproduced signal is larger than L _H , the logic 1
When L is smaller than _L, -1 (1), and less than L _H, determines that 0 when greater than L _L. Level demodulator 1
In this way, 6 demodulates the logic of the reproduced signal with the threshold as a reference, and outputs the demodulation result.

In the case of a ROM disc, if the pit size is not optimal due to fluctuations in cutting power, asymmetry will occur. However, as mentioned above, 2
The two thresholds L _H and L _L change corresponding to this asymmetry. Therefore, if the logic is judged based on the thresholds L _H and L _L , the data can be accurately demodulated regardless of the asymmetry.

[0038]

As described above, according to the disc reproducing apparatus of the first aspect, since the disc type is discriminated and the demodulating means is selected according to the discrimination result, the constitution is simple and the cost is low. With this device, appropriate demodulation is always possible.

Further, according to the disc reproducing apparatus of the second aspect, since the demodulation performed based on the level and the demodulation using the Viterbi decoding are performed, the digital data is irrespective of the type of the disc. It becomes possible to read accurately.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a magneto-optical disk device to which a disk reproducing device of the present invention is applied.

FIG. 2 is a diagram for explaining a sector format of the disc 1 of FIG.

3 is a diagram illustrating data recorded in a reference area in FIG.

FIG. 4 is a diagram illustrating a signal obtained by reproducing the recorded data of FIG.

5 is a state transition diagram illustrating the operation of the Viterbi demodulator 15 of FIG.

FIG. 6 is a trellis diagram for explaining the operation of the Viterbi demodulator 15.

FIG. 7 is a diagram illustrating asymmetry of an optical disc.

[Explanation of symbols]

 1 disk 3 magnetic head 4 optical head 5 recording data generation circuit 6 pre-encoder 7 laser drive circuit 8 RF amplifier 9 PLL circuit 10 delay circuit 11 A / D converter 12 equalizer 13 switch 14 disk discrimination circuit 15 Viterbi demodulator 16 level demodulation Device 17 threshold setting circuit

Claims (2)

[Claims] 1. A first demodulating means for demodulating a digital signal reproduced from a first disc dedicated to reproduction, and a first demodulating means for demodulating a digital signal reproduced from a second disc capable of both recording and reproduction. The second demodulating means, the discriminating means for discriminating the disc type, and the selecting means for selecting one of the first and second demodulating means in accordance with the output of the discriminating means. Disc player. 2. The first demodulating means performs demodulation based on the level of a digital signal reproduced from the first disc, and the second demodulating means reproduces from the second disc. The disc reproducing apparatus according to claim 1, wherein the digital signal is Viterbi-decoded.