Apparatus for reproducing recorded data

Details Apparatus for reproducing recorded data Apparatus for reproducing recorded data

2001-11-29

2004-04-20

Edun, Muhammad (Department: 2653)

Dynamic information storage or retrieval

Control of storage or retrieval operation by a control...

Control of information signal processing channel

C369S053100, C369S059100, C369S044320

Reexamination Certificate

active

06724702

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an apparatus for reproducing recorded data and a record format to record data, and more particularly to an apparatus for reproducing recorded data that reproduces a target track to be reproduced and an adjacent track by one beam, a crosstalk signal is generated, and the crosstalk is cancelled by deducting the crosstalk signal from a reproduction signal.
2. Description of the Related Art
To record data, various recording media have been provided such as a magnetic disk, a magnetic tape, an optical disc, and a magneto-optical disc. In order to record data on these recording media, a magnetic record mark is mainly used, since compared with semiconductor memory, data can be permanently stored at a low cost. Thus, apparatus using these recording media have been essentially needed to record information such as a graphic, image information or the like, for computers, at a present age in which much information is dealt with.
FIG. 1
is a diagram showing an example of a circuit configuration of a conventional data reproducing apparatus.
An optical head
11
reproduces a signal from a recording medium
10
such as an optical disk or a magneto-optical disc. In order to recognize an address at which information is recorded, an SUM/ID detector
19
detects address information from a SUM signal or a Wobble signal, and then an ODC (optical control circuit)
20
recognizes the address.
Moreover, a reference clock CLK is made from a PLL (Phase-Locked Loop)
18
synchronizing with a signal from a clock mark provided on the recording medium
10
for reproducing data. A signal process is conducted based on this reference clock CLK and then data is detected.
A reproduction signal from the optical head
11
is amplified by an amplifier
12
, a high frequency noise is eliminated by a LPF (low pass filter)
13
, and then the reproduction signal is supplied to an ADC (A/D converter)
14
. A high-pass filter is not shown in
FIG. 1
but is generally provided for low-pass fluctuation suppression and circuit saturation prevention. Alternatively, an analog equalizer may be used for waveform equalization.
The ADC
14
samples by a reference clock CLK supplied from the PLL
18
. In a case in which data recording condition is different for each of data reproducing apparatuses, a phase of the reproduction signal may be shifted from that of the clock synchronized with the clock mark formed by the pre-pit. For this reason, the phase of the reference clock CLK (not shown in
FIG. 1
) may be adjusted.
An EQ (digital equalizer)
15
equalizes and forms a waveform based on a sample value sampled by the ADC
14
. Then, the sample value is equalized into a PR (Partial Response) signal. The PR signal is detected by a ML (most-likelihood) detector
16
and then is decoded by a decoder
17
.
Decoded data is sent to the ODC
20
, and an ECC decode is carried out. An ECC (Error Correcting Code) check is conducted for the decoded data.
FIG. 2
is a schematic diagram showing an example of a format. In
FIG. 2
, a simplified 2K ECC Block disk format of AS-MO (Advanced Storage-Magneto Optical Disk) Physical Specifications (Version1.0 April 1998) is shown.
Referring to
FIG. 2
, a header
21
is provided before data part
29
and either one of 2T-repeated data in which a bit string “1100” is formed, and 8T-repeated data in which a bit string “1111111100000000” is formed, is recorded. For example, an Auto Read Power Control Area
22
is to be used in order to measure amplitude of the 2T-repeated data and the amplitude of the 8T-repeated data and to adjust reproduction power. An Auto Gain Control Area
23
is used to adjust the amplification gain of a signal. A Read Clock Phase Control Area
24
is used to adjust the phase of the reference clock CLK made by PLL synchronization with the clock mark mentioned above, with the phase of the clock for sampling a data signal. A Buffer Area
25
is provided before the data part
29
.
In such general formats including ISO specification or the like, a similar signal is also recorded on an adjoining track. Of course in the data part
29
, unknown random data is recorded on the adjacent track.
However, there are problems described as follows in the conventional data reproducing method.
In order to improve an optical disk in high density, bit density and track density may be enlarged. As to improve in high density of bits, a technology such as a PRML (Partial Response Maximum Likelihood) technology using waveform interference is well known. However, if the track density is made high, cross-write and crosstalk occur.
The cross-write is a phenomenon in which when data is recorded on a track to be recorded by higher power than optimal power, the data is also recorded on an adjacent track of the track. The cross-write deletes information currently recorded on the adjacent track. Thus, an information signal quality of the adjacent track is deteriorated. A heat distribution on an optical disk is controlled by properly conducting strobe luminescence and power adjustment of a LD (Laser Diode), so as to avoid the cross-write. Crosstalk is a phenomenon in which the adjacent track signal intermixes in a beam spot when data is reproduced and a jitter is caused in the signal to be reproduced. Especially if the track density becomes higher, the crosstalk cannot be avoided.
The conventional technology (Japanese Laid-Open Patent Application No.58-121138, Japanese Laid-Open Patent Application No.5-205280) is known in which data recorded on the adjacent track is detected, the crosstalk signal is generated from the data, a crosstalk amount is measured, and then the crosstalk is canceled by deducting the crosstalk signal generated from a reproduction signal. In this conventional technology, the adjacent track signal is also simultaneously reproduced by three beams, and the crosstalk is canceled by adjusting and deducting gain. However, since three beams are needed in order to carry out simultaneous reproduction of the adjacent track signal in this conventional technology, it is difficult to adjust phase differences by distance differences among the three beams.
Moreover, in the conventional technology (Laid-Open Patent Application No.5-205280), a reproduction waveform by scanning two tracks including an adjacent track by one beam is sampled by an ADC (Analog to Digital Converter), and a sample value is stored in a storage area, beforehand. The sample value is used and the crosstalk is cancelled when data recorded on a target track is reproduced. However, the ADC, which converts one sample value into 6 bit (through 8 bit) data, is used. The huge storing area, that is, 6 bit (through 8 bit)×sample number (waveform length in which the crosstalk is cancelled)×two tracks, is needed as a storage area.
Furthermore, it is known that the pre-pit signal and the Wobble signal in an area to which address information is stored depend on a diameter of the beam spot. If track density is raised, the pre-pit signal or the Wobble signal is influenced by the adjacent track signal before an MO signal that read data information (such as user data) Consequently, crosstalk data cannot be reproduced. For this reason, in a conventional technology (Laid-Open Patent Application No.8-231139), a method of suppressing interference is proposed in that an adjacent pre-pit signal is shifted in a direction of arranging bits. However, in such a configuration, since an additional area is needed in the direction of arranging bits, a format effect becomes degraded. Even in such a configuration, when the track density is raised further, the crosstalk occurs. That is, in a case in which the track density is raised further, when the beam spot overflows a track, a signal for reproduction is superimposed with an adjacent track signal by the crosstalk. Then, the signal superimposed causes a jitter and a reproduction signal quality is degraded. Accordingly, an error rate of data is increased and the data cannot be reproduced correctly.
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