JP2655064B2 - Magneto-optical disk signal detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording / reproducing method capable of multi-value recording.

[0002]

2. Description of the Related Art In a magneto-optical recording method of recording / reproducing and erasing a recording medium comprising a magnetic film by using a laser beam, information of three or more values is recorded by switching the laser light power at the time of recording to three or more stages. A magneto-optical recording method characterized by writing on the top is described in JP-A-1-290143.
JP, JP-A-2-267756, JP-A-4-0
No. 10256, Japanese Patent Application Laid-Open No. 5-169372 and the like are known. In these, a mark is detected by setting a slice level only for an unprocessed signal during reproduction.

[0003]

In the conventional method, a slice level is set only for an unprocessed reproduced signal to detect the presence or absence of a mark. Since the difference between the level and the two levels is small, there is a problem that the error rate during reproduction is high.

It is an object of the present invention to provide a low error rate 3 at the time of reproduction.
An object of the present invention is to provide a method of detecting a reproduced signal in value recording.

[0005]

A slice level is provided for both an unprocessed reproduced signal and a signal obtained by differentiating the reproduced signal twice, and the signal detection results of both are compared. The case where no mark is detected in the unprocessed reproduced signal but the case where the mark is detected in the twice differential signal is associated with 1, and the case where both signals are detected is associated with 2.

[0006]

In the unprocessed signal, a signal corresponding to a large recording level is sufficiently large to be detected by a slice level, but a signal corresponding to a small recording level is too small to be detected by a slice level. On the other hand, a small signal level is emphasized in the twice differential signal, so that any signal is detected by the slice level (FIG. 1). Therefore, the slice level is set for both the unprocessed reproduced signal and the twice-differentiated reproduced signal, and the signal detection results of both signals are compared. If no mark is detected, no mark is detected. If no unprocessed reproduced signal, no mark is detected. TAGA2
By associating the case where the signal is detected with the time differential signal with 1 and the case where both signals are detected with 2 with each other, it is possible to easily and surely detect three levels of signal levels.

[0007]

EXAMPLE When recording was performed on a magneto-optical disk made of TbFeCo at a power of 5 mW and 10 mW and a read signal was read, the amplitude of each signal was 30 m.
V and 100 mV. The playback signal when not recorded is 1
0 mV. On the other hand, when a slice level of 50 mV was set, a reproduced signal was detected only when recording was performed with a power of 10 mW. Next, when a reproduced signal recorded at a power of 5 mW and 10 mW was differentiated twice and the signal was detected, the signals corresponding to the respective recording powers were 100 mW and 150 mW. When a slice level of 70 mW was set for this signal, both signal levels were detected. Next, the signal detection for the unprocessed signal and the signal detection for the second derivative signal are performed at the same time. Was not detected, the bit error rate was measured, and a value of 1 × 10 ⁻⁶ was obtained.

For signal detection for the twice differentiated signal, a known method such as Japanese Patent Application Laid-Open No. 4-162237 can be used.

Recording was performed on a magneto-optical disk made of NdDyFeCo at a power of 10 mW and 15 mW, and the reproduced signals were read. The amplitudes of the signals were 60 mV and 40 mV, respectively. The reproduction signal at the time of unrecording is 20 mV. On the other hand, when a slice level of 50 mV was set, a reproduced signal was detected only when recording was performed with a power of 10 mW. Next, when a reproduced signal recorded at a power of 10 mW and 15 mW was differentiated twice and the signal was detected, the signals corresponding to the respective recording powers were 100 mW and 80 mW. When a slice level of 60 mW was set for this signal, both signal levels were detected. Next, the signal detection for the unprocessed signal and the signal detection for the second derivative signal are performed simultaneously, and when the mark is detected from both signals, the signal is detected when the mark is detected only from the twice differential signal. Was detected and the bit error rate was measured, and a value of 5 × 10 ⁻⁶ was obtained.

When recording was performed on a magneto-optical disk composed of a TbFeCo / GdTbFeCp two-layer film at a power of 7 mW and 11 mW and a read signal was read, the amplitude of each signal was 100 mV and 30 mV. The reproduction signal at the time of unrecording is 20 mV. On the other hand, when a slice level of 50 mV was set, a reproduced signal was detected only when recording was performed with a power of 7 mW. Next, 7mW
And a reproduction signal recorded at a power of 11 mW were subjected to a second differentiation, and the signals were detected. The signals corresponding to the respective recording powers were 130 mW and 90 mW.
W. When a slice level of 50 mW was set for this signal, both signal levels were detected. Next, signal detection for the unprocessed signal and signal detection for the twice-differentiated signal are performed simultaneously, and the case where the mark is detected from both signals is 2, and the case where the mark is detected only from the twice-differential signal is 1,
The case where no signal was detected from any of them was associated with 0, and the bit error rate was measured. As a result, a value of 2 × 10 ⁻⁶ was obtained.

[0011]

As described above, according to the present invention, three levels of reproduced signal can be easily and reliably detected, and a good bit error rate can be obtained.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating the principle of the present invention.

[Explanation of symbols]

 Reference Signs List 1 Low-level signal in raw reproduction signal 2 High-level signal in raw reproduction signal 3 Slice level for raw signal 4 Low-level signal in twice differential reproduction signal 5 High-level signal in twice differential reproduction signal 6 Double differential signal Slice level for 7 Unprocessed reproduction signal after slice 8 Second derivative reproduction signal after slice 9 Synthesis result of signal after slice

Claims (1)

(57) [Claims] 1. A method for detecting a signal from a recording medium on which information having three or more values is recorded by switching a laser beam power at the time of recording to three or more steps. A slice level is provided for both of the signals obtained by differentiating the reproduced signal twice, and the signal detection results of the two signals are compared. When no mark is detected, zero is obtained when no mark is detected. A signal detection method for a magneto-optical disk, wherein a case where a signal is detected is associated with 1 and a case where both signals are detected is associated with 2.