Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – By medium defect indicative control signal
Reexamination Certificate
1998-11-19
2001-12-18
Huber, Paul W. (Department: 2651)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
By medium defect indicative control signal
C369S053160
Reexamination Certificate
active
06331968
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to memory systems and more particularly to a system and method to compensate for data defects within a magneto-optical computer memory device.
2. Description of the Background Art
Providing reliable storage and retrieval techniques for digital information is an important consideration of manufacturers, designers and users of computing systems. In magneto-optical storage devices that use flying heads, digital data is written onto and read from the front surfaces of rotating disks of MO storage media. Referring now to FIG.
1
(
a
), a plan view of a front surface
112
of a magneto-optical storage medium
110
is shown. In magneto-optical storage devices, digital data is typically written into and read from a series of concentric or spiral tracks
114
located on the surface
112
of storage medium
110
. In practice, the digital data is read from the front surface
112
of storage medium
110
by projecting a laser-generated light beam from a flying head onto a selected track
114
while storage medium
110
is rotating, and then sensing the amplitude and polarization of light reflected back from the surface
112
of storage medium
110
.
Referring now to FIG.
1
(
b
), a cross-sectional view of the
FIG. 1
magneto-optical storage medium
110
is shown. In operation, a flying head (not shown) is positioned above front surface
112
. FIG.
1
(
b
) includes several examples which illustrate possible causes of unreliable or invalid data in magneto-optical storage devices. The FIG.
1
(
b
) examples include a corrosion defect
116
, particulate contamination
118
and a “bright spot”
120
. These examples are presented for purposes of illustration and defective data may readily be caused by various other factors.
The FIG.
1
(
b
) examples each significantly alter the data read from the surface
112
of storage medium
110
. Corrosion defect
116
and particulate contamination
118
each reduce the reflective properties of surface
112
. This change in reflectivity reduces the MO signal amplitude of data read from storage medium
110
. In contrast, bright spot
120
causes increased reflectivity in surface
112
. This increase also reduces the mark sizes of data stored on storage medium
110
, because bright spot
120
reflects the laser beam used to heat storage medium
110
during the data writing process. Bright spot
120
thus prevents data from being effectively written to storage medium
110
.
In addition, front surface media is more prone to significant data defects due to causes such as particulate contamination
118
. Conventional MO media has an active layer buried some distance below the media surface. Particulate contamination on conventional MO media may therefore be out-of-focus and hence unreadable. In contrast, the present invention uses front surface media
110
above which a flying recording head (containing optics and magnetic-field modulation coils) is used to record and sense MO data marks directly from the front surface
112
of storage medium
110
. Particulate contamination
118
on front surface
112
thus has a greater impact on the data signal read from storage medium
110
.
As discussed above, corrosion defects
116
, particulate contamination
118
, and bright spots
120
may cause data defects in front surface magneto-optical storage devices. Furthermore, magneto-optical storage devices may be unable to compensate for these data defects. Magneto-optical devices often contain automatic gain controls (AGCs) to control data amplitude and phase-locked oscillators (PLOs) to synchronize the data flow. A significant dropout or data defect, however, may disrupt AGC and PLO operation so severely that the magneto-optical device is unable to restore normal data amplitude or data synchronization. From the above discussion,. it becomes apparent that the magneto-optical data is not sufficiently robust to defects. Therefore, an improved system and method are needed to compensate for data defects within a front surface media magneto-optical memory device.
SUMMARY OF THE INVENTION
In accordance with the present invention, a system and method are disclosed to compensate for data defects within a magneto-optical memory device. In the preferred embodiment of the present invention, a magneto-optical drive optically reads information stored on a magneto-optical storage medium and then derives separate electrical MO+ and MO− signals using an optics assembly which includes a polarizing beam splitter and separate photo-detectors for the MO+ and MO− signals. A data channel coupled to the magneto-optical drive then subtracts the MO+ and MO− signals using an inverting amplifier and a summing amplifier to responsively generate and provide an analog data signal to a converter device.
A reflectivity channel coupled to the data channel accesses and combines the MO+ and MO− signals using a summing amplifier to responsively generate and provide a reflectivity signal to a detector device. The detector then preferably detects the received reflectivity signal using threshold detection techniques to generate a coast signal to both a phase-locked oscillator and to an automatic gain controller in the converter device. The detector device also provides the coast signal to a delay device for generating an error pointer signal to an error-correction coding (ECC) decoder device in the data channel.
When a data defect occurs, the magneto-optical drive uses the generated coast signal to maintain constant automatic gain control (AGC) or phase-locked oscillator (PLO) control signals during the period of the data defect period. In practice, the defective data signal is delayed so the generated coast signal may then be applied in a timely manner to automatic gain control and the phase-locked oscillator within the converter device. The automatic gain control and phase-locked oscillator responsively maintain their pre-defect states until the data defect passes through and valid data levels return. The coast signal thus effectively serves as a “defect-skipping” pulse.
The magneto-optical drive also uses the coast signal to provide the location of the data defect to the ECC decoder device for error correction. In practice, a delay device receives the coast signal and responsively generates an error pointer signal that is advantageously synchronized with the corresponding data defect. The decoder device may then specifically identify the location of the particular data defect to more efficiently perform selected error-correction functions. The present invention thus effectively permits magneto-optical drive devices to provide more robust and reliable data to system users.
REFERENCES:
patent: 5363352 (1994-11-01), Tobita et al.
patent: 5892745 (1999-04-01), Belser
Huber Paul W.
Seagate Technology
Simon & Koerner LLP
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