Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data clocking
Reexamination Certificate
2000-12-21
2004-01-06
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data clocking
C360S046000
Reexamination Certificate
active
06674592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a demodulation method for demodulation by converting analog signal obtained by reading information memorized in a recording medium to digital signal so as to generate data representing the information and a demodulator.
2. Description of the Related Art
Since before, there has been an information recording/reproducing apparatus for recording information in a recording medium and reproducing information by reading it from that recording medium. The information recording/reproducing apparatus includes, for example, a magnetic disc unit in which information is recorded on a magnetic disc and the information is reproduced by reading out from the magnetic disc.
FIG. 9
is an outline diagram showing a magnetic disc unit, which is an example of such an information recording/reproducing apparatus.
A magnetic disc
10
is rotated in a direction indicated by an arrow A around a center shaft
11
by a spindle motor (not shown).
An actuator
20
is rotated around a rotation shaft
21
so as to move a magnetic head
30
provided on a front end thereof in a radius direction (a direction of arrow B) of the magnetic disc
10
along the surface of the magnetic disc
10
. The magnetic head
30
records information based on signal sent from a signal recording/reproducing portion
40
into the magnetic disc
10
and picks up information recorded in the magnetic disc
10
and sends it to the signal recording/reproducing portion
40
.
The signal recording/reproducing portion
40
receives data signal carrying recording information form outside when the information is recorded to the magnetic disc
10
and carries out a predetermined processing including run length limited (RLL) coding. The magnetic head
30
is driven according to a signal after the processing, so as to record information in the magnetic disc
10
. On the other hand, when the information is reproduced from the magnetic disc
10
, error correction processing and RLL decoding processing are carried out on signal picked up by the magnetic head
30
and sent out of this magnetic disc unit.
Servo information for controlling the position of the magnetic head
30
with respect to the magnetic disc
10
as well as ordinary information for read/write are recorded in the magnetic disc
10
. This servo information is picked up by the magnetic head
30
and sent to the position control portion
50
through the signal recording/reproducing portion
40
. The position control portion
50
controls an operation of the actuator
20
for the magnetic head
30
provided at a front end of the actuator
20
to move with respect to the magnetic disc
10
to a desired position based on the information.
FIG. 10
is a block diagram of a conventional demodulator which composes a signal reproducing portion for reproducing data indicating information recorded in the magnetic disc
30
from signal picked up by the magnetic head
30
, in the signal recording/reproducing portion
40
of the magnetic disc unit shown in FIG.
9
.
Analog signal obtained by a signal pickup of the magnetic head
30
is inputted to gain control amplifier (GCA)
101
capable of changing amplification factor in the demodulator
100
and amplified appropriately. Output analog signal from the GCA
101
is inputted to an analog equalizer
102
and equalized by this equalizer. After that, this signal is converted to digital signal by the A/D converter
103
and maximum likelihood is detected by a maximum likelihood detector
102
. A result of maximum likelihood detection is RLL decoded by a RLL decoder. Then, an error is corrected by error correction code (ECC)
106
so as to reproduce right data.
Here, the digital signal outputted from the A/D converter
103
is also inputted to an automatic gain control (AGC)
107
and phase locked loop (PLL)
108
.
Prior to description of an operation of the AGC
107
and PLL
108
, first, data structure of information to be picked up from the magnetic disc
30
will be described.
FIG. 11
is a diagram showing data structure of information to be picked up from the magnetic disc.
First, acquisition portion GAP is disposed and next, sync byte portion SB for indicating a start of proper data is disposed followed by the proper data.
The AGC
107
and PLL
108
shown in
FIG. 10
use signal from the acquisition portion GAP. The AGC
107
adjusts amplification factor of the GCA
101
based on the output digital signal from the A/D converter
103
of the acquisition portion GAP so that appropriately amplified signal is outputted from the GCA
101
. The PLL
108
generates a clock signal which is a reproduction of a clock upon recording of information, based on the output digital signal from the A/D converter
103
. Signal amplified appropriately depending on the size of signal picked up by the magnetic head is outputted from the GCA
101
to the sync byte portion SB at a timing in which actual data is inputted. A/D conversion is carried out by the A/D converter
103
at a clock reproduced to be same as the clock upon recording information.
Because in recent years, high density recording has been accelerated in information recording/reproducing apparatus such as magnetic disc unit, noise increases in the acquisition portion GAP resulting therefrom, so that a minute defect in a recording medium affects relatively largely. If the defects in the recording medium are accumulated in the recording portion of the acquisition portion GAP, adjustment of the amplification factor and reproduction of the clock by the AGC
107
and PLL
108
are not carried out excellently. Consequently, so-called cycle skip and A/D converter clamp occur so that a long burst error may occur. If the burst error occurs, correction is disabled even if a high performance ECC
106
is employed, so that accurate data reproduction is disabled. Thus, the performance of the demodulator is determined depending on how accurately the AGC and PLL are operated.
SUMMARY OF THE INVENTION
In views of the above-described problem, the present invention intends to provide a demodulation method and a demodulator capable of obtaining correct data even if S/N ratio is lower than conventional.
To achieve the above object, according to an aspect of the present invention, there is provided a demodulation method for demodulation by converting analog signal carrying a first clock of a predetermined first frequency obtained by reading information recorded in a recording medium to digital signal so as to generate data representing the information, wherein
the analog signal is converted to a first digital signal by over-sampling synchronous with a second clock of a second frequency higher than the frequency of the first clock and
a phase error of the first clock with respect to the second clock is obtained based on the first digital signal.
According to another aspect of the present invention, there is provided a demodulator for demodulation by converting analog signal carrying a first clock of a predetermined first frequency obtained by reading information recorded in a recording medium to digital signal so as to generate data representing the information, the demodulator comprising:
an A/D converter for converting the analog signal to a first digital signal by over-sampling synchronous with a second clock of a second frequency higher than the frequency of the first clock;
a buffer for storing the first digital signal; and
an operating portion for obtaining a phase error of the first clock with respect to the second clock based on the first digital signal stored in the buffer.
According to the demodulation method and demodulator of the present invention, over-sampling is carried out synchronously with a clock (second clock) having a higher frequency (second frequency). A first digital signal obtained by the over-sampling is converted to a second digital signal synchronous with a clock (first clock) of a proper frequency (first frequency). Then, the second digital signal obtained in that way is decoded. Therefore, the necessity of the a
Fujitsu Limited
Greer Burns & Crain Ltd.
Holder Regina N.
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