Magnetic disk drive

Details Magnetic disk drive Magnetic disk drive

1999-09-28

2002-12-10

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

General recording or reproducing

Specifics of equalizing

C360S046000, C375S232000

Reexamination Certificate

active

06493165

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a magnetic disk drive (HDD) and particularly to a reproduction control method for avoiding deterioration of drive performance caused by application of coefficient learning in a state in which the positional divergence of a read head is large.
The configuration and reproducing operation of a background-art magnetic disk drive will be described below.
FIG. 12
shows an example of the configuration of a magnetic disk drive (HDD)
10
.
The HDD
10
comprises a head disk assembly (HDA)
20
, and a packaged circuit board (PCB)
30
.
The HDA
20
includes magnetic disks
2
-
1
to
2
-
5
, suspension
108
provided with magnetic heads
1
-
1
to
1
-
10
attached thereto, a carriage
103
, a read/write IC (R/WIC)
104
attached on the carriage
103
, a spindle motor
105
, and a flexible printed cable (FPC)
106
.
The PCB
30
is constituted by a signal processing LSI (SPC)
21
, a hard disk controller chip (HDC)
22
, a servo controller (SRVC)
23
, a micro-processor (MP)
24
, a host bus interface chip (HBI)
25
, an ROM
26
, a buffer RAM
27
, etc.
The read operation of the HDD
10
will be described below with reference to
FIGS. 12 through 15
.
A read signal corresponding to a magnetic field and detected from the magnetic disk
2
-
1
by an MR (Magneto-Resistive) head of the magnetic head
1
-
1
in
FIG. 12
is supplied to the R/WIC
104
through wiring on the suspension
108
.
In the R/WIC
104
, selection of one of the magnetic heads
1
-
1
to
1
-
10
and the sense current value of the selected MR head are set in advance through the MP
24
.
A resistance change of the MR head due to the magnetic field in the magnetic disk
2
-
1
is converted into a voltage change. Further, the R/WIC
104
amplifies the read signal to a value of from the order of tens of mVp-p to the order of hundreds of mvp-p and outputs the amplified read signal
33
to the SPC
21
.
This signal
33
is supplied to a read signal processing circuit (RSPC)
201
of the SPC
21
in FIG.
13
.
FIG. 14
shows the configuration of the RSPC
201
.
The signal
33
is amplified to have a suitable amplitude by a variable gain amplifier (VGA)
210
in the first stage of the RSPC
201
. Unnecessary high-frequency noise is removed from the amplified signal and the read waveform of the amplified signal is roughly equalized by an active equalizer (AF)
211
.
Then, the analog signal of the AF
211
is converted into a digital signal by an A/D converter (ADC)
212
. The digital signal is equalized accurately by a digital equalizer (FIR)
213
in the latter stage.
Further, the signal of the FIR
213
is detected to a row of serial data by a maximum likelihood detector (ML)
214
. A sync byte (SB) indicating the start of user data is detected in this serial data row by a sync byte detector (SBDET)
215
.
On the basis of a result of the detection, the serial data row is converted into parallel data and decoded by a decoder (DEC)
216
. Further, the parallel data is restored to data
34
through a descrambler (DSC)
217
. Further, read data
35
is supplied to the HDC
22
through an interface (INT)
202
in FIG.
13
.
Further, the data
35
supplied to the HDC
22
is subjected to error detection and error correction by an error correction circuit (ECC)
22
-
1
in the HDC
22
, and supplied as data
48
to a user (host PC, or the like) through the HBI
25
.
A control operation will be described below in the case where a cylinder is sought from Cn to Cm to read a plurality of data sectors DS
1
, DS
2
, DS
3
. . . as shown in FIG.
15
.
TRK_WDTH shows an arrangement of servo and data regions.
The servo controller (SRVC)
23
successively reproduces servo signals SRVi recorded on a disk surface to thereby obtain a positioning signal
42
through a servo signal processing circuit (SSPC)
204
to thereby perform positioning control.
The MP
24
gives a seek command (SEEK)
40
to the SRVC
23
. The SRVC
23
analyzes the positioning signal
42
obtained in a signal SRV
1
(
FIG. 13
) in servo region. If a judgment is made from the analysis that data is enabled to read, the SRVC
23
outputs a “read seek complete” signal (RD_SK_COMP)
47
to the HDC
22
. As a result, the HDC
22
outputs a “read gate” signal (RG)
36
from the data region DS
1
.
The threshold value of completion of positioning for issuing the RD_SK_COMP
47
in the read operation is generally set to be larger than the threshold value in the write operation to attain reduction of the seek completion time.
At read time, as shown in
FIG. 14
, the RG
37
supplied to the RSPC
201
through the INT
202
operates most of portions in the RSPC
201
and also operates a coefficient learning circuit (ADAPT)
218
which adaptively learns the coefficient of the FIR
213
.
As a result, the coefficient value registered in an equalizing characteristic setting register (COEF)
219
is consecutively changed to a coefficient value for giving good reproducing characteristic even in the case where the resolving power of the reproductive signal
33
varies in accordance with the change of head/disk characteristic, head spacing, or the like, caused by the change of the operating environment, such as temperature, atmospheric pressure, or the like, of the HDD
10
.
In such a background art, however, there were two problems as follows.
The first problem is increase of error caused by divergence occurs in the equalizing coefficient of the FIR
213
.
As shown in
FIG. 15
, the effective track width (TRK_WDTH) varies in accordance with the positional divergence of the MR head and the positioning state at write time. Particularly just after seeking, there is the possibility that the positional divergence is widened because of the influence of settling of head, or the like.
When, for example, a data sector DS
1
to be read is present just after the RD_SK_COMP
47
, the read gate (RG)
37
is opened in the position of DS
1
in the condition in which the sufficiently effective track width cannot be obtained because of the aforementioned deterioration, or the like.
In this condition, the ADAPT
218
cannot operate normally. As a result, the initial value Km(init) of the coefficient value of the FIR
213
registered in the equalizing characteristic setting register (COEF)
219
may diverge to a coefficient value Km(adapt) in which data reproduction cannot be performed normally on the basis of a learning operation.
In this case, the data row produced from the NRZ data
34
contains a lot of channel byte errors as shown in FIG.
15
. Accordingly, there is a high possibility that the errors cannot be perfectly corrected by the error correction circuit (ECC)
22
-
1
in the HDC
22
.
Further, if the performance for checking the miscorrection of the ECC is insufficient, the possibility that the erroneously corrected data may be sent to the host becomes high (mischecking).
Because the data sector DS
2
following the data sector DS
1
also uses the aforementioned abnormal coefficient value as an initial value, there is a high possibility that the same problem as described above occurs consecutively.
The data sectors DS
3
. . . following the data sector DS
2
form a (substantially on-track) sector region having a large effective track width. Also in the sectors DS
3
. . . , there is a very high possibility that channel byte error occur frequently.
To correct this error, it is necessary to restart a read operation with the effective track width kept sufficient while rotating the disk to wait for the same sectors (DS
1
. . . ) to come in the condition in which the COEF is reset to the initial value Km(init) in a data restoration sequence (retry).
If the aforementioned condition occurs frequently, the performance of the device is lowered greatly.
The second problem is that reproducing characteristic at ordinary time deteriorates.
In the background art shown in
FIG. 14
, the “read gate” signal (RG) is used as a signal for starting the ADAPT
218
. Accordingly, in the read state, the coefficient of the FIR
213
registered in the COEF
219

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