Dynamic magnetic information storage or retrieval – General processing of a digital signal – Head amplifier circuit
Reexamination Certificate
1999-12-06
2002-11-05
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Head amplifier circuit
C360S031000, C360S065000, C360S075000
Reexamination Certificate
active
06476992
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic disk apparatus using combination heads in each of which a write head and a read head are arranged at an edge of a rotary actuator and relates to an offset measuring method of such an apparatus. More particularly, the invention relates to a magnetic disk apparatus for accurately measuring an offset caused by a core deviation between the write head and the read head in a default state of apparatus parameters and relates to an offset measuring method of such an apparatus.
2. Description of the Related Arts
As a head which is currently used in a magnetic disk apparatus, a combination head in which a read only MR head and a write only inductive head are arranged is used. The combination head is supported at an edge of an actuator, moved in the radial direction which transverses medium tracks, and positioned. Further, a data surface servo in which servo frames on which position information had been recorded have previously been arranged on a data surface of the medium at predetermined intervals in the direction of tracks is used. Therefore, when data is written, the data is written onto the medium by the inductive head in a state where the center of the MR head is positioned to the track center so as to enter an on-track state by a position signal demodulated from a reproduction signal of the MR head. In the reading mode for reproducing the data written on the medium, in a state where the center of the MR head is positioned to the track center so as to enter an on-track state by the position signal demodulated from the reproduction signal of the MR head, the data is read out from the medium by the MR head and demodulated. Since the write head and the read head are separately arranged on the combination head as mentioned above, a deviation generally occurs between the write center position of the write head at the time of the data writing and the read center position of the read head at the time of the data reading. It is, therefore, necessary to previously measure a deviation amount between the write center position and the read center position and perform a control to position the read head to the write center by offsetting it by such a deviation amount when the data is read out. According to a method of measuring such an offset amount, first, random data is written as a reference signal indicating the position of the write head, after that, the data is read out while the read head is gradually offset, and the center of a range of the offset amount in which an error rate is the minimum or the offset amount in which no error occurs is set to the optimum offset amount.
However, in the measurement of the offset caused by such a separate arrangement of the write head and the read head, even when parameters of a read channel are set as default parameters, the data has to be accurately read out to a certain extent. This is because since the data written on the medium is used for adjustment of the parameters of the read channel, the parameters for adjustment written on the medium have to be able to be read out by the default parameters before adjustment of the parameters. In the conventional read channel, since the number of parameters which need the adjustment by the data read out from the medium is relatively small, an error rate of a certain degree can be assured even in the setting state of default. In recent years, however, owing to the progress of the read channel, even in case of a low S/N ratio, an error rate equivalent to the conventional one can be assured. The setting of parameters, however, becomes fine by an amount of such progress. In the default setting state in which the parameters are not adjusted at all, it is a present situation that no data can be read out. As for the evaluation in the measurement of the offset caused by the separate arrangement of the write head and the read head, it is a general way that a data correcting function by an ECC is used and an offset amount in which one track is read and the number of sectors in which errors that cannot be corrected by the ECC occurred, namely, a sector error rate when one cylinder is read becomes the minimum, or the center of a range of the offset in which uncorrectable errors are not generated is set to the optimum offset amount. This is because the discrimination about whether the correction of the ECC is possible or not can be performed by hardware, and the deterioration of the error rate due to unadjustment of the parameters of the read channel can be compensated by the ECC. However, there is a problem that the evaluation by the error rate of the ECC is weak for a medium defect. That is, it is assumed that at the time of offset measurement, a medium defect locally exists on either one of the sides of the measuring track, for example, on the outer side in the disk radial direction. In this case, when the position of the read head is close to the outer side, a burst error occurs by the medium defect on the outer side and it cannot be corrected by the ECC, so that the error rate deteriorates. Consequently, the normal error rate is evaluated by the ECC in the area on the inner side where there is no defect. The optimum offset amount in this case is deviated to the inner side as compared with the inherent optimum offset amount in the case where there is no medium defect, and it is weak for the medium defect.
SUMMARY OF THE INVENTION
According to the invention, there is provided a magnetic disk apparatus in which parameters of a read channel can be easily set at the time of measurement and, even when there is a medium defect or the like, an optimum offset can be accurately obtained in a default setting state and to provide an offset measuring method of such an apparatus.
First, according to the invention, there is provided a magnetic disk apparatus which has combination heads formed by arranging read heads and write heads at an edge of an actuator and in which information is recorded or reproduced while the head is positioned to a target track so as to enter an on-track state on the basis of a position signal of a medium demodulated from a reproduction signal of the read head, further upon reproduction, the reproduction signal from the read head is equalized to a Partial Response waveform, and after that, it is maximum likelihood detected, thereby demodulating information. According to the invention, a measurement pattern writing unit and an optimum offset measuring unit are provided for the magnetic disk apparatus. The measurement pattern writing unit writes random patterns to adjacent tracks locating on both sides of a measuring track whose offset is measured, or writes a preamble pattern. The optimum offset measuring unit obtains the sum &Sgr;(y−W)
2
of the squares of errors between sampling values y of a Partial Response waveform obtained by equalizing the reproduction signal of the preamble pattern and a predetermined ideal sampling value W in the case where there is no noise while changing an offset amount, calculates a mean per sample [hereinbelow, referred to as a “mean square error (MSE)”] by dividing the sum &Sgr;(y−W)
2
of the square errors by the number of samples (N), and determines an offset amount in which the mean square error MSE becomes the minimum for a change in offset amount as an optimum offset. In case of Partial Response Class
4
maximum likelihood detection (hereinbelow, referred to as a “PR4ML”), when assuming that the magnetization inversion is set to bit “1” and the non-magnetization inversion is set to bit “0” as a preamble pattern, the measurement pattern writing unit writes a preamble pattern “01010101 . . . ” in which “0” and “1” are repeated onto the measuring track. In the offset measurement of the invention, therefore, in case of PR4ML, by using the preamble pattern which is repeated like “01010101 . . . ”, a waveform passed through a low pass filter is equivalent to the waveform which was correctly equalized to the Partial Response waveform. Consequently, the mean s
Fujitsu Limited
Greer Burns & Crain Ltd.
Holder Regina N.
Slavitt Mitchell
LandOfFree
Magnetic disk apparatus and optimum offset measuring method does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Magnetic disk apparatus and optimum offset measuring method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Magnetic disk apparatus and optimum offset measuring method will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2980483