U.S. patent application number 09/191664 was filed with the patent office on 2001-10-18 for ac erase system and method for data storage media.
Invention is credited to DIXON, GLENN B..
Application Number | 20010030824 09/191664 |
Document ID | / |
Family ID | 22706411 |
Filed Date | 2001-10-18 |
United States Patent
Application |
20010030824 |
Kind Code |
A1 |
DIXON, GLENN B. |
October 18, 2001 |
AC ERASE SYSTEM AND METHOD FOR DATA STORAGE MEDIA
Abstract
A system and method for AC erasing fields on tracks in a disk is
provided. An AC three-pass write technique is used in a disk drive
to erase old data from an older generation, wide track disk with a
newer generation, narrower read/write head, and write new data to
the wide track disk with the narrower head. A strong AC bias field
(instead of a DC bias field) is applied to the read/write head
during the erase passes in the multipass technique, thereby
reducing the net signal-to-noise ratio when the written data is
read back in an older drive with a wider head. Moreover, a request
from a disk drive controller for a DC erase is detected and the DC
erase signal is automatically replaced with an AC erase signal.
Inventors: |
DIXON, GLENN B.; (WEST
POINT, UT) |
Correspondence
Address: |
JONATHAN M WALDMAN
WOODCOCK WASHBURN KURTZ MACKIEWICZ
AND NORRIS
46TH FLOOR ONE LIBERTY PLACE
PHILADELPHIA
PA
19103
|
Family ID: |
22706411 |
Appl. No.: |
09/191664 |
Filed: |
November 13, 1998 |
Current U.S.
Class: |
360/57 ;
G9B/5.024; G9B/5.027 |
Current CPC
Class: |
G11B 5/012 20130101;
G11B 5/024 20130101 |
Class at
Publication: |
360/57 |
International
Class: |
G11B 005/02; G11B
005/03 |
Claims
What is claimed:
1. A system for erasing a signal in a recording track formed on a
magnetic disk comprising: a magnetic head for at least erasing a
first edge portion and a second edge portion of the magnetic disk;
and an AC erase controller for sequentially generating a first AC
erasing signal and a second AC erasing signal, said AC erase
controller comprising a terminal for receiving an erase command
signal, said AC erase controller supplying said magnetic head with
said erasing signals responsive to said erase command signal, said
first AC erasing signal for erasing said first edge portion and
said second AC erasing signal for erasing said second edge portion
of the magnetic disk.
2. The system according to claim 1, wherein said first edge portion
of the magnetic disk is opposite said second edge portion of the
magnetic disk.
3. The system according to claim 1, wherein said AC erase
controller comprises a gate oscillator.
4. The system according to claim 3, wherein said gate oscillator
comprises a plurality of XOR gates.
5. The system according to claim 1, further comprising a pulse
detector for detecting said erase command signal and activating
said AC erase controller responsive to said erase command
signal.
6. The system according to claim 1, wherein said erase command
signal is a DC erase command signal.
7. The system according to claim 1, wherein said erase command
signal is an AC erase command signal.
8. The system according to claim 1, wherein said first AC erasing
signal has a first frequency and said second AC erasing signal has
a second frequency, said first and second frequency being
substantially equal.
9. The system according to claim 8, wherein said first and second
frequency are approximately 50 MHz.
10. A method for erasing a signal in a recording track formed on a
magnetic disk, comprising the steps of: erasing a first portion of
the recording track by supplying through a magnetic head a first AC
erasing signal; and erasing a second portion of the recording track
by supplying through said magnetic head a second AC erasing signal,
wherein the first portion of the recording track is along one edge
of the recording track and the second portion of the recording
track is along the opposite edge of the recording track.
11. The method according to claim 10, wherein said first AC erasing
signal bas a first frequency and said second AC erasing signal has
a second frequency, said first and second frequency being
substantially equal.
12. The method according to claim 11, wherein said first and second
frequency are approximately 50 MHz.
13. A method for erasing a signal in a recording track formed on a
magnetic disk, comprising the steps of: receiving an erase command
signal at an AC erase controller; supplying a magnetic head with a
first AC erasing signal responsive to said erase command signal;
and supplying said magnetic head with a second AC erasing signal
responsive to said erase command signal.
14. The method according to claim 13, further comprising the steps
of: erasing a first portion of the recording track by supplying
through said magnetic head said first AC erasing signal; and
erasing a second portion of the recording track by supplying
through said magnetic head said second AC erasing signal.
15. The method according to claim 13, wherein said erase command
signal is a DC erase command signal.
16. The method according to claim 13, wherein said erase command
signal is an AC erase command signal.
17. The method according to claim 13, wherein said first AC erasing
signal has a first frequency and said second AC erasing signal has
a second frequency, said first and second frequency being
substantially equal.
18. The method according to claim 17, wherein said first and second
frequency are approximately 50 MHz.
Description
FIELD OF THE INVENTION
[0001] The present invention relates in general to a method of and
an apparatus for erasing a magnetic disk. More particularly, the
present invention relates to a method of and a device for erasing a
recording track formed on the magnetic disk.
BACKGROUND OF THE INVENTION
[0002] Signals representing data are generally recorded on magnetic
recording media such as magnetic disks, magnetic tapes, or the like
by residual magnetism. The data on disks is written by a read/write
head located in a disk drive that writes the data in concentric
circles on the disk called tracks. Disk drives with removable media
preferably have the capability to read and write disks from earlier
generation drives (i.e., older disks). These older disks typically
have a lower capacity, and therefore have wider data tracks than
the newer disks. For example, a 1.44 megabyte 3.5" floppy disk
drive preferably has the capability to read and write older 750
kilobyte disks, which have substantially wider data tracks. In the
older disk drives, wider read/write heads are used to read and
write data to the tracks. As technology has improved and the
density of data on disks has increased, read/write heads have
become narrower. To be able to produce newer generation disk drives
economically, the same read/write head is used to read and write
both current (narrow track) and older generation (wide track)
disks. Because the head's recording width matches the narrower
track width of newer drives, special techniques must be used to
correctly write a track on the wider tracks found in older
generation disks.
[0003] FIG. 1 is a top view diagram of a wider track (from an older
generation disk) that has been overwritten with a narrow head (in a
later generation disk drive having a narrow head). Old data 110
along the edges of the track 101 remain after the new data 105 has
been written. The narrow head writes new data on a track width WN.
The wider head reads and writes data on a track width WW. The old
data remaining after the narrow head writes on a track has a width
of WO1 and WO2, where WW=WN+WO1+WO2. Typically, WO1 is
substantially equal to WO2. The old data 110 will likely interfere
with the desired signal (which comprises only the new data 105 and
not the old data 110) if the disk is read in an older drive that is
equipped with a wider read/write head. When the track 101 written
by a narrow head is read back by a wide head (e.g., in an older
drive), both the old data 110 remaining along the track edges and
the new data 105 are read back.
[0004] One method of overcoming this problem is to utilize a second
erase head in the newer drive. This head is not designed to record
data, but instead is designed to simply erase the track edges of
the older disk's track. In other words, the recorded signals or
data can be erased by removing the residual magnetism under a
magnetic field generated by an erasing head positioned closely to
the magnetic recording medium. One conventional way for erasing the
recorded magnetic signals is known as a DC (direct current) erase
process which utilizes either an erasing head with a direct current
flowing through its coil or an erasing head having a permanent
magnet. Such an erasing head produces a magnetic field in a
prescribed direction to magnetize the magnetic recording medium
uniformly until it is magnetically saturated. The DC erasing head
is however disadvantageous in that it leaves noises of high level
on the magnetic recording tape when erasing the recorded signals
therefrom, thus increasing the distortion rate of signal waveforms
which will be recorded and reproduced.
[0005] Another method that does not use a separate erase head is to
first erase the entire wide track of the older generation disk
before writing the data. This technique, called "three-pass write"
is performed in accordance with the top view diagrams shown+WO2. in
FIGS. 2A-2C. Here, the track 101 is first erased by doing two erase
passes on the wide track with the narrower read/write head 120. On
the first pass, as shown in FIG. 2A, old data 110 on one track edge
125 is erased by passing a DC erase current through the read/write
head 120 while the head passes along track edge. On the second
pass, as shown in FIG. 2B, the remaining edge 130 is erased.
Finally, as shown in FIG. 2C, the new data signal 135 is written
down the center of the wider track 101 by the narrower head 120.
Thus, the new data 135 is not corrupted by the old data 110 when
the track is read by a wider read/write head, for example, in an
older generation disk drive.
[0006] One drawback of the above described downward compatibility
techniques is that the actual signal written is narrower than what
the earlier generation head writes. This causes the readback signal
read by the wider head to be lower. Additionally, because DC erased
media still generates some noise in a readback head, the erased
track edges still contribute noise to the readback signal. The
result is poor signal-to-noise ratio when an older generation drive
reads a disk written by a newer generation drive.
[0007] Additionally, it has been found that the DC-magnetized edges
of a wide track that has been DC erased and then written with a
narrow head adversely affects the edges of the written flux changes
by coupling flux to the edges of the written signal that have
opposite polarity to the DC field. When read by a wide head, this
coupling causes an undesirable effect known as pulse-pairing, where
readback pulses of one polarity are shifted early in time, and
those of the opposite polarity are shifted late. Thus, leaving DC
erase fields on track edges when the track is written by a narrow
head degrades both signal linearity and signal-to-noise ratio.
[0008] In both audio magnetic recording and in data recording, it
is known that erasing the recording medium with a high-frequency AC
(alternating current) signal instead of a DC erase field results in
lower readback noise. This is because DC erased media is still
strongly magnetized in one direction, and any flaws in the media's
distribution of magnetic particles (caused by media defects, random
magnetic particle fluctuations, particle clumping, and surface
roughness) will result in an external magnetic field that is picked
up by the system readback head as unwanted noise.
[0009] In a prior art AC erase technique, an erasing head having a
coil is supplied with an alternating current for magnetizing the
magnetic recording medium as it passes the erasing head. The
magnetic recording media is magnetized until it is saturated. As
the magnetic recording medium travels away from the AC erasing
head, the recording medium is less subject to the alternating
magnetic field produced by the AC erasing head, and hence the
residual magnetism on the recording medium is progressively
reduced, and any residual that remains on the disk is at a
frequency above the recording bandwidth, which can be removed by
appropriate low-pass filtering.
[0010] Thus, the DC magnetized media causes external fields in any
anomalous regions including bit edges. By erasing with an AC signal
whose frequency is substantially higher than any recorded data
frequency, the media magnetization switches polarity over short
readback spacings, and the perturbations mentioned above cause
lower external fields. Because polarity shifts frequently with AC
erase, externally generated fields are smaller. This results in
lower unwanted readback noise. However, conventional AC erase
systems are single pass.
[0011] Although the art of reading and writing data to disks is
well developed, there remain some problems inherent in this
technology, particularly the integrity of data written to and read
from different generations of disks and disk drives having
different size read/write heads. Therefore, a need exists for a
system and method for erasing unwanted data that overcomes the
drawbacks of the prior art.
SUMMARY OF THE INVENTION
[0012] The present invention is directed to a system for erasing a
signal in a recording track formed on a magnetic disk comprising a
magnetic head for at least erasing a first edge portion and a
second edge portion of the magnetic disk, and an AC erase
controller for sequentially generating a first AC erasing signal
and a second AC erasing signal. The AC erase controller comprises a
terminal for receiving an erase command signal, and the AC erase
controller supplies the magnetic head with the erasing signals
responsive to the erase command signal. The first AC erasing signal
is for erasing the first edge portion and the second AC erasing
signal is for erasing the second edge portion of the magnetic
disk.
[0013] According to one aspect of the present invention, the first
edge portion of the magnetic disk is opposite the second edge
portion of the magnetic disk.
[0014] In accordance with an aspect of the present invention, the
AC erase controller comprises a gate oscillator. Preferably, the
gate oscillator comprises XOR gates.
[0015] In accordance with a further aspect of the present
invention, the system further comprises a pulse detector for
detecting the erase command signal and activating the AC erase
controller responsive to the erase command signal.
[0016] In accordance with a further aspect of the present
invention, the erase command signal is a DC erase command signal or
an AC erase command signal.
[0017] According to further aspects of the invention, the first AC
erasing signal has a first frequency and the second AC erasing
signal has a second frequency. The first and second frequency are
substantially equal, and preferably equal about 50 MHz.
[0018] In a further embodiment within the scope of the present
invention, a method for erasing a signal in a recording track
formed on a magnetic disk is provided. The method comprises the
steps of erasing a first portion of the recording track by
supplying through a magnetic head a first AC erasing signal, and
erasing a second portion of the recording track by supplying
through the magnetic head a second AC erasing signal. The first
portion of the recording track is along one edge of the recording
track and the second portion of the recording track is along the
opposite edge of the recording track.
[0019] Another embodiment within the scope of this invention
includes a method for erasing a signal in a recording track formed
on a magnetic disk, comprising the steps of receiving an erase
command signal at an AC erase controller, supplying a magnetic head
with a first AC erasing signal responsive to the erase command
signal, and supplying the magnetic head with a second AC erasing
signal responsive to the erase command signal.
[0020] According to another aspect of the present invention, the
method further comprises the steps of erasing a first portion of
the recording track by supplying through the magnetic head the
first AC erasing signal, and erasing a second portion of the
recording track by supplying through the magnetic head the second
AC erasing signal.
[0021] The foregoing and other aspects of the present invention
will become apparent from the following detailed description of the
invention when considered in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 (prior art) is a diagram of a wider track (from an
older generation disk) that has been overwritten with a narrow head
(in a later generation disk drive having a narrow head);
[0023] FIGS. 2A-2C (prior art) are diagrams showing various stages
of a conventional DC three-pass write technique;
[0024] FIG. 3 is a schematic diagram of an exemplary AC erase
system in accordance with the present invention; and
[0025] FIG. 4 is a flowchart of an exemplary method of operation in
accordance with the present invention.
DESCRIPTION OF EXEMPLARY EMBODIMENTS AND BEST MODE
[0026] The present invention is directed to a system and method for
AC erasing fields within tracks in a disk. An AC multiple-pass
(e.g., three-pass) write technique is used in a disk drive to erase
and write an older generation, wide track disk with a newer
generation, narrower head. By applying a strong AC bias field
(instead of a DC bias field) to the head during the erase passes
(e.g., two erase passes in the three-pass technique as described in
FIG. 2), a net signal-to-noise reduction is realized when the
written data is read back in an older drive with a wider head. The
reduction occurs because the AC-erased track edges generate less
unwanted noise in the wider readback head. Thus, in the present
invention, signal-to-noise is improved in a downward compatible
mode on older disk drives. Moreover, the present invention detects
the request for a DC erase and automatically replaces the DC erase
signal with AC erase signal.
[0027] A multiple-pass write technique involves multiple passes of
erasing, followed by a pass of writing. For example, from FIG. 2, a
three-pass write technique involves two passes of erasing, followed
by one pass of writing. However, FIG. 2 is described with respect
to a DC erase, whereas the present invention is directed to AC
erase.
[0028] FIG. 3 shows a schematic circuit diagram of an AC erase
system in accordance with the present invention. The present
invention includes an AC erase controller comprising a gate
oscillator circuit 200, a pulse detector comprising a resistor 221,
a capacitor 223, and a diode 225, and conventional AC erase
circuitry to perform the AC erase as directed by the AC erase
controller and pulse detector. The gate oscillator 200 comprises
XOR (exclusive OR) gates 210, 220 to enable/disable the oscillator
200 yet still pass normal data pulses. Preferred component values
and part numbers are shown.
[0029] Referring to FIG. 3, during an erase pass (which occurs
prior to writing when a write has been ordered), a "write" signal
that is provided from the disk drive controller 280 to terminal 240
goes active (e.g., low). The "write" signal from the controller 280
is used in a typical disk drive to order a disk drive write or a DC
erase. During an erase pass, the write signal remains low, and
there are no data pulses on the write data line (input 214 into the
XOR gate 220). In conventional disk drives, the absence of data
pulses is a DC erase. The no pulse condition is detected by the
circuit formed by resistor 221, capacitor 223, and diode 225. After
a predetermined time (related to the time constant formed by the
components 221, 223, 225), the input 209 to the XOR gate 210 goes
high. The gate oscillator 200 comprising gates 210, 220, and
resistor 201, resistor 203, and capacitor 205 starts up. The XOR
gate 210 acts as an inverter to input 207.
[0030] Resistors 201, 203 and a capacitor 205 provide a
high-frequency AC erase signal (preferably about 50 MHz) to the
disk write circuitry 250 through the XOR gate 220. Thus, the DC
erase signal from the disk drive controller 280 is automatically
replaced by an AC erase signal during the erase process. The AC
erase that takes place in the disk write circuitry 250 along the
edges of the track is conventional AC erase, as would be understood
by those skilled in the art.
[0031] After the desired number of erases take place (e.g., two
erase passes in a three-pass write technique), a conventional write
is ordered by the disk drive controller. In accordance with the
present invention, the writing is conventional; i.e., writing takes
place as in a conventional disk drive. In FIG. 3, a "write" signal
is provided from the disk drive controller 280 to the terminal 240.
The "write" signal is used to indicate when writing is taking place
on the disk. During writing, the "write" data signal is high, and
provides a low-going pulse at the substantially precise instant a
flux change is to be written to the disk by the recording head.
During a normal data write, data pulses are provided to the XOR
gate 220 via the input 214 and to the disk drive write circuitry
250 unaltered, or possibly inverted, depending on the state of XOR
input 212. The disk drive write circuitry is not affected by the
write pulse polarity. As long as data pulses are present in the
write data signal, the input 209 to the XOR gate 210 is held low by
diode 225 connected to the write data terminal 240. This has the
effect of turning off the gate oscillator 200 comprising gates 210,
200 and resistor 201, resistor 203, and capacitor 205. Thus, the
input 212 to gate 220 does not toggle during data writes, and a
conventional writes occurs.
[0032] The time constants formed by the resistor 221 and the
capacitor 223 are chosen so that the oscillator 200 starts
sufficiently quickly when an erase is ordered by the disk drive
controller 280, and still prevents the AC erase oscillator 200 from
starting during a normal data write. The AC erase frequency is
determined primarily by two factors: it is preferably high enough
so that no significant interaction occurs between the harmonics of
data signals and the AC erase frequency, yet low enough that the
recording head and associated write circuitry can write the signal
to the disk. Preferably, the AC erase frequency is about 50
MHz.
[0033] A transistor 229 is used as a switch to ensure that the AC
erase oscillator 200 is off when the drive is not writing (i.e.,
erasing and then writing). The present invention provides
approximately a 2 dB signal/noise improvement on a typical disk
drive.
[0034] FIG. 4 is a flowchart of an exemplary method of operation in
accordance with the present invention. A disk write routine is
called at step 300. The track that data is being written to is
desirably erased prior to being written on. At step 305, the disk
drive controller orders an erase (a DC erase is shown), which
activates the AC gate oscillator, as described above with respect
to FIG. 3, at step 310. The gate oscillator sends an appropriate AC
erase signal to AC erase circuitry in the disk drive at step 315.
The AC erase is performed at step 320. It is then determined if
another erase pass is desired, at step 325, for example, to further
erase the track. If another erase pass is desired, processing
returns to step 305. If another erase pass is not desired, then
data is written to the disk at step 330 and the routine ends at
step 335.
[0035] Thus, in accordance with the present invention, a circuit
receives signals ordering a DC three-pass write, and then shuts off
the DC erase portion, and instead activates an AC three-pass write.
The combination of an active write enable and no data pulses on the
write data line (input 214 into the XOR gate 220) within a certain
period of time (depending on the drive, etc.) indicates to the
circuit that a DC erase is in progress. The circuit responds by
starting the oscillator 200 and substituting an AC erase signal in
place of the DC signal. This happens quickly enough so that the
data area of the disk is fully AC erased.
[0036] An advantage of the circuit of the present invention is that
it can be easily installed in a disk drive originally outfitted to
perform DC erase only. The circuit automatically detects the DC
erase condition and substitutes an AC erase signal in its place.
Data writes pass through the circuit with no effect. The circuit
can then be implemented in a drive that is already outfitted for DC
erase without having to have an extra control line to signal when
AC erase is desired. The circuit also uses a small number of parts
resulting in a low cost, easily implemented device. Furthermore,
the present invention eliminates the undesirable pulse-pairing
effect which degrades the time position of the bits depending on
their polarity, as described above.
[0037] It should be noted that although the present invention has
been described with respect to a disk drive which orders a DC erase
signal, the present invention can be implemented in a disk drive
that does not order a DC erase signal, but instead orders an AC
erase signal.
[0038] It should be further noted that although the above described
embodiment is directed to a three-pass writing technique (two
erases followed by one write, similar to that described above with
respect to FIG. 2), any number of erase and writing passes can be
used in accordance with the present invention.
[0039] Although illustrated and described herein with reference to
certain specific embodiments, the present invention is nevertheless
not intended to be limited to the details shown. Rather, various
modifications may be made in the details within the scope and range
of equivalents of the claims and without departing from the
invention.
* * * * *