Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
1998-09-10
2001-02-20
Tupper, Robert S. (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Core
Reexamination Certificate
active
06191917
ABSTRACT:
TECHNICAL FIELD
The present invention relates to thin film tape write heads for recording digital data transitions and equalization pulses onto magnetic tape.
BACKGROUND ART
A write head converts a current signal carrying digital information into a magnetic field. This magnetic field impresses a flux pattern on a magnetic tape as the tape passes the write head. A read head then senses the recorded flux pattern to recover the digital signal. One common input write signal is shown in
FIG. 1
a
. Binary signal
20
is converted to input write signal
22
. Input write signal
22
is a non-return-to-zero inverted (NRZI) signal. In this particular NRZI code, each one is represented by a data transition, one of which is indicated by
24
, and each zero is indicated by the lack of a transition as related to a data clock in receiver electronics. When input write signal
22
is fed to a write head, and tape
26
is moved over the write head, data fields
28
,
30
are written onto tape
26
as shown in
FIG. 2
a
. Each data transition
24
causes a change in magnetization direction between adjacent data fields
28
,
30
.
When tape
26
is passed over a read head, data fields
28
,
30
are converted to read output signal
32
. Electronics connected to the read head use means such as a threshold detector to recover binary signal
20
from read output signal
32
. However, as can be seen in
FIG. 3
a
, a long string of zeros in binary signal
20
causes a large swing in read output signal
32
. This complicates the read electronics.
One way of considering the problem is that the long string of zeros in binary signal
20
results in long data field
30
on tape
26
. Flux field
30
is a magnet. The greater the length of data field
30
, the greater the strength of the resulting magnet. Therefore, reducing the large swings in amplitude of read output signal
32
can be achieved by breaking up long data field
30
.
A method for breaking up long data field
30
is to include short pulses at high frequency in input write signal
22
. This produces a signal known as write-equalized input signal
34
shown in
FIG. 1
b
. Equalization pulse
36
is added to input write signal
22
at locations representing some or all of the zeros in binary signal
20
. Equalization pulse
36
consists of a signal outside the effective frequency range of the read head and channel. When write-equalized signal
34
is written onto tape
38
, as shown in
FIG. 2
b
, equalization pulse
36
is written as high frequency field
40
. This may be likened to high frequency erasure as the high frequency recording is not reproduced by the read head.
When tape
38
including high frequency fields
40
is read by the read head, each high frequency field
40
is sensed as a region producing no flux density. Read output signal
42
, shown in
FIG. 3
b
, therefore does not include the large amplitude swings seen in read output signal
32
from tape
26
not having high frequency fields
40
. Hence, simpler thresholding circuitry may be used in read electronics.
Many techniques are possible for determining where to place equalization pulses
36
in write-equalized input signal
34
. For example, each zero in binary signal
20
can generate a corresponding equalization pulse
36
. The technique for generating the pattern shown in
FIG. 1
b
together with additional techniques for generating write-equalized input signal
34
and a discussion of write equalization is included in “Write Equalization For Generalized (d,k) Codes” by Richard C. Schneider, IEEE TRANSACTIONS ON MAGNETICS, Vol. 24, No. 6, November 1988, pp. 2533-2535, which is hereby incorporated by reference.
A cross-sectional view of a prior tape head for writing write-equalized input signal
34
onto tape
38
is shown in FIG.
4
. Write head
50
includes bottom pole
52
, top pole
54
, and conductive coil
56
which together form an electromagnet. Referring to
FIGS. 2
b
and
4
, operation of write head
50
will be described. When current is applied to conductive coil
56
, a magnetic field is produced across the gap, shown generally by
58
. As tape
38
moves past gap
58
, fields
28
,
30
,
40
are written onto tape
38
.
One difficulty with prior tape head
50
is that the amplitude of input current required to produce a desired magnitude of magnetic field at gap
58
for equalization pulse
36
is much greater than the amplitude of current required to produce a magnetic field at gap
58
that has substantially the same magnitude for data transition
24
. This results in complicated write equalization circuitry to produce write-equalized input signal
34
.
Other difficulties arise if sufficient equalization cannot be added when tape
38
is written. First, complicated read equalization circuitry is required to reshape detected data transitions
24
. This reshaping may require boosting high frequency components which may degrade the read signal-to-noise ratio. Second, the lack of sufficient equalization causes larger swings in the magnetization seen by the read head. These larger swings increase distortion due to nonlinearities in the read head. Third, record depth is greater than necessary since low frequency signals record at greater depth on tape
38
than high frequency signals. Increased record depth may result in degraded overwrite of tape
38
and limited range on the velocity of tape
38
over head
50
.
What is needed is a thin film write head that does not require substantially greater input current magnitude for equalization pulse
36
than for data transition
24
to produce substantially equal magnetic field strength amplitude in gap
58
. This tape head should be economical to produce and should be similar in construction to prior tape heads.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thin film tape head that does not require a substantially greater input current magnitude to produce equalization pulses than to produce data transitions for a desired magnetic field level.
Another object of the present invention is to provide a thin film tape head that produces substantially the same field strength on a magnetic tape for data fields and for high frequency equalization fields.
Still another object of the present invention is to provide a thin film write head that is economical to produce.
Yet another object of the present invention is to provide a thin film write head that, when used in a tape deck, requires simpler write equalization circuitry.
A further object of the present invention is to provide a thin film write head that, when used in a tape deck, requires simpler read equalization circuitry.
A still further object of the present invention is to provide a thin film write head that, when used in a tape deck, improves read signal-to-noise ratio.
Yet another object of the present invention is to provide a thin film write head that, when used in a tape deck, reduces read distortion.
Yet a further object of the present invention is to provide a thin film write head that, when used in a tape deck, produces a record depth that is generally independent of tape media thickness and write current magnitude.
Yet a still further object of the present invention is to provide a thin film write head that, when used in a tape deck, allows uniform recording at various tape velocities.
In carrying out the above objects and other objects and features of the present invention, a thin film write head is provided for writing a write-equalized digital data stream onto a magnetic tape. The write-equalized data stream includes data transitions and equalization pulses. The data transitions occur at a frequency no greater than a data frequency. Each equalization pulse is a signal written at an equalization frequency much greater than the data frequency. The thin film write head includes a top pole, a bottom pole, and a conductive coil disposed between the top and bottom poles. The top pole, bottom pole, and conductive coil form an electromagnet for writing the write-equalized digital data stream onto the magnetic tape by converting an i
Dee Richard H.
Engel Bradley N.
Brooks & Kushman P.C.
Storage Technology Corporation
Tupper Robert S.
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