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TECHNICAL FIELD
The present invention relates to a composite magnetic head for a magnetic
read/write apparatus used in a still image recording electronic camera or
a digital data recording disk unit and, more particularly, to improvements
in a head, a data signal erasing means, and a read/write control means.
BACKGROUND ART
In a conventional magnetic read/write apparatus of this type, and in
particular, in a magnetic read/write apparatus for a compact electronic
camera, separate read using separate read and write decks, neither read
nor re-write can be performed immediately after the write operation.
Therefore, the apparatuses cannot satisfy the user's demand for read and
re-write, if necessary, immediately after the writing of an image or the
like. This also applies to digital data write. A magnetic read/write
apparatus devised to solve this problem to a certain extent is known. The
apparatus comprises a read/write head (hereinafter called R/W head) with
integrally formed read and write heads and a read/write circuit, and, read
and re-write can both be performed immediately after data write for
digital data. Image information can also be read immediately after the
write operation. Since an erase head is not provided, however, written
data cannot be erased for rewrite, making re-write of image data
immediately after the write operation impossible. The main reasons why the
apparatus includes no erase head are as follows. First, overwrite can be
performed in writing digital data, and an erase head is not necessary.
Second, all parts must be small since the space available for mounting
such parts is limited in a compact electronic camera, and a relatively
large part such as an erase head, cannot be used.
In addition, even if space is available and an erase head can be mounted in
addition to a R/W head, the following problem is still presented. When the
two heads are assembled in a compact magnetic disk apparatus using a
compact magnetic disk having a diameter of about 2 inches as a recording
medium, it is extremely difficult to set the head positions so that both
heads maintain good head touch. As a result, the so-called spacing loss
increases. When high-density write is performed with write wavelengths in
the order of 0.5 .mu.m or less, the spacing loss due to poor head touch
must be reduced to a minimum. However, since good head touch for each head
cannot be obtained as described above, the spacing loss increases and
high-density write cannot be performed.
A frame write mode using 2 tracks is known as one image write scheme. When
applied to a compact magnetic disk unit for recording in the frame write
mode, two erase heads must be included besides two R/W heads. Therefore, a
total of 4 heads must be assembled in a limited deck space, and it is
still difficult to obtain space for mounting the heads while maintaining
good head touch for each head. In this manner, assembly of an erase head
involves various difficulties. In practice, therefore, image information
is erased by a separate erase unit. For this reason, the above-mentioned
demand for read and re-write of an image or the like immediately after it
has been written has not been satisfied.
The gap width and track width of an erase head must be larger than those of
an R/W head. Crosstalk must also be considered if the erase head is too
close to the R/W head. In view of this, it has been considered impossible
to assemble erase and R/W heads together while still maintaining the
read/write performance of the apparatus.
It is, therefore, an object of the present invention to provide a compact
composite magnetic head which offers good head touch, which can
satisfactorily read and write various information such as image
information without increasing crosstalk or spacing loss, which allows
re-write immediately after write operation, and which is easy to
manufacture.
It is another object of the present invention to provide a composite
magnetic head which can produce a read output with an excellent S/N ratio
even if the head touch is not satisfactory and crosstalk is great.
It is still another object of the present invention to provide a compact
composite magnetic head which can satisfactorily read and write various
information such as image information, which can re-write information
immediately after writing it, which realizes a read system with an
exceptionally wide band and low noise, which can suppress degradation in
frequency characteristics due to increases in external noise, stray
capacitance, or lead inductance, and which is easy to manufacture.
DISCLOSURE OF INVENTION
In order to achieve the above objects, a composite magnetic head of the
present invention is characterized by the following construction.
A composite magnetic head according to the present invention has a
read/write head section wherein a plurality of thin film heads are joined
such that respective head gaps are aligned at predetermined intervals in
the widthwise direction of tracks; and an erase head section wherein a
plurality of bulk heads respectively corresponding to the thin film heads
are joined such that respective head gaps are aligned at predetermined
intervals in the widthwise direction of the tracks, wherein the read/write
head section and the erase head section are joined in the longitudinal
direction of the tracks, such that the head gaps of the respective
sections are relatively close to each other.
Another composite magnetic head according to the present invention has a
read/write head section wherein a plurality of bulk heads are joined such
that respective head gaps are aligned at predetermined intervals in a
widthwise direction of tracks; and an erase head section wherein a
plurality of bulk heads respectively corresponding to the bulk heads are
joined such that respective head gaps are aligned at predetermined
intervals in the widthwise direction of the tracks, wherein the read/write
head section and the erase head section are joined in the longitudinal
direction of the tracks, such that the head gaps of the respective
sections are relatively close to each other.
Still another composite magnetic head of the present invention has two
magnetic heads, comprising thin film heads or bulk heads, for
simultaneously picking up signals recorded on two adjacent tracks on a
magnetic recording medium, and additionally has a means for switching and
amplifying so that a predetermined voltage division signal of a read
signal from one magnetic head differentially acts on a read signal from
the other magnetic head.
Still another composite magnetic head of the present invention has a base,
a head chip mounted on the base, and a step-up transformer, mounted on the
base, for stepping up the level of the signal picked up by the head chip.
Still another composite magnetic head of the present invention has a head
chip mounted on a base, a read/write switch circuit for switching the head
chip to a read or write system, a write amplifier for amplifying a write
current and supplying the amplified current to the head chip when the head
chip is connected to the write system by the read/write switch circuit, a
step-up transformer, mounted on the base, for stepping up the level of a
signal picked up by the head chip when the head chip is connected to the
read system by the read/write switch circuit, and a differential input
read amplifier for amplifying the signal stepped up by the step-up
transformer, wherein the read/write switch circuit, the write amplifier,
and the differential input amplifier are formed into a hybrid IC and
mounted on the base.
There is provided according to the present invention, therefore, a compact
composite magnetic head which has excellent head touch, which can
satisfactorily read and write various information such as image
information without increasing crosstalk or spacing loss, which allows
re-write immediately after the write operation, and which is easy to
manufacture.
There is also provided according to the present invention a composite
magnetic head in which a crosstalk component included in one read signal
is cancelled by a crosstalk component included in the other read signal,
so that a high read output with an excellent S/N ratio can be obtained
even if head touch is poor and crosstalk is considerable.
There is also provided according to the present invention a compact
composite magnetic head apparatus which has a step-up transformer inserted
between a magnetic head and a differential amplifier to obtain a read
system with a wide band and low noise, which has a read amplifier, a write
amplifier, and a read/write switch circuit formed into a hybrid IC mounted
on a head base to suppress degradation in frequency characteristics due to
increases in external noise, stray capacitance or lead inductance, and
which is easy to manufacture.
BRIEF DESCRIPTION OF DRAWINGS
FIGS. 1 and 2 show the schematic head arrangement and structure according
to a first embodiment of the present invention;
FIGS. 3 and 4 the schematic head arrangement and structure according to a
second embodiment of the present invention;
FIGS. 5 and 6 are a plan view and a longitudinal sectional view,
respectively, of a composite head according to a third embodiment of the
present invention;
FIG. 7 is a block diagram showing the configuration of a control system
which allows the composite head of the third embodiment to perform write
and erase operations;
FIG. 8 is a timing chart showing the operation timings of the respective
blocks of the control system shown in FIG. 7;
and FIGS. 9 to 11 are views showing the construction of a composite head
with a read step-up transformer according to a fourth embodiment of the
present invention, in which
FIG. 9 is a plan view,
FIG. 10 is a side view, and
FIG. 11 is a sectional view.
FIG. 12 is a circuit diagram for when the composite head shown in FIGS. 9
to 11 is used.
FIG. 13 is a sectional view showing the structure of a bulk-type composite
magnetic head according to a fifth embodiment of the present invention;
and
FIG. 14 shows a crosstalk removing circuit used together with the bulk-type
composite head in FIG. 13.
FIG. 15 is an equivalent circuit diagram of noise in a read amplifier
system in a sixth embodiment of the present invention;
FIG. 16 illustrates the principle of the sixth embodiment;
FIG. 17 is a circuit diagram showing the circuit configuration of the sixth
embodiment; and
FIGS. 18 to 20 are views showing the mounting state of a hybrid IC in the
sixth embodiment, in which
FIG. 18 is a plan view from the rear surface of a base,
FIG. 19 is a plan view from the front surface of the base, and
FIG. 20 is a side view.
FIG. 21 shows the frequency characteristics of a read system of the sixth
embodiment; and
FIG. 22 shows the total head noise voltage in the sixth embodiment; and
FIGS. 23 to 25 show a modification in the surface shape of the composite
head in FIGS. 2 to 4, in which
FIG. 23 is a plan view, FIG. 24 is an end view, and FIG. 25 is a side view.
FIGS. 26 to 28 show a composite magnetic head having a structure different
from those of the composite magnetic heads shown in FIGS. 2 and 4;
FIG. 29 is a partial diagram showing a partial modification of the control
system in FIG. 7;
FIG. 30 is a timing chart showing the operation timing of the circuit shown
in FIG. 29;
FIGS. 31 and 32 show a partial modification of the control system shown in
FIG. 7; and
FIG. 33 is a timing chart showing the operation timing of the circuit shown
in FIGS. 31 and 32.
BEST MODE OF CARRYING OUT THE INVENTION
FIGS. 1 and 2 show a schematic head arrangement and structure according to
a first embodiment of the present invention. Referring to FIG. 1,
reference numeral 1 denotes a rotary magnetic disk as a magnetic recording
medium. Disk 1 is rotated by a motor (not shown) at a rotational frequency
of 3,600 rpm (in the case of the NTSC system) counterclockwise as
indicated by the arrow around point P. Write tracks T1, T2, . . . are
concentrically formed on a write surface of magnetic disk 1 by composite
magnetic head 2. PG yoke 4 as a rotational position detection index for
disk 1 is mounted at one point on the circumference of hub 3 at the center
of disk 1. PG coil 5 as a pulse detection means is mounted at one point on
a rotation path of PG yoke 4 of the apparatus housing (not shown). PG coil
5 is arranged at the non-write side of magnetic disk 1, i.e., at the
opposite side of composite magnetic head 2. PG coil 5 extracts a pulse
signal induced upon interlinkage with the magnetic fluxes produced by PG
yoke 4 upon rotation of magnetic disk 1.
When field write is performed during still image write on magnetic disk 1,
still image information for different fields is written in first and
second tracks T1 and T2. When frame write is performed, still image
information for two consecutive fields is written in tracks T1 and T2. In
either case, the write start and end points are defined when PG yoke 4
comes to the position illustrated in FIG. 1, i.e., when it is on line O-Y
when the line connecting central point O of magnetic disk 1 and the center
of PG coil 5 is represented by line Y--Y'. In other words, composite
magnetic head 2 is switched by a PG pulse obtained when PG yoke 4 comes to
the center of PG coil 5. When image write is performed, in the NTSC
system, 262 H (H means a horizontal line) are written in one track. The
switching point is set at a timing which is, e.g., 7 H earlier than
leading edge VS1 of vertical sync signal VS. Therefore, leading edge VS1
of vertical sync signal VS is written at angle O--O' shifted by .theta. {
360.degree..times.(7.262) from line O-Y as a switching point on magnetic
disk 1. As a result, the noise component generated at the switching point
is located near a corner of the read image and can be ignored in practice.
FIG. 2 is a plan view showing the structure of composite magnetic head 2
shown in FIG. 1. Composite magnetic head 2 can continuously read or write,
without moving, various information such as image information or digital
data and can erase written information as needed. In composite magnetic
head 2, first read/write gap R/W-1 and first erase gap E1 matched with
first track T1 are set apart by predetermined distance d1 along track T1
substantially along the relative movement direction of magnetic disk 1,
i.e., a magnetic recording medium. Second read/write gap R/W-2 and second
erase gap E2 matched with second track T2 are similarly set apart by
predetermined distance d2 along second track T2.
According to a method of manufacturing composite head 2 as described above,
a portion of 2-track read/write head 2A to the left of line Y--Y' and a
portion of 2-track read/write head 2B to the right of line Y--Y' are
arranged separately. These portions are joined together with crosstalk
preventing magnetic shielding member 2C sandwiched therebetween. Head 2
can be easily manufactured by this method.
Referring to FIG. 2, reference symbol P denotes a track pitch; W, a
read/write gap width; and Wb, an erase gap width. Composite magnetic head
2 is mounted on the apparatus housing such that the joint portion
sandwiching magnetic shielding member 2C is on line O-Y in FIG. 1. Then,
the four gaps, i.e., read/write gaps R/W-1 and R/W-2 and erase gaps E1 and
E2, are set to provide substantially the same head touch with respect to
the write side of disk 1.
In this manner, only one composite magnetic head 2 is needed, and
installation space is the same as for the conventional head in an
electronic camera or the like. When a read/write circuit (not shown) is
connected to head 2, read, write, and erase operations can be performed as
needed.
In the first embodiment shown in FIGS. 1 and 2, read/write gaps R/W-1 and
R/W-2 of composite magnetic head 2 are set off sideways from line Y--Y' by
distance
d2 (about 1/2 distance d1), thus from the switching point by distance d2.
When composite magnetic head 2 is moved in the radial direction of disk 1,
inclination angles of read/write gaps R/W-1 and R/W-2 with respect to
tracks T1, T2, . . . change, and the azimuth angles also change. In order
to prevent this, read/write gaps R/W-1 and R/W-2 must be inclined slightly
with respect to line Y--Y' in advance. However, with such an arrangement,
the positional relationship of gaps R/W-1 and R/W-2 with erase gaps E1 and
E2 becomes hard to control, making head manufacture difficult. In
composite magnetic head 2 shown in FIGS. 1 and 2, magnetic shielding
member 2C for preventing crosstalk is present at the head joint portion.
Therefore, distance d1 between read/write gaps R/W-1 and R/W-2 and erase
gaps E1 and E2 increases accordingly. It then becomes relatively difficult
to obtain optimal head touch.
FIGS. 3 and 4 show the schematic head arrangement and head structure
according to a second embodiment of the present invention, which includes
an improvement over the first embodiment described above. The overall
construction of the head according to the second embodiment is the same as
that of the first embodiment. However, in this embodiment, read/write gaps
R/W-1 and R/W-2 of composite magnetic head 6 are at the portion of head 6
most close to the recording medium (i.e., the "head center" and on line
Y--Y'. Erase gaps E1 and E2 are at positions shifted from read/write gaps
R/W-1 and R/W-2 to the upstream side by X (about 400 .mu.m, corresponding
to a time difference of about 1H of the video signal). The head touch is
on the recording medium on the recording medium is therefore optimal on
read/write gaps R/W-1 and R/W-2.
In this embodiment, the spacing loss is reduced and performance is improved
over the first embodiment. Erase gaps E1 and E2 provide poorer head touch
than read/write gaps R/W-1 and R/W-2. However, since gap width Wb is
larger than gap width Wa of read/write gaps R/W-1 and R/W-2, a slight
degradation in performance can be neglected. As will be described later,
the write operation is performed only once for each rotation of the disk.
However, the erase operation can be continuously performed over numerous
rotations of the disk. Therefore, the poor head touch of erase gaps E1 and
E2 can be compensated for.
In this embodiment, read/write gaps R/W-1 and R/W-2 are on line Y--Y'.
Therefore, when composite magnetic head 6 is moved in the radial direction
of disk 1, the inclination angles (azimuth angles) of gaps R/W-1 and R/W-2
with respect to the tracks do not change. Azimuth loss is thus prevented.
Since the azimuth angles of erase gaps E1 and E2 are not affected for the
reason described above, erase gaps E1 and E2 can be arranged substantially
parallel to read/write gaps R/W-1 and R/W-2. The head of the second
embodiment is therefore easier to manufacture than that of the first
embodiment.
In order to obtain good head touch, distance X between read/write heads
R/W-1 and R/W-2 and erase heads E1 and E2 is preferably at a minimum.
Thus, magnetic shielding member 6C at the joint portion between read/write
head section 6A and erase head section 6B is preferably as thin as
possible. However, with such an arrangement, crosstalk between read/write
gaps R/W-1 and R/W-2 and erase gaps E1 and E2 poses a problem. This can be
solved with suitable control of the write and erase timings by a control
system to be described later.
In general, a thin film head is considered to be preferable as a
multi-channel head with little crosstalk. A known read/write thin film
head is described in, e.g., "Thin film head for high-density recording
sheet", Denshi-Tsushingakkai, Giken-Hokoku, VR-63-8, (June 6, 1984) pp.
55-60. While a thin film read/write head can be manufactured, it is
difficult to manufacture a thin film erase head for assembly with the
read/write head. The reason for this is as follows. When a 7-MHz luminance
signal recorded on a metal disk having coercive force Hc.apprxeq.1,400 Oe
is erased at -40 dB, a magnetization of 2 ampere-turns or more is
required. However, it is difficult to increase the number of turns, and it
is also difficult to obtain a large cross-sectional coil area in a thin
film head. Thus, it is difficult to obtain a high ampere-turn. In order to
prepare a core for passing large magnetic fluxes, the cross-sectional area
of the core must be increased. However, in a thin film head, since the
core Is formed by sputtering or the like, manufacture of a core having a
large cross-sectional area is time-consuming and costly.
FIGS. 5 and 6 show the structure of a composite head according to a third
embodiment of the present invention made in consideration of the above
situation. As shown in FIG. 5, composite head 6 is mounted at an end of
mounting base 7, and the head coil is connected to printed circuit board 8
on base 7 through lead wires 9. Referring to FIG. 5, reference numeral 10
denotes a mount hole. In general, a sufficient space margin is not
available around the head. Therefore, small mounting base 7 having an area
of about 5.times.10 M mm.sup.2 is used.
FIG. 6 is a longitudinal sectional view of composite head 6. Thin film
read/write head section 6A is obtained in the following manner. A magnetic
material having a high saturation magnetic flux density such as sendust is
deposited by sputtering or the like on ferrite substrate 6-1 with polished
ends to a thickness of about several microns to provide lower core 6-2.
After insulating lower core 6-2 by SiO.sub.2 deposition, thin film coil
6-3 of copper or the like is formed for 5 to 10 turns by a processing
technique such as sputtering or a combination of deposition and etching.
SiO.sub.2 is sputtered thereover to a thickness of about 0.1 .mu.m to 0.2
.mu.m to form read/write gap section 6-4. Upper core 6-5 of the same
material as that of the lower core is formed on section 6-4 by sputtering
or the like, protective film 6-6 is formed thereover, and protective plate
6-8, is adhered thereon with adhesive glass 6-7. A bulk erase head section
6B is prepared in the following manner. Magnetic core 6-9 of sendust or
the like is joined with magnetic core 6-11 of the same material around
which coil 6-10 having 10 to 20 turns is wound to provide erase gap
section 6-12. Composite head 6 is obtained by integrally forming head
sections 6A and 6B. A magnetic shielding plate is preferably sandwiched
between sections 6A and 6B.
In composite magnetic head 6 of such a construction, since the thickness
from gap 6-4 to plate 6-8 in thin-film read/write head section 6A can be
set to be 30 .mu.m or less, the distance between the gaps can be
significantly reduced. Therefore, good head touch can be obtained at both
read/write gap section 6-4 and erase gap section 6-12. Even if read/write
head section 6A is formed for two channels along the widthwise direction
of tracks, since read/write head section 6A consists of a thin film,
crosstalk during signal read can be suppressed to about -40 dB. Section 6A
is therefore suitable for a multi-head structure and is easy to
manufacture. Since erase head section 6B is a conventional bulk head,
i.e., a head whose coil section is not made of thin films, a high current
can be easily flowed and a large magnetic flux can be generated.
Therefore, a luminance signal of about 7 MHz can be erased to a level of
-40 dB or less.
FIG. 7 is a block diagram showing the configuration of a control system for
performing write and erase operations using composite head 6. The
characteristic feature of the control system is that a PG pulse for
switching the write head is also used for switching the erase head. A
video signal from an imaging device such as a solid-state imaging element
or from an external TV signal generator is supplied to terminal 11, at the
left end of the drawing. The video signal is supplied to vertical sync
signal separator 12 and FM modulator 13. The video signal supplied to
vertical sync signal separator 12 is subject to separation only of
vertical sync signal VS, which is supplied to motor servo circuit 14. In
response to an FG pulse supplied as a rotational frequency signal from
disk drive motor 15, motor servo circuit 14 performs speed servo of motor
15 and keeps the speed of motor 15 at 3,600 rpm. Magnetic disk 1 is
mounted on the shaft of motor 15. The PG yoke mounted near the center of
disk 1 is detected by PG coil 5, and 60 PG pulses are sent per second. The
PG pulses are shaped by PG pulse detector 16, and supplied to motor servo
circuit 14 and to write/erase control circuit 17 to be described later. In
response to the vertical sync signal and PG pulse, motor servo circuit 14
performs motor phase servo so that the PG pulse and leading edge VS1 of
the vertical sync signal have a time difference of 7H (63.5
.mu.m.times.7).
After the video signal supplied to FM modulator 13 is FM modulated, it is
current-amplified by write amplifier 18 and supplied to excitation coils
21 and 22 corresponding to read/write gaps R/W-1 and R/W-2 of head 6
through switches 19 and 20.
An erase signal output from erase signal generator 23 comprising an
oscillator is current-amplified by erase amplifier 24 into an erase
current. The erase current is supplied to excitation coils 27 and 28
corresponding to erase gaps E1 and E2 of head 6 through switches 25 and
26.
The ON/OFF and selection control of switches 19, 20, 25, and 26 is
performed by control circuit 17. In response to an operation instruction
from operation instruction switch 29 (a release switch in the case of an
electronic camera), control circuit 17 is activated in synchronism with
the PG pulse and controls switches 19, 20, 25, and 26.
FIG. 8 is a timing chart showing the operation timing of the control system
shown in FIG. 7. Assume a case wherein vertical sync signal VS is supplied
every 1/60 sec and the PG pulse is input at a timing 7H before the leading
edge of signal VS, as shown in FIG. 8. When operation instruction switch
29 is turned on at time t1, control circuit 17 generates a control signal
at time t2 at which the first PG pulse is input. In response to the
control signal, switch 25 is turned on, and switch 26 assumes the state
shown in FIG. 7, i.e., it is switched to contact a side. Then, erasing by
erase gap E1 can be performed. In this example, erasing by erase gap E1 is
performed for a time interval corresponding to 2 rotations of disk 1. At
time t3, only switch 26 is switched to contact b side. Therefore, erasing
by erase gap E2 can be performed. When operation instruction switch 29 is
turned off at time t4, the erase operation ends after only 1 cycle (4
rotations of the disk) and the write operation is started. When a PG pulse
is input at time t5, the erase operation is ended, switch 19 is turned on
in response to an output from control circuit 17, and switch 20 is
switched to contact a side. Therefore, the write operation by read/write
gap R/W-1 can be performed for a time interval corresponding to one
rotation of disk 1. Switch 20 is switched to contact b side at time t6, at
which the next PG pulse is supplied. Then, the write operation by
read/write gap R/W-2 can be performed.
In this manner, erase and write can be performed for 6 fields (1/10 sec)
over 2 tracks. Since gaps E1 and R/W-1 and gaps E2 and R/W-2 are activated
with time differences, there is little crosstalk. Since not only
read/write gaps R/W-1 and R/W-2 but also erase gaps E1 and E2 are
controlled in synchronism with the PG pulse, dead time is not generated.
Since erasing is performed for at least a time interval corresponding to
one rotation of disk 1, a non-erased portion does not remain. The erase
cycle can be extended to a time interval corresponding to 2 rotations of
disk by shifting the timing for turning off operation instruction switch
29.
FIGS. 9 to 11 show a fourth embodiment of the present invention and
illustrate a case wherein read stepup transformers 31 and 32 are added to
the composite head apparatus in FIG. 5. As shown in FIGS. 9 to 11, two
read step-up transformers 31 and 32 are mounted through insulating layers
(not shown) for a 2 channel read operation on mounting base 7 having
composite head 6 fixed to one end thereof. Although not illustrated in
FIGS. 9 and 10 , magnetic shielding cases 33 and 34 are provided to cover
transformers 31 and 32 as shown in FIG. 11).
With the composite head apparatus having the above construction, the
distance from the head to transformers 31 and 32 is minimized, noise
pickup is reduced, and the S/N ratio is improved. Since the wiring
resistance is reduced to a minimum, frequency characteristics are
improved. Magnetic permeability .mu. of transformers 31 and 32 is
preferably high. In this example, transformers 31 and 32 have magnetic
permeability .mu.=500 at 10 MHz. When magnetic permeability .mu. is low,
the number of turns at the secondary windings in transformers 31 and 32
must be increased, thus degrading frequency characteristics.
FIG. 12 is a circuit diagram of the case wherein step-up transformers 31
and 32 are mounted. Since first and second channels 40 and 50 have an
identical structure, a description will be made only for first channel 40.
The parts of second channel 50 are designated by reference numerals 50 to
59 and a detailed description thereof will be omitted.
In the write mode, write information input at terminal 41 is supplied to
write amplifier 42, and the gate signal supplied to terminal 43 goes to
"H" level. Therefore, write transistor 44 is turned on. At this time,
since the gate signal of read transistor 45 is set at "L" level by
inverter 46, transistor 45 is OFF. The write information therefore flows
through coil 21 of the read/write head and transistor 44 and is written.
The primary winding coil of read step-up transformer 31 does not influence
the write operation.
In the read mode, the gate signal goes to "L" level. Therefore, write
transistor 44 is turned off, and read transistor 45 is turned on. The read
information obtained at coil 21 of the read/write coil is stepped up by
read step-up transformer 31 and is output from terminal 48 through read
amplifier 47. Since the output terminal of write amplifier 42 is
short-circuited by transistor 45, the write circuit does not influence the
read operation. In FIG. 12, reference numeral 49 denotes an erase signal
supply terminal. When the overall circuit shown in FIG. 12 is formed into
a hybrid IC and mounted on mounting base 7, the number of wiring layers to
be formed is reduced and the S/N ratio and frequency characteristics are
improved.
FIG. 13 shows bulk-type composite head 60 in a fifth embodiment of the
present invention. As shown in FIG. 13, in this bulk-type composite head
60, winding 63 and magnetic cores 61 and 62 of sendust or the like
constitute bulk-type read/write head section 60A with gap 64. Similarly,
winding 67 and magnetic cores 65 and 66 of sendust or the like constitute
bulk-type erase head section 60B. Two sections 60A and 60B are joined and
fixed with magnetic shielding member 69 sandwiched therebetween. Winding
63 of read/write head section 60A has about 10 turns and can flow a write
current of about 50 to 70 mA. Winding 67 of erase head section 60B has
about 10 to 20 turns and can flow an erase current of about 100 to 200 mA.
In bulk-type composite head 60 in FIG. 13, a conventional bulk head
manufacturing technique can be directly utilized, and manufacture is thus
easy. When a multi-head is to be obtained, however, crosstalk in the read
mode is higher than in the composite heads described above. If such a
multi-head is used in combination with the crosstalk removing circuit to
be described below, crosstalk can be suppressed to a satisfactory level.
FIG. 14 is a circuit diagram showing crosstalk removing circuit 70. In FIG.
14, reference symbol SW0 denotes a write mode head selection switch which
selects one of first and second read/write heads 71 and 72. Reference
symbols SW1 and SW2 denote read/write switches for first and second
read/write heads 71 and 72; the solid lines correspond to the write side
and the broken lines correspond to the read side. Reference symbol SW3
denotes a read mode head selection switch; the solid line corresponds to
first head 71 and the broken line corresponds to second head 72. Reference
symbol SW4 denotes a read signal selection switch as a crosstalk
countermeasure. When switch SW3 selects first read/write head 71, switch
SW4 selects the second read/write head. However, when switch SW3 selects
second read/write head 72, switch SW4 selects first read/write head 71.
Crosstalk removing circuit 70 described above operates in the following
manner. In the write mode, switches SW0, SW1, and SW2 are set as indicated
by the solid lines. When a write signal is supplied to terminal 73, it is
FM modulated by FM modulator 74, amplified by write amplifier 75, and
supplied to and written by first read/write head 71 through switches SW0
and SW1. When switch SW0 is switched as indicated by the broken line, the
write signal is supplied to and written by second head 72 through switch
SW2. In the read mode, switches SW1 and SW2 are switched as indicated by
the broken lines. When the read operation by first read/write head 71 is
performed, switches SW3 and SW4 are set as indicated by the solid lines.
The read signal picked up by first read/write head 71 is supplied as one
input of differential amplifier 77 through switch SW1, read amplifier 76,
and switch SW3. The signal from differential amplifier 77 is demodulated
by FM demodulator 78 and output from terminal 79. The read signal picked
up by second read/write head 72 is supplied to voltage divider 81 through
switch SW2 and read amplifier 80, divided thereby into a signal voltage of
a predetermined ratio, and supplied as the other input to differential
amplifier 77 through switch SW4. Therefore, differential amplifier 77
produces a difference signal between the read signal from the first
read/write head and the voltage-divided signal of the read signal from
second read/write head 72. As a result, the crosstalk component is
cancelled in the signal from differential amplifier 77, and the signal is
output as a final read signal. When the read output from second read/write
head 72 is extracted, switches SW3 and SW4 are switched to the side
indicated by the broken lines. Then, the difference between the read
signal from second read/write head 72 and the read signal from first
read/write head 71 is obtained, and the crosstalk component is cancelled
in the same manner as described above.
FIGS. 15 to 22 show a sixth embodiment of the present invention, wherein a
hybrid IC is mounted on a base.
FIG. 15 is an equivalent circuit diagram of noise in a head-read amplifier
system including a step-up transformer. Referring to FIG. 15, reference
symbol Lh denotes the inductance of head H; Rh, the resistance of head H;
Lp, the inductance of the primary winding of step-up transformer T; Rp,
the resistance of the primary winding of step-up transformer T, Ls, the
inductance of the secondary winding of step-up transformer T; and Rs, the
resistance of the secondary winding of step-up transformer T. Reference
symbol Eh denotes the head output voltage; Enh, the thermal noise of Rh;
Enp, the thermal noise of Rp; Ens, the thermal noise of Rs; Ena and Enb,
the noise voltages of differential input read amplifier 90; and Ina and
Inb, the noise currents of differential input read amplifier 90.
In order to obtain a head-read amplifier system with a good S/N ratio, all
noise must be reduced, and the turn ratio Ns/Np of step-up transformer T
must be increased. When the read amplifier receives differential inputs
rather than a single input, En is doubled and In is halved. The input
capacitance (not shown) is also halved. When the step-up ratio, i.e., the
turn ratio Ns/Np is increased, the values of Is and Rs are increased and
considerable noise is generated by the flowing of In. However, in the case
of differential inputs, since In is halved, the above effect is minimized.
Ci is also halved to obtain a high band. Therefore, the read amplifier
comprises a differential input amplifier and its input elements, and
operation conditions are set so that En is small and In is large (En and
In are inversely proportional), e.g., by using a transistor.
FIG. 16 shows the principle of the embodiment based on this arrangement. In
the read mode, read/write switch 91 is OFF and read/write switch 92 is ON.
A write signal is supplied to coil 21 of read/write head R/W-1 through
write amplifier 93 consisting of amplifier 93c and reverse-parallel
connected diodes 93a and 93b. In the read mode, read/write switches 91 and
92 are turned off. A read voltage induced at coil 21 is stepped up by
stepup transformer 31, and amplified by differential input amplifier 90.
FIG. 17 is a circuit diagram showing the circuit configuration of this
embodiment. In FIG. 17, reference numeral 100 denotes a read/write switch
circuit having two transistors corresponding to read/write switches 91 and
92 described above. Read/write switch circuit 100 consists of four
transistors 101, 102, 103, and 104, and inverter 105. Reference symbols 8a
to 8u denote terminals. When a signal of "H" level is input from terminal
8i in the write mode, the "H" level signal is directly supplied to the
bases of transistors 102 and 104, and is inverted by inverter 105 to an
"L" level signal which is supplied to the bases of transistors 101 and
103. Therefore, transistors 102 and 104 are turned on, and transistors 101
and 103 are turned off. When an "L" level signal is supplied from terminal
8i in the read mode, transistors 101 and 103 are turned on and transistors
102 and 104 are turned off, in the opposite manner to the case described
above.
The portions surrounded by the dotted lines in FIG. 17, i.e., differential
input amplifiers 90A and 90B, write amplifiers 93A and 93B, and read/write
switch circuit 100, are formed into a hybrid IC and mounted on a head
base.
FIG. 18 shows the mounting state of the hybrid IC and is a plan view taken
from the rear side of base 7. Two read/write heads and two erase heads are
assembled in head chip 6. Reference symbols 8a to 8u denote conductive
films of copper or the like. Circle marks attached to the conductive films
indicate through holes, and electrically connect the conductive films on
the front and rear sides of base 7. Conductive films 8a, 8b, 8p, and 8q
serve as erase current input terminals; 8r and 8u, write current input
terminals; 8s and 8t, read output terminals; and 8i, a read/write signal
input terminal.
FIGS. 19 and 20 also show the mounting state of the hybrid IC and are a
plan view and a side view taken from the front side of base 7. Reference
numerals 31 and 32 in FIGS. 19 and 20 denote step-up transformers
described above, having respective primary windings connected to terminals
8f, 8h, 8j, and 8i, and respective secondary windings connected to
conductive films 8c, 8d, 8n, and 8o.
A material having a high magnetic permeability is selected as a core
material for step-up transformers 31 and 32 so that a high inductance is
obtained with a small number of turns. Then, the influence of noises Enp
and Ens described with reference to FIG. 15 can be reduced. For example,
when the primary winding has 5 turns and the secondary winding has 25
turns, a good result can be obtained. With a read amplifier which has an
input capacitance of 10 pF in a single input mode, it can provide an input
capacitance of 5 pF in the differential input mode. As a result, the
resonant frequency of the input capacitance 5 pF and the inductance 35
.mu.m as viewed from the secondary windings of step-up transformers 31 and
32 beco | | |
