Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
2001-09-10
2002-07-30
Neyzari, Ali (Department: 2653)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C360S059000
Reexamination Certificate
active
06426923
ABSTRACT:
TECHNICAL FIELD
The present invention relates to magnetic recording devices for recording information on recording media with use of magnetism, such as optomagnetic disk drives, hard disk drives, etc., and more particularly to a magnetic head drive circuit for use in the magnetic recording device. Stated more specifically, the present invention relates to improvements in the switching characteristics of a switch circuit for changing the direction of the current to be passed through the field coil of a magnetic head.
BACKGROUND ART
The magnetic recording device is adapted to convert information to a recording signal which is a digital voltage signal and to hold a recording medium magnetized in directions corresponding to the recording signal to record the information on the medium. The device comprises a magnetic head for setting up a magnetic field on the recording medium, and the magnetic head has a field coil for producing the magnetic field from current. The magnetic recording device further comprises a magnetic head drive circuit for energizing the field coil and changing the direction of the current for energizing the field coil based on the recording signal.
FIG. 4
is a diagram showing a conventional magnetic head drive circuit. The magnetic head drive circuit
100
comprises a control circuit
110
for producing a control signal based on a recording signal, and a switch circuit
120
for changing the direction of current for energizing a field coil
101
based on the control signal received from the control circuit
110
. The switch circuit
120
comprises switch elements for turning on or off a current path based on the control signal received from the control circuit
110
.
The switch elements to be used in the magnetic head drive circuit are preferably those which are short in switching time taken for a change of the current state to an on state or off state after the reception of the control signal from the control circuit. For this reason, FETs (field-effect transistors) are used specifically as illustrated.
There are two types of FETs: the N-channel type and the P-channel type. The Nch (channel) FET is such that the drain is connected to the high potential side and the source to the low potential side. The transistor conducts, permitting current to flow from the drain to the source, when the voltage between the gate and the source (hereinafter referred to as “gate voltage”) rises beyond a threshold voltage. When the gate voltage drops below the threshold voltage, the transistor is brought out of conduction to block the passage of current. On the other hand, the Pch FET is such that the source is connected to the high potential side, and the drain to the low potential side. The transistor conducts when the gate voltage drops below the threshold voltage, permitting current to flow from the source to the drain. When the gate voltage rises above the threshold voltage, the transistor is brought out of conduction to block the passage of current.
To obtain a stabilized gate voltage, it is desirable to use the Nch FET which is connected at the source to the low potential side in the case where the potential at the low potential side is stable. In the case where the high potential side is stable, the Pch FET is preferable to use which is connected to the high potential side at its source.
Accordingly, the switch elements connected to a power source terminal
102
of positive potential as shown in
FIG. 4
are preferably Pch FETs, while the switch elements connected to a ground terminal
103
are preferably Nch FETs.
With reference to the magnetic head drive circuit of
FIG. 4
, the power source terminal
102
of positive potential Vd is connected to the sources S of first and second Pch FETs
121
,
122
. The drain D of the first Pch FET
121
is connected to one end of the field coil
101
and the drain of a first Nch FET
123
. The drain of the second Pch FET
122
is connected to the other end of the field coil
101
and the drain of a second Nch FET
124
. The sources of the first and second Nch FETs
123
,
124
are connected to the ground terminal
103
. In this way,the switch elements arranged on sides of an electric path surrounding a rectangle, the power from the power source is supplied between two nodes
125
,
126
on one pair of opposed sides, and the field coil
101
is connected between two nodes
127
,
128
on the other pair of opposed sides. The circuit thus constructed is generally termed a “bridge circuit.”
The control circuit
110
comprises amplifiers
111
,
112
for amplifying recording signals and recording signals as inverted, respectively. Power is supplied to the amplifiers
111
,
112
from the power source terminal
102
. The first amplifier
111
receives the recording signal, amplifies voltage of high (H) level to Vd volts and feeds the resulting voltage to the first Pch and first Nch FETs
121
,
123
. The second amplifier
112
receives the recording signal as inverted, amplifies voltage of high (H) level to Vd and feeds the resulting voltage to the second Pch and second Nch FETs
122
,
124
.
When the control circuit
110
of the magnetic head drive circuit
100
thus constructed receives a recording signal of H level, the first amplifier
111
applies voltage of H level to the gates of the first Pch and first Nch FETs
121
,
123
, and the second amplifier
112
applies voltage of L level to the gates of the second Pch and second Nch FETs
122
,
124
. This brings the first Pch FET
121
and the second Nch FET
124
out of conduction, and the second Pch FET
122
and the first Nch FET
123
into conduction. Accordingly, current can be passed from the power source terminal
102
to the ground terminal
103
via the second Pch FET
122
, the field coil
101
and the first Nch FET
123
. The current flows through the field coil
101
in the direction of arrow A.
Next, when the control circuit
110
receives a recording signal of L level, the first amplifier
111
applies voltage of L level to the gates of the first Pch and first Nch FETs
121
,
123
, and the second amplifier
112
applies voltage of H level to the gates of the second Pch and second Nch FETs
122
,
124
. This brings the first Pch FET
121
and the second Nch FET
124
into conduction, and the second Pch FET
122
and the first Nch FET
123
out of conduction. Accordingly, current can be passed from the power source terminal
102
to the ground terminal
103
via the first Pch FET
121
, the field coil
101
and the second Nch FET
124
. The current flows through the field coil
101
in the direction of arrow B.
Thus, the direction of the current through the field coil
101
can be changed by the magnetic head drive circuit
110
of the construction described in accordance with the voltage level of the recording signal.
However the conventional construction has the following problem.
While the current (hereinafter referred to as “head current”) flowing through the field coil
101
is given the desired value for the magnetic head to set up a magnetic field of desired intensity on the recording medium, it is desired that the period during which the magnetic field retains the desired intensity be longer. For this purpose, it is desirable that the switching FETs
121
,
122
,
123
,
124
of the magnetic head drive circuit
100
can be changed over rapidly. However, the Pch FET is greater than the Nch FET in the time constant of charging or discharging at the gate. Accordingly, the period Tp taken for the Pch FETs
121
,
122
to change the on-off state thereof after the reception of the control signal until the gate is charged or discharged past the threshold voltage for the change is longer than the corresponding period Tn taken for the Nch FETs. Accordingly, the head current will not become the desired value during the period T
1
from the change of on-off state of the Nch FETs until the change of on-off state of the Pch FETs. As a result, the period TO becomes shorter during which the head current is given the desired value ±I
1
.
An object of the present invention
Armstrong Westerman & Hattori, LLP
Neyzari Ali
Sanyo Electric Co,. Ltd.
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