JP2845322B2 - Magnetic head drive circuit in magnetic field modulation overwrite method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a magnetic head drive circuit in a magnetic field modulation overwrite system.

[0002]

2. Description of the Related Art When a magnetic head is driven at a constant voltage, the impedance increases in proportion to the driving frequency due to the inductance of the magnetic head coil. Therefore, as the magnetic head is driven at a higher speed, a higher voltage and higher power are required.

As a drive method for solving this problem, a magnetic head drive circuit in a magnetic field modulation overwrite method using a constant current effect of inductive reactance is reported in Technical Report VIR90-14 of the Institute of Television Engineers of Japan.

FIG. 23 is a circuit diagram of a magnetic head drive circuit in the magnetic field modulation overwrite method, and FIG. 24 is an operation waveform diagram of each part of the drive circuit.

This circuit 100 includes inductors 101 and 102,
The switching device includes switching elements 103 and 104 and a magnetic head coil 105.

[0006] One ends of the inductors 101 and 102 are commonly connected to a power supply (voltage + V). The other end of the inductor 101 is grounded via the switching element 103, and the inductor 10
The other end of 2 is grounded via a switching element 104.

The other ends of the inductors 101 and 102 are interconnected via a magnetic head coil 105.

In this circuit configuration, the switching element 103 is turned off from the state where the switching element 103 is turned on and the switching element 104 is turned off, and the switching element 1 is turned off.
When the switch 04 is turned on, the current from the power supply is not transmitted to the inductor 101, and back electromotive force is generated (FIG. 24D).

From the inductor 101 to the switching element 103
The current flowing through the inductor 101 continues to flow from the inductor 101 through the magnetic head coil 105 and the switching element 104 due to the constant current effect of the inductive reactance of the inductor 101 (FIG. 24c).

On the other hand, the current flowing through the inductor 102 flows through the switching element 104 (FIG. 24b).

When the switching element 103 is turned off and the switching element 104 is turned on and the switching element 103 is turned on and the switching element 104 is turned off, the current from the power source is supplied to the inductor 102. The transmission is lost and a back electromotive force is generated (FIG. 24).
e).

From the inductor 102 to the switching element 104
The current flowing through the inductor 102 continues to flow from the inductor 102 through the magnetic head coil 105 and the switching element 103 due to the constant current effect of the inductive reactance of the inductor 102 (FIG. 24c).

On the other hand, the current flowing from the inductor 101 through the magnetic head coil 105 and the switching element 104 continues to flow from the inductor 101 through the switching element 103 (FIG. 24A).

Thus, each switching element 103,
The direction of the current flowing through the magnetic head coil 105 can be switched (inverted) at a high speed by alternately turning on and off the 104 at a high speed.

If the inductance values of the inductors 101 and 102 are selected to be sufficiently larger than the inductance value of the magnetic head coil 105, the driving current value is the power supply voltage, the internal resistance of the inductors 101 and 102, and the magnetic head coil. Internal resistance of 105 and switching element 103,1
The resistance of the magnetic head coil 105 is not affected by the on-resistance of the magnetic head coil 04.

Therefore, when the power supply voltage is low, the magnetic head can be driven at high speed with low power by using a switching element having a small on-resistance.

[0017]

However, since the switching element generally has a capacitance, when the switching element is switched from on to off, the mutual capacitance between the capacitance of the switching element and the inductance of the magnetic head coil is reduced. As a result, a transient current having an excessive overshoot is generated in the drive current as shown in FIG. 24C, and the inversion time characteristic is impaired.

Further, when the switching elements are controlled by the modulation signal, the maximum value of the drive current varies according to the time interval from ON to OFF and from OFF to ON of each switching element.

In the magnetic field modulation overwriting of the magneto-optical disk, the generation of a transient current with an excessive overshoot and the fluctuation of the maximum value of the driving current of the magnetic head coil are directly reflected on the magnetic field intensity, so that the recording characteristics deteriorate. This can cause

Further, the temperature of the magnetic head coil and the switching element is raised, the magnetic field generation efficiency of the magnetic head coil is reduced, the characteristics of the switching element are deteriorated, and the power consumption is increased.

The present invention has been made to solve such a problem, and has a magnetic field modulation overwrite system having means for controlling the overshoot of the drive current to an appropriate amount without changing the maximum value of the drive current. It is an object of the present invention to provide a magnetic head drive circuit.

[0022]

In order to solve the above-mentioned problems, a magnetic head drive circuit in a magnetic field modulation overwrite system according to the present invention has an inductor or a switching element connected in parallel with an element including a resistor or a resistor. .

By selecting a resistance value according to the inductance value of the inductor coil or the switching element, the overshoot of the drive current is suppressed to an appropriate amount and the maximum value of the drive current is kept constant.

[0024]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a circuit diagram of a magnetic head drive circuit in a magnetic field modulation overwrite method according to a first embodiment of the present invention, and FIG. 2 is an operation waveform diagram of each part of the drive circuit.

A magnetic head drive circuit (hereinafter, referred to as a magnetic head drive circuit) 1 in the magnetic field modulation overwrite system includes inductors 2 and 3, switching elements 4 and 5, resistors 6 and 7, and a magnetic head coil 8.

One ends of the inductors 2 and 3 are commonly connected to a power supply. The other end of the inductor 2 is grounded via the switching element 4, and the other end of the inductor 3 is grounded via the switching element 5.

The other ends of the inductors 2 and 3 are interconnected via a magnetic head coil 8.

Up to now, the circuit configuration is the same as the conventional circuit configuration. However, in the circuit shown in FIG. 1, resistors 6 and 7 are connected in parallel to the inductors 2 and 3, respectively.

These resistors 6 and 7 are connected to the magnetic head coil 8
In order to suppress the overshoot of the driving current, the resistors 6 and 7 are hereinafter referred to as damping resistors.

That is, by selecting an appropriate value of the damping resistance according to the inductance value of the magnetic head coil 8, the overshoot can be suppressed to an appropriate amount without impairing the high-speed inversion time characteristic of the drive current. In addition, the maximum value of the drive current can be kept constant (see FIG. 2).
c).

For example, when the inductance value of the magnetic head coil 8 is 2.5 μH, the value of the damping resistance is 1
Around 00Ω is appropriate.

The damping resistors 6 and 7 absorb a part of the back electromotive force generated when the switching element 4 or 5 changes from on to off, and reduce the inductance of the magnetic head coil and the capacitance of the switching element. (FIG. 2f, g).

Although one end of each of the resistors 6 and 7 is connected to the power supply in FIG. 1, it may be grounded as shown in FIG.

FIG. 4 shows a specific example of a driving device using this magnetic head driving circuit, and FIG. 5 shows the relationship between a magnetic head driven by the driving device and a magneto-optical disk.

The driving device 9 includes a waveform shaping circuit 10, an antiphase signal generating circuit 11, and a level shift signal generating circuit 12
And the magnetic head drive circuit 1 are connected in this order.

The waveform shaping circuit 10 uses a Schmitt trigger circuit or the like and has a characteristic having hysteresis.

The waveform shaping circuit 10 is used to shape the modulated signal input from the input terminal 10a as a pulse train signal, that is, a digital signal with the terminating resistor 13 as a reference.

The anti-phase signal generation circuit 11 has one input terminal 1
1a and two output terminals 11b and 11c, and outputs a non-inverted signal and an inverted signal to the output terminal 11 according to the state of the signal applied from the waveform shaping circuit 10 to the input terminal 11a.
b and 11c.

The level shift signal generation circuit 12 converts the output logic voltage range (0 to 5 V) of the reverse phase signal generation circuit 11 into a different logic voltage range.

In this embodiment, a two-input type NAND circuit 12 is used.
a, 12b, the signal applied to one of the input terminals 12c, 12d is fixed at H level, and the other input terminals 12e, 12f are fixed.
The inverted output corresponding to the signal applied to the output terminals 12g, 1
Although the output inversion type level shift signal generation circuit obtained from 2h is shown, it may be a non-inversion type level shift signal generation circuit.

The terminal 12i is a power supply terminal for logic operation, the terminal 12j is an output voltage application terminal, and 12k is a ground terminal.

The level shift signal generating circuit may be constituted by using an FET or a transistor switch without using a gate circuit or the like.

The switching elements 4 and 5 of the magnetic head drive circuit 1 are FETs having the source S as a common terminal.
(Q1, Q2) is used.

FET (Q1) as switching element 4
Is connected to the power supply + V via the inductor 2 and the resistor 6 connected in parallel, the output signal of the NAND circuit 12a is applied to the gate G, and the source S is grounded.

Similarly, the FET which is the switching element 5
The drain D of (Q2) is connected to the power supply + V via the inductor 3 and the resistor 7 connected in parallel, the output signal of the NAND circuit 12b is applied to its gate G, and its source S
Is grounded.

With the configuration described above, when a modulation signal input is applied, the driving device 9 turns on / off the FETs (Q1, Q2) at timings corresponding to the time intervals of the input pulses to generate a modulation magnetic field.

The magnetic field modulation overwrite method is configured as shown in FIG. 5 and always irradiates a laser beam 14 of a constant intensity to invert the magnetization of the recording surface of the magneto-optical disk 15 in accordance with the modulation magnetic field to overwrite. Write.

In FIG. 5, reference numeral 16 denotes a laser pickup, 17 denotes a spindle motor, and the distance between the magnetic head and the magneto-optical disk is 100 μm or more.

FIG. 6 shows that the inductance values of the inductors 2 and 3 constituting the magnetic head drive circuit 1 are 100 μH, the resistance values of the damping resistors 6 and 7 are 100Ω, and the magnetic head coil 8
Are 2.5 μH, and FETs (model number 2SK310) Q1 and Q2 are used as switching elements 4 and 5.
7 is a graph showing the magnetic field reversal speed characteristics shown in comparison with the case where the inductance value of the magnetic head coil 8 when 1.2 is used is 1.2 μH.

Here, the vertical axis indicates the magnetic head drive current reversal speed, and the horizontal axis indicates the drive current.

When a magnetic head using a coil having an inductance value of 2.5 μH is driven at ± 0.8 A, it can be seen that good characteristics with a rise and fall time of about 37 ns can be obtained.

FIG. 7 shows an FET having the same configuration as the above.
(Model name 2SK310) Output capacity of Q1 and Q2 is 100p
A graph showing an appropriate damping resistance value obtained by simulation and experiment as F is shown.

Here, the vertical axis indicates the damping resistance value, and the horizontal axis indicates the inductance of the magnetic head coil.

FIGS. 8 and 9 are current waveform diagrams of the magnetic head (drive frequency: about 420 kHz, duty: 50%).

FIG. 8 shows an inductance value of the magnetic head coil of 2.5 μH, an inductance value of the inductor of 100 μH,
FIG. 9 shows a waveform under the condition that the resistance value of the damping resistor is 100Ω, and FIG. 9 shows a waveform under the same condition as FIG.

From these figures, it can be seen that overshoot and undershoot at the edge are improved by connecting the damping resistor.

FIGS. 10 and 11 are waveform diagrams of a magnetic head drive current when the magnetic head is driven by an EFM signal used in a compact disk (CD) (referred to as a CD transfer rate). FIG. With resistance,
FIG. 11 shows a case without a damping resistor.

From these figures, it can be seen that the transient current can be suppressed by providing the damping resistor even for the pulse period (about 700 ns to 2.5 ms) of the EFM signal.

Here, the inductance value of the magnetic head coil, the inductance value of the inductor, and the resistance value of the damping resistor are the same as those in FIG.

FIG. 12 is a circuit diagram of a magnetic head drive circuit in a magnetic field modulation overwrite system according to a third embodiment of the present invention, and the same parts as those in the first and second embodiments are denoted by the same reference numerals.

In the third embodiment, a damping resistor 18 is provided in parallel with the magnetic head coil 8 instead of providing the damping resistors 6 and 7 in parallel with the inductors 2 and 3 as in the first embodiment.

FIGS. 13 to 18 show a drive circuit in which the magnetic head coil is divided into two systems by using bifilar winding, and an inductor and a damping resistor are added. The description is omitted.

In order to obtain a magnetic field of N or S pole applied to the recording surface of the magneto-optical disk, the switching circuit 4 and 5 are alternately turned on and off in the circuit constituted by the above-described one-system magnetic head coil. While the direction of the current flowing through the head coil 8 is switched, in a circuit using a bifilar winding, the switching elements 4 and 5 are alternately turned on and off to respectively change the magnetic head coils 8-1 and 8-. 2 by passing a current through only one of them.

Therefore, in the circuit using the bifilar winding, the direction of the drive current may be the same, and the reversal of the polarity of the magnetic field can be performed only by on / off control of the switching element. Power consumption can be reduced to about half.

Further, since an inductor and a damping resistor are added to this drive circuit, as shown in FIG. 21, these can suppress an excessive current without impairing the inversion time characteristic of the magnetic head drive circuit, Transient characteristics of the head drive current can be improved.

FIG. 19 is a magnetic head drive current characteristic diagram in a conventional circuit having no inductor and damping resistance, and FIG. 20 is a magnetic head drive current characteristic diagram when an inductor is added to this conventional circuit.

At this time, the inductance value of the magnetic head coil is 2.5 μH, and the inductance value of the inductor is 10 μH.
0 μH, and the resistance value of the damping resistor is 150Ω.

Further, as shown in FIGS. 22A to 22F, a series connection of a resistor (Rd) and a capacitor (C), a resistor (Rd) and a coil (L) are substituted for the damping resistor.
Or a resistor (Rd) and a diode (D) connected in series.

[0069]

Since the magnetic head drive circuit in the magnetic field modulation overwrite method according to the present invention has the above-described configuration, the following effects can be obtained by selecting a resistor having an appropriate value according to the inductance value. Play.

(1) The overshoot of the magnetic head can be suppressed to an appropriate amount. Further, the overshoot amount can be set arbitrarily.

(2) The maximum value of the drive current of the magnetic head coil can be made constant, and the transient characteristics are greatly improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a magnetic head drive circuit in a magnetic field modulation overwrite method according to a first embodiment.

FIG. 2 is an operation waveform diagram of each part of a magnetic head drive circuit in the magnetic field modulation overwrite method according to the first embodiment.

FIG. 3 is a circuit diagram of a magnetic head drive circuit in a magnetic field modulation overwrite method according to the first embodiment.

FIG. 4 is a specific example using a magnetic head drive circuit in a magnetic field modulation overwrite method.

FIG. 5 is a diagram showing a relationship between a magnetic head and a magneto-optical disk.

FIG. 6 is a graph showing magnetic field reversal speed characteristics.

FIG. 7 is a graph showing an appropriate damping resistance value.

FIG. 8 is a current waveform diagram of the magnetic head of the first embodiment.

FIG. 9 is a current waveform diagram of a conventional magnetic head.

FIG. 10 is a waveform chart of a CD transfer rate according to the first embodiment.

FIG. 11 is a waveform diagram of a conventional CD transfer rate.

FIG. 12 is a circuit diagram of a magnetic head drive circuit in a magnetic field modulation overwrite method according to a third embodiment.

FIG. 13 is a circuit diagram of a magnetic head drive circuit when the magnetic head coil is wound by bifilar.

FIG. 14 is a circuit diagram of a magnetic head drive circuit when the magnetic head coil is wound by bifilar.

FIG. 15 is a circuit diagram of a magnetic head drive circuit when the magnetic head coil is wound by bifilar.

FIG. 16 is a circuit diagram of a magnetic head drive circuit when the magnetic head coil is wound by bifilar.

FIG. 17 is a circuit diagram of a magnetic head drive circuit when the magnetic head coil is wound by bifilar.

FIG. 18 is a circuit diagram of a magnetic head drive circuit when the magnetic head coil is wound by bifilar.

FIG. 19 is a characteristic diagram of a magnetic head drive current when there is no inductor and no damping resistance.

FIG. 20 is a diagram showing a magnetic head driving current characteristic when an inductor is added.

FIG. 21 is a diagram showing a magnetic head drive current characteristic when an inductor and a damping resistor are added.

FIG. 22 shows an alternative example of a damping resistor.

FIG. 23 is a circuit diagram of a magnetic head drive circuit in a conventional magnetic field modulation overwrite method.

FIG. 24 is an operation waveform diagram of each part of a magnetic head drive circuit in a conventional magnetic field modulation overwrite method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Magnetic head drive circuit, 2, 3 ... Inductor, 4, 5 ... Switching element, 6, 7, 13, 18 ... Resistance, 8 ... Magnetic head, 9 ... Drive circuit, 10 ... Waveform shaping circuit, 10a,
11a: input terminal, 11: phase difference signal generation circuit, 11
b, 11c, 12g, 12h: output terminals, 12: timing signal generation circuit, 14: laser light, 15: magneto-optical disk, 16: laser pickup, 17: spindle motor.

Claims (1)

(57) [Claims] A magnetic head disposed on a recording surface of a magneto-optical disk; an inductor having one end connected to a power supply and the other end connected to a coil of the magnetic head; and an inductor connected to a coil of the magnetic head. In a magnetic head drive circuit in a magnetic field modulation overwrite system configured to alternately turn on and off the pair of switching elements to generate a modulation magnetic field, the inductor, or A magnetic head drive circuit in a magnetic field modulation overwrite method, wherein an element including a resistor or a resistor is connected in parallel to a switching element.