JPH04295603A - magnetic head drive circuit - Google Patents

Abstract

PURPOSE:To reduce the counter electromotive force produced at the time of switching electric currents so as to improve the withstand voltage and saturation margins of transistors constituting an amplifier by providing a time constant circuit which relieves changes in control signals between a differential amplification type write amplifier for driving magnetic heads and a prestage circuit which forms the control signal of the write amplifier. CONSTITUTION:Data are written on a disk in such a way that the direction of the electric current made to flow to a magnetic head is decided by giving in advance an input signal D and its opposite phase signal D' corresponding to write data to a transistor pair Q1 and Q2 constituting a drive circuit and signals (d) and d' which are obtained by level-shifting the signals D and D' to another transistor pair Q3 and Q4 so as to complementarily switch the transistor pairs Q1 and Q2 and Q3 and Q4 and to turn on a transistor Q6 by changing a signal (a) to a high level and a magnetic field is generated corresponding to the direction of the current flowing to the magnetic head by making an electric current flow to a write amplifier 10. When such a constitution is used, the switching speed of the transistor Q6 is reduced by providing a time constant circuit to the output node of a drive control circuit 20 which gives driving timing to the amplifier 10.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a semiconductor integrated circuit technology and a technology that is particularly effective when applied to a magnetic head drive circuit, such as a structure of a head drive section of a semiconductor integrated circuit for recording and reproducing in a magnetic disk drive. Concerning techniques that can be used effectively.

0002

2. Description of the Related Art FIG. 4 shows a write amplifier for writing that constitutes a head drive circuit of a recording and reproducing IC (semiconductor integrated circuit) in a magnetic storage device such as a hard disk driver or a floppy disk driver, particularly in a magnetic disk device. It is shown. That is, the light amplifier 10 is
Bipolar transistors Q1 and Q2 are connected in a pair between read/write terminals A and B, to which power supply voltage Vcc and inductance load L are connected, and terminal A.
, B and constant current source CC0, transistors Q3 and Q4 are similarly connected to each other in a pair. and,
An inductance load L constituting a magnetic head such as a thin film head is externally connected between the terminals A and B. Complementary write data signals D, D' and d, d' are applied to base terminals of transistors Q1, Q2 and Q3, Q4, respectively. Signals d and d' are level-shifted signals of D and D'. As a result, when the write data signal changes, transistors Q1 and Q2 and Q3 and Q4 are switched in a complementary manner to change the direction of the current i flowing to the head, and due to the accompanying reversal of the magnetic field, Data is written. An example of an invention related to a magnetic head drive circuit is Japanese Patent Application No. 60-95498.

0003

SUMMARY OF THE INVENTION In magnetic head drive circuits, increasing the writing speed is an issue. In conventional magnetic head drive circuits, in order to increase the speed of writing, it is necessary to increase the switching speed of the current switch that makes up the write amplifier, but if the switching speed of the current switch is too fast, the current switching speed will be reduced. Initially, a relatively large back electromotive force is generated across the head L, and the transistors Q1 and Q2 forming the write amplifier
There is a risk that the base and emitter of the transistors will be reverse biased and cause PN junction breakdown.
There was a problem in that the collector potential of the transistor No. 4 became lower than the base potential, causing the transistor to become saturated and the operating speed to slow down.

An object of the present invention is to control the switching speed of the current switch of the write amplifier in the magnetic head drive circuit to an appropriate speed, thereby improving the withstand voltage margin and saturation margin of the transistors constituting the write amplifier. . The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[0005]

[Means for Solving the Problems] Representative inventions disclosed in this application will be summarized as follows. That is, a time constant circuit is provided between the differential amplification type write amplifier for driving the magnetic head and the preceding stage circuit that forms the control signal, so as to make the change in the control signal gradual.

[0006]

[Operation] According to the above-mentioned means, since the control signal of the light amplifier changes slowly, the current switching speed of the current switch constituting the light amplifier becomes slow.
The above object of improving the withstand voltage margin and saturation margin of the transistors constituting the write amplifier can be achieved by reducing the back electromotive force generated when the current is switched.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of a magnetic head drive circuit according to the present invention. The circuit of this embodiment is formed on a silicon single crystal semiconductor substrate by known monolithic integrated circuit technology.

A write amplifier 10 as a write circuit of this embodiment includes a pair of transistors Q1 and Q2 connected between a pair of read/write terminals A and B to which a power supply voltage Vcc and an inductance load L are connected; - Consists of a transistor pair Q3, Q4 connected between write terminals A, B and constant current source CC1. Also,
A switch transistor Q6 is connected between the transistor pair Q3, Q4 and the constant current source CC1, and a transistor Q5 has its emitter commonly connected in parallel with this transistor Q6, and a reference voltage Vref is connected to the base terminal of this transistor Q5. A current switch is configured in which a constant current i is applied and one of them is turned on depending on the base potential of the transistor Q6, and a constant current i is caused to flow. A transistor Q6 is provided at a stage before the transistor Q6 in response to control signals a and a' giving drive timing for the write amplifier 10.
A drive control circuit 20 for forming a base voltage of 6 is provided. This drive control circuit 20 includes a pair of differential transistors Q7 and Q8 whose base terminals receive the control signals a and a', and a resistor R1 connected to the collector terminals of the differential transistors Q7 and Q8.
It is constituted by a differential amplifier circuit consisting of R2 and a constant current source CC2 connected to the common emitter terminal of Q7 and Q8. Moreover, in this embodiment, this drive control circuit 20
A capacitor Cd is connected between the collector terminals of the differential transistors Q7 and Q8 constituting the transistor Q6.

Next, the operation of the magnetic head drive circuit will be explained. In the circuit of this embodiment, input signals D and D according to write data are applied to the transistor pair Q1 and Q2.
'(D' is the opposite phase signal of D), and the transistor pair Q3
, Q4 are given input signals d, d' (level-shifted signals of D, D') in advance to determine the direction of the current, and the transistors Q1 and Q2 and Q3 and Q4 are switched in a complementary manner. By changing the signal a to high level, the transistor Q6 is turned on. Then, a current is passed through the write amplifier 10, a magnetic field is generated according to the direction of the current i passed through the head L, and data is written onto the magnetic disk. When the write data changes, the input signals D, D' and d, d' are inverted, the direction of the current i flowing through the head L changes, and data is written by the accompanying reversal of the magnetic field.

In this embodiment, since the output node of the drive control circuit 20 that provides the drive timing of the write amplifier 10 is provided with a time constant circuit that makes the signal change slowly, when the current flows through the write amplifier 10, The switching speed of the transistor Q6 is slowed down, thereby reducing the back electromotive force generated across the head L.

Another embodiment of the invention is shown in FIGS. 2 and 3. Among these, in the embodiment shown in FIG. 2, a time constant circuit for slowing down the change in the signal provided at the output node of the drive control circuit 20 that provides the drive timing of the write amplifier 10 is fixed at the output nodes n1 and n2. It is composed of a pair of capacitors C1 and C2 connected between the voltage terminal P and the voltage terminal P.

In the embodiment shown in FIG. 3, the time constant circuit is constructed by a resistor Rd connected between the output node n1 of the drive control circuit 20 and the base terminal of the transistor Q6. A time constant circuit may be constructed by combining not only the resistor Rd shown in FIG. 3 but also the resistor Rd and the capacitor shown in FIG. 1 or 2. These time constant circuits also allow the first
The same effects as in the embodiment can be obtained.

Note that in the above embodiment, the light amplifier 10
A time constant circuit is provided at the output node of the drive control circuit 20 that provides the drive timing for slowing down the change in the signal.
and input signals D, D' and d provided before Q3 and Q4.
, d' may be provided with a time constant circuit within the preamplifier. In addition, in the embodiment, the constant current source CC
1 and CC2 are provided in the semiconductor chip, however, the constant current sources CC1 and CC2 in the chip may be omitted and the current may be drawn from an external constant current source.

As explained above, in the above embodiment, a time constant is provided between the differential amplification type write amplifier for driving the magnetic head and the preceding stage circuit that forms the control signal to slow the change in the control signal. Since a circuit is provided, the current switching speed of the current switch that makes up the light amplifier is slowed down, and the back electromotive force generated when switching the current is reduced, which reduces the withstand voltage margin and saturation margin of the transistor that makes up the light amplifier. The effect is that it can be improved.

[0015] The invention made by the present inventor has been specifically explained based on examples, but the present invention is not limited to the above examples, and can be modified in various ways without departing from the gist thereof. Needless to say. For example, in the above embodiment, a case has been described in which the circuit at the front stage of the write amplifier is composed of a differential amplifier circuit, but the present invention can also be applied to a case where other types of circuits are provided.

In the above description, the invention made by the present inventor was mainly applied to a magnetic head drive circuit, which is the background field of application, but the invention is not limited thereto, and It can be used generally for semiconductor integrated circuits including circuits that drive loads.

[0017]

Effects of the Invention The effects obtained by typical inventions disclosed in this application are briefly explained below. That is, by controlling the switching speed of the current switch of the write amplifier in the magnetic head drive circuit to an appropriate speed, it is possible to improve the withstand voltage margin and saturation margin of the transistors forming the write amplifier.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a magnetic head drive circuit according to the present invention.

FIG. 2 is a circuit diagram showing another configuration example of a time constant circuit.

FIG. 3 is a circuit diagram showing still another configuration example of the time constant circuit.

FIG. 4 is a circuit diagram showing an example of a conventional magnetic head drive circuit.

[Explanation of symbols]

L Inductance load 10 Light amplifier 20 Drive control circuit CC constant current source

Claims (3)

[Claims] 1. A pair of connection terminals to which a magnetic head forming an inductance load is connected; In the magnetic head drive circuit, the write circuit includes a first transistor pair and a second transistor pair connected to terminals for the write circuit, and a constant current source that supplies current to one of these transistors. A magnetic head drive circuit characterized in that a time constant circuit is connected between a preceding circuit that forms a drive signal and a time constant circuit that slows down changes in the drive signal. [Claim 2] When the preceding stage circuit is configured with a differential amplifier circuit, the time constant circuit includes a capacitor connected between the output nodes of the differential amplifier circuit or between the output node and a constant potential point. 2. The magnetic head drive circuit according to claim 1, wherein the magnetic head drive circuit is comprised of: [Claim 3] When the preceding stage circuit is configured with a differential amplifier circuit, the time constant circuit is configured with a resistor or a resistor and a capacitor connected between the output node of the differential amplifier circuit. 3. The magnetic head drive circuit according to claim 1, further comprising a magnetic head drive circuit.