JPH0572646B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field] The present invention relates to a technology for detecting wire breakage abnormalities and a technology that is particularly effective when applied to detecting wire breakage abnormalities in magnetic heads. It relates to techniques that are effective in detecting anomalies.

[Background technology]

For example, in thin film magnetic heads for recording digital data in magnetic disk devices, abnormalities often occur due to wire breaks. If such an abnormality occurs, a system must be in place to detect it immediately. Furthermore, it is desirable that the abnormality can be detected during the write operation. This is because if an abnormality during a write operation can be discovered, there is no need to continue any more wasteful write operations, and appropriate measures can be taken at an early stage.

Therefore, the inventors of the present invention have developed a technique for detecting a disconnection, particularly a disconnection abnormality detection technique for a magnetic head for recording digital data, as described below.

That is, by detecting the terminal voltage of a magnetic head driven by a current switched in accordance with a digital input signal, a disconnection abnormality in the magnetic head is detected. This will be explained in more detail below.

First, FIG. 1 shows the connection state of a disconnection abnormality detection circuit that was studied prior to the present invention. Also, the second
The figure shows the disconnection abnormality detection circuit.

In FIG. 1, a digital input signal Din is input from an input section 10 to a drive circuit 12. The drive circuit 12 receives mutually complementary write drive signals VinX and VinY.
is applied to the write circuit 14. The write circuit 14 is composed of four npn bipolar transistors Q1, Q2, Q3, Q4 connected in a bridge shape and a constant current circuit 16, and the direction of the current flowing through the thin film magnetic head 20 is determined by the write drive signal VinX. , VinY
Depending on the situation, the switching operation is performed alternately. The magnetic head 2 is driven for writing by this writing circuit 14.
The voltages Vx and Vy appearing at both terminals of 0 are input to a magnetic head disconnection abnormality detection circuit 30.

The write circuit 14 operates between the positive side (ground potential) and the negative side Vee of the power supply. Further, resistors R1 and R2 are connected in parallel to transistors Q1 and Q3 on the positive side (ground side) of the power supply, respectively.

The magnetic head disconnection abnormality detection circuit 30 is constituted by a current switch in which the common emitters of NPN bipolar transistors Q11, Q12 and Q13 are connected to the negative side of the power supply via a constant current circuit 32. One transistor Q11, Q12
The terminal voltages Vx and Vy of the magnetic head 20 are input to each base thereof, and the common collector serves as an abnormality detection output OUT. Also,
The other transistor Q13 has its collector connected to the ground potential, and has a predetermined reference voltage Vrefl input to its base. Then, one of the terminal voltages Vx and Vy is the reference voltage above.
The configuration is such that when it becomes higher than Vrefl, that is, when it approaches the ground potential side, a current flows from the output OUT, and this state becomes an abnormality detection state.

Here, FIG. 3 shows the waveforms of the voltages Vx and Vy appearing at both terminals of the magnetic head 20 as a write drive signal.
This is shown along with VinX and VinY. In the figure, A indicates a voltage waveform during normal operation, and B indicates a voltage waveform during abnormal disconnection. Both voltages Vx,
Vy takes the same waveform alternately.

Here, one terminal voltage Vx in normal state (A)
Looking at the waveform of the drive signal VinX, first
is at the "H" level and VinY is at the "L" level, so that the transistor Q of the write circuit 14
In a period t1 where Q1 and Q4 are ON (conducting) and Q2 and Q3 are OFF (non-conducting), a constant current 1W flows through the constant voltage circuit 16 through the transistor Q1, the head 20, and the transistor Q4. Voltage Vx at this time
takes the voltage VH obtained by subtracting the base-emitter voltage Vbe of the transistor Q1 from the ground potential GD.

Next, when the drive signals VinX and VinY are switched,
A little later than this switching timing, transistors Q1 and Q4 are turned off and transistors Q2 and Q3 are turned on, and the direction of the drive current flowing through the head 20 is switched. In the initial period t2 of switching, the voltage _V Calm down to VM. At this time, the voltage VM is calculated from the voltage VH to the magnetic head 2.
Voltage drop Vir due to resistance component Ri of 0 (Vir=Iw・
(VM = VH - Iw・Ri).

After this, the voltage VM continues for a period t3 until the direction of the drive current of the head 20 is switched.

Then, when the drive signals VinX and VinY switch again, transistors Q1 and Q4 turn on and Q2 and Q3 turn off with a slight delay from this switching timing, and the direction of the drive current flowing to the head 20 is switched, and the voltage The state returns to the state in section t1 where Vx becomes VH.

As described above, the terminal voltage Vx is set in the interval t1,
The states of t2 and t3 are repeated. Other terminal voltage Vy
repeats the same changes.

In the abnormal situation (B) when the magnetic head 20 is disconnected, no current flows through the head 20, so the above voltage
Vx and Vy simply take VH and VL alternately.
At this time, the voltage Vx in the interval t1,
Vy exceeds the voltage VH (VH=-Vbe) and approaches the ground potential GND by the resistor R1 connected in parallel to the transistor Q1. Therefore, if the reference voltage Vref1 is set between VH and GND, the abnormal output will be activated when a disconnection abnormality occurs.
A current now flows into OUT, thereby making it possible to detect a disconnection abnormality in the magnetic head 20 during a write operation.

However, in this technology, the width of change in the terminal voltages Vx and Vy of the transistors Q1 and Q
The voltage drop Vbe between the base and emitter of 2 is only the width, and the time constant due to the resistors R1 and R2 and the parasitic capacitance around them causes
The rise after exceeding this point is very slow. Therefore, if the setting conditions for the reference voltage Vref1 are very strict and the digital input signal Din changes quickly, the rise in the voltages Vx and Vy becomes even smaller, making it impossible to perform reliable detection. That is, the inventor has found that a problem arises in that the detection sensitivity depends on the input signal frequency (the period t4 in FIG. 3 becomes shorter as the frequency increases).

[Purpose of the invention]

It is an object of the present invention to provide a margin in the reference voltage setting range for determining a disconnection abnormality in a magnetic head during a write operation, and to ensure that the detection operation can be performed reliably even when the digital input signal is high speed. The present invention provides a disconnection abnormality detection technology that enables the detection of wire breakage.

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.

[Summary of the Invention] A brief overview of typical inventions disclosed in this application is as follows.

In other words, by detecting a disconnection abnormality by capturing the timing immediately before the drive current of the magnetic head is switched, it is possible to provide a margin for the setting range of the reference voltage for determining a disconnection abnormality, and also to ensure that the digital input signal is This achieves the purpose of ensuring that the detection operation can be performed reliably even at high speeds, that is, that the detection sensitivity does not depend on the input signal frequency.

〔Example〕

Hereinafter, typical embodiments of the present invention will be described with reference to the drawings.

In addition, the same or corresponding parts are indicated by the same reference numerals in the drawings.

First, FIG. 4 shows the connection state of the disconnection abnormality detection circuit according to the present invention. Moreover, FIG. 5 shows the disconnection abnormality detection circuit.

In FIG. 4, a digital input signal Din is input from an input section 10 to a drive circuit 12. The drive circuit 12 receives mutually complementary write drive signals VinX and VinY.
is applied to the write circuit 14. The write circuit 14 is composed of four npn bipolar transistors Q1, Q2, Q3, Q4 connected in a bridge shape and a constant current circuit 16, and the direction of the current flowing through the thin film magnetic head 20 is determined by the write drive signal VinX. , VinY
Depending on the situation, the switching operation is performed alternately. The magnetic head 2 is driven for writing by this writing circuit 14.
The voltages Vx and Vy appearing at both terminals of 0 are input to a magnetic head disconnection abnormality detection circuit 30.

The write circuit 14 operates between the positive side (ground potential) and the negative side Vee of the power supply. In addition, the transistors Q1 and Q3 on the positive side of the power supply have resistors R1 and R1, respectively.
R2 is connected in parallel.

The magnetic head disconnection abnormality detection circuit 30 has two sets of npn bipolar transistors Q21, Q22 and Q23, Q24 whose emitters are connected to each other. One bipolar transistor Q2 in each set
1 and Q24 have their collectors connected to the ground potential, and the terminal voltages Vx and Vy of the magnetic head 20 are input to their bases. In addition, the other bipolar transistor Q2 in each set
2 and Q23 have their collectors connected in common to provide an abnormality detection output OUT, and a predetermined reference voltage Vref2 is input to their bases. Further, the common emitters of transistors Q21 and Q22 of one set are connected to a constant current circuit 32 via an npn bipolar transistor Q25 in series. Similarly, the common emitter of the other coarse transistors Q23 and Q24 is also connected to the npn bipolar transistor Q26.
The constant current circuit 32 is connected to the constant current circuit 32 in series. The constant current circuit 32 is connected to the negative side of the power supply.
It is connected to Vee and allows a constant current to flow through it. As a result, transistors Q21 and Q2
2. Transistors Q23 and Q24 operate complementary to each other as current switches. Further, transistors Q25 and Q26 control the operation of the two current switches. In other words, one current switch has transistor Q25.
The other current switch operates only when the transistor Q26 is in the ON state. The transistor Q25,Q
ON/OFF of 26 is controlled by the drive signals VinX and VinY.

Due to an abnormal configuration, when Vx<Vref2 and VinX is “H”, or Vy<
Only when Vref2 and VinY are "H" is a state in which current Io flows from the abnormality detection output OUT, and this state becomes an abnormality detection state.

FIG. 6 shows the waveforms of the voltages Vx and Vy appearing at both terminals of the magnetic head 20 as the write drive signals VinX and Vy.
This is shown together with VinY. In the figure, A indicates a voltage waveform during normal operation, and B indicates a voltage waveform during abnormal disconnection. Both voltages Vx and Vy alternately take the same waveform.

Here, if we pay attention to the waveform of one voltage V _x in the normal state (A), first, the drive signal VinX becomes "H" level and VinY becomes "L" level, so that the write circuit 14 transistor Q1,
Q4 is ON (conducting) and Q2 and Q3 are OFF (non-conducting)
In the interval t1, the constant current circuit 16 passes through the transistor Q1, the head 20, and the transistor Q4.
A constant current of 1W flows through. The voltage Vx at this time is
From the ground potential GND to the base of transistor Q1
Take the voltage VH subtracted by the emitter voltage Vbe.

Next, when the drive signals VniX and VinY are switched,
A little later than this switching timing, transistors Q1 and Q4 are turned off and transistors Q2 and Q3 are turned on, and the direction of the drive current flowing through the head 20 is switched. In the initial period t2 of the switching, the voltage Vx once drops significantly to the negative side voltage VL due to the transient state caused by the inductance component L of the head 20, and then rises as the transient state ends, and finally the voltage Calm down to VM. The voltage VM at this time is a voltage drop Vi (Vi=
It is equivalent to minus Iw・Ri).

After this, the voltage VM continues for a period t3 until the direction of the drive current of the head 20 is switched.

Then, when the drive signals VinX and VinY switch again, with a slight delay from this switching timing, transistors Q1 and Q4 turn on and Q2 and Q3 turn off, and the direction of the drive current flowing to the head 20 is switched, and the voltage The state returns to the state in section t1 where Vx becomes VH.

As described above, the terminal voltage Vx is set in the interval t1,
The states of t2 and t3 are repeated. Other terminal voltage Vy
repeats the same changes.

In the abnormal situation (B) when the magnetic head 20 is disconnected, no current flows through the head 20, so the above voltage
Xx and Vy simply take VH and VL alternately.

Here, the reference voltage Vref2 is set between VM and VL. If a disconnection abnormality occurs even in this state, the above drive signal VinX (VinY)
Delay time from when is switched from "L" to "H" until the drive current of the magnetic head 20 is switched
During td, Vx<Vref2 and VinX
The condition that is “H” (or the condition that Vy<Vref2 and VinY is “H”) is established, and during this period (td), the current from the abnormality detection output OUT is
Io is in a state of flowing. In other words, the abnormality detection state is output from the output OUT. That is, by measuring the time td during which the current Io flows, it is possible to detect whether or not there is an abnormality.

As described above, a disconnection abnormality in the magnetic head 20 is detected during the write operation.What should be noted here is that the setting range of the reference voltage Vref2 for determining the abnormal state is from VL to This means that it has a wide range up to VM. As a result, the reference voltage Vref2 can be set with a margin, and even if there is a slight voltage fluctuation, the current
By measuring the time during which Io is flowing, it is possible to reliably determine the presence or absence of an abnormality. Also,
The above terminal voltages Vx and Vy immediately before the drive current of the magnetic head 20 is switched definitely show a large difference between abnormal and normal times, and the period td is due to circuit delay and does not depend on the input signal frequency. Therefore, even if the switching speed of the digital input signal Din increases, the presence or absence of a disconnection abnormality can be reliably detected.

〔effect〕

(1) A disconnection abnormality in the magnetic head is detected by detecting the terminal voltage of the magnetic head driven by a current that is switched according to a digital input signal, and the driving current of the magnetic head is switched. By comparing the immediately preceding terminal voltage of the magnetic head with a predetermined reference voltage and detecting the presence or absence of a disconnection abnormality based on the comparison result, it can be used as a reference for determining a disconnection abnormality of the magnetic head during a write operation. It is possible to provide a margin for the voltage setting range, and as a result, it is possible to obtain the effect that a disconnection abnormality can be reliably detected.

(2) In addition, by detecting the terminal voltage of the magnetic head driven by a current switched according to a digital input signal, a disconnection abnormality in the head is detected, and the driving current of the magnetic head is By comparing the terminal voltage of the magnetic head immediately before switching with a predetermined reference voltage and detecting the presence or absence of a disconnection abnormality based on the comparison result, it is possible to reliably detect changes in voltage due to the presence or absence of a disconnection abnormality. As a result, even if the digital input signal is high-speed, the detection operation can be performed reliably.

(3) Furthermore, by determining the detection timing of the terminal voltage of the magnetic head based on the delay time difference between the switching timing of the digital input signal and the switching timing of the drive current of the magnetic head, the input The detection is independent of the signal frequency, and the detection timing of disconnection abnormality can be easily and optimally set.

Although the invention made by the present inventor has been specifically explained above based on examples, this invention is not limited to the above-mentioned examples, and may be modified in various ways without departing from the gist thereof. Needless to say. For example, the write circuit 14, the abnormality detection circuit 30, etc. may be constructed using MOS type elements. Also, Q25 of the abnormality detection circuit,
The base input of Q26 may be the input side of the drive circuit instead of VinX, VinY (drive circuit output side).

[Application field]

In the above explanation, the invention made by the present inventor is mainly applied to the field of application which is the background of the invention, which is the disconnection abnormality detection technology of thin film magnetic heads. However, the present invention is not limited to this, for example The present invention can also be applied to disconnection abnormality detection technology in ordinary magnetic recording heads. It can be applied at least to detecting disconnection abnormalities in current-driven magnetic heads.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the connection state of a magnetic head disconnection abnormality detection circuit that was studied prior to the present invention.
Figure 2 is a circuit diagram showing the main parts of the abnormality detection circuit shown in Figure 1, Figure 3 is a waveform diagram for operating the circuit shown in Figures 1 and 2, and Figure 4 is a circuit diagram showing the main parts of the abnormality detection circuit shown in Figure 1. A circuit diagram showing the connection state of the magnetic head disconnection abnormality detection circuit according to the invention, FIG. 5 is a circuit diagram showing the main part of the abnormality detection circuit shown in FIG. 4, and FIG. FIG. 3 is a waveform diagram for explaining the operation of the circuit. 10... Digital signal input section, 12... Drive circuit, 14... Write circuit, 16... Constant current circuit, 2
0... Thin film magnetic head, 30... Disconnection abnormality detection circuit, 32... Constant current circuit, Din... Digital input signal, VinX, VinY... Write drive signal, V _x , V _y
...Magnetic head terminal voltage, OUT...Abnormality detection output, L...Magnetic head inductance component,
Ri...Resistance component of magnetic head, Vee...Negative side of power supply, GND...Ground potential (positive side of power supply), Vref1,
Vref2...Reference voltage, Q1~Q4, Q11~Q
13, Q21 to Q26...transistors (npn bipolar transistors).

Claims (1)

[Scope of Claims] 1. A first switch operated by a write drive signal of a write circuit which forms an output signal for bridge driving a magnetic head in a pair of output terminals in accordance with the write drive signal. a second transistor whose base is connected to one output terminal of the pair of output terminals of the write circuit; whose base is connected to a reference power supply and whose emitter is connected to the second transistor; at least a third transistor which is connected in common with the emitters of the transistors so as to operate differentially with the second transistor; A non-disconnection of the magnetic head that appears at the one output terminal after being turned on by the write drive signal until the output signal changes according to the write drive signal applied to the one output terminal. and the potential in the case of disconnection, and the disconnection of the magnetic head is detected by the current flowing in the series path of the first transistor and the third transistor. A disconnection abnormality detection circuit for a magnetic head, characterized in that the circuit is configured as follows. 2. The write drive signals are mutually complementary write drive signals, and a fourth transistor is provided which is differentially operated together with the first transistor by the complementary write drive signals, the base of which is A fifth transistor is connected to the other output terminal of the pair of output terminals, and its base is connected to the reference power source, and its emitter is commonly connected to the emitter of the fifth transistor. further comprising a sixth transistor configured to operate differentially with the fifth transistor, and a current flowing in a series path between the first transistor and the third transistor; Detection of a disconnection abnormality in the magnetic head according to claim 1, wherein a disconnection in the magnetic head is detected by a current flowing in a series path between the magnetic head and the sixth transistor. circuit.