JPH0532803B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a magnetoresistive magnetic head signal reproducing device.

BACKGROUND ART AND PROBLEMS First, with reference to FIG. 1, an example of the structure of a head section h of a conventional magnetoresistive (hereinafter referred to as MR) type magnetic head signal reproducing device will be described.
On a magnetic substrate 1 made of Ni-Zn ferrite, Mn-Zn ferrite, etc. (if this substrate 1 has conductivity, an insulating layer 2 such as SiO ₂ deposited thereon) ), a bias conductor 3 made of a strip-shaped conductive film is deposited to serve as a current path for generating a bias magnetic field to apply a bias magnetic field to the MR magnetic sensing part 5, which will be described later. For example, Ni-Fe alloy,
Alternatively, it consists of an MR magnetic thin film such as Ni-Co alloy.
An MR magnetic sensing section 5 is arranged. A magnetic conductor is placed on this MR magnetic sensing part 5 via a thin insulating layer 6, with each end straddling the bias conductor 3 and extending in a direction across the MR magnetic sensing part 5, each forming a part of a magnetic circuit. A pair of magnetic layers 7 and 8, for example made of Mo permalloy, is deposited as a core. A protective substrate 10 is bonded onto the substrate 1 with a nonmagnetic insulating protective layer 9 interposed therebetween.

Thus, a non-magnetic gap spacer layer 11 made of, for example, an insulating layer 6 and having a required thickness is interposed between one magnetic layer 7 and the front end of the substrate 1 to form a front magnetic gap g. Ru. Then, the substrate 1, facing this magnetic gap g,
The front surfaces of the gap spacer layer 11, the magnetic layer 7, the protective layer 9, and the protective substrate 10 are polished to form a contact surface 12 with a magnetic recording medium such as a magnetic tape.

Furthermore, although the rear end of the magnetic layer 7 and the front end of the other magnetic layer 8 constituting the magnetic gap g are formed so as to straddle the MR magnetic sensing part 5 via the insulating layer 6, both ends are Discontinuous portions 13 spaced apart from each other are formed therebetween. The rear and front ends of both magnetic layers 7 and 8 are electrically insulated by the presence of the insulating layer 6, but are magnetically coupled at the discontinuous portion 13. Thus, substrate 1 - magnetic gap g - magnetic layer 7 - MR magnetic sensing part 5 - magnetic layer 8
- a magnetic circuit consisting of a closed magnetic path of the substrate 1 is formed;

In such an MR type magnetic head section h,
As the signal magnetic flux from the front gap g that is in contact with the magnetic recording medium flows through the above-mentioned magnetic circuit, the resistance value of the MR magnetic sensing part 5 in this magnetic circuit is
It changes depending on the external magnetic field caused by this signal magnetic flux.
Therefore, a detection current is applied to the MR magnetic sensing section 5, and this change in resistance value is detected as a voltage change across the MR magnetic sensing section 5, thereby reproducing the recorded signal on the magnetic medium.

In this case, in order for the MR magnetic sensing section 5 to operate linearly as a magnetic sensor and have high sensitivity, this
It is necessary to magnetically bias the MR magnetic sensing section 5. This bias magnetic field is a DC magnetic field provided by a magnetic field generated by energizing the bias conductor 3 and a magnetic field itself generated by the detection current flowing to the MR magnetic sensing section 5.

That is, this type of MR type magnetic head device has a second
As shown in the figure, the MR magnetic sensing section 5
, the magnetic field generated by the application of DC current i _B to the bias conductor 3 and the detection current i _MR to the MR magnetic sensing part 5
The signal magnetic field H _S from the magnetic medium described above is applied while the bias magnetic field H _B is applied by the magnetic field generated by the energization of the magnetic medium. Then, the MR magnetic sensing part 5 based on the resistance change due to this signal magnetic field H _S
, that is, a change in the potential at point A, is supplied to an amplifier 14 via a low-frequency blocking capacitor 16, amplified, and outputted from an output terminal 15.

FIG. 3 shows the magnetic field H applied to this MR magnetic sensing part 5.
This curve shows an upwardly convex quadratic curve in the range -H _BR to +H _BR where the absolute value of the magnetic field H is small. When the absolute value of becomes large and deviates from this range, the magnetization of the central part of the MR magnetic thin film constituting the MR magnetosensitive section 5 begins to saturate in the direction of the magnetic circuit, departing from the quadratic curve, and its resistance R becomes Minimum value R _nio
Asymptotes to . Incidentally, the maximum value R _nax of this resistance R
is the value when all the magnetization of the MR magnetic thin film is oriented in the current direction. Then, in the characteristic portion of the quadratic curve in this operating characteristic curve, the signal magnetic field from the magnetic medium shown with reference numeral 17 in FIG. 3 is applied while the bias magnetic field H _B described above is applied. Accordingly, an output based on the change in resistance value indicated by reference numeral 18 in the figure is obtained. In this case, it can be seen that as the magnitude of the signal magnetic field increases, the second harmonic distortion increases.

Furthermore, the second magnetic head device in the MR type magnetic head device described above
The potential at point A in the figure is a potential determined by the combination of the fixed resistance and the variable resistance of the MR magnetic sensing section 5.
In this case, the fixed portion is about 98%, and the temperature dependence of the fixed portion of this resistance is large, so there is a drawback that the temperature drift of the potential at point A is large. The resistance value R of this MR magnetic sensing part 5
R = Ro (1 + α cos ² θ) ... (1) (However, Ro is the fixed resistance, α is the maximum resistance change rate, and θ is the angle between the current direction and the magnetization direction in the MR magnetic sensing part 5. ), for example MR
When the magnetically sensitive part 5 is made of an MR magnetic thin film of 250 Å thick made of 81Ni-19Fe (permalloy) alloy, the actual value of α is about 0.017. The value of this α is
Although there are some differences depending on the thickness and material of the MR magnetic thin film of the MR magnetosensitive section 5, α=0.05 at most. On the other hand, the fixed portion Ro of this resistance is Ro=Ri(1+aΔt)...(2) (However, Ri is the initial value of resistance, a temperature coefficient,
Δt is the temperature change), and the above MR
The actual measured value of the temperature coefficient a in the example of the magnetically sensitive part 5 is a
= approximately 0.0027/deg. This causes a large amount of noise in the detection of a DC magnetic field.

Furthermore, in the case of this type of MR type magnetic head section, since its temperature coefficient is large as described above, heat generated by, for example, energization to the MR magnetic sensing section 5 or bias current to the bias conductor 3, etc. However, if the temperature of the head changes due to unstable heat dissipation due to the sliding contact between the head and the magnetic recording medium,
A large noise, so-called sliding noise, will be generated.

Furthermore, when the amplifier 14 in the configuration shown in FIG.
The required capacitance C is as follows, where R is the resistance of the MR magnetic sensing section 5: C=1/R〓 _p (3) (ωo=2πfo). Now, if the MR magnetic sensing part 5 is made of permalloy with a thickness of 250 Å as mentioned above and its length is 50 μm, its resistance R will be about 120 Ω, so if fo = 1 kHz, the capacitor 16 should be C = 1.3 μF. This is a problem especially when constructing a multi-track type magnetic head device for digital audio signals.

Furthermore, it is desired that the magnetic permeability in the magnetic circuit, particularly in the magnetic layers 7 and 8, which are relatively thin and have a small cross-sectional area, be as high as possible, and this magnetic permeability is maximum when the external magnetic field is zero. So,
Applying a bias magnetic field as described above causes a decrease in magnetic permeability.

The above-mentioned DC bias type MR type magnetic head device has the advantage of having a wide effective track width and being easily made into a narrow track, but on the other hand, it has poor linearity, difficulty in DC regeneration, large sliding noise, and Barkhausen. It has the drawbacks of high noise and wide variation in output.

As other conventional MR type magnetic head devices, a differential type MR type magnetic head device, a barber pole type MR type magnetic head device, etc. have been proposed.
A differential MR type magnetic head device is provided with a pair of MR magnetic sensing parts in its MR type magnetic head part, and the same bias magnetic field is applied to the pair of MR magnetic sensing parts by a common bias conductor. Differential outputs are obtained from the magnetosensitive sections using the same signal magnetic field, the differential outputs are supplied to a differential amplifier, and a reproduced signal is obtained from the differential amplifier.

This differential MR type magnetic head device is capable of direct current regeneration (however, the offset variation is large).
It has the advantages of low Barkhausen noise, little output variation, and requires only an amplifier as a circuit, but the disadvantages are that the effect of reducing sliding noise is small, the effective track width is narrow, and it is difficult to create a narrow track. There is.

In addition, the barber pole type MR type magnetic head device has a large number of mutually parallel conductor bars made of gold etc. attached to the MR magnetic sensing part of the MR type magnetic head part so as to be diagonal in the longitudinal direction. It was formed.

This barber-pole type MR type magnetic head device has the advantage of having low Barkhausen noise, little variation in output, and requires only an amplifier as a circuit, but it is difficult to reproduce DC, has large sliding noise, and has a small track. It has the drawbacks that it is difficult to carry out and the effective track width is not very wide.

Therefore, in order to eliminate or improve the above-mentioned drawbacks, the present applicant previously filed a novel magnetoresistive magnetic head signal reproducing device as Japanese Patent Application No. 59-38980.

An example of the previously proposed MR type magnetic head signal reproducing device will be described below with reference to FIG. In this example, the MR type magnetic head section h is the first
The configuration is similar to that explained in FIGS. 1 and 2, and in FIG. 4, parts corresponding to those in FIGS. 1 and 2 are denoted by the same reference numerals, and redundant explanation will be omitted. In this example, a low-level AC bias current i _A of high frequency fc is passed through the bias conductor 3 of the MR type magnetic head section h, superimposed on the DC bias current i _B , and the high frequency magnetic field is superimposed on the DC magnetic field. is applied to the MR magnetic sensing part 5. Here, the waveform of the alternating bias current _iA , and thus the waveform of the alternating magnetic field, may be a sine wave, a rectangular wave, or any other waveform.

In this way, since the AC bias magnetic field is applied to the MR magnetic sensing unit 5 superimposed on the DC bias magnetic field,
An alternating current signal of frequency fc is taken out between both ends of this MR magnetic sensing section 5, ie, at point A in FIG.

FIG. 5A shows the relationship between the DC bias magnetic field H _B , the magnetic field H and the resistance R of the MR magnetic sensing section 5 in a state where the AC bias magnetic field H _A is superimposed on the signal magnetic field H _S . Here, the change in AC bias magnetic field H _A is ΔH
When ΔR is small, the magnitude of the resistance change ΔR with respect to the change in the alternating current bias magnetic field at a certain moment is obtained as the absolute value of the differential of the quadratic curve in FIG.
As shown in FIG. B, the relationship between the magnitude of the DC bias magnetic field H _B and the signal magnetic field H _S and the resistance change that is the output is, in principle, a straight line. Therefore, the magnitude of the AC signal obtained at point A in FIG. 4 is an output that changes depending on the change in the sum of the DC bias magnetic field H _B and the signal H _S from the magnetic recording medium.

Then, as shown in FIG. 4, this output is supplied to a rectifier 20 for rectification via a high-pass filter (preamplifier) 19 that passes the above-mentioned frequency fc component, and the rectified output is passed through a low-pass filter. It is supplied to the filter 21. In this way, a signal output can be obtained according to the signal magnetic field H _S from the magnetic medium. In this case, the frequency fc of the alternating current _iA is now, for example, the band of the output finally obtained from the output terminal 15 is 0.
If ~100kHz is required, a frequency sufficiently higher than this, for example fc = 1MHz, may be selected. In this case, the high-pass filter 19 has a low cutoff frequency higher than 100kHz and a frequency fc, for example 1M
For example, select 500kHz, which is lower than Hz. As described above, the output of the high-pass filter is rectified by the rectifier 20 and then passed through the low-pass filter 21 with a cutoff frequency of 100kHz, so that a signal in the band of 0 to 100kHz is output to the output terminal 15. can get.

In the magnetic head device having such a configuration, when the external magnetic field (signal magnetic field + bias magnetic field) shown in FIG. 6A is applied to the MR magnetic sensing section 5, the fourth
At point B in the figure, as shown in Fig. 6B, an output is obtained by amplitude modulating the carrier of frequency fc with a signal, and as shown in Fig. 6C, an output is obtained from the output terminal 15.
In this case, an output corresponding to the signal magnetic field is extracted.

According to such a magnetic head signal reproducing device, MR
Since an output with a linear operating characteristic corresponding to the differentiation of the operating characteristic by the magnetic field vs. resistance quadratic characteristic curve of the magnetic sensing section 5 is extracted, a reliable reproduced signal can be extracted.

Furthermore, even if the fixed portion of the low resistance of the MR magnetic sensing section 5 has a large temperature dependence, the operating characteristic curve of the MR magnetic sensing section 5 is differentiated and depends on the characteristics, so the temperature of the fixed portion of this resistance is The influence of drift can be significantly reduced.

Furthermore, by eliminating the influence of the temperature dependence of the fixed resistance of the MR magnetic sensing section 5 as described above, the generation of noise due to the sliding of the MR type magnetic head section with the magnetic medium described above is reduced. be able to.

Further, since the capacitor 16 in such a magnetic head device only needs to pass a component of the frequency fc, for example, if fc=500kHz, the capacitance C of the capacitor 16 can be C=2600pF.
If this frequency fc is further increased, this capacitance C can be further reduced.

FIG. 7 shows another example of the previously proposed MR type magnetic head signal reproducing device. In FIG. 7, parts corresponding to those in FIG. 4 are given the same reference numerals, and redundant explanation will be omitted. In this case, no DC bias current is passed through the bias conductor 3, but an AC bias current i _A
Make sure that only the water is flowing. FIG. 8 schematically shows this operation. In this figure, the solid line curve is the operating characteristic curve of the magnetic field versus resistance of the actual MR magnetic sensing part, but if you extrapolate the quadratic curve part of this characteristic, it will become as shown by the broken line, and this will result in the minimum resistance value Let the magnetic fields corresponding to R _nio be +Ho and -Ho.
In this example, an alternating current bias magnetic field H _A is applied superimposed on the signal magnetic field H _S to obtain a low resistance change of the MR magnetic sensing section 5 that corresponds to the polarity and magnitude of the signal magnetic field and corresponds to the alternating current bias magnetic field.

The operating characteristic curve in this case is a quadratic curve.
The resistance value R of the MR magnetic sensing part 5 is expressed as follows.

R = R _nax - ΔR _nax (H/Ho) ² ... (4) Here, ΔR _nax is given by ΔR _nax = ΔR _nax - ΔR _nao . The magnetic field H given to the MR magnetic sensing part 5 is
As shown in the following equation, it is expressed as the sum of the bias magnetic field H _A (t) and the signal magnetic field H _S (t).

H(t)=H _A (t)+H _S (t) ...(5) Here, the magnetic field H _A (t) is obtained by the current flowing through the bias conductor 3, and H _A (t)=H _AO・sin(ω _C t) ...(6) It is expressed as follows. However, the angular frequency ω _C is expressed as the following equation.

ω _C =2πfc...(7) The output voltage V(t) of the MR magnetic sensing section 5 is as follows, where I is the MR detection current, V(t)=I・R...(8), and the above (4) ), (5), and (6), it can be expressed as follows.

V(t)=I・R _nax −I・ΔR _nax /Ho ² × [H _AO ²・si
n ² ω _C +2H _AO・H _S (t)×sinω _C + {H _S (t)} ² ]...(9) Next, this output voltage V(t) and the AC bias magnetic field
Signal with in-phase synchronous frequency with H _A , e.g. sin(ω _C t)
is multiplied by the multiplier 22. Its output Vz(t)
is expressed as the following equation.

Vz(t)=V(t)・sin(ω _C t)=I・R _nax・sin
(ω _C t)−I・ΔR _nax /Ho ²・[H _AO ²・sin ² (ω _C t
) +2H _AO・H _S (t)・sin (ω _C t) + {H _S (t)} ² ]
・sin(ω _C t)...(10) Then, when this is passed through the low-pass filter 21, the term having an ω _C component in the following (10) I・R _nax・sin(ω _C t)=0... …(11) H _AO ²・sin ² (ω _C t)=H _AO /2{sin(ωt)−cos
(2ωt)×sin(ωt)}=0……(12) 2H _AO・H _S (t)・sin ² (ωt)=H _AO・H _S (t)・{1−co
s(2ωt)}=H _AO・H _S (t)……(R) {H _S (t)} ²・sin(ωt)=0 (14). Therefore, the output voltage available at terminal 15
Vo(t) becomes Vo(t)=−I·ΔR _nax ×H _AO ·H _S (t)/Ho ² (15), and a voltage proportional to the signal magnetic field H _S (t) is obtained. In this case, even if the signal magnetic field H _S (t) is included in the input to the multiplier 22, there is little possibility that it will be mixed into the output, so the high-pass filter 19 can be omitted.

According to the MR type magnetic head signal reproducing device,
It is possible to extract an output according to the polarity of the external magnetic field, and in addition to the same advantages as in the previous example, there is an advantage that the dynamic range is increased. Further, in this case, there is an advantage that by using only the alternating current component as the magnetic bias, it is possible to avoid a decrease in the magnetic permeability of the magnetic circuit due to the direct current bias.

The previously proposed MR type magnetic head signal regenerator can obtain output with excellent linearity and low distortion, is capable of direct current regeneration, has small temperature drift, improves sliding noise, and has effective track performance. It has the advantage that it has a large width, can be made into a sandwich track, and can further reduce the capacitance of the capacitor, and when it has the configuration explained in FIG. 7, it can have a large dynamic range. In some cases it is also possible to avoid a decrease in permeability of the magnetic circuit.

By the way, for example, the frequency characteristic of the output from the output terminal 15 of the MR type magnetic head device shown in FIG. 7 is such that when the running speed of the magnetic tape is 4.8 cm/sec, the frequency is around 1 kHz, as shown by curve a in FIG. It has a characteristic that the response is maximum at , and as the frequency becomes gradually larger or smaller, the response gradually decreases. MR of various other methods mentioned above
Similar trends can be seen in the output frequency characteristics of the type magnetic head device.

Therefore, in order to flatten the frequency characteristics of the output of the MR type magnetic head signal reproducing device, curve b is shown in Fig. 9.
It is conceivable to connect equalizer circuits having frequency characteristics opposite to curve a in cascade on the output side, as shown in FIG.

However, in MR type magnetic head signal reproducing devices, distortion increases as the output level increases.
It exhibits a characteristic that the S/N decreases as the output level decreases. Therefore, if an equalizer circuit like the one described above is connected in cascade on the output side of an MR type magnetic head device, the high-frequency S/N will decrease when trying to reduce distortion near the frequency where the output response is maximum. However, if an attempt is made to increase the S/N ratio in the high range, the distortion near the frequency where the output response is maximum will increase.

OBJECTS OF THE INVENTION In view of these points, the present invention proposes a magnetoresistive magnetic head signal reproducing device in which the output frequency characteristics are flattened, distortion is reduced, and S/N is increased.

Summary of the Invention The magnetoresistive magnetic head signal reproducing device according to the present invention includes a magnetoresistive magnetic sensing section to which a signal magnetic field is applied, and a signal extractor for extracting a signal output according to the signal magnetic field from the output of the magnetoresistive magnetic sensing section. means, an equalizer circuit, and a negative feedback magnetic field generating means for supplying the signal output from the signal extraction means to the equalizer circuit and applying a negative feedback magnetic field to the magnetoresistive magnetic sensing part according to the equalizer output obtained, This is characterized in that the frequency characteristics of the signal output are made flat.

According to the present invention, it is possible to obtain a magnetoresistive magnetic head signal reproducing device in which the frequency characteristics of the output are flattened, distortion is reduced, and S/N is increased.

Embodiment An embodiment of the present invention will be described below with reference to FIG. This embodiment is a case in which the present invention is applied to the magnetoresistive magnetic head signal reproducing device shown in FIG. 7. In FIG. 10, parts corresponding to those in FIG. omitted. That is, the low-pass filter 21 converts the signal output to the ninth
The current is supplied to the equalizer circuit 23 having the frequency characteristic of curve a in the figure, and the current from this is applied to the bias conductor 3.
and this bias conductor 3 (a separate bias conductor can also be provided to carry current through it)
A negative feedback magnetic field H _FB is generated from the MR magnetic sensing part 5.
Try to give it to

A circuit example of such an equalizer circuit 23 is shown in FIG. 24 and 25 are input/output terminals, respectively, and 31 is an operational amplifier. Connect to the inverting input terminal,
Ground its non-inverting input terminal. A resistor 3 is connected between the output terminal 25 and the inverting input terminal of the operational amplifier 31.
2 and a series circuit of capacitor 33 and resistor 3
Connect 4 parallel circuits. Examples of the constants of the circuit elements are shown in FIG. 13, but they vary depending on the running speed of the magnetic tape, its magnetic material, and the type of magnetic head device.

It should be noted that the present invention is not limited to the methods shown in FIGS. 4 and 2 described above.
The case of application to an MR type magnetic head signal reproducing device is shown in FIGS. 11 and 12, respectively. In this case as well, as in FIG. 10, the signal output from the low-pass filter 21 or the amplifier 14 is supplied to the equalizer circuit 23 having the frequency characteristic of curve a in FIG.
This current is passed through the bias conductor 3 to generate a negative feedback magnetic field H _FB from the bias conductor 3 and apply it to the MR magnetic sensing section 5 . The present invention can also be applied to other differential type, barber pole type, and non-bias type MR type magnetic head devices. Note that detailed explanations of these will be omitted.

According to the present invention described above, it is possible to obtain a magnetoresistive magnetic head signal reproducing device in which the frequency characteristics of the output are flattened, distortion is reduced, and S/N is increased.

Note that the playback signal is not limited to digital audio signals, but also digital video signals, analog audio/
Video signals etc. are also possible.

Effects of the Invention According to the present invention described above, it is possible to obtain a magnetoresistive magnetic head signal reproducing device in which the frequency characteristics of the output are flattened, distortion is reduced, and S/N is increased.

[Brief explanation of drawings]

FIG. 1 is a schematic enlarged sectional view of a magnetoresistive magnetic head signal reproducing device used to explain the present invention, FIG. 2 is a block diagram of a conventional magnetoresistive magnetic head signal reproducing device, and FIG. Figure 4 is a characteristic curve diagram of the magnetoresistive magnetic sensing part; Figure 4 is a configuration diagram of an example of the previously proposed magnetoresistive magnetic head signal reproducing device;
Fig. 6 is a waveform diagram for explaining its operation, Fig. 7 is a configuration diagram of another example of the previously proposed magnetoresistive magnetic head signal reproducing device, and Fig. 8 is a diagram of its operating characteristic curve. Characteristic curve diagram for explanation, No. 9
10 is a characteristic curve diagram for explaining the present invention, FIGS.
FIG. 3 is a circuit diagram showing a specific example of the equalizer circuit. h is a magnetic head part, 1 is a substrate, 3 is a bias conductor, 5 is a magnetoresistive effect magnetic sensing part, 7 and 8 are magnetic layers, 19 is a high-pass filter, 20 is a rectifier, 2
1 is a low-pass filter, 22 is a multiplier, and 23 is an equalizer circuit.

Claims (1)

[Claims] 1. Magnetoresistive magnetic sensing means to which a signal magnetic field is applied, signal extraction means for extracting a signal output according to the signal magnetic field from the output of the magnetoresistive magnetic sensing means, an equalizer circuit, and a signal from the signal extraction means. negative feedback magnetic field generating means for supplying the output to the equalizer circuit and applying a negative feedback magnetic field to the magnetoresistive magnetic sensing means according to the equalizer output obtained, so as to flatten the frequency characteristics of the signal output. A magnetoresistive magnetic head signal reproducing device characterized by: