JPH0350322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a regenerative amplifier circuit for a magnetic head using the magnetoresistive effect.

The magnetic heads used in magnetic recording and reproducing devices such as tape recorders have traditionally been of the electromagnetic induction type, but in recent years, with advances in thin film technology, magnetoresistive elements ( Magnetic heads using MR elements (MR elements) have come into use.

This magnetic head utilizes the resistance change caused by the magnetic field of a thin film of ferromagnetic material such as permalloy.
Also called head. An example of such a magnetic head is shown in FIG.

In FIG. 1, 1 and 2 are metal electrodes, 3 is a ferromagnetic thin film, 4 is a recording medium, M _T is the magnetization vector of the recording medium 4, M is the magnetization vector of the ferromagnetic thin film 3, and is the current of the ferromagnetic thin film 3. The current vector is configured to flow a current between the metal electrodes 1 and 2, and when there is no external magnetic field, the angle θ between the current vector and the magnetization vector M of the ferromagnetic thin film 3 is 45°. Note that 10 indicates the entire MR head.

When such a MR head 10 comes into contact with a magnetic recording medium 4 whose external signal magnetization vector M _T changes by ΔM _T , the magnetic field of the magnetization vector M _T changes the magnetization vector M of the ferromagnetic thin film 3 and the current. The angle θ with the vector changes according to the change ΔM _T in the magnetization vector M _T , and as shown in FIG.
A resistance change ΔR of the ferromagnetic thin film 3 corresponding to a change ΔM _T in the magnetization vector M _T can be obtained. Therefore, by detecting this resistance change ΔR as a potential difference between the metal electrodes 1 and 2, the signal recorded on the recording medium 4 can be read out as an electrical signal.

Therefore, in order for the MR head 10 to read and reproduce recorded signals, the MR head 10 must be
This requires a drive current circuit that supplies a constant current to the MR element, and a regenerative amplifier circuit that detects the resistance change ΔR of the MR element.

Therefore, in the prior art, the first conventional example shown in FIG. 3, for example, in which these components are configured separately, has been used.

In the circuit shown in Figure 3, 10 is MR
Head, 11 is a transistor, 12 is an operational amplifier, 13-16 are capacitors, 17-
22 is a resistor, 23 is a DC power supply terminal, and 24 is an output signal terminal. In this circuit, the transistor 11 is used to drive the current of the MR head 10, and the drive current is determined by the power supply voltage Vc.c. supplied to the resistors 17 to 19 and the DC power supply terminal 23. MR head 1
If 0 is driven with a constant current, the resistance of the MR head 10 changes in proportion to the external magnetic field applied to the MR head 10, so the collector voltage of the transistor 11 changes, and this voltage change is transferred to the operational amplifier 12 and the capacitor. The signal from the recording medium 4 can be read by amplifying and extracting it by a reproduction amplification circuit composed of resistors 14 to 16 and resistors 20 to 22.

However, in this first conventional example, the current drive circuit and the regenerative amplifier circuit are provided independently, so there is a drawback that the configuration is complicated. Moreover, the signals read out by such an MR head 10 are generally extremely low-level signals, so in order to improve and maintain the S/N ratio to the required level, it is necessary to eliminate noise in the circuit system. (N) It is necessary to suppress the level to a sufficiently low level. However, in the first conventional example described above, the noise source is MR.
In addition to the resistance noise of the head 10 and the noise caused by the transistor in the operational amplifier 12, many other things are included, such as thermal noise caused by the resistors 19, 21, etc., and noise from the transistor 11. For this reason, there is a drawback that it is difficult to reduce the noise and it is impossible to maintain a sufficient S/N ratio.

By the way, the resistance characteristics of the MR head 10 have a large temperature dependence, and therefore, for example, the third
In the first conventional example shown in the figure, the output level and S/N ratio change greatly depending on the temperature change ΔT.

That is, in the circuit of FIG.
The current flowing through the head is I _M , the resistance value of the MR head 10 is R _M ,
Assuming that the resistance values of the resistors 21 and 22 are R ₂₁ and R ₂₂ respectively, the bias current (current flowing to the input section) of the operational amplifier 12 is generally extremely small, so the output signal (AC signal) V ₁ is expressed by equation (1). shown.

V ₁ = I _M・_RM・(1+R ₂₂ /R ₂₁ )...(1) Also, due to the change in the ambient temperature T, the MR head 1
Output signal when 0 temperature T _M changes by △T
V ₂ is expressed by equation (2).

V ₂ = I _M・_RM・f(△T)・(1+R ₂₂ /R ₂₁ )...(2) In this equation (2), f(△T) is the MR head 1
It is a function (multiplying factor) related to the temperature T _M (or T) of the resistance value R _M of 0.

As is clear from these equations (1) and (2), in the first conventional circuit shown in FIG. The disadvantage is that it changes over time.

Further, a related regenerative amplifier circuit for this type of magnetic head includes, for example, a circuit suggested in Japanese Patent Laid-Open No. 1698/1983 (hereinafter referred to as the second conventional example).

This second conventional example is shown in FIG. 8 and will be briefly described. In FIG. 8, 61 is a first magnetoresistive element forming the MR head. In the case of the regenerative amplifier circuit shown in FIG. 8, the circuit is designed to prevent instability caused by the bias magnetic field applied to the magnetoresistive element 61 having the wrong polarity. It is configured.

The series circuit of the current source 66 and the magnetoresistive element 61 and the series circuit of the current source 66' and the resistor _R3 constitute a bridge circuit. A bridge circuit having a magnetoresistive element 61 and a resistor R ₃ is connected to two inputs of an operational amplifier 65 . Here, the current source 66 supplies current i ₃ as shown, and the current source 66
6' likewise supplies current _i4 . This current _i4 causes the output signal of the operational amplifier 65 to become negative, and the resistance
Control is performed so that a negative current flows to the negative feedback wire 63 via R ₅ , transistor T ₁ and resistor R ₄ . Transistor T ₁ can only carry negative current, so adjustment is possible only in the stable region. A minute negative bias current is adjusted by the resistor _R6 .

Note that the first negative feedback circuit of the operational amplifier 65 (resistor _R1 , magnetoresistive element 61, and current source 6
Negative feedback circuit consisting of 6. ), the magnetoresistive element 61 is connected between the position of the common potential 0 and the position where the common potential is 0. However, the current source 66 is only for driving the magnetoresistive element 61. Further, the resistor R ₃ is connected between the non-inverting (+: plus) input part of the operational amplifier 65 and the position of the common potential 0.

By the way, in this second conventional example, in order to obtain thermal stability, the above-mentioned resistor R ₃ is also the first one.
It has been suggested that the second magnetoresistive element be provided on the same substrate as the magnetoresistive element 61. However, even if the resistor R ₃ is replaced with a magnetoresistive element, the temperature characteristics of the magnetoresistive element 61 cannot be sufficiently compensated for. Therefore, this point will be explained below.

Now, according to FIG. 8, the input impedance of the operational amplifier 65 is generally very large, so the resistance
It can be assumed that R ₃ is supplied with all of the current i ₄ flowing out from the current source 66'. Therefore, if the back electromotive force due to resistor R ₃ is V ₊ , then this back electromotive voltage V ₊
is directly supplied to the non-inverting (+: plus) input section of the operational amplifier 65 as a non-inverting input voltage.

Further, the current i ₃ flowing from the current source 66 is divided into a current i ₅ supplied to the magnetoresistive element 61 side and a current i ₆ supplied to the inverting (-: minus) input part side of the operational amplifier 65. be done. Since the input impedance of the operational amplifier 65 is generally very large, a current i ₆ is applied to the negative feedback resistor R ₁ provided between the output section and the inverting input section of the operational amplifier 65.
All of the above will be provided.

Therefore, if the resistance of the magnetoresistive element 62 is R _M and the inverting input voltage generated at the inverting input section is V _- when the output voltage of the operational amplifier 65 is Vu, then V ₊ = V due to the imaginary short. _- , so the output voltage Vu is V ₊ = i ₄・R ₃ i ₆ = i ₃ −i ₅ = (V ₋ −Vu)/R ₁ V ₋ = i ₅・R _M ∴Vu=i ₄・It is expressed as R ₃ ·(1+R ₁ /R _M )−i ₃ ·R = i ₄ ·( _RM + R ₁ ) ·R ₃ /R _M −i ₃ ·R ₁ (3). Here, assuming that due to the change ΔT in the ambient temperature T, the resistance value R _M and the resistance value R ₃ of the magnetoresistive element 61 in the above equation (3) are respectively increased by f(ΔT) times, The output voltage Vu in this case is Vu=i ₄・{R _M・f (△T) + R ₁ } ・R ₃・f (△T) / _RM・f (△T) ・i ₃・R ₁ = i ₄・{
It is expressed as R _M ·f(△T)+R ₁ }·R ₃ /R _M −i ₃ ·R ₁ (4).

Therefore, the output voltage expressed by equation (4) above
According to Vu, even if the resistor R ₃ in FIG. 8 is set as a magnetoresistive element provided on the same substrate, the output voltage Vu is not proportional to the mere ratio of the resistor R ₃ and the resistor _RM . (The function f(ΔT) still exists.) Therefore, the temperature characteristics of the magnetoresistive element 61 cannot be sufficiently compensated for.

Moreover, according to the output voltage Vu expressed by the above equation, the current i ₄ supplied from the current source 66' and the current i ₃ supplied from the current source 66 may each individually generate noise or have temperature characteristics. When the current value fluctuates due to this, the S/N ratio of the output voltage Vu decreases, and the temperature characteristics deteriorate.

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, have a simple circuit configuration, easily reduce noise, obtain a high S/N ratio, and provide a magnetoresistance effect that compensates for the temperature characteristics of an MR head. An object of the present invention is to provide a regenerative amplifier circuit for a magnetic head.

In order to achieve the above object, the reproducing amplifier circuit for a magnetoresistive magnetic head of the present invention includes a first magnetoresistive element for magnetically detecting information from a recording medium on which information is recorded, and a first magnetoresistive element for magnetically detecting information from a recording medium on which information is recorded. electrically connected in series with the first magnetoresistive element;
a second magnetoresistive element that is physically arranged in the vicinity of the first magnetoresistive element to perform temperature compensation of the first magnetoresistive element; and an amplifier circuit having a feedback section from an output section to an input section; , at least one of a first magnetoresistive element and a second magnetoresistive element.

Furthermore, in order to effectively achieve the above object, the amplifier circuit has a non-inverting input part and an inverting input part, and by keeping one of these input parts at a substantially constant potential, the other input part is connected to the non-inverting input part. The first input terminal is configured such that a substantially constant potential appears, and forms a magnetic head between the other input section and a common potential.
The first magnetoresistive element is provided with a magnetoresistive element, and is configured to commonly supply a drive current to the first magnetoresistive element and amplify the reproduced signal.

Embodiments of the regenerative amplifier circuit for an MR head according to the present invention will be described in detail below with reference to the drawings.

FIG. 4 is a diagram showing the first embodiment of the present invention, in which 10 is an MR head, 12 is an operational amplifier, 16 is a capacitor, 23 is a DC power supply terminal, 24 is an output signal terminal, 25 is for temperature compensation
In the MR element, 26 is a capacitor, and 27 and 28 are resistors. Here, the temperature compensation MR element 25 is
It is made in the same way as the MR head 10, and is electrically connected in series with the MR head 10, and
This element is physically located in the vicinity of the MR head 10 and is therefore configured to have the same temperature resistance characteristics as the MR head 10.

In FIG. 4, if the open-loop gain of the operational amplifier 12 is sufficiently higher than the closed-loop gain, and the frequency characteristics extend to a sufficiently high range, the temperature compensation MR element 25 The voltage V _- at the connection point between and the MR head 10 is the voltage at the connection point between the resistors 27 and 28.
MR element 25 for temperature compensation so that it is equal to V ₊
A current I _M is supplied to the MR head 10 from the output of the operational amplifier 12 via. Here, since the bias current of the operational amplifier 12 is generally extremely small,
It can be considered that the same current I _M flows through the temperature compensation MR element 25 and the MR head 10. Therefore, it is clear that the amount of heat generated by the temperature compensation MR element 25 due to the supplied current I _M and the amount of power generated by the MR head 10 maintain a predetermined ratio.

Furthermore, if the resistance value R _M of the MR head 10 changes due to the external magnetic field applied to the MR head 10, the MR
The voltage at the connection point between the head 10 and the temperature compensation MR element 25 (inverting input voltage) V _- is always the voltage at the connection point between the resistor 27 and the resistor 28 (non-inverting input voltage) V ₊
Since the feedback current (I _M ) changes to be equal to , an output voltage (Vu-
V _- ) is obtained. ((It should be noted that the output signal generated at the output section of the operational amplifier 12 is Vu.) According to the first embodiment shown in FIG. 4, the ambient temperature T
Due to the change in the resistance value R _M of the MR head 10, f
Even if the temperature compensation MR changes by (△T),
Since the resistance R _MS of the element 25 also changes by f(△T), the voltage gain of the regenerative amplifier circuit for the MR head is always constant, and an output signal Vo with a constant amplitude can be obtained regardless of changes in the ambient temperature T. .

Regarding this point, the present invention will be explained below in correspondence with the above equations (3) and (4).

Now, in FIG. 4, the current flowing through the first magnetoresistive element (MR head) 10 is I _M , the resistance value of the first magnetoresistive element 10 is R _M , and the operational amplifier 12 is non-inverting (+: plus). The non-inverting input voltage supplied to the input section is V ₊ (V ₊ is a voltage obtained by dividing the DC voltage Vc.c. supplied to the DC power supply terminal 23, and is made stable by the capacitor 26. ), the resistance value of the second magnetoresistive element 25 for temperature compensation provided between the output section and the inverting (-: minus) input section of the operational amplifier 12 is assumed to be _RMS . If the output voltage at the output section of the operational amplifier 12 is Vu' and the inverting input voltage generated at the inverting input section is V _- , then since the input impedance of the operational amplifier 12 is generally very large, the imaginal short Therefore, current I _M and output voltage Vu _' are expressed as I _M = V _{+ /} R _M Vu' = (1 + R _MS /R _M )・V ₊ ...(5) It will be done. Here, due to the change ΔT in the ambient temperature T, the respective resistance values R _M and R _MS of the two magnetoresistive elements 10 and 25 in the above equation (5) become f
(△T) times, the output voltage Vu′ in this case is Vu′={1+ _RMS・f(△T)/ _RM・f(△T)}・V
₊ =(1+ _RMS / _RM )·V ₊ ...(6), which is the same as equation (5) above.

In other words, the output voltage expressed by equation (6) above is
According to Vu', compared to equation (4) in the case of the second conventional example, the function f(△T) due to the ambient temperature T is removed, temperature compensation is performed, and the number of factors is reduced, so noise is generated. is reduced and the S/N ratio is improved.

Therefore, according to the first embodiment shown in FIG. 4, by using the temperature compensating MR element 25, it is possible to easily and almost completely compensate for the temperature.

By the way, in this first embodiment, the drive current I _M for the MR head 10 is supplied by the operational amplifier 12, which eliminates the need for an independent drive current circuit, which simplifies the configuration and eliminates the need for a noise source. Noga
Since only the resistance noise of the MR head 10 and the noise caused by the transistors of the operational amplifier 12 are generated, the noise can be reduced simply by using low-noise transistors for the first-stage transistors constituting the operational amplifier 12.
A regenerative amplifier circuit for an MR head with a high S/N ratio can be obtained.

Now, in order to correctly perform temperature compensation of the MR head 10, it is necessary to sufficiently match the characteristics of the temperature compensation MR element 25 to the characteristics of the MR head 10, but it is also necessary to ensure that these temperatures T _M are always equal. It is necessary to make it happen. Figure 5 shows the temperature compensation MR element 2 used in the present invention taking this point into consideration.
5 is a diagram showing an embodiment of the MR head 10.

In FIG. 5, 1, 2, 29 are metal electrodes,
3' is a ferromagnetic thin film, 4 is a recording medium, 10 is an MR head for detecting signal magnetization recorded on the recording medium 4, and 25 is an MR element for temperature compensation.

As is clear from this Figure 5, for temperature compensation
The MR element 25 is provided near the MR head 10 so that the influence of the ambient temperature T is applied almost equally. In addition, the temperature compensation MR element 25
The distance between the MR head 10 and the recording medium 4 is designed to be at least five times the distance between the MR head 10 and the recording medium 4. When designed in this way, the signal component detected by the temperature compensating MR element 25 is less than 5% of the signal detected by the MR head 10, so that no practical problem occurs.

Therefore, when the ambient temperature T changes by △T, the MR head 10 for signal magnetization detection and the temperature compensation
The temperature T _M of the MR element 25 changes in the same way, and their resistance values R _M and R _MS each change by f (ΔT) due to the same temperature characteristic. Therefore, the fourth
In the first embodiment shown in the figure, the metal electrode 1 is connected to the - (minus) input terminal (inverting input terminal) constituting the feedback section of the operational amplifier 12, the metal electrode 2 is connected to the ground, and the metal electrode 29 is connected to the negative input terminal (inverting input terminal). By connecting each to the output section of the operational amplifier 12 (the input side of the capacitor 16), it is possible to obtain a regenerative amplifier circuit for the MR head 10 that always provides a constant output Vo regardless of changes in the ambient temperature T. Here, the output signal Vo is a signal generated at the output signal terminal 24 and is an alternating current component of the output signal Vu output from the output section of the operational amplifier 12.

Note that the first embodiment shown in FIGS. 4 and 5 is a case of one channel, but can be similarly applied to a case of multiple channels.

Next, FIG. 6 shows a second embodiment of the present invention.

In this second embodiment, driving power supply and signal amplification are performed using emitter input type (base grounded type) transistors. In Figure 6,
30 is a transistor, and the other components are the same as in the embodiment shown in FIG. That is, the MR head 10 is inserted into the emitter of the transistor 30. Further, the temperature compensation MR element 25 is inserted into the collector of the transistor 30 and forms a collector load resistance of the transistor 30. Here, since the base current of the transistor 30 is sufficiently smaller than the collector current, almost the same current flows through the temperature compensating MR element 25 and the MR head 10. Therefore, it is clear that the amount of heat generated by the temperature compensation MR element 25 due to the supplied current and the amount of heat generated by the MR head 10 maintain a predetermined ratio. In other words, even if the state of the collector current fluctuates, no practical problem occurs.

Furthermore, by using the temperature compensation MR element 25 as the collector load resistance of the transistor 30, temperature compensation is performed by offsetting the resistance change due to the temperature change ΔT of the MR head 10 _. It is possible to obtain a stable regenerative amplifier circuit in which the level of the output signal does not change even if the signal changes.
Here, the temperature compensating MR element 25 is electrically connected in series with the MR head 10 via a transistor 30, and is physically located near the MR head 10.

The base voltage V _B of the transistor 30 is the resistor 27,
28, the DC power supply voltage Vc.c. is maintained at a substantially constant voltage. Therefore, an approximately constant voltage V _E (≈V _B −0.7v) also appears at the emitter. Therefore, the MR head 10 is supplied with the drive current I _M. And MR head 10
The resistance R _M of the recording medium 4 (see Figures 1 and 5)
If the collector current Ic (≒ _IM ) of the transistor 30 changes due to the external magnetic field caused by the
An output signal Vo can be obtained at the output signal terminal 24 via the capacitor 16.

In this second embodiment, the transistor 30 constitutes an amplified signal whose base and emitter are respectively input, and one of them, that is, the base input signal (voltage) is kept at a substantially constant potential (voltage) to achieve MR. The drive current IM is supplied to the head 10 and the signal is amplified.
Also in this second embodiment, as in the first embodiment shown in FIG. 4, it is possible to simplify the configuration and reduce noise by reducing noise sources.

Therefore, according to the embodiment shown in FIG. 6, it is possible to obtain a regenerative amplifier circuit for a magnetoresistive (MR) head with an extremely simple circuit configuration.

Next, FIG. 7 shows a third embodiment of the present invention, in which a DC amplifier circuit is added to the second embodiment shown in FIG. 6 to improve linearity.

In FIG. 7, 35 to 37 are transistors, 3
8 and 39 are level shift diodes, 40 is a capacitor, and 41 to 45 are resistors. The rest of the embodiment is the same as the second embodiment shown in FIG. The signal is amplified by an amplifier and then supplied to the output signal terminal 24 as an output signal. moreover,
Negative feedback is applied from the output of this DC amplifier to the emitter of the transistor 30 via the temperature compensating MR element 25 to compensate for the temperature of the MR head 10. Here, the temperature compensation MR element 25
is electrically connected in series with the MR head 10 and physically located near the MR head 10.

Therefore, according to the third embodiment, it is possible to obtain a regenerative amplifier circuit for the MR head 10 having better linearity than the second embodiment shown in FIG. However, for the current _IA flowing into the MR head 10 via the temperature compensation MR element 25,
The ratio of the drive current I _M flowing through the MR head 10 is worse than in the second embodiment shown in FIG. However, the ratio of the current I _A flowing through the temperature compensation MR element 25 to the drive current I _M flowing through the MR head 10 is still large, so if the state of the current I _A fluctuates, the drive current _IM also fluctuates. Therefore, no practical problems arise. It is also clear that the amount of heat generated by the temperature compensation MR element 25 due to the current I _A and the amount of heat generated by the MR head 10 maintain a predetermined ratio.

In the above embodiment, the supply of the drive current I M to the MR head 10 and the supply of the drive current I _M to the MR head 1
Since the amplification of the 0 output signal can be performed using a common amplifier circuit, the configuration is simple and there is less noise.
It is possible to obtain a regenerative amplifier circuit for an MR head (magnetoresistive head) which can almost completely compensate the temperature of the MR head 10.

Furthermore, in the regenerative amplifier circuit for the MR head of the above embodiment, it is clear that temperature compensation can be performed even if the connection positions of the MR head 10 and the temperature compensation MR element 25 are exchanged; This is a problem.

As explained above, according to the present invention, the temperature compensation of the MR head (a magnetic head using a magnetoresistive element) is achieved by the fact that the equivalent circuit of the MR head can be regarded as almost a pure resistance, and by using thin film technology. MR element (magnetoresistive element) with the same temperature characteristics as the head
Since it is extremely easy to manufacture, it is possible to provide a regenerative amplifier circuit for a magnetoresistive magnetic head that can provide excellent temperature compensation, has stable operation, and has little change in characteristics.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing an example of a magnetoresistive magnetic head, Fig. 2 is a characteristic diagram for explaining the operation of the magnetic head shown in Fig. 1, and Fig. 3 is a conventional magnetoresistive magnetic head. A circuit diagram showing the configuration of a regenerative amplifier circuit for a head, FIG. 4 is a circuit diagram showing a first embodiment of the present invention, and FIG. 5 is a magnetic resistance used in the first embodiment described in FIG. A schematic diagram of an effective magnetic head, FIG. 6 is a circuit diagram showing the configuration of a second embodiment of the invention, FIG. 7 is a circuit diagram showing the configuration of a third embodiment of the invention, and FIG. 8 is a circuit diagram showing the configuration of a third embodiment of the invention. FIG. 2 is a circuit diagram showing a second conventional example of a regenerative amplifier circuit for a magnetoresistive magnetic head. 10... Magnetoresistive magnetic (MR) head,
25... Magnetoresistive (MR) element for temperature compensation, 12... Operational amplifier, 30... Transistor for supplying drive current and amplifying signals.

Claims (1)

[Claims] 1. A first magnetoresistive element for magnetically detecting information from a recording medium on which information is recorded; and a first magnetoresistive element electrically connected in series with the first magnetoresistive element. It also has a second magnetoresistive element that is physically placed nearby and performs temperature compensation for the first magnetoresistive element, and an input section and an output section that are set to a substantially constant potential, A regenerative amplifier circuit for a magnetoresistive magnetic head, comprising: an amplifier circuit having a feedback section from the output section to the input section, the feedback section including the first magnetoresistive element and the second magnetoresistive element. 1. A regenerative amplifier circuit for a magnetoresistive magnetic head, characterized by comprising either one of a magnetoresistive element and a magnetoresistive element. 2. In claim 1, the amplifier circuit has a non-inverting input section and an inverting input section, and by keeping one of these input sections at a substantially constant potential, the other input section is provided with a substantially constant potential. The first magnetoresistive element, which serves as a magnetic head, is arranged between the other input section and the common potential, and the first magnetoresistive element is configured such that a potential appears, and a drive current for the first magnetoresistive element is provided. 1. A re-amplification circuit for a magnetoresistive magnetic head, characterized in that it is configured to commonly supply a signal and amplify a reproduced signal. 3. In claim 2, the amplifier circuit in which a substantially constant potential appears at the other input section includes: an operational amplifier; and a circuit that supplies a substantially constant DC voltage to a non-inverting input section of the operational amplifier. and the second magnetoresistive element connected between the output section of the operational amplifier and the inverting input section, and the first magnetoresistive element connected between the inverting input section and a common potential. A regenerative amplifier circuit for a magnetoresistive magnetic head, characterized in that it is provided with a regenerative amplifier circuit for a magnetoresistive magnetic head. 4. In claim 2, the amplifier circuit in which a substantially constant potential appears at the other input portion includes a first transistor, the first transistor has a base voltage kept substantially constant, A regenerative amplifier circuit for a magnetoresistive head, characterized in that the second magnetoresistive element is provided as a collector load resistor, and the first magnetoresistive element is provided between the emitter and a common potential. . 5. In claim 2, the amplifier circuit in which a substantially constant potential appears at the other input section includes: a first transistor whose base potential is kept substantially constant; and a collector output of the first transistor. a DC amplifier that inverts and amplifies a signal; and the second magnetic low drag effect element provided between the output section of the DC amplifier and the emitter of the first transistor, and the emitter of the first transistor. 1. A regenerative amplifier circuit for a magnetoresistive head, characterized in that said first magnetoresistive element is provided between a common potential and a common potential.