JP2770291B2 - Circuit for detecting change in resistance of magnetoresistive element - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic detection circuit using a magnetoresistive element, and particularly to detecting a change in resistance of a magnetoresistive element suitable for a reproducing circuit of a magnetic recording device. Circuit.

[Prior Art] Conventional resistance value change detection circuits include circuits as shown in FIGS. 12 to 14 depending on how to supply a bias current.

FIG. 12 shows a circuit described in Japanese Patent Application Laid-Open No. 61-87215, in which the intermediate terminals of the differential magnetoresistive elements M1 and M2 are connected to a low voltage source V1, and the other ends are connected via resistors R3 and R4, respectively. Supply current by connecting to low voltage source V2. By amplifying the potential difference between the connection points of M1 and R3, M2 and R4 with a differential amplifier consisting of transistors Q1, Q2, resistors R5, R6, Re, capacitive element Ce, and current sources I7, I8, the resistance of M1 and M2 is increased. A value change was detected.

FIG. 13 shows a circuit described in Japanese Patent Application Laid-Open No. 61-16009, in which intermediate terminals of differential magnetoresistive elements M1 and M2 are connected to a low voltage source V1, and the other ends are respectively Q3, Q4, R3, R4, The current is supplied by connecting to the low voltage source V2 via the current source consisting of V3.
By amplifying the potential difference between the connection point of the collector terminals of M1 and Q3 and the connection point of the collector terminals of M2 and Q4 with a differential amplifier consisting of Q1, Q2, R5, R6, Re, Ce, I7, and I8, The change in the resistance value of M1 and M2 was detected.

FIG. 14 shows a circuit described in JP-A-55-48825, in which the intermediate terminals of the differential magnetoresistive elements M1 and M2 are connected to a low-voltage source V1, and the other ends are respectively connected via inductive elements L3 and L4. Low voltage source V2
To supply current. M1 and L3, M2 and L4
The change in the resistance values of M1 and M2 was detected by amplifying the AC potential difference at the connection point of No. 1 with a differential amplifier consisting of Q1, Q2, R5, R6, Re, Ce, I7, and I8.

[Problems to be Solved by the Invention] The above-described conventional technology has problems in the following points.

In the conventional example of FIG. 12, since the resistors R3 and R4 are connected in parallel with the magnetoresistive effect element in terms of AC, the detection loss increases when the resistors R3 and R4 are reduced. Therefore, in order to reduce this loss, R3 and R4 are generally set to relatively large values.In this case, assuming that the current flowing through the magnetoresistive element is constant, R3 and R4 increase. A problem arises in that the power consumed by these resistors increases in proportion.

In the conventional example of FIG. 13, current is supplied to the magnetoresistive effect element by a current source circuit using a transistor, so that there is no loss due to parallel resistance as shown in FIG. Since the shot noise of Q4 and the thermal noise of resistors R3 and R4 are multiplied by M1 / R3 and M2 / R4 and added to the head noise, there is a problem that the input noise is large.

In addition, in the conventional example of FIG.
Since it uses L3 and L4, it cannot be applied to a circuit board that is mounted at high density. Even if a circuit suitable for integration such as a gyrator is used instead of the inductive elements L3 and L4, a transistor is used for this. Therefore, there arises a problem that noise generated in this portion cannot be ignored.

SUMMARY OF THE INVENTION An object of the present invention is to provide a circuit for detecting a change in resistance of a magnetoresistive element that can be easily integrated without increasing power consumption and noise of the circuit.

[Means for Solving the Problems] In order to achieve the above object, the present invention has taken the following measures.

1. One end of the magnetoresistive element is connected to a first voltage source, and the other end is connected to a second voltage source via a first resistor. Connect the emitter terminal of the first transistor to the connection point, the base terminal of the transistor to a third voltage source, and the collector terminal to the fourth voltage source via a current-to-voltage conversion element;
Each was connected.

FIG. 1 shows an example in which the present means is applied to a differential three-terminal magnetoresistive element.

2. One end of the magnetoresistive element is connected to a first voltage source, the other end is connected to a second voltage source via a first current source, and the magnetoresistive element and the first current source are connected. The emitter terminal of the first transistor is connected to the connection point of the first transistor, the base terminal of the transistor is connected to the third voltage source, and the collector terminal is connected to the fourth voltage source via an element for converting current into voltage. Each was connected.

FIG. 2 shows an example in which the present means is applied to a differential three-terminal magnetoresistive element.

3. One end of the magnetoresistive element is connected to the first voltage source, the other end is connected to the second voltage source via the first inductive element, and the magnetoresistive element and the first inductive element are connected. The emitter terminal of the first transistor is connected to the connection point of the first transistor, the base terminal of the transistor is connected to the third voltage source, and the collector terminal is connected to the fourth voltage source via an element for converting current into voltage. Each was connected.

FIG. 5 shows an example in which this means is applied to a differential three-terminal magnetoresistive element.

4. The center terminals of the two magnetoresistive elements having three differential terminals are connected to the first voltage source, and the resistance change detection circuit according to the first means is provided for each of the other terminals. Is detected as a differential output.

 An example of this means is shown in FIG.

5. The center terminals of two differential three-terminal magnetoresistive elements are connected to the first voltage source, and the other terminals are provided with the resistance change detecting circuit of the above-mentioned second means, and the outputs of both detecting circuits are provided. Is detected as a differential output.

 FIG. 2 shows an example of this means.

6. Connect the center terminals of the two magnetoresistive elements of the three differential terminals to the first voltage source, and provide the resistance change detection circuit of the above-mentioned item 3 for each of the other terminals, Is detected as a differential output.

 FIG. 5 shows an example of this means.

7. In the first means, the differential amplifier and the low frequency filter are further provided, and the non-inverting input of the differential amplifier is connected to the collector output terminal of the first transistor, and the inverting input is connected to the fifth voltage source. The amplifier output is connected to the base terminal of the first transistor via a low-frequency filter.

FIG. 7 shows an example in which this means is applied to a differential three-terminal magnetoresistive element.

8. The center terminals of the two magnetoresistive elements having three differential terminals are connected to the first voltage source, and the other terminals are provided with the resistance value change detection circuit according to the above item 7, and the outputs of both detection circuits are provided. Is detected as a differential output.

 An example of this means is shown in FIG.

9. In the seventh aspect of the above means, the first variable voltage source and the third
, And a third low-frequency filter, an output of the first variable voltage source is connected to one end of the magnetoresistive element, and a second end is connected to the other end via a first resistor. The third differential amplifier is connected to the fifth voltage source, the non-inverted input is connected to the collector output terminal of the first transistor, and the third differential amplifier is connected to the third differential amplifier. The output of the dynamic amplifier is connected to the control terminal of the first variable voltage source via a third low frequency filter.

FIG. 19 shows an example in which the present means is applied to a differential three-terminal magnetoresistive element.

10. In the seventh aspect of the above means, a bias conductor film that is insulated from and magnetically coupled to the magnetoresistive effect element is provided, and the first variable voltage source, the third differential amplifier, and the third A low-frequency filter for connecting the output of the first variable voltage source to the bias conductor film having one end connected to a sixth voltage source via a third resistor; Is connected to the fifth voltage source, the non-inverting input is connected to the collector output terminal of the first transistor, respectively, and the output of the third differential amplifier is passed through a third low-frequency filter. It is connected to the control terminal of the first variable voltage source.

FIG. 20 shows an example in which this means is applied to a differential three-terminal magnetoresistive element.

[Operation] 1. In the first term of the above means, the first resistor supplies a bias current to the magnetoresistive element via the first resistor and also applies a collector current to the first transistor.

In this state, when the resistance of the magnetoresistive element increases, for example, due to an external magnetic field, and the potential at the connection point with the first resistor decreases, the collector current of the first transistor increases to bring the potential at the connection point to a predetermined state. return. That is, the first transistor functions to fix the terminal potential thereof regardless of the change in the resistance of the magnetoresistive element.

That is, a change in the resistance of the magnetoresistive effect element results in a change in the collector current of the first transistor, which is converted into a terminal voltage of the element that converts the current into a voltage and is detected.

Since the terminal potential of the magnetoresistive element is fixed, the first resistor connected to this element is AC grounded by a low input impedance first transistor that operates as a kind of base ground, No detection loss. Therefore, this resistance can be set small.

In addition, the collector current of the first transistor can be set small separately from the bias current of the magnetoresistive element.

As described above, the means of the present invention makes it possible not only to reduce the power consumption of the detection circuit and to make it possible to integrate the detection circuit but also to make it stronger against external noise.

2. In the second means, the first current source supplies a current to the magnetoresistive element and the collector of the first transistor. Further, the terminal potential of the magnetoresistive element is fixed as in the case of the first means. A change in the resistance value of the magnetoresistive element results in a change in the collector current of the transistor, which is converted into a voltage change via the current-voltage conversion element.

Accordingly, this means not only brings about the same advantages as the means of the first item, but also, even if the resistance of the magnetoresistive element increases with time, the output due to the change in the resistance corresponds to the change in the current with respect to a constant collector current. The output is not reduced.

3. In the third means, the inductive element supplies a current to the magnetoresistive element and the collector of the first transistor via the inductive element. Since the inductive element has a high AC impedance, it tries to keep the current flowing through this element constant even if the current changes in response to a change in the resistance of the magnetoresistive element due to an external magnetic field. As a result, a change in the resistance of the magnetoresistive element is converted into a change in the collector current of the first transistor.

Therefore, this means brings about the same advantages as the means of the first item.
In addition, in this case, since the voltage applied to the magnetoresistive effect element in a DC manner is constant, the heat generated when the resistance of the element increases over time decreases. Further, since the power consumption by the inductive element is small, the power consumption can be reduced.

4. The fourth, fifth, and sixth items of the above-mentioned means correspond to the case of a magnetoresistive element having three differential terminals.
Needless to say, it has the same action as in item 3.

5. The seventh term of the means is to make the DC potential of the collector output terminal of the first transistor equal to that of the fifth voltage source, and by fixing this potential, the circuit connection with the subsequent stage is established. It is to make it easier. Needless to say, it has the same function as the means of the first term.

6. The eighth term of the above means is that the DC potential of each output terminal is automatically set to a required potential independently even if the DC resistance values of the two magnetoresistive elements in the case of three differential terminals change separately. In the case of a plurality of circuits, the same operation as in the seventh item is obtained.

7. The characteristic of the change in the resistance value of the magnetoresistive element with respect to the change in the magnetic field applied to the element is not constant but differs depending on the magnetic field bias. If the magnetic field bias is appropriate, an output signal corresponding to a change in the resistance value of the magnetoresistive effect element given by the AC magnetic field applied at the magnetic field bias point can be obtained with little distortion. Is too small or too small, the contrast of the amplitude of the output signal is lost and distortion occurs. Therefore, the magnetic field bias is preferably controlled so as not to be in an excessive or insufficient state.

When the present invention is applied, such control can be easily performed.

The ninth and tenth aspects of the above means provide such means.

That is, in the ninth or tenth term of the above means, the DC potential at the input of the differential amplifier becomes substantially the same as the fifth voltage source potential, but the AC input is amplified. The capacitance of the low-frequency filter connected to the output of the differential amplifier functions as an output integrating element. As a result, the output of the filter can detect the asymmetry of the output voltage of the differential amplifier and provide a control signal of the first variable voltage source with a correction signal for the excess or deficiency of the magnetic field bias.

In the ninth means, a current flowing through the magnetoresistive element is passed through the first variable voltage source, and in the tenth means, a required current flows through the bias conductor film. The magnetic field applied to the element via the magnetic coupling is controlled so that the magnetic field bias is appropriately controlled.

Example (Example 1) A first example of the present invention will be described with reference to FIG.

The center terminals of the three differential magnetoresistive elements M1 and M2 are connected to a voltage source V1, and the other ends are connected to a voltage source V2 via resistors R3 and R4, respectively. Magnetoresistance effect elements M1, M2 and resistance R3,
At the connection point of R4, connect the emitter terminals of the transistors Q1 and Q2 with the voltage sources Vb1 and Vb2 connected to the base terminals, respectively, and further connect the collector terminals Vout of the transistors Q1 and Q2.
1 and Vout2 are connected to a voltage source Vc via resistors R5 and R6, respectively.

The resistors R3 and R4 supply a bias current to the magnetoresistive elements M1 and M2 and a collector current for the transistors Q1 and Q2. The transistors Q1 and Q2 fix the terminal potentials of the magnetoresistive elements M1 and M2. By these, the change in the resistance value due to the external magnetic field of the magnetoresistive elements M1 and M2 is converted into a change in the collector current flowing through the transistors Q1 and Q2, and this is converted into a voltage change by the resistors R5 and R6. . According to the present embodiment, since the resistors R3 and R4 connected to the output terminals of the magnetoresistive element are AC grounded by the low input impedance transistors Q1 and Q2 that operate as a kind of base ground, the detection loss is reduced. It does not become. Therefore, unlike the conventional bias current supply method using a resistor as shown in FIG.
4 can be set small, and power saving of the bias section can be expected.

In the present embodiment, the magnetoresistive effect element is a three-terminal differential.
It is obvious that the same effect can be obtained even if only the resistors R3 and R5 and the voltage source Vb1 are used. Also, as shown in FIG. 3, the same effect can be expected by using the resistors R1 and R2 in place of the magnetoresistive elements M1 and M2 and the magnetoresistive elements M3 and M4 in place of the resistors R3 and R4. Is clear.

Embodiment 2 A second embodiment of the present invention will be described with reference to FIG.

The center terminals of the three differential magnetoresistive elements M1 and M2 are connected to a voltage source V1, and the other ends are connected to a voltage source V2 via current sources I3 and I4, respectively. Connect the emitter terminals of the transistors Q1 and Q2 with the base terminals connected to the voltage sources Vb1 and Vb2, respectively, to the connection points between the magnetoresistive elements M1 and M2 and the current sources I3 and I4, and further connect the collector terminals of the transistors Q1 and Q2. V
out1 and Vout2 are connected to a voltage source Vc via resistors R5 and R6, respectively.

The current sources I3 and I4 supply the bias currents to the magneto-resistive elements M1 and M2 and the collector currents of the transistors Q1 and Q2. The transistors Q1 and Q2 fix the terminal potentials of the magnetoresistive elements M1 and M2. By these, the change in the resistance value due to the external magnetic field of the magnetoresistive elements M1 and M2 is converted into a change in the collector current flowing through the transistors Q1 and Q2, and this is converted into a voltage change by the resistors R5 and R6. . In this embodiment, the magnetoresistive effect element is a three-terminal differential. However, this is a two-terminal M1 only transistor, a transistor Q1, a current source I3, a resistor R5, and a voltage source Vb1.
It is clear that the same effect can be obtained even if the configuration is constituted only by the above. In addition, as shown in FIG.
It is clear that the same effect can be expected by using the current sources I1 and I2 instead of, and the magnetoresistive elements M3 and M4 instead of the current sources I3 and I4.

Embodiment 3 A third embodiment of the present invention will be described with reference to FIG.

The center terminals of the three differential magnetoresistive elements M1 and M2 are connected to a voltage source V1, and the other ends are connected to a voltage source V2 via inductive elements L3 and L4, respectively. Connect the emitter terminals of the transistors Q1 and Q2 with the voltage terminals Vb1 and Vb2 connected to the base terminals to the connection points between the magnetoresistive elements M1 and M2 and the inductive elements L3 and L4, respectively, and further connect the collector terminals of the transistors Q1 and Q2. Vout1 and Vout2 are connected to voltage source Vc via resistors R5 and R6, respectively.
It is a configuration to connect to.

The inductive elements L3 and L4 supply a bias current to the magnetoresistive elements M1 and M2 and a collector current of the transistors Q1 and Q2. By these, the change in the resistance value due to the external magnetic field of the magnetoresistive elements M1 and M2 is converted into a change in the collector current flowing through the transistors Q1 and Q2, and this is converted into a voltage change by the resistors R5 and R6. .

According to this embodiment, since the DC voltage at the output terminal of the magnetoresistive element can be kept constant, even if the resistance value of the magnetoresistive element increases for some reason, the power consumed by the element is the resistance value. It does not accelerate heat generation because it decreases in inverse proportion to the increase in.

In the present embodiment, the magnetoresistive effect element is a three-terminal differential.
1. It is apparent that the same effect can be obtained even if only the inductive element L3, the resistor R5, and the voltage source Vb1 are used. Also, as shown in FIG. 6, instead of the magnetoresistance effect elements M1 and M2, the inductive elements L1 and L2 are used.
L2 is replaced by the magnetoresistive elements M3, M4 instead of the inductive elements L3, L4.
It is clear that the same effect can be expected even if is used.

(Embodiment 4) A fourth embodiment of the present invention will be described with reference to FIGS.

FIG. 7 shows a configuration diagram. The center terminals of the three differential magnetoresistive elements M1 and M2 are connected to a voltage source V1, and the other ends are connected to a voltage source V2 via resistors R3 and R4, respectively. Connect the emitter terminals of the transistors Q1 and Q2 whose base terminals are connected to each other at the connection point between the magnetoresistive elements M1 and M2 and the resistors R3 and R4, and further connect the collector terminals V of the transistors Q1 and Q2.
out1 and Vout2 are connected to a voltage source Vc via resistors R5 and R6, respectively. Further, the collector terminal Vout1 is connected to the non-inverting input of the differential amplifier A1 having the inverting input connected to the voltage source Vref, and this output terminal is connected to the base terminals of the transistors Q1 and Q2 via the resistor Rf. Is the capacitance element Cf
It is the structure grounded by.

The resistors R3 and R4 supply a bias current to the magnetoresistive elements M1 and M2 and a collector current for the transistors Q1 and Q2. At this time, if the collector current of the transistor Q1 is small and the collector terminal potential Vout1 is higher than Vref, the output potential of the differential amplifier A1 increases, the base potentials of the transistors Q1 and Q2 increase, and the collector current increases. Therefore, the DC potential of Vout1 and Vout2 is approximately Vre
is kept equal to f. The signal accompanying the change in the AC resistance value of the magnetoresistive element is not fed back to the base terminals of the transistors Q1 and Q2 by the action of the low-frequency filter composed of the resistor Rf and the capacitive element Cf, and thus is output directly to Vout1 and Vout2. . FIG. 8 shows a circuit in which an emitter follower including transistors Q3 and Q4 and resistors R9 and R10 is introduced as an output buffer, and the differential amplifier A1 is further embodied using two transistors Q5 and Q6 and resistors R7 and R8. Show.

According to the present embodiment, even if the DC resistance value of the magnetoresistive element changes, the collector potential Vout1 of the transistors Q1 and Q2 is
The feedback circuit operates so as to be equal to Vref, and can be automatically adjusted. Further, as shown in FIG. 9, in the resistance driving of the present embodiment, the resistances R3 and R4 for supplying the bias current can be set to be as small (about 1.5 times) as the magnetoresistive elements M1 and M2. Initial resistance values M1o, M2o of magnetoresistive elements M1, M2
Changes with time, the power P (M
1), P (M2) can be hardly changed, and a decrease in detection output can be suppressed.

In the present embodiment, the magnetoresistive effect element is a three-terminal differential.
2. It is obvious that the same effect can be obtained even if the configuration is omitted except for the resistors R4 and R6. The same effect can be obtained by using a current source instead of the resistors R3 and R4.
It is clear that the same effect can be expected even if M1 and M2 are replaced with resistors R3 and R4.

Fifth Embodiment A fifth embodiment of the present invention will be described with reference to FIGS.

FIG. 10 shows a configuration diagram. The center terminals of the three differential magnetoresistive elements M1 and M2 are connected to a voltage source V1, and the other ends are connected to a voltage source V2 via resistors R3 and R4, respectively. Transistors Q1, Q are connected to the connection points of the magnetoresistive elements M1, M2 and the resistors R3, R4.
2 are connected to the emitter terminals, and the collector terminals Vout1 and Vout2 of the transistors Q1 and Q2 are connected to the voltage source Vc via the resistors R5 and R6, respectively. Further, the collector terminal Vout1 is connected to the non-inverting input of the differential amplifier A1 having the inverting input connected to the voltage source Vref, and this output terminal is connected to the base terminal of the transistor Q1 via the resistor Rf1. Connected to one terminal of the capacitive element Cf.
Further, the collector terminal Vout2 is connected to the non-inverting input of the differential amplifier A2 having the inverting input connected to the voltage source Vref, and this output terminal is connected to the base terminal of the transistor Q2 via the resistor Rf2. Connect the base terminal to the capacitive element Cf
Is connected to the other terminal.

Here, the connection point between the resistor Rf1 or Rf2 and the base of the transistor may be grounded via the capacitive element Cf.

The resistors R3 and R4 supply a bias current to the magnetoresistive elements M1 and M2 and a collector current for the transistors Q1 and Q2. At this time, if the collector current of the transistor Q1 is small and the collector terminal potential Vout1 is higher than Vref, the output potential of the differential amplifier A1 increases,
Raise the base potential of the transistor Q1 and increase the collector current of Q1. If the collector current of the transistor Q2 is large and the collector terminal potential Vout2 is lower than Vref, the output potential of the differential amplifier A2 decreases, the base potential of the transistor Q2 decreases, and the collector current of Q2 decreases. Therefore, the DC potentials of Vout1 and Vout2 are kept substantially equal to Vref. The signal associated with the AC resistance change of the magnetoresistive element is output directly to Vout1 and Vout2 because it is not fed back to the base terminals of transistors Q1 and Q2 by the action of the low-frequency filter consisting of resistors Rf1, Rf2 and capacitor Cf. Is done. In FIG. 11, an emitter follower including transistors Q3 and Q4 and resistors R9 and R10 is introduced as an output buffer.
A circuit in which the differential amplifier A1 is embodied by using two transistors Q5 and Q6 and resistors R7 and R8, and a circuit in which the differential amplifier A2 is embodied by using two transistors Q7 and Q8 and resistors R11 and R12. Show.

According to the present embodiment, even if the DC resistance values of the differential magnetoresistive elements change separately, the feedback circuit operates so that the collector potentials Vout1 and Vout2 of the transistors Q1 and Q2 become equal to Vref, respectively. Can be adjusted automatically.

The same effect can be obtained by using a current source instead of the resistors R3 and R4.
It is clear that the same effect can be expected even if R4 is replaced.

The embodiment shown in FIG. 15 to FIG. 17 includes a magnetic head in which the present invention is a multi-track magnetic tape device and a magnetoresistive element as a head detecting element, and a circuit for amplifying a reproduction signal. The case where a cable having a plurality of conductors is used will be described.

(Embodiment 6) A sixth embodiment of the present invention will be described with reference to FIG.

One end of the magnetoresistive elements M1, M2,... Is shared, and the common terminal and the other terminal of each magnetoresistive element are connected to a circuit board using a cable (FPC) having a plurality of conductors.

The potential of each conductor connected to the magnetoresistive element is constant, and the current slightly changes.

According to this embodiment, since the potential of each conductor is constant and the current changes only minutely, a detection circuit with little interference between adjacent conductors can be configured.

Embodiment 7 A seventh embodiment of the present invention will be described with reference to FIG.

A bias current supply resistor R3,... Is provided near the head, one end of the magnetoresistive elements M1, M2,... Is shared, and the other end is connected with a bias current supply resistor R3,. , ... are shared. In this configuration, two common terminals and a terminal that is not shared by each magnetoresistive element are connected to a circuit board using a cable (FPC) having a plurality of conductors.

The potential of each conductor connected to the magnetoresistive element is constant, and the current is a small current required for detecting a change in resistance.

According to the present embodiment, since the potential of each conductor is constant and the current is small, the conductor itself can be made thin, and a detection circuit with little interference between adjacent conductors can be configured.

(Eighth Embodiment) An eighth embodiment of the present invention will be described with reference to FIG.

The resistors R3,... For supplying the bias current and the transistors Q1, Q2,.
, M2, ..., one end is connected, and the other end is connected to a bias current supply resistor R3, ..., and the other terminal of the resistor R3, ... is shared. Further, the magnetoresistive elements M1, M2,.
Are connected to the emitter terminals of the transistors Q1, Q2,..., Respectively, and the base terminals are made common. In this configuration, three common terminals and a collector terminal of each transistor are connected to a circuit board using a base (FPC) having a plurality of conductors.

The current of the conductor connected to the collector terminal of each transistor is a small current necessary for detecting a change in resistance.

According to this embodiment, by providing a resistive load on the substrate side, a circuit having a large output voltage and being resistant to external noise can be configured. In addition, since the current is small, the conductor itself can be made thinner, and a decrease in the distance between adjacent conductors can be expected.

Ninth Embodiment A ninth embodiment of the present invention will be described with reference to FIGS. The present embodiment is applied to a reproducing circuit using a shunt bias type differential magnetoresistive element having a conductor film provided on a magnetoresistive element as a magnetic head.

In FIGS. 12 to 14 of the conventional example, the magnetoresistive element M
1. The resistance change of M2 is changed to voltage change and this is differentially amplified. For this reason, the information of the waveform distortion due to the excess or deficiency of the bias magnetic field disappears at the output of Vout1 or Vout2. Therefore, in order to detect the excess or deficiency, it is necessary to separately amplify the voltage changes of the output terminals of M1 and M2, respectively, which complicates the circuit configuration. In this embodiment, the resistance change of M1 and M2 is
Since the signals are output to 1 and Vout2, the output waveform indicates the excess or deficiency of the bias magnetic field as shown below.

FIG. 18 is a diagram showing how the resistance of the magnetoresistive element changes with respect to an external magnetic field. If the current flowing through the element is set appropriately, the bias point becomes Hb0, and detection with less distortion is possible. However, when the bias magnetic field Hb− has a small current, the resistance change is greatly distorted in the direction in which the external magnetic field decreases, and when the bias magnetic field Hb + has a large current, the resistance change is largely distorted in the direction in which the external magnetic field increases. Therefore,
If the distortion of the reproduction waveform is detected and the current flowing through the element is controlled, an appropriate bias magnetic field can be applied, and the resistance change with less distortion can be detected.

FIG. 19 shows a configuration for realizing the above method. The basic configuration of the detection circuit uses the configuration shown in FIG. 10 of the fifth embodiment. In this embodiment, a differential amplifier A3, a low-frequency filter including a resistor Rg and a capacitor Cg, and a transistor Q9 are added to this configuration. Inverting input of differential amplifier A3 to voltage source
Connect to Vref and the non-inverting input to output terminal Vout1. The output of A3 is connected to the base terminal of the transistor Q9 via the resistor Rg, and the capacitive element Cg whose one end is grounded is connected. Transistor collector terminal to voltage source
Vc, and the emitter terminal is connected to the center tap of the magnetic head instead of the voltage source V1.

The DC potential of the output terminal Vout1 is kept substantially equal to the potential of the voltage source Vref by the function of the amplifier A1. Therefore, when the bias magnetic field is insufficient, the time during which the output of the amplifier A3 is on the positive side increases. By integrating this output and raising the potential of the base terminal of the transistor Q9, the voltage source V1
Is operated to increase the electric current flowing through the head by increasing the potential of the head, and to make the bias magnetic field appropriate.

According to this embodiment, even if the optimum bias magnetic field changes due to the variation of the magnetic head or the change of the resistance value over time, it can be automatically corrected.

In the present embodiment, the magnetic head is of a three-terminal differential type, but it is apparent that a two-terminal head can be similarly realized.

(Embodiment 10) A tenth embodiment of the present invention will be described with reference to FIG. This embodiment is applied to a reproducing circuit using a current bias type differential magnetoresistive element in which a conductor film is provided on a magnetoresistive element via an insulating film as a magnetic head.

Fig. 20 shows the configuration. The basic configuration of the detection circuit uses the configuration shown in FIG. 10 of the fifth embodiment. Magnetoresistance effect element M1,
A bias magnetic field is applied to M2 so as to be differentially detected by the bias conductor films B1 and B2. In this embodiment, a low-frequency filter including a differential amplifier A3, a resistor Rg, and a capacitive element Cg, a transistor Q9, and resistors Ri1, R
Add i2. The inverting input of the differential amplifier A3 is connected to the voltage source Vref, and the non-inverting input is connected to the output terminal Vout1. The output of A3 is connected to the base terminal of the transistor Q9 via the resistor Rg, and the capacitive element Cg whose one end is grounded is connected. A configuration in which the collector terminal of the transistor is connected to a voltage source Vc, the emitter terminal is connected to a bias conductor film B1 having one end grounded via a resistor Ri1, and the bias terminal is connected to a bias conductor film B2 having one end grounded via a resistor Ri2. It is.

The DC potential of the output terminal Vout1 is kept substantially equal to the potential of the voltage source Vref by the function of the amplifier A1. Therefore, when the bias magnetic field is insufficient, the time during which the output of the amplifier A3 is on the positive side increases. By integrating this output and raising the potential of the base terminal of the transistor Q9, the current flowing through the bias conductor films B1 and B2 is increased, and the bias magnetic field is made appropriate.

According to this embodiment, even if the optimum bias magnetic field changes due to the variation of the magnetic head or the change of the resistance value over time, it can be automatically corrected.

In the present embodiment, the magnetic head is of a three-terminal differential type, but it is apparent that a two-terminal head can be similarly realized.

Embodiment 11 An eleventh embodiment of the present invention will be described with reference to FIG.

In the present embodiment, the present invention is applied to a recording / reproducing circuit of a magnetic disk device in which a large number of heads are mounted on a disk surface.

A disk D having a magnetic material attached thereto is mounted on a central axis S, and a large number of magnetic heads H11 to H1n mounted on a head arm HA1 are arranged while keeping a narrow gap in the plane. A magneto-resistance effect element is used as a reproducing element of the magnetic head. In this configuration, a reproducing head terminal is inputted to a detection circuit IC1 according to the present invention via a current supply resistor network RM1.

The magnetization information recorded by rotating the disk D is reproduced by a large number of magnetoresistive heads H11 to H1n. At this time, a current is supplied to the magnetoresistive element by the resistance network RM1, and only a small detection current flows through the detection circuit IC1.
The detection circuit IC1 converts a minute current change generated in the magnetoresistive effect element into a voltage change and performs waveform processing such as amplification.

According to the present invention, as described above, the resistance for applying a bias current to the magnetoresistive element can be reduced, the detection loss is reduced, and integration can be performed.
Further, by providing a resistance network for supplying a current to the magnetoresistance effect element outside the detection circuit of IC1 as in the present embodiment, even if a large number of magnetoresistance effect magnetic heads are driven simultaneously, the portion of this detection circuit can be reduced. Power consumption can be made relatively small, and integration becomes easy. In addition, since the output terminal potential of the magnetoresistive element does not change, simultaneous reproduction with a large number of heads can be realized with low power consumption and low crosstalk, and the access time of the device can be greatly reduced.

In the present invention, the case of one head arm has been described, but by providing a head arm of a similar configuration on the lower surface of the disk or another angle as shown in FIG. 21,
Obviously, a magnetic recording device with a shorter access time can be realized.

[Effects of the Invention] According to the present invention, the impedance of the output terminal of the magnetoresistive element is determined by the small value of the input impedance of the base-grounded transistor. The current flowing through the transistor for detecting the resistance value of the magnetoresistive element can be reduced separately from the bias current of the element, so that the power consumption of the detection circuit can be reduced and a circuit resistant to external noise can be realized.
Further, integration becomes easier.

In particular, according to the present invention, even when a large number of magnetoresistive magnetic heads are driven at the same time, integration can be achieved, and further, access time can be significantly reduced with low crosstalk.

[Brief description of the drawings]

1 and 3 show a first embodiment of the present invention, FIGS. 2 and 4 show a second embodiment of the present invention, and FIGS. 5 and 6 show a third embodiment of the present invention. It is a figure which shows the Example of. FIG. 7 is a block diagram showing a fourth embodiment of the present invention, FIG. 8 is a specific circuit diagram thereof, and FIG. 9 is power consumption with respect to a change over time in the resistance value of the magnetoresistive element. FIG. 6 is a diagram showing the variation of the data. Also,
FIG. 10 is a block diagram showing a fifth embodiment of the present invention, and FIG. 11 is a specific circuit diagram thereof. 12, 13 and 14 are views showing a conventional example, FIG. 15 is a view showing a sixth embodiment,
FIG. 16 is a diagram showing a seventh embodiment, and FIG. 17 is a diagram showing an eighth embodiment. FIG. 18 is a diagram showing the relationship between the applied magnetic field of the magnetoresistive element and the resistance of the same device, FIG. 19 is a diagram showing the ninth embodiment, and FIG. 20 is a diagram showing the tenth embodiment. is there. FIG. 21 is a diagram showing an eleventh embodiment, particularly showing an embodiment in which the present invention is applied to a magnetic recording apparatus using a magnetic disk as a recording medium. Explanation of reference symbols M1, M2, M3, M4 ...: magnetoresistive effect element. R1, R2, R3, R4, R5, R6 ... Resistance. Q1-Q8: Transistors. I1, I2, I3, I4 ... Current sources. L1, L2, L3, L4 …… Inductive elements. V1, V2, Vc, Ve, Vee ... Voltage source. Rf, Rf1, Rf2, Rg ... Low-frequency filter resistors. Cf, Cg: Capacitance element for low frequency filter. A1, A2, A3 …… Differential amplifier. B1, B2 ... Bias conductor film. H11 ~ H2n ... Magnetic head. RM1, RM2 ... Resistance net. IC1, IC2 ... Detection circuit. HA1, HA2 ... Head arm.

────────────────────────────────────────────────── (5) References JP-A-58-189803 (JP, A) JP-A-60-40504 (JP, A) JP-A-60-143419 (JP, A) JP-A 62-189803 245503 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G11B 5/00

Claims (10)

(57) [Claims] In a circuit for detecting a change in the resistance of a magnetoresistive element whose resistance changes due to an external magnetic field, one end of the magnetoresistive element is connected to a first voltage source, and the other end is connected to a first resistor. And the emitter terminal of the first transistor is connected to the connection point between the magnetoresistive element and the first resistor, and the base terminal of the transistor is connected to the third voltage source. And a collector terminal connected to a fourth voltage source via an element for converting a current into a voltage, respectively. 2. A circuit for detecting a change in resistance of a magnetoresistive element whose resistance changes due to an external magnetic field, wherein one end of the magnetoresistive element is connected to a first voltage source, and the other end is connected to a first current source. Connected to a second voltage source via a source,
A first point is connected to a connection point between the magnetoresistive element and the first current source.
The emitter terminal of the transistor is connected, the base terminal of the transistor is connected to a third voltage source, and the collector terminal is connected to a fourth voltage source via an element for converting a current into a voltage. Circuit for detecting a change in the resistance of a magnetoresistive element. 3. A circuit for detecting a change in the resistance of a magnetoresistive element whose resistance changes according to an external magnetic field, wherein one end of the magnetoresistive element is connected to a first voltage source, and the other end is connected to a first induction terminal. The transistor is connected to a second voltage source via an element, an emitter terminal of the first transistor is connected to a connection point between the magnetoresistive element and the first inductive element, and a base terminal of the transistor is connected to the third terminal. A circuit for detecting a change in resistance of a magnetoresistive element, wherein the circuit is connected to a voltage source and a collector terminal is connected to a fourth voltage source via an element for converting a current into a voltage. 4. A circuit for detecting a change in the resistance value of a magnetoresistive element having three differential terminals, wherein the center terminals of the two magnetoresistive elements having three differential terminals are connected to a first voltage source and the other terminal is connected to a first voltage source. A resistance value change detection circuit for a magnetoresistive element, wherein the resistance value change detection circuit according to claim 1 is provided for each of them, and outputs of both detection circuits are detected as differential outputs. 5. A circuit for detecting a change in the resistance value of a three-terminal differential magnetoresistive element, wherein the center terminals of the two differential three-terminal magnetoresistive elements are connected to a first voltage source, and the other terminals are connected to a first voltage source. 3. A resistance value change detection circuit for a magnetoresistive element, wherein the resistance value change detection circuit according to claim 2 is provided for each of them, and outputs of both detection circuits are detected as differential outputs. 6. A resistance change detecting circuit for a magnetoresistive element having three differential terminals, wherein the center terminals of the two magnetoresistive elements of the three differential terminals are connected to a first voltage source, and the other terminal is connected to a first voltage source. A resistance value change detection circuit for a magnetoresistive element, comprising: a resistance value change detection circuit according to claim 3 for each of them; and detecting outputs of both detection circuits as differential outputs. 7. A resistance change detecting circuit according to claim 1, further comprising a differential amplifier and a low-frequency filter, wherein a non-inverting input of the differential amplifier is provided to a collector output terminal of the first transistor, and an inverting input is provided. Is connected to a fifth voltage source, and the amplifier output is connected to the base terminal of the first transistor via a low-frequency filter. 8. A circuit for detecting a change in resistance of a magnetoresistive element having three differential terminals, wherein two circuits for detecting change in resistance according to claim 7 are provided, and outputs of both circuits are detected as differential outputs. And a resistance change detecting circuit for the magnetoresistive element. 9. The resistance change detecting circuit according to claim 7, further comprising a first variable voltage source, a third differential amplifier, and a third low frequency filter, wherein one end of the magnetoresistive element is provided. Is connected to the output of the first variable voltage source, the other end is connected to the second voltage source via the first resistor, and the inverting input of the third differential amplifier is connected to the 5 voltage sources,
A non-inverting input is connected to a collector output terminal of the first transistor, and an output of the third differential amplifier is connected to a control terminal of the first variable voltage source via a third low frequency filter. A circuit for detecting a change in resistance of a magnetoresistive element. 10. A resistance change detecting circuit according to claim 7, further comprising: a bias conductor film insulated from the magnetoresistive effect element and magnetically coupled thereto.
Wherein a variable voltage source, a third differential amplifier and a third low frequency filter are provided, and one end of the output of the first variable voltage source is connected to a sixth voltage source via a third resistor. The third differential amplifier is connected to a fifth voltage source, the non-inverting input is connected to the collector output terminal of the first transistor, and the third differential amplifier is connected to the collector output terminal of the first transistor.
Wherein the output of the differential amplifier is connected to a control terminal of the first variable voltage source via a third low-frequency filter.