JP2017156279A - Magnetoresistive sensor and magnetic sensor probe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress noise of the magnetoresistive sensor and prevent increase in the power source.SOLUTION: The magnetoresistive sensor according to the present invention outputs a set pulse to one magnetoresistive sensor part, and outputs a reset pulse to another magnetoresistive sensor part, the set pulse and the reset pulse having opposite polarities.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a magnetoresistive sensor.

  Patent Document 1 below discloses a technique for reducing noise of a magnetoresistive sensor. In this document, 1 / f noise is reduced by outputting a set pulse / reset pulse from the set / reset circuit 701 to the magnetoresistive sensor unit 105 (Patent Document 1, FIG. 7, 0035 to 0042). reference).

WO2014 / 033904

  The set / reset circuit 701 as described in Patent Document 1 generally consumes a large amount of current. Therefore, the configuration as in Patent Document 1 in which the set / reset circuit 701 is provided for each magnetoresistive sensor unit 105 requires a large power source. In particular, when noise is suppressed by connecting a plurality of magnetoresistive sensor portions 105 in parallel as shown in FIG.

  The present invention has been made in view of the above problems, and an object thereof is to avoid an increase in the size of a power supply while suppressing noise of a magnetoresistive sensor.

  The magnetoresistive sensor according to the present invention outputs a set pulse to any one of the magnetoresistive sensor units, and outputs a reset pulse having a polarity opposite to that of the set pulse to other magnetoresistive sensor units.

  According to the magnetoresistive sensor of the present invention, noise can be suppressed by the set pulse / reset pulse, and an increase in the size of the power supply can be avoided by using the set pulse / reset pulse of opposite polarity.

It is a figure which shows the basic composition of the magnetoresistive sensor which concerns on Embodiment 1. FIG. It is a figure which shows the whole structure of a magnetoresistive sensor. 10 is a time chart showing a waveform of a set pulse / reset pulse output from a set / reset circuit and an operation waveform of a switch 109-2. It is a figure which illustrates the actual measurement result of the current waveform when the set / reset circuit outputs a set pulse / reset pulse. 6 is a configuration diagram of a magnetoresistive sensor according to Embodiment 2. FIG. It is a figure which shows another structural example of the magnetoresistive sensor which concerns on Embodiment 2. FIG. It is a block diagram of the magnetoresistive sensor which concerns on Embodiment 3. It is a block diagram of the magnetic sensor probe which concerns on Embodiment 4. FIG. It is a sectional side view of the magnetic sensor probe which concerns on Embodiment 4.

<Embodiment 1>
FIG. 1 is a diagram showing a basic configuration of a magnetoresistive sensor according to Embodiment 1 of the present invention. In FIG. 1, magnetoresistive elements 101-1, 101-2, 101-3, and 101-4 constitute a bridge circuit (magnetoresistance sensor unit 105) and detect a magnetic field by a minute resistance change due to a varying magnetic field. The DC voltage terminal 102 applies a DC voltage as a drive voltage for the magnetoresistive sensor unit 105. The preamplifier 103 amplifies the voltage across the magnetoresistive sensor unit 105 and outputs it from the output terminal 104.

  The set / reset circuit 106 includes a coil 106-1 that generates a magnetic field using the alternating current supplied from the alternating voltage terminal 106-2 and applies the magnetic field to the magnetoresistive element 101. When a magnetic field is applied to the magnetoresistive element 101, the magnetization direction of the magnetoresistive element 101 is aligned in one direction. Therefore, since the magnetization direction of the magnetoresistive element 101 is switched according to the frequency by the alternating current, an effect of canceling 1 / f noise due to fluctuation of the magnetization direction can be exhibited.

  FIG. 2 is a diagram showing the overall configuration of the magnetoresistive sensor. In FIG. 2, the outputs of the four magnetoresistive sensor units 105 are input in parallel to the detection circuit 110. The detection circuit 110 detects the output of the magnetoresistive sensor unit 105 using the output from the clock 108 as a reference signal. As described in Patent Document 1, noise can be suppressed by connecting the outputs of the plurality of magnetoresistive sensor units 105 in parallel. However, if the magnetoresistive sensor unit 105 is connected in parallel, the set / reset circuit 106 (shown in FIG. 1) is also connected in parallel. Therefore, the current consumed by these increases, and the power supply tends to increase in size. . Therefore, in the present embodiment, an increase in the size of the power source is suppressed by the following configuration.

  The positive power supply 107-1 supplies a positive voltage to the set / reset circuit 106. The negative power source 107-2 supplies a negative voltage to the set / reset circuit 106. These power supplies are connected to a common reference potential (ground potential in FIG. 2). It is desirable that the rated values of the voltages that can be output by these power supplies are equal in absolute value.

  The switch 109-1 is connected to each of the positive power source 107-1 and the negative power source 107-2, and switches which of these power sources receives voltage supply in synchronization with the output from the clock 108. The switch 109-2 operates in the same manner, except that a voltage is supplied from a power source opposite to that of the switch 109-1. For example, when switch 109-1 is set to receive a voltage supply from positive power supply 107-1, switch 109-2 is set to receive a voltage supply from negative power supply 107-2.

  The switch 109-1 supplies a voltage to any one of the plurality of set / reset circuits 106 (the upper half in FIG. 2). The switch 109-2 supplies a voltage to the remaining set / reset circuit 106 (the lower half in FIG. 2). As a result, when the positive power supply 107-1 supplies a positive voltage to any of the set / reset circuits 106, the negative power supply 107-2 supplies a negative voltage to the remaining set / reset circuits 106.

  FIG. 3 is a time chart showing the waveform of the set pulse / reset pulse output from the set / reset circuit 106 and the operation waveform of the switch 109-2. When the switch 109-2 is connected to the negative power source 107-2 side, the set / reset circuit 106 connected to the switch 109-2 receives a negative voltage from the negative power source 107-2 and receives a pulse corresponding thereto. Is output. For example, this can be used as a set pulse. At this time, the switch 109-1 is connected to the positive power source 107-1, and the set / reset circuit 106 connected to the switch 109-1 receives a positive voltage from the positive power source 107-1 and applies a pulse corresponding thereto. Output. For example, this can be used as a reset pulse.

  As shown in FIG. 3, by outputting a set pulse to one of the magnetoresistive sensor units 105 and outputting a reset pulse having the opposite polarity to the other magnetoresistive sensor unit 105, the following advantages are exhibited. Is done.

  If these pulses have the same polarity, set pulses / reset pulses having the same polarity are output to all the magnetoresistive sensor units 105. Since the magnetoresistive sensor units 105 are connected in parallel, the currents for generating these pulses are added by the number, and the current instantaneously becomes a very high value. The power supply needs to be enlarged to support this high current value.

  On the other hand, when set pulses / reset pulses having opposite polarities are used as shown in FIG. 3, the positive pulse current is added by the number of magnetoresistive sensor units 105 to which a positive voltage is supplied (in FIG. 2, two pulses are added). ), The negative pulse current is added by the number of magnetoresistive sensor units 105 to which a negative voltage is supplied (the remaining two in FIG. 2). As a result, the instantaneous value of the pulse current is halved compared to the case where the set pulse / reset pulse having the opposite polarity is not used, and it is sufficient that the power supply has a performance capable of supporting this. Therefore, the enlargement of the power source can be suppressed.

  FIG. 4 is a diagram illustrating an actual measurement result of a current waveform when the set / reset circuit 106 outputs a set pulse / reset pulse. FIG. 4A shows a current waveform in the conventional configuration. FIG. 4B shows a current waveform in the first embodiment. In the conventional configuration, the reset current flows slightly by being dragged by the set current, and similarly, the set current slightly flows by being dragged by the reset current. This can be attributed to the fact that the positive power source and the negative power source interfere with each other through the ground. On the other hand, in the first embodiment, the polarity of the set pulse and the polarity of the reset pulse are opposite and are output almost simultaneously, so that the influence of such interference can be mitigated and more accurate operation can be expected.

<Embodiment 2>
FIG. 5 is a configuration diagram of a magnetoresistive sensor according to Embodiment 2 of the present invention. In the second embodiment, the positive power source 107-1 and the negative power source 107-2 are configured as a dual power source 107 that can output both a positive voltage and a negative voltage. The positive voltage is, for example, + 10V, and the negative voltage is, for example, -10V.

  In FIG. 5, two magnetoresistive sensor portions 105 are connected in series. One end of the first magnetoresistive sensor unit 105 is connected to the positive voltage terminal of both power supplies 107, and the other end is connected to one end of the second magnetoresistive sensor unit 105. The other end of the second magnetoresistive sensor unit 105 is connected to the negative voltage terminals of both power sources 107. Other configurations are the same as those of the first embodiment.

  The contacts of the two magnetoresistive sensor units 105 in FIG. 5 are virtually 0V. According to the circuit configuration as shown in FIG. 5, it is not necessary to ground each magnetoresistive sensor unit 105, so there is an advantage that the circuit configuration can be simplified. Further, the use of both power sources 107 has an advantage that the number of power sources can be further suppressed.

  FIG. 6 is a diagram illustrating another configuration example of the magnetoresistive sensor according to the second embodiment. Three or more magnetoresistive sensor units 105 may be connected in series. In FIG. 6, the positive voltage supplied from both power sources 107 is, for example, + 15V, and the negative voltage is, for example, −15V. In this case, the contact point between the first and second magnetoresistive sensor units 105 is virtually + 5V, and the contact point between the second and third magnetoresistive sensor units 105 is virtually −5V. As a result, each magnetoresistive sensor unit 105 operates in the same manner as in FIG.

<Embodiment 3>
FIG. 7 is a configuration diagram of a magnetoresistive sensor according to Embodiment 3 of the present invention. In the third embodiment, the switch 109-1 switches between the positive voltage terminal and the negative voltage terminal of the both power sources 107. The switch 109-1 supplies a voltage to the sensor unit 111.

  The sensor unit 111 has a configuration in which outputs from the plurality of magnetoresistive sensor units 105 are input in parallel to the preamplifier 103. A set / reset circuit 106 is provided for each magnetoresistive sensor unit 105. The switch 109-1 is connected in parallel to each set / reset circuit 106. Alternatively, a set / reset circuit group may be formed by connecting a plurality of set / reset circuits 106 in series, and the switch 109-1 may be connected in parallel to each set / reset circuit group. The latter is adopted in FIG. Furthermore, a plurality of set / reset circuits 106 can be combined with a series connection and a parallel connection so as to be within the rated voltage and the rated current of both power sources 107. The same applies to the switch 109-2.

  When the sensor units 111 having a plurality of magnetoresistive sensor units 105 connected in parallel as shown in FIG. 7 are further connected in parallel, the total current supplied to each set / reset circuit 106 becomes larger. By adopting the present invention in such a configuration, it is possible to suppress an increase in the size of the power source, so that a magnetoresistive sensor having a plurality of sensor units as shown in FIG. 7 can be suitably constructed.

<Embodiment 4>
FIG. 8 is a configuration diagram of a magnetic sensor probe according to the fourth embodiment of the present invention. FIG. 8A shows a top view. FIG. 8B shows a side view. For convenience of explanation, FIG. 8 shows a state in which a member such as a cover explained in FIG. The magnetic sensor probe shown in FIG. 8 includes 20 units 112 (112-1 to 112-20) in which the magnetoresistive sensor unit 105 and the set / reset circuit 106 are paired. The unit 112 is attached on the substrate 201. A connector 202 is disposed on the substrate 201.

  FIG. 9 is a side sectional view of the magnetic sensor probe according to the fourth embodiment. On the substrate 201 described with reference to FIG. 8, a ground substrate 203 made of copper foil or the like is formed. The heat dissipation sheet 204 is a sheet formed of a material having a high heat transfer coefficient, and is disposed so as to cover the unit 112. The ground substrate 203 and the heat dissipation sheet 204 are in contact with each other, or at least are in thermal contact with each other to such an extent that the heat dissipation effect of the heat dissipation sheet 204 is not impaired.

  Below the ground substrate 203, a heat radiating plate 205 made of a metal plate such as an aluminum plate or a copper plate is disposed. The heat generated from the unit 112 is transmitted to the ground substrate 203 and the heat radiating plate 205 through the heat radiating sheet 204 and is radiated through the heat radiating plate 205. Thereby, heat generated by a large current flowing through the set / reset circuit 106 can be effectively radiated. By increasing the heat dissipation effect, it is possible to suppress the sensitivity of the magnetoresistive sensor from being reduced by heat.

  The entire magnetic sensor probe is covered with a cover 207. A heat insulating sheet 206 made of a material having a low heat transfer coefficient is disposed between the cover 207 and the heat radiating sheet 204. By the heat insulating sheet 206, the heat generated from the unit 112 is mainly directed toward the heat radiating plate 205, and the temperature of the upper surface of the cover 207 can be suppressed to some extent. By appropriately configuring the heat radiating sheet 204, the heat insulating sheet 206, and the like and setting the temperature of the upper surface of the cover 207 to, for example, about 40 ° C. or less, the biomagnetic field can be measured by bringing the upper surface of the cover 207 into contact with the living body.

<Modification of the present invention>
The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  In the above embodiment, the number of the magnetoresistive sensor units 105 that receive the set pulse is the same as the number of the magnetoresistive sensor units 105 that receive the reset pulse, but they are not necessarily the same. For example, when the total number of the magnetoresistive sensor units 105 is an odd number, one of the numbers may be increased by one. Similarly, in the configuration in which the switches 109-1 and 109-2 are connected to the sensor unit 111 as shown in FIG. 7, the number of sensor units 111 that receive a positive voltage and the number of sensor units 111 that receive a negative voltage are as follows. It doesn't have to be the same.

101-1 to 101-4: Magnetoresistive element 102: DC voltage terminal 103: Preamplifier 104: Output terminal 105: Magnetoresistive sensor unit 106: Set / reset circuit 107-1: Positive power supply 107-2: Negative power supply 107: Both Power supply 108: Clock 109-1 to 109-2: Switch 110: Detection circuit 111: Sensor unit 112-1 to 112-20: Unit 201: Substrate 202: Connector 203: Earth substrate 204: Heat radiation sheet 205: Heat radiation plate 206: Thermal insulation sheet 207: Cover

Claims (11)

A plurality of magnetoresistive sensor units in which magnetoresistive elements are bridge-connected,
A plurality of set / reset circuits for generating a set pulse and a reset pulse which are pulse signals for inverting the magnetization of the magnetoresistive element;
A detection circuit for detecting an AC signal output from the magnetoresistive sensor unit by the set pulse and the reset pulse generated by the set / reset circuit;
A positive power supply for supplying a positive voltage to the set / reset circuit;
A negative power supply for supplying a negative voltage to the set / reset circuit;
With
The set pulse and the reset pulse have opposite polarities,
The set / reset circuit generates the pulse signals having opposite polarities when the positive voltage is supplied and when the negative voltage is supplied,
The positive power supply supplies the positive voltage to any of the plurality of set / reset circuits,
The magnetoresistive sensor, wherein the negative power supply supplies the negative voltage to the set / reset circuit to which the positive power supply does not supply the positive voltage. The magnetoresistive sensor according to claim 1, wherein the ground terminal of the positive power source and the ground terminal of the negative power source are connected to a common reference potential. The magnetoresistive sensor according to claim 2, wherein the positive power source and the negative power source are configured as a dual power source having a positive terminal that outputs the positive voltage and a negative terminal that outputs the negative voltage. The magnetoresistive sensor further includes a series circuit in which a plurality of the magnetoresistive sensor units are connected in series,
The magnetoresistive sensor according to claim 3, wherein one end of the series circuit is connected to the positive terminal and the other end is connected to the negative terminal. The magnetoresistive sensor includes an even number of the set / reset circuits,
The positive power supply supplies the positive voltage to half of the plurality of set / reset circuits,
The magnetoresistive sensor according to claim 1, wherein the negative power supply supplies the negative voltage to the other half of the plurality of set / reset circuits. The magnetoresistive sensor includes an odd number of the set / reset circuits,
The positive power supply supplies the positive voltage to half the number obtained by subtracting 1 from the total number of the set / reset circuits, or to half the number obtained by adding 1 to the total number of the set / reset circuits. Against the positive voltage,
The magnetoresistive sensor according to claim 1, wherein the negative power supply supplies the negative voltage to the rest of the plurality of set / reset circuits. The absolute value of the rated value of the output possible voltage of the positive power supply is the same as the absolute value of the rated value of the output possible voltage of the negative power supply. A magnetic sensor probe for detecting magnetism using a magnetoresistive sensor, wherein the magnetoresistive sensor is
A plurality of magnetoresistive sensor units in which magnetoresistive elements are bridge-connected,
A plurality of set / reset circuits for generating a set pulse and a reset pulse which are pulse signals for inverting the magnetization of the magnetoresistive element;
A detection circuit for detecting an AC signal output from the magnetoresistive sensor unit by the set pulse and the reset pulse generated by the set / reset circuit;
A positive power supply for supplying a positive voltage to the set / reset circuit;
A negative power supply for supplying a negative voltage to the set / reset circuit;
With
The set pulse and the reset pulse have opposite polarities,
The set / reset circuit generates the pulse signals having opposite polarities when the positive voltage is supplied and when the negative voltage is supplied,
The positive power supply supplies the positive voltage to any of the plurality of set / reset circuits,
The magnetic sensor probe characterized in that the negative power supply supplies the negative voltage to the set / reset circuit that the positive power supply does not supply the positive voltage. The magnetic sensor probe is
A substrate on which the magnetoresistive sensor is disposed;
A metal foil formed on the substrate;
A heat dissipation sheet that covers the magnetoresistive sensor and dissipates heat generated from the magnetoresistive sensor;
With
The magnetic sensor probe according to claim 8, wherein the heat dissipation sheet is in contact with the metal foil. The magnetic sensor probe according to claim 9, further comprising a heat radiating plate in contact with the metal foil. The magnetic sensor probe further includes:
A cover covering the magnetoresistive sensor and the heat dissipation sheet;
A heat insulating sheet disposed between the cover and the heat dissipation sheet;
The magnetic sensor probe according to claim 10, comprising:

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