JP2020041945A - Magnetic field detection sensor - Google Patents

Abstract

To provide a magnetic field detection sensor with which it is possible to suppress the influence of hysteresis and increase detection accuracy without incurring drawbacks such as an increase in device size and a limitation on detection range.SOLUTION: An AC bias current is supplied to a bias coil 22 of a magnetic impedance element 20 and an AC bias magnetic field of an amplitude equal to or higher than a saturation level is applied. An impedance change of a magnetic thin-film 21 is detected as an output signal Vout1, and the levels of an A output signal SGA and a B output signal SGB equivalent to the peak points of the AC bias magnetic field are detected using a section determining signal SGD synchronized to the waveform of the AC bias magnetic field. With the magneto-sensitive axis of the magnetic impedance element 20, the change axis of the AC bias magnetic field and the direction of an external magnetic field aligned, the A output signal SGA and the B output signal SGB at each peak point are detected synchronously in timing with a section in which the direction of the external magnetic field and the direction of a change of the AC bias magnetic field are aligned. As the directions of change are aligned, it is possible to suppress the influence of hysteresis.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnetic field detection sensor using a magnetic impedance effect.

  Generally, various electric components and the like using a magnetic material have hysteresis characteristics. That is, in the BH curve representing the relationship between the magnetic field H applied to the magnetic body and the magnetic flux density B, the characteristic when the magnetic field H changes in the increasing direction and the characteristic when the magnetic field H decreases in the reverse direction. And a characteristic corresponding to the hysteresis appears. Therefore, in a magnetic field detection sensor or the like using a magnetic material having hysteresis, the effect of hysteresis appears as an error in the detection result. Therefore, it is necessary to suppress the influence of hysteresis in order to increase the detection accuracy.

  For example, the current detector of Patent Document 1 shows a technique for eliminating the effect of hysteresis with a simple configuration without complicated operation. More specifically, a magnetic core is provided in the form of a magnetic core that is annularly arranged along the circumferential direction of the magnetic field generated when the detected current is conducted, and has a gap in which a Hall element is arranged in part, and a magnetic core. A degaussing circuit is provided that applies an alternating current having a predetermined attenuation characteristic at a frequency within a predetermined range to the degaussing coil, thereby eliminating magnetic flux remaining on the magnetic core.

  Further, the current sensor disclosed in Patent Document 2 shows a technique for enabling an increase in hysteresis to be suppressed even when a through hole of a core through which a conductive member is passed is increased. Specifically, a core is formed by bending a plate material, and a projection is formed by a half blanking process on a pair of opposing pieces disposed opposite to both ends of the core, and a Hall element is arranged between the projections. By providing the protrusions to reduce the core gap cross-sectional area, the permeance coefficient decreases, and the hysteresis decreases. Therefore, the increase in hysteresis when the through hole is increased is offset.

  The magnetic sensor disclosed in Patent Document 3 discloses a technique for normally detecting an external magnetic field without being affected by hysteresis. Specifically, the current control unit controls the current so that the intensity of the coil magnetic field H unilaterally increases or unilaterally decreases from the initial value. As a result, the measured magnetic field Ho can be canceled or a part thereof can be canceled. Then, when the detection signal is input, the current control unit controls the current so that the strength of the coil magnetic field H returns to the initial value. Also, as a characteristic configuration, it is shown that the initial value is the intensity of a magnetic field that gives a saturation magnetization to the spin-valve magnetoresistive element. That is, each time the measurement is completed, the intensity of the applied coil magnetic field H is returned to the initial value, the magnetization of the spin-valve magnetoresistive element is saturated, and the operating point of the current control always shows the linearity of the hysteresis curve. It is performed in a certain route portion among the route portions that the user has.

JP-A-2006-188790 JP 2014-10012 A JP 2011-185870 A

  Meanwhile, in a high-permeability alloy magnetic material such as an amorphous alloy wire, the impedance changes sensitively in response to an external magnetic field due to the skin effect. This is the magneto-impedance effect. Even when the magnetic sensor includes a magnetic detection element (MI element) utilizing the magnetic impedance effect, the above-described effect of the hysteresis appears. Therefore, to increase the detection accuracy, it is necessary to suppress the influence of the hysteresis. .

  However, in the technique of Patent Document 1, it is necessary to add a dedicated degaussing circuit and a coil, so that it is inevitable that the sensor becomes large. Further, in the technique of Patent Literature 2, there is a concern that an error may occur due to variation in the positions of the protrusions and the Hall elements (see paragraph “0053” of Patent Literature 2). Further, the technique of Patent Document 3 has a problem that measurement is impossible in a magnetic field environment where the magnetic field is equal to or more than the initial value Hs, and the detectable range is narrow.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to provide a magnetic field detection capable of suppressing the influence of hysteresis and increasing the detection accuracy without causing adverse effects such as an increase in size and a limitation of a detection range. It is to provide a sensor.

In order to achieve the above-mentioned object, a magnetic field detection sensor according to the present invention has the following features (1) to (5).
(1) A magnetic field detection sensor comprising: a magnetic material having a magnetic impedance effect; a magnetic detection element including a bias coil for applying a bias magnetic field to the magnetic material; and a high-frequency oscillation circuit for supplying a high-frequency current to the magnetic material. hand,
An AC bias circuit for supplying an AC bias current for generating an AC bias magnetic field having an amplitude larger than a level at which the magnetic flux density in the magnetic detection element is saturated to the bias coil,
A timing signal generator that generates a timing signal synchronized with the AC waveform of the AC bias current;
According to the timing of the timing signal, a signal detection unit that detects a signal reflecting the detection state of the magnetic detection element,
A magnetic field detection sensor comprising:

(2) The signal detection unit includes a peak detection unit that detects a peak value of a signal in a predetermined section of the AC waveform according to a timing of the timing signal.
The magnetic field detection sensor according to the above (1), wherein:

(3) the magnetic sensing axis of the magnetic sensing element, the axis of change of the AC bias magnetic field, and the axis of change of the external magnetic field to be detected in the magnetic sensing element are arranged in the same direction;
The signal detection unit detects a signal reflecting a magnetic detection state of the magnetic detection element at a timing when the direction of the external magnetic field and the direction of the AC bias magnetic field match.
The magnetic field detection sensor according to the above (1) or (2), wherein

(4) The signal detection unit has a plurality of peak detection units that individually detect signals in the respective directions when the external magnetic field and the AC bias magnetic field appear in a plus direction and a minus direction with respect to a predetermined direction. ,
The magnetic field detection sensor according to the above (3), wherein:

(5) A bridge circuit including the magnetic detection element is configured, and a change in impedance in the magnetic detection element is detected as the signal by the bridge circuit.
The magnetic field detection sensor according to any one of (1) to (4), wherein:

  According to the magnetic field detection sensor having the configuration (1), when the signal detection unit grasps the magnetic detection state of the magnetic detection element, it is possible to suppress the influence of the hysteresis characteristic of the magnetic detection element. That is, due to the effect of the AC bias magnetic field generated by the AC bias current, even when no external magnetic field is applied, the magnetic detection element transitions to a state where the magnetic flux density is saturated, and thus is less affected by hysteresis. Further, since the signal detection unit grasps the magnetic detection state of the magnetic detection element according to the timing of the timing signal, it is possible to specify the timing at which the direction of the change of the external magnetic field and the direction of the change of the AC bias magnetic field are aligned. That is, by detecting the external magnetic field at a timing when the direction of the change of the external magnetic field and the direction of the change of the AC bias magnetic field are aligned, it is possible to avoid the influence of the difference in the direction on the hysteresis characteristic. Further, since the AC bias magnetic field is used, both the positive and negative external magnetic fields can be detected.

  According to the magnetic field detection sensor having the configuration (2), the peak value detected by the peak detection unit indicates the signal level at the timing immediately before the direction of change of the AC bias magnetic field applied to the magnetic detection element is switched. Therefore, necessary signal information can be obtained before the influence of the difference in the direction on the hysteresis characteristic of the magnetic sensing element appears. Further, since the peak detector follows the timing of the timing signal, it can detect the timing when the direction of the change in the external magnetic field and the direction of the change in the AC bias magnetic field are aligned, that is, the peak value of the signal in a predetermined section of the AC waveform.

  According to the magnetic field detection sensor having the above configuration (3), the detection sensitivity to the external magnetic field can be increased by aligning the magnetic sensing axis of the magnetic detection element and the change axis of the external magnetic field in the same direction. In addition, the change axis of the external magnetic field and the change axis of the AC bias magnetic field are aligned in the same direction, and the signal detection unit grasps the timing at which these directions match, thereby avoiding the influence of the difference in the direction on the hysteresis characteristics. It becomes possible.

  According to the magnetic field detection sensor having the configuration (4), the magnitudes of the external magnetic field in both the plus direction and the minus direction can be detected by the plurality of peak detection units. Further, each peak value can be detected at a timing when the external magnetic field in the plus direction and the negative direction and the change direction of the AC bias magnetic field are aligned.

  According to the magnetic field detection sensor having the configuration (5), when the impedance of the magnetic detection element changes according to the external magnetic field, a signal that changes with high sensitivity according to the external magnetic field can be output from the bridge circuit.

  According to the magnetic field detection sensor of the present invention, since the influence of hysteresis can be suppressed, it is possible to increase the detection accuracy. Further, since a degaussing circuit is not required, miniaturization is possible. Further, since no special magnetic core is required, it is not necessary to consider the hysteresis of the magnetic core. Further, since the hysteresis can be suppressed without affecting the detection range of the external magnetic field, the external magnetic field can be detected over a wide range.

  The present invention has been briefly described above. Further, details of the present invention will be further clarified by reading through embodiments for carrying out the invention described below (hereinafter, referred to as “embodiments”) with reference to the accompanying drawings. .

FIG. 1 is a block diagram illustrating a configuration example of a magnetic field detection sensor according to an embodiment of the present invention. FIG. 2 is a graph showing an example of a BH curve and impedance characteristics of a magnetic impedance element. FIG. 3 is a schematic diagram illustrating an example of a relationship between a magnetic field of a magneto-impedance element and a sensor output signal. FIG. 4 is a graph showing an example of a magnetic field-output voltage characteristic of a magnetic impedance element when an AC bias magnetic field is not used. FIGS. 5A, 5B, 5C, and 5D are time charts showing the time-series change of each signal in a state where the conditions of the external magnetic field are different from each other. FIG. 6 is a graph showing an example of the relationship between the external magnetic field of the magneto-impedance element and the voltages of the A output and the B output. FIG. 7 is a schematic diagram showing the relationship between the magnetic sensing axis of the magnetic impedance element, the axis of change of the AC bias magnetic field, and the direction of the external magnetic field.

  Specific embodiments of the present invention will be described below with reference to the drawings.

<Configuration example of magnetic field detection sensor>
FIG. 1 shows a configuration example of the magnetic field detection sensor 10 according to the embodiment of the present invention.

  The magnetic field detection sensor 10 shown in FIG. 1 includes a magnetic impedance element 20 for detecting an external magnetic field. The magneto-impedance element 20 includes a magnetic thin film 21 made of a magnetic material that produces a magneto-impedance effect. Further, a bias coil 22 is arranged so as to be wound around the magnetic thin film 21 so that an AC bias magnetic field can be applied to the magnetic thin film 21. In the present embodiment, an AC bias magnetic field is used to suppress the influence of hysteresis of the magnetic thin film 21 in particular.

  In the configuration shown in FIG. 1, the magnetic thin film 21 of the magnetic impedance element 20 forms a full bridge circuit 13 together with the resistors 13a, 13b and 13c. That is, the configuration is such that the change in the resistance value of the magnetic thin film 21 can be detected by the full bridge circuit 13.

  Note that the magnetic impedance element 20 employed in the present embodiment has a characteristic in which the impedance is maximized in a reference state where no external magnetic field is applied. The resistances of the resistors 13a, 13b, and 13c are selected so that the full bridge circuit 13 is in an equilibrium state with the impedance of the magnetic impedance element 20 being maximized.

  One of the two input terminals of the full bridge circuit 13 is connected to the output of the buffer 12, and the other is grounded. The oscillator 11 is connected to the input of the buffer 12. The oscillator 11 supplies a high-frequency voltage having a frequency of about several tens to several hundreds [MHz] to the full bridge circuit 13 via the buffer 12. The oscillator 11 can output a signal having a waveform such as a rectangular wave, a sine wave, and a triangular wave.

  Two output terminals of the full bridge circuit 13 are connected to two differential input terminals 14a and 14b of the differential amplifier 14. The bias coil 22 has one terminal connected to the output of the amplifier (AMP) 15 and the other terminal grounded. The amplifier 15 amplifies the AC bias signal SGC and supplies the signal to the bias coil 22.

  A filter 16 is connected to the output of the differential amplifier 14. The filter 16 is a low-pass filter (LPF). An amplifier 17 is connected to an output of the filter 16, and a filter 18 is further connected to an output of the amplifier 17. The filter 18 is also a low-pass filter. The output signal Vout1 of the filter 18 includes a component representing the magnitude of the external magnetic field detected by the magneto-impedance element 20.

  Input terminals of two analog switches 23 and 24 are connected to the output of the filter 18, respectively. The input terminal of the peak hold circuit 25 is connected to the output terminal of the analog switch 23, and the input terminal of the peak hold circuit 26 is connected to the output terminal of the analog switch 24.

  The microcomputer (microcomputer) 27 operates according to a program incorporated in advance and controls the magnetic field detection sensor 10. Specifically, the microcomputer 27 generates the AC bias signal SGC. The waveform of the AC bias signal SGC is a triangular wave, and the frequency of the AC bias signal SGC is much lower than the signal output from the oscillator 11. Further, the microcomputer 27 generates a section determination signal SGD whose timing is synchronized with the waveform of the AC bias signal SGC. The section determination signal SGD is applied to control input terminals of the peak hold circuits 25 and 26.

  The microcomputer 27 calculates and grasps the magnitude of the external magnetic field applied to the magnetic impedance element 20 based on the A output signal SGA output from the peak hold circuit 25 and the B output signal SGB output from the peak hold circuit 26. .

<Overview of the operation of the magnetic field detection sensor>
The magnetic impedance element 20 shown in FIG. 1 is a device whose impedance changes with respect to a magnetic field by applying a high-frequency carrier current to the magnetic thin film 21. Therefore, a high-frequency signal output from the oscillator 11 is supplied to the full bridge circuit 13 via the buffer 12, and a high-frequency carrier current flows through the magnetic thin film 21.

  Further, the AC bias signal SGC is supplied to the bias coil 22 via the amplifier 15. Therefore, the AC bias magnetic field generated by the bias coil 22 is constantly applied to the magnetic thin film 21. Here, the amplitude of the AC bias magnetic field is equal to or higher than the level at which the magnetic flux density of the magnetic thin film 21 is saturated.

  The full bridge circuit 13 including the magnetic impedance element 20 outputs a change in impedance of the magnetic thin film 21 according to a magnetic field applied to the magnetic thin film 21 as a voltage. The voltage output from the full bridge circuit 13 is amplified by the differential amplifier 14 and high frequency noise is removed by the filter 16. Further, the output voltage of the filter 16 is amplified by the amplifier 17 and noise is removed by the filter 18 to become an output signal Vout1.

  In order to process each signal component included in the output signal Vout1 output from the filter 18 into a plurality of sections and individually process the signal components, on / off control of the analog switches 23 and 24 using the section determination signal SGD output from the microcomputer 27. Is carried out. Specifically, in the A reading section T1 (see FIG. 5) in which the voltage of the section determination signal SGD becomes low, the analog switch 23 is turned on and the analog switch 24 is turned off, and the voltage of the section determination signal SGD becomes high. In the level B reading section T2, the analog switch 23 is turned off and the analog switch 24 is turned on. Thus, necessary signal components can be extracted at timings synchronized with the waveform of the AC bias signal SGC.

  The peak hold circuit 25 monitors the voltage of the output signal Vout1 input via the analog switch 23 at the timing of the A reading section T1, and detects the maximum value in this section. The peak hold circuit 26 monitors the voltage of the output signal Vout1 input via the analog switch 24 at the timing of the B reading section T2, and detects the maximum value in this section.

  The microcomputer 27 converts the A output signal SGA representing the maximum value detected by the peak hold circuit 25 in the A reading section T1 and the B output signal SGB representing the maximum value detected by the peak hold circuit 26 in the B reading section T2, respectively. Analog / digital (A / D) conversion and reading. The A / D converter to be used may be built in the microcomputer 27 or may be an external circuit.

  The microcomputer 27 recognizes the magnitude of the external magnetic field applied to the magneto-impedance element 20 by performing predetermined arithmetic processing based on the levels of the A output signal SGA and the B output signal SGB. That is, the magnitude of the external magnetic field is calculated from the maximum value of the output signal Vout1 detected in the A reading section T1 and the maximum value of the output signal Vout1 detected in the B reading section T2.

<BH curve and impedance characteristics>
FIG. 2 shows an example of the BH curve and the impedance characteristic of the magnetic impedance element. 2 shows the relationship between the magnetic field H and the magnetic flux density B in the magnetic thin film 21, and the lower graph shows the magnitude [Oe] of the external magnetic field and the impedance Z of the magnetic thin film 21. Represents the relationship.

  As shown in the upper graph, in the magneto-impedance element 20, the magnetic flux density B greatly changes according to the magnetic field H when the magnetic field H is in the non-saturation area A0, but the magnetic flux density B is almost constant in the saturation areas Ap and An. become. Further, since there is hysteresis, when the magnetic field H changes in the increasing direction, the magnetic flux density B changes according to the increasing curve Ci, and when the magnetic field H changes in the decreasing direction, the magnetic flux density B changes according to the decreasing curve Cd. Change.

  Also in the graph shown on the lower side, a large influence of the hysteresis appears in the hysteresis section Zh where the external magnetic field is small. That is, a large difference occurs between the change in the impedance Z when the external magnetic field increases in the α direction shown in FIG. 2 and the change in the impedance Z when the external magnetic field decreases in the opposite β direction. Therefore, when an external magnetic field is detected using the magnetic impedance element 20 or the like, different impedance values are detected when the external magnetic field is applied from different directions, even if the strength of the external magnetic field is the same. That is, the hysteresis causes deterioration of accuracy in detecting the magnetic field. The magnetic field detection sensor 10 shown in FIG. 1 has a function for reducing the influence of the above-described hysteresis.

<Relationship between magnetic field of magnetic impedance element and sensor output signal>
FIG. 3 shows an example of the correlation between the input magnetic field and the output signal in the magneto-impedance element 20 in the full bridge circuit 13 shown in FIG. 3, the horizontal axis of the graph of the impedance characteristic 41 represents the magnitude and direction of the external magnetic field H [A / m] applied to the magnetic impedance element 2, and the vertical axis represents the impedance Z (DC resistance value) of the magnetic impedance element 20. ) Represents [Ω].

  As shown in FIG. 3, an AC bias magnetic field 42 is applied to the magnetic thin film 21 by an AC current flowing through the bias coil 22 so as to operate around the reference point 41 r of the impedance characteristic 41. In the example of FIG. 3, it is assumed that an AC bias magnetic field 42 having a triangular waveform with a magnitude of the amplitude Vp is applied. Therefore, the direction of the AC bias magnetic field 42 changes alternately with the amplitude of Vp in the plus and minus directions around the reference point 41r.

  Then, in addition to the AC bias magnetic field 42, an external magnetic field to be detected is applied to the magnetic thin film 21. Therefore, the sums 42P and 42N of the external magnetic field and the AC bias magnetic field are applied to the magnetic thin film 21 as shown in FIG. That is, when the external magnetic field is in the positive direction, a waveform obtained by shifting the waveform of the AC bias magnetic field 42 in the positive direction by the magnitude of the external magnetic field is applied to the magnetic thin film 21 as the sum 42P of the external magnetic field and the AC bias magnetic field. When the external magnetic field is in the negative direction, a waveform obtained by shifting the waveform of the AC bias magnetic field 42 in the negative direction by the magnitude of the external magnetic field is applied to the magnetic thin film 21 as the sum 42N of the external magnetic field and the AC bias magnetic field.

  The impedance Z changes according to the magnetic field applied to the magnetic thin film 21, that is, the AC bias magnetic field 42, the sums 42 P and 42 N of the external magnetic field and the AC bias magnetic field, and the impedance characteristic 41. The change in the impedance Z can be extracted as sensor output signals 43, 43P, and 43N by using, for example, the full bridge circuit 13 shown in FIG.

  In FIG. 3, the sensor output signals 43, 43P, and 43N correspond to the AC bias magnetic field 42 and the sums 42P, 42N of the external magnetic field and the AC bias magnetic field, respectively. That is, the states of the sensor output signals 43, 43P, and 43N are determined according to the change in the AC bias magnetic field 42 and the external magnetic field. Further, in the sensor output signals 43, 43P, 43N shown in FIG. 3, the vertical direction represents the potential and the amplitude of the signal, and the horizontal direction represents a change in time.

  When the external magnetic field is zero, the sensor output signal 43 is output. That is, a sensor output signal 43 that changes with a change in the AC bias magnetic field 42 between a potential corresponding to the resistance value of the reference point 41r and a potential V1 shifted from this point by a potential difference corresponding to the amplitude Vp. can get.

  Further, when an external magnetic field in the positive direction is applied, a potential difference between the potential at the reference point 41r and a potential shifted up and down by a potential difference corresponding to the amplitude Vp around a potential shifted by the magnitude of the external magnetic field is used as a center. , A sensor output signal 43P that changes with the change in the AC bias magnetic field 42 is obtained. When an external magnetic field in the negative direction is applied, a potential difference between the potential at the reference point 41r and a potential shifted up and down by a potential difference corresponding to the amplitude Vp around a potential shifted by the magnitude of the external magnetic field. , A sensor output signal 43N that changes with the change in the AC bias magnetic field 42 is obtained.

  As shown in FIG. 3, a change appears between the sensor output signals 43, 43P, and 43N according to the difference in the magnitude and direction of the external magnetic field. Therefore, the magnitude and direction of the external magnetic field can be specified based on the sensor output signals 43P and 43N. However, due to the effect of hysteresis in the magnetic thin film 21, there is a possibility that a detection error occurs due to the difference between the α direction and the β direction shown in FIG.

  Therefore, in the present embodiment, the peak detection points Pa and Pb shown in FIG. 3 are determined so that the directions of the change of the AC bias magnetic field 42 and the change of the external magnetic field are aligned. Here, the peak detection point Pa indicates the timing of the peak (the top of the triangular wave) in the section where the AC bias magnetic field 42 increases in the positive direction (corresponding to the “α direction” in FIG. 2). The peak detection point Pb represents the timing of the peak (the peak of the triangular wave) in a section where the absolute value of the AC bias magnetic field 42 increases in the negative direction (corresponding to the “α direction”).

  The peak detection point Pa in the sensor output signal 43P corresponds to the peak detection point Pa in the sum 42P of the external magnetic field and the AC bias magnetic field. Similarly, the peak detection point Pb in the sensor output signal 43N corresponds to the peak detection point Pb in the sum 42N of the external magnetic field and the AC bias magnetic field.

  For example, in the sum 42P of the external magnetic field and the AC bias magnetic field shown in FIG. 3, the peak detection point Pa corresponds to the timing immediately before the AC bias magnetic field 42 reaches the peak while increasing in the positive direction and changes its direction. . Therefore, assuming that the external magnetic field changes from 0 to the plus direction, detecting the level of the peak detection point Pa of the sensor output signal 43P means that the external magnetic field and the AC bias magnetic field 42 are aligned in the “α direction”. Means the state.

  In addition, in the sum 42N of the external magnetic field and the AC bias magnetic field shown in FIG. 3, the peak detection point Pb reaches the peak while the absolute value of the AC bias magnetic field 42 increases in the negative direction, and is the timing immediately before the direction changes. Is equivalent to Therefore, assuming that the external magnetic field changes in the negative direction from 0, detecting the level of the peak detection point Pb of the sensor output signal 43N means that the external magnetic field and the AC bias magnetic field 42 are aligned in the “α direction”. Means the state.

  That is, when the external magnetic field is in the plus direction, the level of the peak detection point Pa of the sensor output signal 43P is detected, and when the external magnetic field is in the minus direction, the level of the peak detection point Pb of the sensor output signal 43N is detected. As a result, the detection can be performed in a state where the directions of the change of the external magnetic field and the AC bias magnetic field 42 are always aligned, so that deterioration of accuracy due to hysteresis can be suppressed.

<Characteristics when no AC bias magnetic field is used>
FIG. 4 shows an example of the magnetic field-output voltage characteristic of the magnetic impedance element when the AC bias magnetic field is not used. For example, in the magnetic field detection sensor 10 shown in FIG. 1, the output signal Vout1 when no current flows in the bias coil 22 has characteristics as shown in FIG.
That is, as shown in FIG. 4, in a region where the magnetic field is relatively small, not only the change in the voltage becomes small, but also the voltage varies depending on the direction of the magnetic field change.

<Example of time series change of each signal>
FIGS. 5A to 5D show time-series changes of each signal in a state where the conditions of the external magnetic field are different from each other. 5 (a), 5 (b), 5 (c), and 5 (d) show AC bias signals under the conditions that the external magnetic field in the positive direction is 0, 2, 4, and 6 [Oe], respectively. 5 shows changes in the SGC, the section determination signal SGD, and the output signal Vout1. 5A to 5D, the horizontal axis represents time t, the left vertical axis represents the voltage [V] of the section determination signal SGD, and the right vertical axis represents the voltage [V] of the AC bias signal SGC. Is shown.

  As shown in FIG. 5A, the A reading section T1 is a section where the section determination signal SGD is at a low level, and the B reading section T2 is a section where the section determination signal SGD is at a high level. Further, each timing of the section determination signal SGD is synchronized with the waveform of the AC bias signal SGC. That is, the section determination signal SGD becomes low level when the voltage of the AC bias signal SGC is positive, and the section determination signal SGD becomes high level when the voltage of the AC bias signal SGC is negative.

  For example, as shown in FIG. 5A, the voltage of the AC bias signal SGC changes in an increasing manner over time until the peak detection point Pa is reached in the A reading section T1. Further, even before reaching the peak detection point Pb in the B reading section T2, the absolute value of the voltage of the AC bias signal SGC changes in a negative direction with the passage of time.

  That is, the maximum value detected at the peak detection point Pa is the maximum value in a state where the magnetic field is in the positive direction region and changes in the α direction shown in FIG. Further, the maximum value detected at the peak detection point Pb is a maximum value in a state where the magnetic field is in the minus direction region and changes in the α direction shown in FIG.

  As shown in FIG. 5A, when the external magnetic field is 0 [Oe], the maximum values detected at the two peak detection points Pa and Pb are equal. Further, when an external magnetic field in the plus direction is applied, the maximum values detected at the two peak detection points Pa and Pb change as shown in FIGS. 5B to 5D. Therefore, the magnitude of the external magnetic field can be detected based on the maximum values detected at the two peak detection points Pa and Pb. The maximum values of the two peak detection points Pa and Pb in the output signal Vout1 appear as the A output signal SGA and the B output signal SGB shown in FIG. Therefore, the microcomputer 27 can calculate the magnitude of the external magnetic field based on the A output signal SGA and the B output signal SGB.

<Relationship between external magnetic field and voltage of A output and B output>
FIG. 6 shows an example of the relationship between the external magnetic field of the magneto-impedance element and the voltages of “A output” and “B output”. FIG. 7 shows the relationship among the magnetic sensing axis of the magnetic impedance element, the axis of change of the AC bias magnetic field, and the direction of the external magnetic field.

  6, the horizontal axis represents the external magnetic field, and the vertical axis represents the voltage. Also, “A output” and “B output” in FIG. 6 correspond to the voltages of the A output signal SGA and the B output signal SGB in FIG. 1, respectively.

  In the magnetic field detection sensor 10 shown in FIG. 1, as shown in FIG. 7, the magnetic sensitive axis 51 of the magnetic impedance element 20 and the change axis 52 of the AC bias magnetic field generated by the bias coil 22 are aligned in the same axial direction. It is arranged as follows. Further, the specifications of the magnetic field detection sensor 10 are defined such that the external magnetic field directions 53p and 53n are aligned in the same direction as the magnetic sensing axis 51 and the change axis 52 of the AC bias magnetic field. The specifications are defined such that the “A direction” and the “B direction” of the AC bias magnetic field change axis 52 coincide with the positive external magnetic field direction 53p and the negative external magnetic field direction 53n, respectively.

  That is, when an external magnetic field is applied to the magneto-impedance element 20 in the external magnetic field direction 53p, the magnetic field detection sensor 10 applies the external bias in the positive direction at the timing of the AC bias magnetic field that changes in the forward direction toward the “A direction”. The magnetic field is detected by the A output signal SGA. In addition, when an external magnetic field is applied to the magnetic impedance element 20 in the external magnetic field direction 53n, the magnetic field detection sensor 10 outputs the negative external bias at the timing of the AC bias magnetic field that changes in the forward direction toward the “B direction”. The magnetic field is detected by the B output signal SGB.

  For example, in a state where the external magnetic field in the external magnetic field direction 53p, that is, a positive external magnetic field is applied to the magneto-impedance element 20 and the AC bias magnetic field is changing in the “A direction” of the change axis 52, the external Changes in the magnetic field and the AC bias magnetic field are aligned in the same direction. Therefore, in this case, a combined magnetic field of the external magnetic field and the AC bias magnetic field is applied to the magnetic impedance element 20. The level corresponding to the composite magnetic field is detected as the “A output” shown in FIG. 6, that is, the A output signal SGA.

  When the AC bias magnetic field changes in the “B direction” of the change axis 52 in the external magnetic field direction 53p, that is, in a state where the external magnetic field in the plus direction is applied to the magnetic impedance element 20, the external magnetic field and the AC bias magnetic field are changed. Change in opposite directions, they cancel each other out. Therefore, the “B output” shown in FIG. 6, that is, the level of the B output signal SGB is lower than the “A output”.

  Further, in the external magnetic field direction 53n, that is, when the external magnetic field in the negative direction is applied to the magnetic impedance element 20 and the AC bias magnetic field changes in the “B direction” of the change axis 52, Changes in the magnetic field and the AC bias magnetic field are aligned in the same direction. Therefore, in this case, a combined magnetic field of the external magnetic field and the AC bias magnetic field is applied to the magnetic impedance element 20.

  When the AC bias magnetic field changes in the “A direction” of the change axis 52 in the external magnetic field direction 53n, that is, in a state where the external magnetic field in the negative direction is applied to the magnetic impedance element 20, the external magnetic field and the AC bias magnetic field are changed. Change in opposite directions, they cancel each other out.

  Therefore, as shown in FIG. 6, in a region where the external magnetic field is positive, the level of “A output” is larger than “B output”. In a region where the external magnetic field is negative, the level of “A output” is smaller than that of “B output”. Regardless of the magnitude of the external magnetic field, among the characteristics of “A output” and “B output” shown in FIG. 6, the influence of the difference in the direction due to the hysteresis like the characteristic shown in FIG. Not appearing.

  Since there is a magnitude relationship between “A output (A output signal SGA)” and “B output (B output signal SGB)” as shown in FIG. 6, the microcomputer 27 outputs the A output signal SGA and the B output signal. By comparing the levels of the signals SGB, the direction of the external magnetic field can be specified. That is, when the condition of “SGA> SGB” is satisfied, it can be recognized that the external magnetic field is in the plus direction, and when the condition of “SGA <SGB” is satisfied, it can be recognized that the external magnetic field is in the minus direction. Therefore, for example, the direction of the external magnetic field is recognized, and the magnitude of the external magnetic field is calculated based on the A output signal SGA when “SGA ≧ SGB”, and based on the B output signal SGB when “SGA <SGB”. Control may be performed to calculate the magnitude of the external magnetic field.

  When the external magnetic field is relatively large, the change range of the combined magnetic field applied to the magnetic impedance element 20 does not pass through the peak (0 [Oe]) of the characteristic of the impedance Z shown in FIG. The combined magnetic field changes in a range such as the sum 42P, 42N of the external magnetic field and the AC bias magnetic field. However, the magnetic field detection sensor 10 detects the level corresponding to the impedance of the peak detection points Pa and Pb only when the change of the external magnetic field and the change of the AC bias magnetic field are aligned in the same direction. Even without using, the detection range is not limited to a narrow range.

<Advantages of the magnetic field detection sensor 10>
As described above, the magnetic field detection sensor 10 can reduce the effect of hysteresis without using a degaussing circuit, and thus can be downsized. Further, since it is not necessary to use a special core, it is not necessary to consider the influence of hysteresis of the core. Further, since it is not necessary to limit the detection range of the magneto-impedance element 20 in order to reduce the influence of the hysteresis, the magnetic field can be detected over a wide range.

Here, the features of the magnetic field detection sensor according to the embodiment of the present invention described above will be briefly summarized and listed below in [1] to [5].
[1] A magnetic detecting element (magnetic impedance element 20) including a magnetic material (magnetic thin film 21) that produces a magnetic impedance effect and a bias coil (22) for applying a bias magnetic field to the magnetic material, and a high-frequency current applied to the magnetic material. A high-frequency oscillation circuit (oscillator 11) for supplying the magnetic field detection sensor,
An AC bias circuit (amplifier 15) for supplying an AC bias current for generating an AC bias magnetic field having an amplitude (Vp) larger than a level at which the magnetic flux density in the magnetic detection element is saturated to the bias coil;
A timing signal generator (microcomputer 27) for generating a timing signal (section determination signal SGD) synchronized with the AC waveform of the AC bias current;
A signal detection unit (analog switches 23 and 24, peak hold circuits 25 and 26) for detecting a signal reflecting the detection state of the magnetic detection element according to the timing of the timing signal;
A magnetic field detection sensor (10), comprising:

[2] The signal detection unit includes a peak detection unit (peak hold circuits 25 and 26) that detects a peak value of the signal in a predetermined section of the AC waveform in accordance with the timing of the timing signal.
The magnetic field detection sensor according to the above [1], wherein:

[3] The magnetic sensing axis (51) of the magnetic detection element, the change axis (52) of the AC bias magnetic field, and the change axis of the external magnetic field to be detected by the magnetic detection element (external magnetic field directions 53p, 53n). Are aligned in the same direction,
The signal detection unit is configured to output a signal (A output signal) reflecting the magnetic detection state of the magnetic detection element at a timing (peak detection points Pa and Pb) at which the direction of the external magnetic field matches the direction of the AC bias magnetic field. SGA, B output signal SGB).
The magnetic field detection sensor according to the above [1] or [2], wherein:

[4] The signal detection unit includes a plurality of peak detection units (peaks) that individually detect signals in each direction when the external magnetic field and the AC bias magnetic field appear in a plus direction and a minus direction with respect to a predetermined direction. Hold circuits 25, 26).
The magnetic field detection sensor according to the above [3], wherein:

[5] A bridge circuit (full bridge circuit 13) including the magnetic detection element is configured, and a change in impedance in the magnetic detection element is detected as the signal (output signal Vout1) by the bridge circuit.
The magnetic field detection sensor according to any one of the above [1] to [4].

Reference Signs List 10 magnetic field detection sensor 11 oscillator 12 buffer 13 full bridge circuit 13a, 13b, 13c resistor 14 differential amplifier 15, 17 amplifier 16, 18 filter 20 magnetic impedance element 21 magnetic thin film 22 bias coil 23, 24 analog switch 25, 26 peak Hold circuit 27 Microcomputer 41 Impedance characteristic 41r Reference point 42 AC bias magnetic field 42P, 42N Sum of external magnetic field and AC bias magnetic field 43, 43P, 43N Sensor output signal 51 Magnetic sensing axis 52 Alternating axis of AC bias magnetic field 53p, 53n External magnetic field Direction Pa, Pb Peak detection point A0 Unsaturated area Ap, An Saturated area Ci Curve when increasing Cd Curve when decreasing SGA A output signal SGB B output signal SGC AC bias signal SGD section determination signal 1 A reading section T2 B reading section Vout1 output signal Z impedance Zh hysteresis interval

Claims (5)

A magnetic detection element including a magnetic material in which a magnetic impedance effect is generated and a bias coil for applying a bias magnetic field to the magnetic material, and a high-frequency oscillation circuit for supplying a high-frequency current to the magnetic material,
An AC bias circuit for supplying an AC bias current for generating an AC bias magnetic field having an amplitude larger than a level at which the magnetic flux density in the magnetic detection element is saturated to the bias coil,
A timing signal generator that generates a timing signal synchronized with the AC waveform of the AC bias current;
According to the timing of the timing signal, a signal detection unit that detects a signal reflecting the detection state of the magnetic detection element,
A magnetic field detection sensor comprising: The signal detection unit has a peak detection unit that detects a peak value of a signal in a predetermined section of the AC waveform according to the timing of the timing signal.
The magnetic field detection sensor according to claim 1, wherein: The magnetic sensing axis in the magnetic detection element, the change axis of the AC bias magnetic field, and the change axis of the external magnetic field to be detected in the magnetic detection element are arranged in the same direction,
The signal detection unit detects a signal reflecting a magnetic detection state of the magnetic detection element at a timing when the direction of the external magnetic field and the direction of the AC bias magnetic field match.
The magnetic field detection sensor according to claim 1 or 2, wherein: The signal detection unit, when the external magnetic field and the AC bias magnetic field appear in a plus direction and a minus direction with respect to a predetermined direction, has a plurality of peak detection units that individually detect signals in each direction,
The magnetic field detection sensor according to claim 3, wherein: A bridge circuit including the magnetic detection element is configured, and an impedance change in the magnetic detection element is detected as the signal by the bridge circuit.
The magnetic field detection sensor according to any one of claims 1 to 4, wherein:

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