Magnetic detector

Abstract

To provide a magnetic detector capable of improving magnetic detection performance by making an output value of a detection circuit unsusceptible to a DC magnetic field.SOLUTION: Magnetic detectors 1, 2 comprise: a magneto-impedance sensor element 10 including a magneto-sensitive material 11 causing magnetization change according to the intensity of a magnetic field when excitation current IIN is supplied, and a detection coil 12 wound around the magneto-sensitive material 11 and outputting induction voltage generated by magnetization change of the magneto-sensitive material 11; sample hold circuits 22, 32 connected to one end of the detection coil 12 and holding output voltage of the detection coil 12 when a sampling switch is in on-operation; amplifier circuits 24, 33 connected to an output side of the sample hold circuits 22, 32; and subsequent stage high pass filters 25, 35 connected to the output side of the amplifier circuits 24, 33.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a magnetic detector. [Background technology]

[0002] Patent documents 1 and 2 disclose a magnetic detector that detects the strength of a target magnetic field using an amorphous magnetic wire as a magnetometer and a detection coil. The amorphous magnetic wire has the property of producing a magneto impedance effect (MI effect). That is, when an excitation current is supplied to the amorphous magnetic wire, it has the property of undergoing a change in magnetization in accordance with the strength of the magnetic field acting on the amorphous magnetic wire. More specifically, the impedance of the amorphous magnetic wire changes as the permeability in the circumferential direction changes in accordance with the strength of the magnetic field acting on it. A detection coil is wound around the amorphous magnetic wire, and the detection coil outputs an induced voltage generated by the change in magnetization of the amorphous magnetic wire.

[0003] The excitation current supplied to the amorphous magnetic wire is, for example, a pulsed current or a high-frequency current. When a pulsed current or high-frequency current is supplied to the amorphous magnetic wire, a change in magnetization corresponding to the strength of the acting magnetic field occurs in the amorphous magnetic wire at the timing of the current's rise. At this time, an induced voltage is generated in the detection coil due to the change in magnetization in the amorphous magnetic wire.

[0004] A detection circuit is connected to the detection coil in order to detect the induced voltage generated in the detection coil. Patent Document 1 discloses a detection circuit configuration comprising a sample-and-hold circuit and an amplification circuit. The sample-and-hold circuit includes a sampling switch that turns on in accordance with the timing of the supply of excitation current, and a hold capacitor for holding the output when the sampling switch is turned on. The amplification circuit is connected to the output side of the sample-and-hold circuit.

[0005] Patent Document 2 discloses a configuration in which a detection circuit includes a sample-and-hold circuit, an amplification circuit, and a feedback circuit. The feedback circuit is configured to connect the output terminal of the amplification circuit and one end of the detection coil to apply magnetic negative feedback. Therefore, in a state where a DC component of a magnetic field acts on the amorphous magnetic wire, a feedback current flows through the detection coil, and a feedback magnetic field capable of canceling the DC component of the magnetic field can be generated.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] There is a demand for further improvement in magnetic detection performance, and in particular, there is a desire to detect a minute AC magnetic field (for example, several nT) under a large DC magnetic field (for example, several hundreds μT) such as geomagnetism or a substance having ferromagnetism.

[0008] Here, it has been discovered that the output value of the detection circuit disclosed in Patent Documents 1 and 2 varies depending on the magnitude of the DC magnetic field. The larger the magnitude of the DC magnetic field, the more likely the output value of the detection circuit is to be a large value. Therefore, it is desirable to make the output value of the detection circuit less susceptible to the influence of the DC magnetic field.

[0009] The present invention has been made in view of such a background, and aims to provide a magnetic detector capable of improving magnetic detection performance by making the output value of a detection circuit less susceptible to the influence of a DC magnetic field.

Means for Solving the Problems

[0010] One aspect of the present invention is a magnetoimpedance sensor element comprising a magnetosensitive body that undergoes a change in magnetization in response to the strength of a magnetic field when an excitation current is supplied, and a detection coil wound around the magnetosensitive body that outputs an induced voltage generated by the change in magnetization of the magnetosensitive body. A sample-and-hold circuit connected to one end of the detection coil, which holds the output voltage of the detection coil when the sampling switch is in the ON position, A pre-stage high-pass filter connected to the output side of the sample-and-hold circuit, The aforementioned pre-stage high-pass filter An amplification circuit connected to the output side, The amplifier circuit is further equipped with a subsequent high-pass filter connected to the output side. 、 The sample-and-hold circuit maintains the output voltage fluctuation of the detection coil while the sampling switch is in the ON position. The amplification circuit performs integration and amplification on the output of the preceding high-pass filter, and converts the output voltage fluctuation into an offset component through the integration process. The aforementioned high-pass filter removes the offset component. It is located in the magnetic detector. Another aspect of the present invention is a magnetoimpedance sensor element comprising a magnetosensitive body that undergoes a change in magnetization in response to the strength of a magnetic field when an excitation current is supplied, and a detection coil wound around the magnetosensitive body that outputs an induced voltage generated by the change in magnetization of the magnetosensitive body. A sample-and-hold circuit connected to one end of the detection coil, which holds the output voltage of the detection coil when the sampling switch is in the ON position, A pre-stage high-pass filter connected to the output side of the sample-and-hold circuit, The amplification circuit connected to the output side of the aforementioned high-pass filter, The amplifier circuit is further equipped with a subsequent high-pass filter connected to the output side, The sample-and-hold circuit maintains the output voltage fluctuation during at least one of the acquisition time and the settling time by the on / off operation of the sampling switch. The amplification circuit performs integration and amplification on the output of the preceding high-pass filter, and converts the output voltage fluctuation into an offset component through the integration process. The aforementioned high-pass filter is located in the magnetic detector and removes the offset component. [Effects of the Invention]

[0011] According to the magnetic detector described above, even if an offset component affected by a DC magnetic field is included in the output of the amplification circuit, this offset component can be removed by the subsequent high-pass filter. Therefore, the output value of the detection circuit can be made free of the offset component affected by the DC magnetic field. As a result, the detection circuit becomes less susceptible to the influence of the DC magnetic field and can detect minute AC magnetic fields with high accuracy.

[0012] As described above, according to the above embodiment, a magnetic detector can be provided that can improve magnetic detection performance by making the output value of the detection circuit less susceptible to the influence of a DC magnetic field. [Brief explanation of the drawing]

[0013] [Figure 1] A diagram showing the configuration of the magnetic detector in Embodiment 1. [Figure 2] (a) is a diagram showing the ideal behavior of the magnetic detector in Embodiment 1 without a subsequent high-pass filter. (b) is a diagram showing the actual behavior of the magnetic detector in Embodiment 1 without a subsequent high-pass filter. (c) is a diagram showing the behavior of the magnetic detector in Embodiment 1. [Figure 3] A diagram illustrating the operation of a sample-and-hold circuit. [Figure 4] This figure shows the relationship between the output values ​​of the detection circuit in Figure 2(b) and (c) and the DC magnetic field. [Figure 5] A diagram showing the configuration of the magnetic detector in Embodiment 2. [Figure 6] (a) is a diagram showing the ideal behavior of the magnetic detector in Embodiment 2 without a subsequent high-pass filter. (b) is a diagram showing the actual behavior of the magnetic detector in Embodiment 2 without a subsequent high-pass filter. (c) is a diagram showing the behavior of the magnetic detector in Embodiment 2. [Figure 7] This figure shows the relationship between the output values ​​of the detection circuit in Figure 6(b) and (c) and the DC magnetic field. [Figure 8] A diagram showing the configuration of a magnetic detector in the first modified form of Embodiment 1. [Figure 9] A diagram showing the configuration of a magnetic detector in a second modified embodiment of Embodiment 1. [Figure 10] A diagram showing the configuration of the magnetic detector in the third modified embodiment of Embodiment 1. [Modes for carrying out the invention]

[0014] Magnetic detectors can be applied in various ways to detect the strength of a magnetic field. For example, magnetic detectors can be used in electronic compasses, foreign object detection sensors, and magnetic positioning systems.

[0015] In the magnetic detector, the magnetosensitive element constituting the magneto impedance sensor element can be a magnetic wire, particularly an amorphous magnetic wire. However, other materials besides amorphous magnetic wires can be used as the magnetosensitive element, as long as they have the property of undergoing a magnetization change in response to the strength of the magnetic field when an excitation current is supplied. Furthermore, the excitation current supplied to the magnetosensitive element can be a periodic current, such as a pulsed current or a high-frequency current.

[0016] In a first embodiment, the magnetic detector may further include a pre-amplifier high-pass filter connected to the output side of the sample-and-hold circuit, and the amplification circuit may be connected to the output side of the pre-amplifier high-pass filter.

[0017] In this case, the magnetic detector comprises a magneto impedance sensor element, a sample-and-hold circuit, a pre-stage high-pass filter, an amplification circuit, and a post-stage high-pass filter. It was thought that by including a pre-stage high-pass filter, all of the influence components of DC magnetic fields could be removed. However, it was found that even with a pre-stage high-pass filter, it was not possible to remove all of the influence components of DC magnetic fields, and that the influence components of DC magnetic fields were included in the components that passed through the pre-stage high-pass filter. However, the influence components of DC magnetic fields included in the components that passed through the pre-stage high-pass filter can be removed by the post-stage high-pass filter. Therefore, the detected value of the detection circuit can be made free of the influence components of DC magnetic fields.

[0018] In particular, the sample-and-hold circuit should maintain the output voltage fluctuation of the detection coil while the sampling switch is ON, the amplification circuit should perform integration and amplification on the output of the preceding high-pass filter, and convert the output voltage fluctuation into an offset component through the integration, and the subsequent high-pass filter should remove the offset component.

[0019] The relationship between the ON operation of the sampling switch and the output of the detection coil can result in the component that passes through the pre-stage high-pass filter containing a component affected by the DC magnetic field (offset component). Even with such a configuration, the subsequent high-pass filter can reliably remove the offset component.

[0020] Furthermore, the sample-and-hold circuit maintains the output voltage fluctuation during at least one of the acquisition time and settling time by the on / off operation of the sampling switch, the amplification circuit performs integration and amplification on the output of the preceding high-pass filter, and converts the output voltage fluctuation into an offset component through the integration, and the subsequent high-pass filter removes the offset component.

[0021] The on / off operation of the sampling switch causes the components that have passed through the preceding high-pass filter to include components affected by the DC magnetic field (offset components). Even with this configuration, the subsequent high-pass filter can reliably remove the offset components.

[0022] Furthermore, in the magnetic detector of the first embodiment, the output side of the amplification circuit and one end of the detection coil are not connected, and there is no feedback circuit.

[0023] In a second embodiment, the magnetic detector may further include a feedback circuit comprising a low-pass filter, connecting the output side of the amplification circuit to one end of the detection coil. In this case, the magnetic detector comprises a magneto impedance sensor element, a sample-and-hold circuit, an amplification circuit, a feedback circuit, and a subsequent high-pass filter.

[0024] With this configuration, for example, when it is desired to detect a small AC magnetic field under a large DC magnetic field, the magneto impedance sensor element becomes less susceptible to the DC magnetic field and can output an induced voltage due to the influence of the small AC magnetic field. Therefore, the detection range of the magneto impedance sensor element can be effectively utilized.

[0025] In particular, in this configuration, the feedback circuit cancels out a portion of the external magnetic field applied to the magneto impedance sensor element by the feedback magnetic field generated by the feedback current in a predetermined frequency band that passes through the low-pass filter, and holds the sum of the induced voltage and the feedback voltage generated by the feedback current in the sample-and-hold circuit. Therefore, the subsequent high-pass filter is preferably configured to remove the component of the feedback voltage generated by the feedback current that is included in the output of the amplification circuit.

[0026] Furthermore, in the magnetic detectors of the first and second embodiments described above, the subsequent high-pass filter can be configured as one of the following: a circuit composed of at least two LCR elements; a high-pass filter circuit having an operational amplifier; an arithmetic processing unit that performs digital signal processing after digital conversion; a processing unit that subtracts a predetermined frequency band component obtained by passing the low-pass filter from the output of the amplification circuit; and a reference voltage correction unit that uses the DC component of the output of the amplification circuit as a reference voltage and applies it to the amplification circuit. In any configuration, the influence of a DC magnetic field can be suppressed. The circuit composed of at least two LCR elements includes, for example, a CR circuit, an RL circuit, an LC circuit, and an RLC circuit.

[0027] (Embodiment 1) 1-1. Configuration of Magnetic Detector 1 The configuration of the magnetic detector 1 in Embodiment 1 will be described with reference to Figure 1. As shown in Figure 1, the magnetic detector 1 in this embodiment comprises a magneto impedance sensor element 10 (hereinafter referred to as "MI sensor element") and a detection circuit 20.

[0028] The MI sensor element 10 is configured to output a voltage corresponding to the strength of the magnetic field B acting on the MI sensor element 10. The MI sensor element 10 includes a magnetosensor 11 and a detection coil 12. IN When the strength of the magnetic field B acting on the magnetosensor 11 causes a magnetization change corresponding to the strength of the magnetic field B. Specifically, when a pulse current or a high-frequency current is supplied as the excitation current I to the magnetosensor 11, the magnetic permeability in the circumferential direction changes corresponding to the strength of the magnetic field B acting thereon, resulting in a change in impedance. That is, when the magnetic field B acts on the magnetosensor 11 and the excitation current I is supplied to the magnetosensor 11, the magnetosensor 11 generates a magnetization change. The magnetosensor 11 applies, for example, a magnetic wire, particularly an amorphous magnetic wire.

[0029] The magnetosensor 11 generates a magnetization change corresponding to the strength of the magnetic field B acting on the magnetosensor 11 when the excitation current I is supplied. IN When the excitation current I is supplied, a magnetization change occurs corresponding to the strength of the magnetic field B acting on the magnetosensor 11. IN When the excitation current I is supplied to the magnetosensor 11, a magnetization change occurs corresponding to the strength of the magnetic field B acting thereon. IN When a pulse current or a high-frequency current is supplied as the excitation current I, the magnetic permeability in the circumferential direction changes corresponding to the strength of the magnetic field B acting thereon, resulting in a change in impedance. IN That is, when the magnetic field B acts on the magnetosensor 11 and the excitation current I is supplied to the magnetosensor 11, the magnetosensor 11 generates a magnetization change. IN When the magnetic field B acts on the magnetosensor 11 and the excitation current I is supplied to the magnetosensor 11, the magnetosensor 11 generates a magnetization change. IN When the excitation current I is supplied, the magnetosensor 11 generates a magnetization change. The magnetosensor 11 applies, for example, a magnetic wire, particularly an amorphous magnetic wire.

[0030] The detection coil 12 is wound around the magnetosensor 11. When the magnetic field B acts on the magnetosensor 11 and the excitation current I is supplied, an induced voltage is generated in the detection coil 12 due to the magnetization change of the magnetosensor 11. Therefore, the detection coil 12 outputs the induced voltage generated by the magnetization change of the magnetosensor 11. IN When the magnetic field B acts on the magnetosensor 11 and the excitation current I is supplied, an induced voltage is generated in the detection coil 12 due to the magnetization change of the magnetosensor 11. IN When the magnetic field B acts on the magnetosensor 11 and the excitation current I is supplied, an induced voltage is generated in the detection coil 12 due to the magnetization change of the magnetosensor 11. Therefore, the detection coil 12 outputs the induced voltage generated by the magnetization change of the magnetosensor 11.

[0031] The detection circuit 20 is electrically connected to the MI sensor element 10 and is configured to detect the strength of the magnetic field B acting on the magnetosensor 11. The detection circuit 20 includes an excitation circuit 21, a sample-and-hold circuit 22 ("S / H" in FIG. 1), a pre-stage high-pass filter 23 ("HPF1" in FIG. 1), a preamplifier 24, a post-stage high-pass filter 25 ("HPF2" in FIG. 1), a buffer amplifier 26, and a reference voltage generation amplifier 27. IN The excitation circuit 21 supplies the excitation current I to the magnetosensor 11.

[0032] The excitation circuit 21 supplies the excitation current I to the magnetosensor 11. INIt supplies pulsed current or high-frequency current as an excitation current I. IN In sync with the supply, a signal S1 is output to hold the induced voltage of the detection coil 12. The sample-and-hold circuit 22 is connected to one end of the detection coil 12 and comprises a sampling switch and a hold capacitor. The sampling switch of the sample-and-hold circuit 22 operates on and off based on the signal S1 output from the excitation circuit 21. The sample-and-hold circuit 22 then holds the output voltage of the detection coil 12 when the sampling switch is in the ON position.

[0033] The pre-stage high-pass filter 23 is connected to the output side of the sample-and-hold circuit 22 and extracts signals with a frequency band higher than a predetermined frequency band. The pre-stage high-pass filter 23 can be a known high-pass filter circuit, such as a circuit composed of at least two LCR elements or a circuit using an operational amplifier such as a differentiating circuit. Furthermore, the pre-stage high-pass filter 23 can be configured in any other way that can perform the desired function.

[0034] The preamplifier 24 is an amplification circuit connected to the output side of the pre-stage high-pass filter 23. The preamplifier 24 performs integration and amplification on the output of the pre-stage high-pass filter 23.

[0035] The subsequent high-pass filter 25 is connected to the output side of the preamplifier 24 and extracts signals with a frequency band higher than a predetermined frequency band. The subsequent high-pass filter 25 can be a known high-pass filter circuit, such as a circuit composed of at least two LCR elements or a circuit using an operational amplifier such as a differentiating circuit. Furthermore, the subsequent high-pass filter 25 can be configured in any other way that can perform the desired function.

[0036] The buffer amplifier 26 is an amplification circuit connected to the output side of the subsequent high-pass filter 25. The buffer amplifier 26 performs amplification on the output of the subsequent high-pass filter 25. The output of the buffer amplifier 26 becomes the output of the detection circuit 20. The reference voltage generation amplifier 27 is a circuit that generates a reference voltage for the MI sensor element 10, the sample-and-hold circuit 22, the preceding high-pass filter 23, the preamplifier 24, the subsequent high-pass filter 25, and the buffer amplifier 26. For example, if the output voltage of the detection circuit 20 is in the range of 0V to 5V, the reference voltage is set to the median value of 2.5V.

[0037] In this embodiment, the magnetic detector 1 has a configuration in which the output side of the preamplifier 24 and one end of the detection coil 12 are not connected, and there is no feedback circuit.

[0038] 1-2. Operation of Magnetic Detector 1 Next, the operation of the magnetic detector 1 in this embodiment will be explained with reference to Figures 2 to 4. However, in order to explain the operation of the magnetic detector 1 in this embodiment, a configuration without the subsequent high-pass filter 25 shown in Figure 1 will be referred to for comparison. In detail, Figure 2(a) will be used to explain the ideal behavior of the output of each part in the configuration without the subsequent high-pass filter 25, and Figure 2(b) will be used to explain the actual behavior of the output of each part in the configuration without the subsequent high-pass filter 25. Then, Figure 2(c) will be used to explain the behavior of the output of each part in this embodiment. In Figures 2(a), (b), and (c), B IN S1 to S7 represent the outputs of each part shown in Figure 1.

[0039] 1-2-1. Explanation of Figure 2(a) The ideal behavior of the magnetic detector 1 in a configuration without a subsequent high-pass filter 25 will be described. First, as shown in the first stage of Figure 2(a), the magnetic field B IN Let's assume a state where an arbitrary magnetic field is applied, starting from a zero state. In the first stage of Figure 2(a), the magnetic field B INFor example, a predetermined DC magnetic field is applied. As shown in the second stage of Figure 2(a), the excitation circuit 21 periodically outputs a signal S1 to turn on the sampling switch of the sample-and-hold circuit 22. When signal S1 is an ON signal, the sampling switch is turned ON, and when signal S1 is an OFF signal, the sampling switch is turned OFF. The signal S1 from the excitation circuit 21 supplies an excitation current I to the magnetometer 11. IN It synchronizes with that.

[0040] Excitation current I IN At the timing of supply, the excitation current I IN The change in the rising edge of the magnetic field B acting on the magnetic sensor 11 IN In response to the strength of the magnetic field, the magnetization of the magnetic sensor 11 changes. This change in magnetization of the magnetic sensor 11 induces a voltage in the detection coil 12. The input S2 of the sample-and-hold circuit 22 (corresponding to the output of the detection coil 12) behaves as shown in the third stage of Figure 2(a).

[0041] Ideally, the output S3 of the sample-and-hold circuit 22 should behave as shown in the fourth stage of Figure 2(a). That is, magnetic field B IN After the signal is applied, when the sampling switch is first turned on, the output S3 of the sample-and-hold circuit 22 rises in accordance with the rising edge of the input S2 of the sample-and-hold circuit 22. Thereafter, the output S3 of the sample-and-hold circuit 22 is affected by the magnetic field B IN It maintains a constant value as long as it is a constant DC magnetic field.

[0042] Consequently, the output S4 of the pre-stage high-pass filter 23 extracts the high-frequency components from the output S3 of the sample-and-hold circuit 22, resulting in the behavior shown in the fifth stage of Figure 2(a). In other words, when the output S3 of the sample-and-hold circuit 22 increases, the output S4 of the pre-stage high-pass filter 23 also increases. After the output S3 of the sample-and-hold circuit 22 becomes constant, the low-frequency components of the output S4 of the pre-stage high-pass filter 23 are gradually removed, and after some time, it becomes the reference voltage.

[0043] The preamplifier 24 integrates and amplifies the output S4 of the preceding high-pass filter 23. Therefore, when the output S4 of the preceding high-pass filter 23 behaves as shown in the fifth stage of Figure 2(a), the output S5 of the preamplifier 24 behaves similarly to the output S4 of the preceding high-pass filter 23, as shown in the sixth stage of Figure 2(a). Since the output S5 of the preamplifier 24 is input to the buffer amplifier 26, the output S7 of the buffer amplifier 26 behaves as an amplified version of the output S5 of the preamplifier 24, as shown in the seventh stage of Figure 2(a).

[0044] 1-2-2. Explanation of Figure 2(b) Next, we will describe the actual behavior of the magnetic detector 1 in a configuration without a subsequent high-pass filter 25. As shown in the first to third stages of Figure 2(b), the magnetic field B IN The signal S1 from the excitation circuit 21 and the input S2 to the sample-and-hold circuit 22 are the same as in Figure 2(a).

[0045] The output S3 of the sample-and-hold circuit 22 does not behave as shown in the fourth stage of Figure 2(a), but rather as shown in the fourth stage of Figure 2(b). The first reason for this is that the sample-and-hold circuit 22 retains the output voltage fluctuation of the detection coil 12 while the sampling switch is ON. The second reason is that the sample-and-hold circuit 22 retains the output voltage fluctuation during at least one of the acquisition time and the settling time due to the ON / OFF operation of the sampling switch.

[0046] These reasons will be explained in detail with reference to Figure 3. As shown in the upper part of Figure 3, the sampling switch is assumed to turn on and off based on the signal S1 output from the excitation circuit 21. At this time, the input S2 of the sample-and-hold circuit 22, which is the output of the detection coil 12, is assumed to behave as shown by the dashed line in the middle part of Figure 3.

[0047] Consequently, due to the characteristics of the sample-and-hold circuit 22, as shown in section T1, the sample-and-hold circuit 22 has an acquisition time, which is the time from immediately after the sampling switch is turned on (immediately after entering sample mode) until it starts tracking the output voltage of the detection coil 12 (input S2 of the sample-and-hold circuit 22). In other words, in section T1, the output S3 of the sample-and-hold circuit 22 experiences an output voltage fluctuation as it approaches the input S2 of the sample-and-hold circuit 22.

[0048] Next, as shown in section T2, the sample-and-hold circuit 22 tracks the output voltage of the detection coil 12 (input S2 of the sample-and-hold circuit 22) while the sampling switch remains on. Because there is a fluctuation in the output voltage of the detection coil 12, in section T2, the output S3 of the sample-and-hold circuit 22 fluctuates in accordance with the fluctuation in the output voltage of the detection coil 12.

[0049] Next, in section T3, the sample-and-hold circuit 22 has a delay time, i.e., an aperture time, from immediately after the sampling switch is turned off until it finishes tracking and starts holding.

[0050] Next, in section T4, when the circuit enters hold mode, there is a settling time (settling time) from the time the circuit enters hold mode until the hold value settles within the error range. In other words, in section T4, the output S3 of the sample-and-hold circuit 22 experiences output voltage fluctuations. After section T4, the output S3 of the sample-and-hold circuit 22 holds the hold value until the next sample mode.

[0051] In summary, as shown in the middle of Figure 3, the output S3 of the sample-and-hold circuit 22 fluctuates to retain the output voltage fluctuation of the detection coil 12 during the ON operation of the sampling switch in interval T2. Furthermore, the output S3 of the sample-and-hold circuit 22 fluctuates by at least one of the acquisition time interval T1 and the settling time interval T4 due to the ON / OFF operation of the sampling switch.

[0052] Let's return to Figure 2 and explain. For the reasons stated above, as shown in the fourth row of Figure 2(b), the output S3 of the sample-and-hold circuit 22 is in the magnetic field B IN Even if the magnetic field B is constant, it does not remain constant and fluctuates. In particular, the magnitude of the fluctuation of the output S3 of the sample-and-hold circuit 22 is related to the magnetic field B IN It depends on the size.

[0053] The output S3 of the sample-and-hold circuit 22 is input to the preceding high-pass filter 23. As shown in the fourth stage of Figure 2(b) and the middle section of Figure 3, the output S3 of the sample-and-hold circuit 22 fluctuates during and near the ON operation of the sampling switch. When the output S3 of the sample-and-hold circuit 22 fluctuates in this way, the preceding high-pass filter 23 extracts the high-frequency components of the output S3 of the sample-and-hold circuit 22, and behaves as shown in the fifth stage of Figure 2(b) and the lower section of Figure 3.

[0054] In other words, as shown in the fifth stage of Figure 2(b) and the lower part of Figure 3, the output S4 of the pre-stage high-pass filter 23 coincides with the reference voltage (potential shown by the horizontal dashed line) before the sampling switch is turned on, but fluctuates immediately after the sampling switch is turned on, and then returns to the reference voltage. Note that in the fifth stage of Figure 2(b) and the lower part of Figure 3, the output S4 of the pre-stage high-pass filter 23 is shown as fluctuating in the negative direction when the sampling switch is turned on, but it may also fluctuate in the positive direction.

[0055] Then, after a predetermined time has elapsed since the sampling switch was turned off, the output S4 of the pre-stage high-pass filter 23 coincides with the reference voltage again. In this way, the output S4 of the pre-stage high-pass filter 23 exhibits a transient waveform that is asymmetrical with respect to the reference voltage during and near the ON operation of the sampling switch.

[0056] In other words, after time has elapsed, the output S4 of the pre-stage high-pass filter 23 matches the reference voltage in the portion where the output S3 of the sample-and-hold circuit 22 is not fluctuating, but the portion where the output S3 of the sample-and-hold circuit 22 is fluctuating remains fluctuating. In particular, the output S4 of the sample-and-hold circuit 22 becomes a transient waveform that is asymmetrical with respect to the reference voltage in the fluctuating portion.

[0057] The preamplifier 24 integrates and amplifies the output S4 of the preceding high-pass filter 23. Therefore, if the output S4 of the preceding high-pass filter 23 behaves asymmetrically with respect to the reference voltage, as shown in the fifth stage of Figure 2(b) and the lower part of Figure 3, the output S5 of the preamplifier 24 will have an offset component from the reference voltage generated after time has elapsed, as shown in the sixth stage of Figure 2(b).

[0058] In other words, the preamplifier 24, through integration processing, converts the output voltage fluctuation of the detection coil 12 while the sampling switch is ON, and the output voltage fluctuation during at least one of the acquisition time and settling time due to the ON / OFF operation of the sampling switch, into an offset component from the reference voltage.

[0059] Then, the output S5 of the preamplifier 24 is input to the buffer amplifier 26, so the output S7 of the buffer amplifier 26 behaves as an amplified version of the output S5 of the preamplifier 24, as shown in the seventh stage of Figure 2(b). Consequently, after time has elapsed, the output S7 of the buffer amplifier 26 will have a residual offset component from the reference voltage.

[0060] Here, as shown in Figure 2(b), the output S7 of the buffer amplifier 26, i.e., the output of the detection circuit 20, has the relationship shown by the dashed line (b) in Figure 4 with respect to the DC magnetic field. In other words, the output S7 of the buffer amplifier 26 has a different offset amount from the reference voltage of 2.5V depending on the magnitude of the DC magnetic field. Although it is not a linear relationship, generally speaking, the larger the DC magnetic field, the larger the offset component of the output S7 of the buffer amplifier 26.

[0061] 1-2-3. Explanation of Figure 2(c) Next, the behavior of each part of the magnetic detector 1 in this embodiment will be described. As shown in the first to sixth stages of Figure 2(c), the magnetic field B IN The signal S1 from the excitation circuit 21, the input S2 to the sample-and-hold circuit 22, the output S3 to the sample-and-hold circuit 22, the output S4 to the pre-stage high-pass filter 23, and the output S5 to the preamplifier 24 are the same as in Figure 2(b). Furthermore, the behavior shown in the upper, middle, and lower panels of Figure 3 is also the same for the magnetic detector 1 of this embodiment.

[0062] In this embodiment, the magnetic detector 1 is equipped with a subsequent high-pass filter 25 on the output side of the preamplifier 24 and on the input side of the buffer amplifier 26. The subsequent high-pass filter 25 receives the output S5 of the preamplifier 24 as input. The subsequent high-pass filter 25 extracts the high-frequency components of the output S5 of the preamplifier 24 and behaves as shown in the seventh stage of Figure 2(c). In other words, the subsequent high-pass filter 25 removes the offset component of the output S5 of the preamplifier 24 after time has elapsed. Therefore, the output S6 of the subsequent high-pass filter 25 matches the reference voltage after time has elapsed.

[0063] Then, the output S6 of the subsequent high-pass filter 25 is input to the buffer amplifier 26, so the output S7 of the buffer amplifier 26 behaves as an amplified version of the output S6 of the subsequent high-pass filter 25, as shown in the eighth stage of Figure 2(c). Consequently, the output S7 of the buffer amplifier 26 matches the reference voltage after a period of time. In other words, the output S7 of the buffer amplifier 26 in this embodiment matches the output S7 of the buffer amplifier 26 in ideal behavior, as shown in the seventh stage of Figure 2(a).

[0064] Here, as shown in Figure 2(c), the output S7 of the buffer amplifier 26, i.e., the output of the detection circuit 20, with respect to the DC magnetic field has the relationship shown by the solid line (c) in Figure 4. In other words, the output S7 of the buffer amplifier 26 is always 2.5V, which is the reference voltage, regardless of the magnitude of the DC magnetic field.

[0065] 1-3. Effects In this embodiment of the magnetic detector 1, even if an offset component affected by a DC magnetic field is included in the output S5 of the preamplifier 24, this offset component can be removed by the subsequent high-pass filter 25. Therefore, the output value of the detection circuit 20 can be free from the offset component affected by the DC magnetic field. As a result, the detection circuit 20 becomes less susceptible to the influence of the DC magnetic field and can detect minute AC magnetic fields with high accuracy. In this way, the magnetic detector 1 in this embodiment can improve magnetic detection performance.

[0066] (Embodiment 2) 2-1. Configuration of Magnetic Detector 2 The configuration of the magnetic detector 2 in Embodiment 2 will be described with reference to Figure 5. Note that, unless otherwise specified, reference numerals used in Embodiment 2 that are the same as those used in previously described embodiments represent the same components as those in the previously described embodiments.

[0067] As shown in Figure 5, the magnetic detector 2 of this embodiment comprises an MI sensor element 10 and a detection circuit 30. The detection circuit 30 is electrically connected to the MI sensor element 10 and detects the magnetic field B acting on the magnetosensitive body 11. INThe detection circuit 30 is configured to detect the strength of the signal. The detection circuit 30 includes an excitation circuit 31, a sample-and-hold circuit 32 (labeled "S / H" in Figure 1), a preamplifier 33, a feedback circuit 34, a subsequent high-pass filter 35 (labeled "HPF2" in Figure 1), a buffer amplifier 36, and a reference voltage generation amplifier 37.

[0068] Here, the excitation circuit 31, sample-and-hold circuit 32, and reference voltage generation amplifier 37 in this embodiment are the same as the excitation circuit 21, sample-and-hold circuit 22, and reference voltage generation amplifier 27 in Embodiment 1.

[0069] The preamplifier 33 is an amplification circuit connected to the output side of the sample-and-hold circuit 32. The preamplifier 33 performs integration and amplification on the output of the sample-and-hold circuit 32.

[0070] The feedback circuit 34 connects the output side of the preamplifier 33 to one end of the detection coil 12 and is configured as a low-pass filter. The feedback circuit 34 extracts a predetermined frequency component using the low-pass filter and generates a feedback current I related to the predetermined frequency component. FB Due to the return magnetic field B FB This generates a feedback current I in a predetermined frequency band that passes through the low-pass filter. FB Due to the return magnetic field B FB This generates the feedback magnetic field B. Then, the feedback circuit 34 uses the generated feedback magnetic field B. FB As a result, the external magnetic field B is applied to the MI sensor element 10. IN It cancels out a portion of the signal. In other words, the feedback circuit 34 provides frequency-selective negative feedback of the magnetic field to the MI sensor element 10. In this case, the MI sensor element 10 cancels out the magnetic field signal (mainly DC low-frequency components) in a predetermined frequency band through frequency-selective negative feedback of the magnetic field, and responds only to AC signals other than the canceled-out components.

[0071] The subsequent high-pass filter 35 is connected to the output side of the preamplifier 33 and extracts signals with a frequency band higher than a predetermined frequency band. The subsequent high-pass filter 35 can be a known high-pass filter circuit, such as a circuit composed of at least two LCR elements or a circuit using an operational amplifier such as a differentiating circuit. Furthermore, the subsequent high-pass filter 35 can be configured in any other way that can perform the desired function.

[0072] The buffer amplifier 36 is an amplification circuit connected to the output side of the subsequent high-pass filter 35. The buffer amplifier 36 performs amplification on the output of the subsequent high-pass filter 35. The output of the buffer amplifier 36 becomes the output of the detection circuit 30.

[0073] 2-2. Operation of Magnetic Detector 2 Next, the operation of the magnetic detector 1 in this embodiment will be described with reference to Figures 6 and 7. However, in order to explain the operation of the magnetic detector 2 in this embodiment, a configuration without the subsequent high-pass filter 35 in Figure 5 will be referred to for comparison. In detail, Figure 6(a) will be used to explain the ideal behavior of the output of each part in the configuration without the subsequent high-pass filter 35, and Figure 6(b) will be used to explain the actual behavior of the output of each part in the configuration without the subsequent high-pass filter 35. Then, Figure 6(c) will be used to explain the behavior of the output of each part in this embodiment. In Figures 6(a), (b), and (c), B IN S11, I FB S12 to S16 represent the outputs of each part shown in Figure 5.

[0074] 2-2-1. Explanation of Figure 6(a) The ideal behavior of the magnetic detector 2 in a configuration without a subsequent high-pass filter 35 will be described. First, as shown in the first stage of Figure 6(a), the magnetic field B IN Let's assume a state where an arbitrary magnetic field is applied, starting from a zero state. In the first stage of Figure 6(a), the magnetic field B INFor example, a predetermined DC magnetic field is applied. As shown in the second stage of Figure 6(a), the excitation circuit 31 periodically outputs a signal S11 to turn on the sampling switch of the sample-and-hold circuit 32. When signal S11 is an ON signal, the sampling switch is turned ON, and when signal S11 is an OFF signal, the sampling switch is turned OFF. The signal S11 from the excitation circuit 31 supplies an excitation current I to the magnetometer 11. IN It synchronizes with that.

[0075] In this embodiment, the magnetic detector 2 has a feedback circuit 34. In the feedback circuit 34, a feedback voltage is generated from the output S14 of the preamplifier 33, and a feedback current I is generated according to the potential difference between the feedback voltage and the reference voltage. FB This occurs. However, the feedback voltage is due to the magnetic field B IN From the moment a change occurs, the response becomes one that corresponds to the time constant of the low-pass filter. The feedback voltage, after time has elapsed, is affected by the magnetic field B IN This voltage can magnetically cancel out the low-frequency components, mainly DC, contained within. In other words, the feedback current I FB This increases with increasing feedback voltage, resulting in the behavior shown in the third stage of Figure 6(a).

[0076] The input S12 of the sample-and-hold circuit 32 ideally behaves as shown in the fourth stage of Figure 6(a). Magnetic field B IN Before the magnetic field B changes, the input S12 of the sample-and-hold circuit 32 is approximately the reference voltage. IN Immediately after the fluctuation, the input S12 of the sample-and-hold circuit 32 undergoes a large fluctuation due to the induced voltage of the detection coil 12. Magnetic field B IN After the fluctuation of magnetic field B IN If there is no change, then magnetic field B IN After some time has elapsed since the fluctuation, the input S12 of the sample-and-hold circuit 32 becomes approximately the reference voltage. In other words, magnetic field B IN The input S12 of the sample-and-hold circuit 32 and the magnetic field B before the change IN If there is no change in magnetic field B INThe fluctuations result in behavior that closely matches that of the input S12 of the sample-and-hold circuit 32 after a period of time.

[0077] Ideally, the output S13 of the sample-and-hold circuit 32 should behave as shown in the fifth stage of Figure 6(a). That is, magnetic field B IN After the fluctuation, when the sampling switch is first turned on, the output S13 of the sample-and-hold circuit 32 rises in accordance with the rising edge of the input S12 of the sample-and-hold circuit 32. After that, the feedback current I FB As a result of this action, the voltage held by the sample-and-hold circuit 32 gradually decreases, so that the output S13 of the sample-and-hold circuit 32 becomes equal to the reference voltage after a period of time.

[0078] The preamplifier 33 integrates and amplifies the output S13 of the sample-and-hold circuit 32. Therefore, when the output S13 of the sample-and-hold circuit 32 behaves as shown in the fifth stage of Figure 6(a), the output S14 of the preamplifier 33 behaves similarly to the output S13 of the sample-and-hold circuit 32, as shown in the sixth stage of Figure 6(a). Since the output S14 of the preamplifier 33 is input to the buffer amplifier 36, the output S16 of the buffer amplifier 36 behaves as an amplified version of the output S14 of the preamplifier 33, as shown in the seventh stage of Figure 6(a).

[0079] 2-2-2. Explanation of Figure 6(b) Next, we will describe the actual behavior of the magnetic detector 2 in a configuration without a subsequent high-pass filter 35. As shown in the first to third stages of Figure 6(b), the magnetic field B IN , the signal S11 from the excitation circuit 21, and the feedback current I FB The same applies.

[0080] The input S12 of the sample-and-hold circuit 32 does not behave as shown in the fourth stage of Figure 6(a), but rather as shown in the fourth stage of Figure 6(b). This is because the feedback circuit 34 is connected to one end of the detection coil 12. As a result, the feedback circuit 34 receives the induced voltage and feedback current I from the detection coil 12. FB The sample-and-hold circuit 32 holds the sum of the feedback voltages generated by this process. Therefore, the input S12 of the sample-and-hold circuit 32 is the feedback current I, as shown in the fourth stage of Figure 6(b). FB It is rising in line with the rise in [another factor].

[0081] The output S13 of the sample-and-hold circuit 32 behaves as shown in the fifth stage of Figure 6(b). The operation of the sample-and-hold circuit 32 is the same as the operation described using Figure 3 in Embodiment 1. That is, the output S13 of the sample-and-hold circuit 32 fluctuates during the acquisition time at the beginning of the sample mode. Subsequently, from the middle of the sample mode, the output S13 of the sample-and-hold circuit 32 tracks the sum of the induced voltage from the detection coil 12 and the feedback voltage. Then, after the sampling switch is turned off, the output S13 of the sample-and-hold circuit 32 holds the hold value after a delay time and a settling time.

[0082] Therefore, as shown in the fifth stage of Figure 6(b), the output S13 of the sample-and-hold circuit 32, after a period of time, is offset from the reference voltage due to the influence of the feedback voltage, and the fluctuations associated with the on / off operation of the sampling switch are added on top of that.

[0083] The preamplifier 33 integrates and amplifies the output S13 of the sample-and-hold circuit 32. Therefore, if the output S13 of the sample-and-hold circuit 32 behaves as shown in the fifth stage of Figure 6(b), the output S14 of the preamplifier 33 will have an offset component from the reference voltage after time has elapsed, as shown in the sixth stage of Figure 6(b). Thus, after time has elapsed, a component of the feedback voltage is generated as an offset component in the output S14 of the preamplifier 33.

[0084] Furthermore, the preamplifier 33 converts the output voltage fluctuation of the detection coil 12 while the sampling switch is ON, and the output voltage fluctuation during at least one of the acquisition time and settling time due to the ON / OFF operation of the sampling switch, into an offset component from the reference voltage through integration. However, in this embodiment, the offset component in the output S14 of the preamplifier 33 has a relatively large component of the feedback voltage and a relatively small component due to the operation of the sampling switch.

[0085] Then, the output S14 of the preamplifier 33 is input to the buffer amplifier 36, so the output S16 of the buffer amplifier 36 behaves as an amplified version of the output S14 of the preamplifier 33, as shown in the seventh stage of Figure 6(b). Consequently, after time has elapsed, the output S16 of the buffer amplifier 36 will have a residual offset component from the reference voltage.

[0086] Here, as shown in Figure 6(b), the output S16 of the buffer amplifier 36, i.e., the output of the detection circuit 30, has the relationship shown by the dashed line (b) in Figure 7 with respect to the DC magnetic field. In other words, the output S7 of the buffer amplifier 36 has a different offset amount from the reference voltage of 2.5V depending on the magnitude of the DC magnetic field. There is a linear relationship where the offset component of the output S7 of the buffer amplifier 36 increases as the DC magnetic field increases.

[0087] 2-2-3. Explanation of Figure 6(c) Next, the behavior of each part of the magnetic detector 2 in this embodiment will be described. As shown in the first to sixth stages of Figure 6(c), the magnetic field B IN , signal S11 from excitation circuit 21, feedback current I FB The input S12 of the sample-and-hold circuit 32, the output S13 of the sample-and-hold circuit 32, and the output S14 of the preamplifier 33 are the same as in Figure 6(b).

[0088] In this configuration, the magnetic detector 2 is equipped with a subsequent high-pass filter 35 on the output side of the preamplifier 33 and on the input side of the buffer amplifier 36. The subsequent high-pass filter 35 receives the output S14 of the preamplifier 33 as input. The subsequent high-pass filter 35 extracts the high-frequency components of the output S14 of the preamplifier 33 and behaves as shown in the seventh stage of Figure 6(c). In other words, the subsequent high-pass filter 35 removes the offset component of the output S14 of the preamplifier 33 after time has elapsed. Therefore, the output S15 of the subsequent high-pass filter 35 matches the reference voltage after time has elapsed.

[0089] Then, the output S15 of the subsequent high-pass filter 35 is input to the buffer amplifier 36, so the output S16 of the buffer amplifier 36 behaves as an amplified version of the output S15 of the subsequent high-pass filter 35, as shown in the eighth stage of Figure 6(c). Consequently, the output S16 of the buffer amplifier 36 matches the reference voltage after time has elapsed. In other words, the output S16 of the buffer amplifier 36 in this embodiment matches the output S16 of the buffer amplifier 36 in ideal behavior, as shown in the seventh stage of Figure 6(a).

[0090] Here, as shown in Figure 6(c), the output S16 of the buffer amplifier 36, that is, the output of the detection circuit 30, has the relationship shown by the solid line (c) in Figure 7 with respect to the DC magnetic field. In other words, the output S16 of the buffer amplifier 36 is always 2.5V, which is the reference voltage, regardless of the magnitude of the DC magnetic field.

[0091] 2-3. Effects According to the magnetic detector 2 of this embodiment, even if an offset component affected by the DC magnetic field is included in the output S14 of the preamplifier 33, this offset component can be removed by the subsequent high-pass filter 35. Therefore, the output value of the detection circuit 30 can be made free from the offset component affected by the DC magnetic field. As a result, the feedback current I FB At the DC magnetic field value that can be canceled out by this, the detection circuit 30 becomes less susceptible to the influence of the DC magnetic field, and can detect minute AC magnetic fields with high precision. In this way, the magnetic detector 2 of this embodiment can improve its magnetic detection performance.

[0092] (First variation of Embodiment 1) The magnetic detector 3 of the first modified embodiment of Embodiment 1 will be described with reference to Figure 8. The only difference is the high-pass filter 25 after the detection circuit 40. However, although the configuration of the high-pass filter 25 in this modified form is different, it has the same function as the high-pass filter 25 after Embodiment 1.

[0093] In this modified configuration, the subsequent high-pass filter 25 comprises an A / D converter 101, a signal processing unit 102, and a D / A converter 103. The A / D converter 101 converts the output of the preamplifier 24 into a digital signal, the signal processing unit 102 performs correction processing on the digital signal including the offset component, and the D / A converter 103 converts the corrected digital signal into an analog signal.

[0094] In other words, the subsequent high-pass filter 25 in this modified embodiment is composed of a signal processing unit 102 that performs digital signal processing after digital conversion. The signal processing unit 102 can, for example, perform a Fourier transform to extract only the desired high-frequency components, and then perform an inverse Fourier transform on the extracted conversion result to remove the offset components. In this case, since all offset components are removed, if it is necessary to offset by the amount of the reference voltage value, it is advisable to add the reference voltage value as a correction value.

[0095] Alternatively, the signal processing unit 102 may calculate the difference between the digital signal voltage and the reference voltage and perform a correction process by adding or subtracting this difference to the digital signal. Furthermore, the signal processing unit 102 may perform a digital filter process, such as an FIR filter, and perform a correction process using the average value of the processing result or the digital value at a specific time as the reference voltage.

[0096] This modified embodiment also produces the same effects as Embodiment 1. Note that the subsequent high-pass filter 25 in this modified embodiment is different from a high-pass filter circuit such as a circuit composed of at least two LCR elements, but since it functions as a high-pass filter, this expression is used to represent it as a concept included in high-pass filters. The same applies to the following modified embodiments.

[0097] (Second variation of Embodiment 1) The magnetic detector 4 in the second modified form of Embodiment 1 will be described with reference to Figure 9. The only difference is the high-pass filter 25 after the detection circuit 50. However, although the configuration of the high-pass filter 25 in this modified form is different, it has the same function as the high-pass filter 25 after Embodiment 1.

[0098] In this modified embodiment, the subsequent high-pass filter 25 includes a low-pass filter 201 and a differential amplifier 202 (corresponding to the processing unit). The low-pass filter 201 extracts signals with a frequency band lower than a predetermined frequency band from the output of the preamplifier 24. The differential amplifier 202 subtracts the component obtained via the low-pass filter 201 from the output of the preamplifier 24. This modified embodiment also achieves the same effects as Embodiment 1.

[0099] (Third variation of Embodiment 1) A third modified form of the magnetic detector 5 of Embodiment 1 will be described with reference to Figure 10. The only difference is the high-pass filter 25 after the detection circuit 60. However, although the configuration of the high-pass filter 25 in this modified form is different, it has the same function as the high-pass filter 25 after Embodiment 1.

[0100] In this modified configuration, the subsequent high-pass filter 25 functions as a reference voltage correction unit 301. The reference voltage correction unit 301 is connected to the output side of the preamplifier 24 and is configured to apply the DC component of the output of the preamplifier 24 as a reference voltage to the preamplifier 24 and other components. Specifically, the reference voltage correction unit 301 extracts the DC component from the output of the preamplifier 24. The reference voltage correction unit 301 corrects the reference voltage of the reference voltage generation amplifier 27 so that the extracted DC component becomes the reference voltage. The reference voltage generation amplifier 27 applies the corrected reference voltage as the reference voltage to the MI sensor element 10, sample-and-hold circuit 22, preceding high-pass filter 23, preamplifier 24, and buffer amplifier 26.

[0101] In this modified detection circuit 60, the output of the preamplifier 24 becomes the input of the buffer amplifier 26. This modified embodiment also achieves the same effects as the first embodiment.

[0102] (others) The first to third modified embodiments described above can also be applied to Embodiment 2. [Explanation of Symbols]

[0103] 1,2,3,4,5 Magnetic detectors 11 Magnetically sensitive body 12 detection coils 10. Magnetoimpedance sensor element (MI sensor element) 22,32 Sample-and-Hold Circuit 23. Pre-stage high-pass filter 24,33 Preamplifier (Amplification Circuit) 25,35 Post-stage high-pass filter 34 Feedback Circuit I IN Excitation current

Claims

1. A magneto impedance sensor element comprising a magnetosensitive element that undergoes a change in magnetization in response to the strength of a magnetic field when an excitation current is supplied, and a detection coil wound around the magnetosensitive element that outputs an induced voltage generated by the change in magnetization of the magnetosensitive element, A sample-and-hold circuit connected to one end of the detection coil, which holds the output voltage of the detection coil when the sampling switch is in the ON position, A pre-stage high-pass filter connected to the output side of the sample-and-hold circuit, The amplification circuit connected to the output side of the aforementioned high-pass filter, The amplifier circuit is further equipped with a subsequent high-pass filter connected to the output side, The sample-and-hold circuit maintains the output voltage fluctuation of the detection coil while the sampling switch is in the ON position. The amplification circuit performs integration and amplification on the output of the preceding high-pass filter, and converts the output voltage fluctuation into an offset component through the integration process. The aforementioned high-pass filter is a magnetic detector that removes the offset component.

2. A magneto impedance sensor element comprising a magnetosensitive element that undergoes a change in magnetization in response to the strength of a magnetic field when an excitation current is supplied, and a detection coil wound around the magnetosensitive element that outputs an induced voltage generated by the change in magnetization of the magnetosensitive element, A sample-and-hold circuit connected to one end of the detection coil, which holds the output voltage of the detection coil when the sampling switch is in the ON position, A pre-stage high-pass filter connected to the output side of the sample-and-hold circuit, The amplification circuit connected to the output side of the aforementioned high-pass filter, The amplifier circuit is further equipped with a subsequent high-pass filter connected to the output side, The sample-and-hold circuit maintains the output voltage fluctuation during at least one of the acquisition time and the settling time by the on / off operation of the sampling switch. The amplification circuit performs integration and amplification on the output of the preceding high-pass filter, and converts the output voltage fluctuation into an offset component through the integration process. The aforementioned high-pass filter is a magnetic detector that removes the offset component.

3. The magnetic detector according to claim 1 or 2, wherein the output side of the amplification circuit and one end of the detection coil are not connected, and there is no feedback circuit.

4. The aforementioned subsequent high-pass filter is A circuit consisting of at least two LCR elements, A high-pass filter circuit with an operational amplifier. A signal processing unit that performs digital signal processing after digital conversion. A processing unit that subtracts a component obtained through a low-pass filter from the output of the amplification circuit from the output of the amplification circuit. A reference voltage correction unit configured to apply the DC component of the output of the amplification circuit as a reference voltage to the amplification circuit, A magnetic detector according to claim 1 or 2, comprising one of the following:

Images